JSON export for Config-Key generation

pom.xml

@@ -246,6 +246,10 @@
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter-cache</artifactId>
     </dependency>
+    <dependency>
+      <groupId>com.fasterxml.jackson.dataformat</groupId>
+      <artifactId>jackson-dataformat-xml</artifactId>
+    </dependency>
     <!-- NOTE since org.springframework.security.oauth is not fully migrated 
       to spring-boot-starter-security we have to declare a separate version here. 
       This refers to the latest version of spring-security-oauth2 and should be 

src/main/java/ch/ethz/seb/sebserver/gbl/api/APIMessage.java

@@ -86,12 +86,18 @@ public class APIMessage implements Serializable {
 
         public ResponseEntity<List<APIMessage>> createErrorResponse() {
             final APIMessage message = of();
-            return new ResponseEntity<>(Arrays.asList(message), this.httpStatus);
+            return new ResponseEntity<>(
+                    Arrays.asList(message),
+                    Utils.createJsonContentHeader(),
+                    this.httpStatus);
         }
 
         public ResponseEntity<Object> createErrorResponse(final String details, final String... attributes) {
             final APIMessage message = of(details, attributes);
-            return new ResponseEntity<>(Arrays.asList(message), this.httpStatus);
+            return new ResponseEntity<>(
+                    Arrays.asList(message),
+                    Utils.createJsonContentHeader(),
+                    this.httpStatus);
         }
     }
 

src/main/java/ch/ethz/seb/sebserver/gbl/model/sebconfig/ConfigurationAttribute.java

@@ -8,8 +8,10 @@
 
 package ch.ethz.seb.sebserver.gbl.model.sebconfig;
 
+import java.text.Collator;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.Locale;
 import java.util.Map;
 import java.util.stream.Collectors;
 
@@ -36,6 +38,10 @@ public final class ConfigurationAttribute implements Entity, Comparable<Configur
 
     private static final Logger log = LoggerFactory.getLogger(ConfigurationAttribute.class);
 
+    /** This is used to compare the attribute names for sorting used to generate the Config-Key
+     * See: https://www.safeexambrowser.org/developer/seb-config-key.html */
+    private static final Collator CULTURE_INVARIANT_COLLATOR = Collator.getInstance(Locale.ROOT);
+
     /** This configuration attribute dependency key can be used to set a specific localized text key prefix for
      * resources. This is usually convenient if two different attributes use the same resources and to avoid
      * to multiply the resources for each attribute with the attribute name prefix, we can set a specific
@@ -162,8 +168,9 @@ public final class ConfigurationAttribute implements Entity, Comparable<Configur
 
     @Override
     public int compareTo(final ConfigurationAttribute attribute) {
-        // TODO check if this is correct in reference to https://www.safeexambrowser.org/developer/seb-config-key.html
+        return CULTURE_INVARIANT_COLLATOR.compare(
-        return this.name.compareToIgnoreCase(attribute.name);
+                this.name,
+                attribute.name);
     }
 
     @Override

src/main/java/ch/ethz/seb/sebserver/gbl/util/Utils.java

@@ -33,6 +33,9 @@ import org.joda.time.DateTime;
 import org.joda.time.DateTimeZone;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
+import org.springframework.http.HttpHeaders;
+import org.springframework.util.LinkedMultiValueMap;
+import org.springframework.util.MultiValueMap;
 
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
@@ -391,4 +394,12 @@ public final class Utils {
         }
     }
 
+    public static final MultiValueMap<String, String> createJsonContentHeader() {
+        final MultiValueMap<String, String> headers = new LinkedMultiValueMap<>();
+        headers.set(
+                HttpHeaders.CONTENT_TYPE,
+                org.springframework.http.MediaType.APPLICATION_JSON_UTF8_VALUE);
+        return headers;
+    }
+
 }

src/main/java/ch/ethz/seb/sebserver/webservice/servicelayer/sebconfig/AttributeValueConverter.java

@@ -10,7 +10,10 @@ package ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig;
 
 import java.io.IOException;
 import java.io.OutputStream;
+import java.util.Collections;
 import java.util.Set;
+import java.util.function.Function;
+import java.util.stream.Stream;
 
 import ch.ethz.seb.sebserver.gbl.model.sebconfig.AttributeType;
 import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationAttribute;
@@ -18,7 +21,14 @@ import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationValue;
 
 /** Defines the interface of a XML converter to be used to convert
  * ConfigurationValue for defined ConfigurationAttribute */
-public interface XMLValueConverter {
+public interface AttributeValueConverter {
+
+    /** This can be overwritten if a XMLValueConverter needs the XMLValueConverterService.
+     * The XMLValueConverterService is then injected by its self on initialization.
+     *
+     * @param xmlValueConverterService */
+    default void init(final AttributeValueConverterService xmlValueConverterService) {
+    }
 
     /** Gives a Set of AttributeType's a concrete converter is able to
      * handle and convert ConfigurationValue of attributes of given types.
@@ -26,26 +36,42 @@ public interface XMLValueConverter {
      * @return a Set of supported AttributeType's of the converter */
     Set<AttributeType> types();
 
-    /** The name of the Converter. This can be used if a Converter is specific to
+    /** The attribute names of the Converter. This can be used if a Converter is specific to
      * an ConfigurationAttribute and not specific on a type of attribute.
-     * This must give either the name if a specific ConfigurationAttribute or null/emptyString
+     * This must give either the name if a specific ConfigurationAttribute or empty set
      *
      * @return The name of a specific ConfigurationAttribute the converter works for. */
-    String name();
+    default Set<String> names() {
+        return Collections.emptySet();
+    }
 
-    /** Used to convert the a given ConfigurationAttribute / ConfigurationValue
+    /** Used to convert the a given ConfigurationAttribute to plain XML text or block of SEB Configuration attribute.
-     * pair to plain XML text for block of this SEB Configuration attribute.
      *
      * @param out The output stream to write the plain XML text block to
      * @param attribute The ConfigurationAttribute containing all attribute information
-     * @param value The ConfigurationValue containing the value
+     * @param valueSupplier The ConfigurationValue supplier
-     * @param xmlValueConverterService
      * @throws IOException */
     void convertToXML(
             OutputStream out,
             ConfigurationAttribute attribute,
-            ConfigurationValue value) throws IOException;
+            Function<ConfigurationAttribute, ConfigurationValue> valueSupplier) throws IOException;
 
+    /** Used to convert the a given ConfigurationAttribute to plain JSON text or block of SEB Configuration attribute.
+     *
+     * @param out The output stream to write the plain JSON text block to
+     * @param attribute The ConfigurationAttribute containing all attribute information
+     * @param valueSupplier The ConfigurationValue supplier
+     * @throws IOException */
+    void convertToJSON(
+            OutputStream out,
+            ConfigurationAttribute attribute,
+            Function<ConfigurationAttribute, ConfigurationValue> valueSupplier) throws IOException;
+
+    /** Get the real name of the SEB configuration attribute
+     * by cutting of the prefixed used for nested attributes
+     *
+     * @param attribute
+     * @return the SEB configuration attribute name */
     default String extractName(final ConfigurationAttribute attribute) {
         final int lastIndexOf = attribute.name.lastIndexOf('.');
         if (lastIndexOf > 0) {
@@ -55,11 +81,8 @@ public interface XMLValueConverter {
         }
     }
 
-    /** This can be overwritten if a XMLValueConverter needs the XMLValueConverterService.
+    default Stream<ConfigurationAttribute> convertAttribute(final ConfigurationAttribute attr) {
-     * The XMLValueConverterService is then injected by its self on initialization.
+        return Stream.of(attr);
-     * 
-     * @param xmlValueConverterService */
-    default void init(final XMLValueConverterService xmlValueConverterService) {
     }
 
 }

src/main/java/ch/ethz/seb/sebserver/webservice/servicelayer/sebconfig/AttributeValueConverterService.java

@@ -11,12 +11,12 @@ package ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig;
 import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationAttribute;
 
 /** Interface of a SEB Exam Configuration XML conversion service */
-public interface XMLValueConverterService {
+public interface AttributeValueConverterService {
 
     /** Use this to get a XMLValueConverter for a given ConfigurationAttribute.
      *
      * @param attribute The ConfigurationAttribute instance
      * @return a XMLValueConverter for a given ConfigurationAttribute */
-    XMLValueConverter getXMLConverter(ConfigurationAttribute attribute);
+    AttributeValueConverter getAttributeValueConverter(ConfigurationAttribute attribute);
 
 }

src/main/java/ch/ethz/seb/sebserver/webservice/servicelayer/sebconfig/impl/AttributeValueConverterServiceImpl.java

@@ -12,7 +12,6 @@ import java.util.Collection;
 import java.util.HashMap;
 import java.util.Map;
 
-import org.apache.commons.lang3.StringUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.context.annotation.Lazy;
@@ -21,26 +20,26 @@ import org.springframework.stereotype.Service;
 import ch.ethz.seb.sebserver.gbl.model.sebconfig.AttributeType;
 import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationAttribute;
 import ch.ethz.seb.sebserver.gbl.profile.WebServiceProfile;
-import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.XMLValueConverter;
+import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.AttributeValueConverter;
-import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.XMLValueConverterService;
+import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.AttributeValueConverterService;
 
 @Lazy
 @Service
 @WebServiceProfile
-public class XMLValueConverterServiceImpl implements XMLValueConverterService {
+public class AttributeValueConverterServiceImpl implements AttributeValueConverterService {
 
-    private static final Logger log = LoggerFactory.getLogger(XMLValueConverterServiceImpl.class);
+    private static final Logger log = LoggerFactory.getLogger(AttributeValueConverterServiceImpl.class);
 
-    private final Map<String, XMLValueConverter> convertersByAttributeName;
+    private final Map<String, AttributeValueConverter> convertersByAttributeName;
-    private final Map<AttributeType, XMLValueConverter> convertersByAttributeType;
+    private final Map<AttributeType, AttributeValueConverter> convertersByAttributeType;
 
-    public XMLValueConverterServiceImpl(final Collection<XMLValueConverter> converters) {
+    public AttributeValueConverterServiceImpl(final Collection<AttributeValueConverter> converters) {
         this.convertersByAttributeName = new HashMap<>();
         this.convertersByAttributeType = new HashMap<>();
-        for (final XMLValueConverter converter : converters) {
+        for (final AttributeValueConverter converter : converters) {
             converter.init(this);
-            if (StringUtils.isNotBlank(converter.name())) {
+            for (final String attributeName : converter.names()) {
-                this.convertersByAttributeName.put(converter.name(), converter);
+                this.convertersByAttributeName.put(attributeName, converter);
             }
 
             for (final AttributeType aType : converter.types()) {
@@ -56,7 +55,7 @@ public class XMLValueConverterServiceImpl implements XMLValueConverterService {
     }
 
     @Override
-    public XMLValueConverter getXMLConverter(final ConfigurationAttribute attribute) {
+    public AttributeValueConverter getAttributeValueConverter(final ConfigurationAttribute attribute) {
         if (this.convertersByAttributeName.containsKey(attribute.name)) {
             return this.convertersByAttributeName.get(attribute.name);
         }

src/main/java/ch/ethz/seb/sebserver/webservice/servicelayer/sebconfig/impl/ExamConfigIO.java

@@ -15,6 +15,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.function.Function;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 import org.apache.commons.io.IOUtils;
 import org.slf4j.Logger;
@@ -32,7 +33,8 @@ import ch.ethz.seb.sebserver.gbl.util.Utils;
 import ch.ethz.seb.sebserver.webservice.servicelayer.dao.ConfigurationAttributeDAO;
 import ch.ethz.seb.sebserver.webservice.servicelayer.dao.ConfigurationDAO;
 import ch.ethz.seb.sebserver.webservice.servicelayer.dao.ConfigurationValueDAO;
-import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.XMLValueConverterService;
+import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.AttributeValueConverter;
+import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.AttributeValueConverterService;
 
 @Lazy
 @Component
@@ -51,18 +53,18 @@ public class ExamConfigIO {
     private final ConfigurationAttributeDAO configurationAttributeDAO;
     private final ConfigurationValueDAO configurationValueDAO;
     private final ConfigurationDAO configurationDAO;
-    private final XMLValueConverterService xmlValueConverterService;
+    private final AttributeValueConverterService attributeValueConverterService;
 
     protected ExamConfigIO(
             final ConfigurationAttributeDAO configurationAttributeDAO,
             final ConfigurationValueDAO configurationValueDAO,
             final ConfigurationDAO configurationDAO,
-            final XMLValueConverterService xmlValueConverterService) {
+            final AttributeValueConverterService attributeValueConverterService) {
 
         this.configurationAttributeDAO = configurationAttributeDAO;
         this.configurationValueDAO = configurationValueDAO;
         this.configurationDAO = configurationDAO;
-        this.xmlValueConverterService = xmlValueConverterService;
+        this.attributeValueConverterService = attributeValueConverterService;
     }
 
     @Async(AsyncServiceSpringConfig.EXECUTOR_BEAN_NAME)
@@ -75,17 +77,11 @@ public class ExamConfigIO {
             log.debug("Start export SEB plain XML configuration asynconously");
         }
 
-        // get all defined root configuration attributes
+        // get all defined root configuration attributes prepared and sorted
-        final Map<Long, ConfigurationAttribute> attributes = this.configurationAttributeDAO.getAllRootAttributes()
+        final List<ConfigurationAttribute> sortedAttributes = this.configurationAttributeDAO.getAllRootAttributes()
                 .getOrThrow()
                 .stream()
-                .collect(Collectors.toMap(
+                .flatMap(this::convertAttribute)
-                        ConfigurationAttribute::getId,
-                        Function.identity()));
-
-        final List<ConfigurationAttribute> sortedAttributes = attributes
-                .values()
-                .stream()
                 .sorted()
                 .collect(Collectors.toList());
 
@@ -94,14 +90,8 @@ public class ExamConfigIO {
                 .getFollowupConfiguration(configurationNodeId)
                 .getOrThrow().id;
 
-        // get all values for that attributes for given configurationId
+        final Function<ConfigurationAttribute, ConfigurationValue> configurationValueSupplier =
-        final Map<Long, ConfigurationValue> values = this.configurationValueDAO
+                getConfigurationValueSupplier(institutionId, configurationId);
-                .allRootAttributeValues(institutionId, configurationId)
-                .getOrThrow()
-                .stream()
-                .collect(Collectors.toMap(
-                        ConfigurationValue::getAttributeId,
-                        Function.identity()));
 
         try {
             // write headers
@@ -114,13 +104,10 @@ public class ExamConfigIO {
 
             // write attributes
             for (final ConfigurationAttribute attribute : sortedAttributes) {
-                final ConfigurationValue configurationValue = values.get(attribute.id);
+                this.attributeValueConverterService.getAttributeValueConverter(attribute).convertToXML(
-                if (configurationValue != null) {
+                        out,
-                    this.xmlValueConverterService.getXMLConverter(attribute).convertToXML(
+                        attribute,
-                            out,
+                        configurationValueSupplier);
-                            attribute,
-                            configurationValue);
-                }
             }
 
             // plist close
@@ -144,9 +131,34 @@ public class ExamConfigIO {
         }
     }
 
+    private Stream<ConfigurationAttribute> convertAttribute(final ConfigurationAttribute attr) {
+        final AttributeValueConverter attributeValueConverter =
+                this.attributeValueConverterService.getAttributeValueConverter(attr);
+        if (attributeValueConverter != null) {
+            return attributeValueConverter.convertAttribute(attr);
+        } else {
+            return Stream.of(attr);
+        }
+    }
+
     @Async(AsyncServiceSpringConfig.EXECUTOR_BEAN_NAME)
     void importPlainXML(final InputStream in, final Long institutionId, final Long configurationNodeId) {
         // TODO version 1
     }
 
+    private Function<ConfigurationAttribute, ConfigurationValue> getConfigurationValueSupplier(
+            final Long institutionId,
+            final Long configurationId) {
+
+        final Map<Long, ConfigurationValue> mapping = this.configurationValueDAO
+                .allRootAttributeValues(institutionId, configurationId)
+                .getOrThrow()
+                .stream()
+                .collect(Collectors.toMap(
+                        ConfigurationValue::getAttributeId,
+                        Function.identity()));
+
+        return attr -> mapping.get(attr.id);
+    }
+
 }

src/main/java/ch/ethz/seb/sebserver/webservice/servicelayer/sebconfig/impl/SebExamConfigServiceImpl.java

@@ -161,6 +161,9 @@ public class SebExamConfigServiceImpl implements SebExamConfigService {
 
     @Override
     public String generateConfigKey(final Long configurationNodeId) {
+
+        //DigestUtils.sha1Hex(data)
+
         // TODO https://www.safeexambrowser.org/developer/seb-config-key.html
         throw new UnsupportedOperationException("TODO");
     }

src/main/java/ch/ethz/seb/sebserver/webservice/servicelayer/sebconfig/impl/converter/ArrayOfStringConverter.java

@@ -14,6 +14,7 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.function.Function;
 
 import org.apache.commons.lang3.StringUtils;
 import org.springframework.context.annotation.Lazy;
@@ -25,23 +26,29 @@ import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationAttribute;
 import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationValue;
 import ch.ethz.seb.sebserver.gbl.profile.WebServiceProfile;
 import ch.ethz.seb.sebserver.gbl.util.Utils;
-import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.XMLValueConverter;
+import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.AttributeValueConverter;
 
 @Lazy
 @Component
 @WebServiceProfile
-public class ArrayOfStringConverter implements XMLValueConverter {
+public class ArrayOfStringConverter implements AttributeValueConverter {
 
-    public static final String ATTRIBUTE_NAME = "ExceptionsList";
+    public static final Set<String> ATTRIBUTE_NAMES = Utils.immutableSetOf("ExceptionsList");
 
     public static final Set<AttributeType> SUPPORTED_TYPES = Collections.unmodifiableSet(
             new HashSet<>(Arrays.asList(
                     AttributeType.MULTI_CHECKBOX_SELECTION,
                     AttributeType.MULTI_SELECTION)));
 
-    private static final String TEMPLATE = "<key>%s</key><array>";
+    private static final String XML_TEMPLATE = "<key>%s</key><array>";
-    private static final String TEMPLATE_ENTRY = "<string>%s</string>";
+    private static final String XML_TEMPLATE_ENTRY = "<string>%s</string>";
-    private static final String TEMPLATE_EMPTY = "<key>%s</key><array></array>";
+    private static final String XML_TEMPLATE_EMPTY = "<key>%s</key><array></array>";
+    private static final String XML_ARRAY_CLOSE = "</array>";
+
+    private static final String JSON_TEMPLATE = "\"%s\":[";
+    private static final String JSON_TEMPLATE_ENTRY = "\"%s\"";
+    private static final String JSON_TEMPLATE_EMPTY = "\"%s\":[]";
+    private static final String JSON_ARRAY_CLOSE = "]";
 
     @Override
     public Set<AttributeType> types() {
@@ -49,28 +56,63 @@ public class ArrayOfStringConverter implements XMLValueConverter {
     }
 
     @Override
-    public String name() {
+    public Set<String> names() {
-        return ATTRIBUTE_NAME;
+        return ATTRIBUTE_NAMES;
     }
 
     @Override
     public void convertToXML(
             final OutputStream out,
             final ConfigurationAttribute attribute,
-            final ConfigurationValue value) throws IOException {
+            final Function<ConfigurationAttribute, ConfigurationValue> valueSupplier) throws IOException {
+
+        convert(out, attribute, valueSupplier.apply(attribute), true);
+    }
+
+    @Override
+    public void convertToJSON(
+            final OutputStream out,
+            final ConfigurationAttribute attribute,
+            final Function<ConfigurationAttribute, ConfigurationValue> valueSupplier) throws IOException {
+
+        convert(out, attribute, valueSupplier.apply(attribute), false);
+    }
+
+    private void convert(
+            final OutputStream out,
+            final ConfigurationAttribute attribute,
+            final ConfigurationValue value,
+            final boolean xml) throws IOException {
 
         final String val = (value.value != null) ? value.value : attribute.getDefaultValue();
         if (StringUtils.isNotBlank(val)) {
+
             final String[] values = StringUtils.split(val, Constants.LIST_SEPARATOR);
             final StringBuilder sb = new StringBuilder();
-            sb.append(String.format(TEMPLATE, extractName(attribute)));
+            sb.append(String.format(
+                    (xml) ? XML_TEMPLATE : JSON_TEMPLATE,
+                    extractName(attribute)));
+
             for (final String v : values) {
-                sb.append(String.format(TEMPLATE_ENTRY, v));
+                sb.append(String.format(
+                        (xml) ? XML_TEMPLATE_ENTRY : JSON_TEMPLATE_ENTRY,
+                        v));
+                if (!xml) {
+                    sb.append(Constants.LIST_SEPARATOR);
+                }
             }
-            sb.append("</array>");
+
+            if (!xml) {
+                // delete tailing LIST_SEPARATOR (',') from loop
+                sb.deleteCharAt(sb.length() - 1);
+            }
+
+            sb.append((xml) ? XML_ARRAY_CLOSE : JSON_ARRAY_CLOSE);
             out.write(Utils.toByteArray(sb.toString()));
         } else {
-            out.write(Utils.toByteArray(String.format(TEMPLATE_EMPTY, extractName(attribute))));
+            out.write(Utils.toByteArray(String.format(
+                    (xml) ? XML_TEMPLATE_EMPTY : JSON_TEMPLATE_EMPTY,
+                    extractName(attribute))));
         }
     }
 

src/main/java/ch/ethz/seb/sebserver/webservice/servicelayer/sebconfig/impl/converter/BooleanConverter.java

@@ -14,8 +14,8 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.function.Function;
 
-import org.apache.commons.lang3.StringUtils;
 import org.springframework.context.annotation.Lazy;
 import org.springframework.stereotype.Component;
 
@@ -25,23 +25,19 @@ import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationAttribute;
 import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationValue;
 import ch.ethz.seb.sebserver.gbl.profile.WebServiceProfile;
 import ch.ethz.seb.sebserver.gbl.util.Utils;
-import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.XMLValueConverter;
+import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.AttributeValueConverter;
 
 @Lazy
 @Component
 @WebServiceProfile
-public class BooleanConverter implements XMLValueConverter {
+public class BooleanConverter implements AttributeValueConverter {
 
     public static final Set<AttributeType> SUPPORTED_TYPES = Collections.unmodifiableSet(
             new HashSet<>(Arrays.asList(
                     AttributeType.CHECKBOX)));
 
-    private static final String TEMPLATE = "<key>%s</key><%s />";
+    private static final String XML_TEMPLATE = "<key>%s</key><%s />";
-
+    private static final String JSON_TEMPLATE = "\"%s\":%s";
-    @Override
-    public String name() {
-        return StringUtils.EMPTY;
-    }
 
     @Override
     public Set<AttributeType> types() {
@@ -52,14 +48,31 @@ public class BooleanConverter implements XMLValueConverter {
     public void convertToXML(
             final OutputStream out,
             final ConfigurationAttribute attribute,
-            final ConfigurationValue value) throws IOException {
+            final Function<ConfigurationAttribute, ConfigurationValue> valueSupplier) throws IOException {
+
+        convert(out, attribute, valueSupplier.apply(attribute), XML_TEMPLATE);
+    }
+
+    @Override
+    public void convertToJSON(
+            final OutputStream out,
+            final ConfigurationAttribute attribute,
+            final Function<ConfigurationAttribute, ConfigurationValue> valueSupplier) throws IOException {
+
+        convert(out, attribute, valueSupplier.apply(attribute), JSON_TEMPLATE);
+    }
+
+    private void convert(
+            final OutputStream out,
+            final ConfigurationAttribute attribute,
+            final ConfigurationValue value,
+            final String template) throws IOException {
 
         out.write(Utils.toByteArray(
                 String.format(
-                        TEMPLATE,
+                        template,
                         extractName(attribute),
                         (value.value != null) ? value.value : Constants.FALSE_STRING)));
-
     }
 
 }

src/main/java/ch/ethz/seb/sebserver/webservice/servicelayer/sebconfig/impl/converter/IntegerConverter.java

@@ -14,8 +14,10 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.function.Function;
 
-import org.apache.commons.lang3.StringUtils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.springframework.context.annotation.Lazy;
 import org.springframework.stereotype.Component;
 
@@ -24,12 +26,14 @@ import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationAttribute;
 import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationValue;
 import ch.ethz.seb.sebserver.gbl.profile.WebServiceProfile;
 import ch.ethz.seb.sebserver.gbl.util.Utils;
-import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.XMLValueConverter;
+import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.AttributeValueConverter;
 
 @Lazy
 @Component
 @WebServiceProfile
-public class IntegerConverter implements XMLValueConverter {
+public class IntegerConverter implements AttributeValueConverter {
+
+    private static final Logger log = LoggerFactory.getLogger(IntegerConverter.class);
 
     public static final Set<AttributeType> SUPPORTED_TYPES = Collections.unmodifiableSet(
             new HashSet<>(Arrays.asList(
@@ -38,31 +42,52 @@ public class IntegerConverter implements XMLValueConverter {
                     AttributeType.SINGLE_SELECTION,
                     AttributeType.RADIO_SELECTION)));
 
-    private static final String TEMPLATE = "<key>%s</key><integer>%s</integer>";
+    private static final String XML_TEMPLATE = "<key>%s</key><integer>%s</integer>";
-    private static final String TEMPLATE_EMPTY = "<key>%s</key><integer />";
+    private static final String JSON_TEMPLATE = "\"%s\":%s";
 
     @Override
     public Set<AttributeType> types() {
         return SUPPORTED_TYPES;
     }
 
-    @Override
-    public String name() {
-        return StringUtils.EMPTY;
-    }
-
     @Override
     public void convertToXML(
             final OutputStream out,
             final ConfigurationAttribute attribute,
-            final ConfigurationValue value) throws IOException {
+            final Function<ConfigurationAttribute, ConfigurationValue> valueSupplier) throws IOException {
+
+        convert(out, attribute, valueSupplier.apply(attribute), XML_TEMPLATE);
+    }
+
+    @Override
+    public void convertToJSON(
+            final OutputStream out,
+            final ConfigurationAttribute attribute,
+            final Function<ConfigurationAttribute, ConfigurationValue> valueSupplier) throws IOException {
+
+        convert(out, attribute, valueSupplier.apply(attribute), JSON_TEMPLATE);
+    }
+
+    private void convert(
+            final OutputStream out,
+            final ConfigurationAttribute attribute,
+            final ConfigurationValue value,
+            final String template) throws IOException {
 
         final String val = (value.value != null) ? value.value : attribute.getDefaultValue();
-        if (StringUtils.isNotBlank(val)) {
+        int intVal = 0;
-            out.write(Utils.toByteArray(String.format(TEMPLATE, extractName(attribute), val)));
+
-        } else {
+        try {
-            out.write(Utils.toByteArray(String.format(TEMPLATE_EMPTY, extractName(attribute))));
+            intVal = Integer.parseInt(val);
+        } catch (final NumberFormatException nfe) {
+            log.error("Failed to convert SEB configuration attribute value of type integer: {}", val, nfe);
+            intVal = 0;
         }
 
+        out.write(Utils.toByteArray(String.format(
+                template,
+                extractName(attribute),
+                intVal)));
     }
+
 }

src/main/java/ch/ethz/seb/sebserver/webservice/servicelayer/sebconfig/impl/converter/KioskModeConverter.java

@@ -12,6 +12,8 @@ import java.io.IOException;
 import java.io.OutputStream;
 import java.util.Collections;
 import java.util.Set;
+import java.util.function.Function;
+import java.util.stream.Stream;
 
 import org.springframework.context.annotation.Lazy;
 import org.springframework.stereotype.Component;
@@ -22,20 +24,28 @@ import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationAttribute;
 import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationValue;
 import ch.ethz.seb.sebserver.gbl.profile.WebServiceProfile;
 import ch.ethz.seb.sebserver.gbl.util.Utils;
-import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.XMLValueConverter;
+import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.AttributeValueConverter;
 
 @Lazy
 @Component
 @WebServiceProfile
-public class KioskModeConverter implements XMLValueConverter {
+public class KioskModeConverter implements AttributeValueConverter {
 
-    public static final String NAME = "kioskMode";
+    public static final String ATTR_NAME_KIOSK_MODE = "kioskMode";
+    public static final String ATTR_NAME_CREATE_NEW_DESKTOP = "createNewDesktop";
+    public static final String ATTR_NAME_KILL_SHELL = "killExplorerShell";
 
-    private static final String TEMPLATE = "<key>createNewDesktop</key><%s /><key>killExplorerShell</key><%s />";
+    public static final Set<String> NAMES = Utils.immutableSetOf(
+            ATTR_NAME_KIOSK_MODE,
+            ATTR_NAME_CREATE_NEW_DESKTOP,
+            ATTR_NAME_KILL_SHELL);
+
+    private static final String XML_TEMPLATE = "<key>%s</key><%s />";
+    private static final String JSON_TEMPLATE = "\"%s\":%s";
 
     @Override
-    public String name() {
+    public Set<String> names() {
-        return NAME;
+        return NAMES;
     }
 
     @Override
@@ -43,18 +53,53 @@ public class KioskModeConverter implements XMLValueConverter {
         return Collections.emptySet();
     }
 
+    @Override
+    public Stream<ConfigurationAttribute> convertAttribute(final ConfigurationAttribute attr) {
+        return Stream.of(
+                convertFrom(attr, ATTR_NAME_CREATE_NEW_DESKTOP),
+                convertFrom(attr, ATTR_NAME_KILL_SHELL));
+    }
+
+    private ConfigurationAttribute convertFrom(final ConfigurationAttribute attr, final String name) {
+        return new ConfigurationAttribute(
+                attr.id, attr.parentId, name,
+                attr.type, attr.resources, attr.validator,
+                attr.dependencies, attr.defaultValue);
+    }
+
     @Override
     public void convertToXML(
             final OutputStream out,
             final ConfigurationAttribute attribute,
-            final ConfigurationValue value) throws IOException {
+            final Function<ConfigurationAttribute, ConfigurationValue> valueSupplier) throws IOException {
 
-        final String val = value.getValue();
+        convert(out, valueSupplier.apply(attribute), attribute.name, XML_TEMPLATE);
-        out.write(Utils.toByteArray(
+    }
-                String.format(
+
-                        TEMPLATE,
+    @Override
-                        (val != null == "0".equals(val)) ? Constants.TRUE_STRING : Constants.FALSE_STRING,
+    public void convertToJSON(
-                        (val != null == "1".equals(val)) ? Constants.TRUE_STRING : Constants.FALSE_STRING)));
+            final OutputStream out,
+            final ConfigurationAttribute attribute,
+            final Function<ConfigurationAttribute, ConfigurationValue> valueSupplier) throws IOException {
+
+        convert(out, valueSupplier.apply(attribute), attribute.name, JSON_TEMPLATE);
+    }
+
+    private void convert(
+            final OutputStream out,
+            final ConfigurationValue value,
+            final String name,
+            final String template) throws IOException {
+
+        final String val = (ATTR_NAME_CREATE_NEW_DESKTOP.equals(name))
+                ? value.getValue() == null || "0".equals(value.getValue())
+                        ? Constants.TRUE_STRING
+                        : Constants.FALSE_STRING
+                : value.getValue() == null || "0".equals(value.getValue())
+                        ? Constants.FALSE_STRING
+                        : Constants.TRUE_STRING;
+
+        out.write(Utils.toByteArray(String.format(template, name, val)));
     }
 
 }

src/main/java/ch/ethz/seb/sebserver/webservice/servicelayer/sebconfig/impl/converter/StringConverter.java

@@ -14,6 +14,7 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.function.Function;
 
 import org.apache.commons.lang3.StringUtils;
 import org.springframework.context.annotation.Lazy;
@@ -24,12 +25,12 @@ import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationAttribute;
 import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationValue;
 import ch.ethz.seb.sebserver.gbl.profile.WebServiceProfile;
 import ch.ethz.seb.sebserver.gbl.util.Utils;
-import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.XMLValueConverter;
+import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.AttributeValueConverter;
 
 @Lazy
 @Component
 @WebServiceProfile
-public class StringConverter implements XMLValueConverter {
+public class StringConverter implements AttributeValueConverter {
 
     public static final Set<AttributeType> SUPPORTED_TYPES = Collections.unmodifiableSet(
             new HashSet<>(Arrays.asList(
@@ -39,32 +40,61 @@ public class StringConverter implements XMLValueConverter {
                     AttributeType.DECIMAL,
                     AttributeType.COMBO_SELECTION)));
 
-    private static final String TEMPLATE = "<key>%s</key><string>%s</string>";
+    private static final String XML_TEMPLATE = "<key>%s</key><string>%s</string>";
-    private static final String TEMPLATE_EMPTY = "<key>%s</key><string />";
+    private static final String XML_TEMPLATE_EMPTY = "<key>%s</key><string />";
+
+    private static final String JSON_TEMPLATE = "\"%s\":\"%s\"";
+    private static final String JSON_TEMPLATE_EMPTY = "\"%s\":";
 
     @Override
     public Set<AttributeType> types() {
         return SUPPORTED_TYPES;
     }
 
-    @Override
-    public String name() {
-        return StringUtils.EMPTY;
-    }
-
     @Override
     public void convertToXML(
             final OutputStream out,
             final ConfigurationAttribute attribute,
-            final ConfigurationValue value) throws IOException {
+            final Function<ConfigurationAttribute, ConfigurationValue> valueSupplier) throws IOException {
+
+        convert(
+                out,
+                attribute,
+                valueSupplier.apply(attribute),
+                XML_TEMPLATE, XML_TEMPLATE_EMPTY);
+    }
+
+    @Override
+    public void convertToJSON(
+            final OutputStream out,
+            final ConfigurationAttribute attribute,
+            final Function<ConfigurationAttribute, ConfigurationValue> valueSupplier) throws IOException {
+
+        convert(
+                out,
+                attribute,
+                valueSupplier.apply(attribute),
+                JSON_TEMPLATE, JSON_TEMPLATE_EMPTY);
+    }
+
+    private void convert(
+            final OutputStream out,
+            final ConfigurationAttribute attribute,
+            final ConfigurationValue value,
+            final String template,
+            final String emptyTemplate) throws IOException {
 
         final String val = (value.value != null) ? value.value : attribute.getDefaultValue();
         if (StringUtils.isNotBlank(val)) {
-            out.write(Utils.toByteArray(String.format(TEMPLATE, extractName(attribute), val)));
+            out.write(Utils.toByteArray(String.format(
+                    template,
+                    extractName(attribute),
+                    val)));
         } else {
-            out.write(Utils.toByteArray(String.format(TEMPLATE_EMPTY, extractName(attribute))));
+            out.write(Utils.toByteArray(String.format(
+                    emptyTemplate,
+                    extractName(attribute))));
         }
-
     }
 
 }

src/main/java/ch/ethz/seb/sebserver/webservice/servicelayer/sebconfig/impl/converter/TableConverter.java

@@ -13,16 +13,18 @@ import java.io.OutputStream;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 
-import org.apache.commons.lang3.StringUtils;
 import org.springframework.context.annotation.Lazy;
 import org.springframework.stereotype.Component;
+import org.springframework.util.CollectionUtils;
 
+import ch.ethz.seb.sebserver.gbl.Constants;
 import ch.ethz.seb.sebserver.gbl.model.sebconfig.AttributeType;
 import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationAttribute;
 import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationValue;
@@ -31,13 +33,13 @@ import ch.ethz.seb.sebserver.gbl.util.Utils;
 import ch.ethz.seb.sebserver.webservice.servicelayer.dao.ConfigurationAttributeDAO;
 import ch.ethz.seb.sebserver.webservice.servicelayer.dao.ConfigurationValueDAO;
 import ch.ethz.seb.sebserver.webservice.servicelayer.dao.FilterMap;
-import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.XMLValueConverter;
+import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.AttributeValueConverter;
-import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.XMLValueConverterService;
+import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.AttributeValueConverterService;
 
 @Lazy
 @Component
 @WebServiceProfile
-public class TableConverter implements XMLValueConverter {
+public class TableConverter implements AttributeValueConverter {
 
     public static final Set<AttributeType> SUPPORTED_TYPES = Collections.unmodifiableSet(
             new HashSet<>(Arrays.asList(
@@ -45,16 +47,23 @@ public class TableConverter implements XMLValueConverter {
                     AttributeType.INLINE_TABLE,
                     AttributeType.COMPOSITE_TABLE)));
 
-    private static final String KEY_TEMPLATE = "<key>%s</key>";
+    private static final String XML_KEY_TEMPLATE = "<key>%s</key>";
-    private static final byte[] ARRAY_START = Utils.toByteArray("<array>");
+    private static final byte[] XML_ARRAY_START = Utils.toByteArray("<array>");
-    private static final byte[] ARRAY_END = Utils.toByteArray("</array>");
+    private static final byte[] XML_ARRAY_END = Utils.toByteArray("</array>");
-    private static final byte[] DICT_START = Utils.toByteArray("<dict>");
+    private static final byte[] XML_DICT_START = Utils.toByteArray("<dict>");
-    private static final byte[] DICT_END = Utils.toByteArray("</dict>");
+    private static final byte[] XML_DICT_END = Utils.toByteArray("</dict>");
-    private static final byte[] EMPTY_ARRAY = Utils.toByteArray("<array />");
+    private static final byte[] XML_EMPTY_ARRAY = Utils.toByteArray("<array />");
+
+    private static final String JSON_KEY_TEMPLATE = "\"%s\":";
+    private static final byte[] JSON_ARRAY_START = Utils.toByteArray("[");
+    private static final byte[] JSON_ARRAY_END = Utils.toByteArray("]");
+    private static final byte[] JSON_DICT_START = Utils.toByteArray("{");
+    private static final byte[] JSON_DICT_END = Utils.toByteArray("}");
+    private static final byte[] JSON_EMPTY_ARRAY = Utils.toByteArray("[]");
 
     private final ConfigurationAttributeDAO configurationAttributeDAO;
     private final ConfigurationValueDAO configurationValueDAO;
-    private XMLValueConverterService xmlValueConverterService;
+    private AttributeValueConverterService attributeValueConverterService;
 
     public TableConverter(
             final ConfigurationAttributeDAO configurationAttributeDAO,
@@ -65,8 +74,8 @@ public class TableConverter implements XMLValueConverter {
     }
 
     @Override
-    public void init(final XMLValueConverterService xmlValueConverterService) {
+    public void init(final AttributeValueConverterService attributeValueConverterService) {
-        this.xmlValueConverterService = xmlValueConverterService;
+        this.attributeValueConverterService = attributeValueConverterService;
     }
 
     @Override
@@ -74,76 +83,127 @@ public class TableConverter implements XMLValueConverter {
         return SUPPORTED_TYPES;
     }
 
-    @Override
-    public String name() {
-        return StringUtils.EMPTY;
-    }
-
     @Override
     public void convertToXML(
             final OutputStream out,
             final ConfigurationAttribute attribute,
-            final ConfigurationValue value) throws IOException {
+            final Function<ConfigurationAttribute, ConfigurationValue> valueSupplier) throws IOException {
 
-        out.write(Utils.toByteArray(String.format(KEY_TEMPLATE, extractName(attribute))));
+        convert(out, attribute, valueSupplier.apply(attribute), true);
+    }
+
+    @Override
+    public void convertToJSON(
+            final OutputStream out,
+            final ConfigurationAttribute attribute,
+            final Function<ConfigurationAttribute, ConfigurationValue> valueSupplier) throws IOException {
+
+        convert(out, attribute, valueSupplier.apply(attribute), false);
+    }
+
+    private void convert(
+            final OutputStream out,
+            final ConfigurationAttribute attribute,
+            final ConfigurationValue value,
+            final boolean xml) throws IOException {
 
         final List<List<ConfigurationValue>> values = this.configurationValueDAO.getOrderedTableValues(
                 value.institutionId,
                 value.configurationId,
-                attribute.id).getOrThrow();
+                attribute.id)
+                .getOrThrow();
 
-        if (values == null || values.isEmpty()) {
+        final boolean noValues = CollectionUtils.isEmpty(values);
-            out.write(EMPTY_ARRAY);
-            out.flush();
-            return;
-        }
 
         if (attribute.type != AttributeType.COMPOSITE_TABLE) {
-            out.write(ARRAY_START);
+
+            out.write(Utils.toByteArray(String.format(
+                    (xml) ? XML_KEY_TEMPLATE : JSON_KEY_TEMPLATE,
+                    extractName(attribute))));
+
+            if (noValues) {
+                out.write((xml) ? XML_EMPTY_ARRAY : JSON_EMPTY_ARRAY);
+                out.flush();
+                return;
+            } else {
+                out.write((xml) ? XML_ARRAY_START : JSON_ARRAY_START);
+            }
+        } else {
+            if (noValues) {
+                return;
+            } else {
+                out.write(Utils.toByteArray(String.format(
+                        (xml) ? XML_KEY_TEMPLATE : JSON_KEY_TEMPLATE,
+                        extractName(attribute))));
+            }
         }
 
         writeRows(
                 out,
-                getAttributes(attribute),
+                getSortedChildAttributes(attribute),
                 values,
-                this.xmlValueConverterService);
+                this.attributeValueConverterService,
+                xml);
 
         if (attribute.type != AttributeType.COMPOSITE_TABLE) {
-            out.write(ARRAY_END);
+            out.write((xml) ? XML_ARRAY_END : JSON_ARRAY_END);
         }
 
         out.flush();
     }
 
-    private Map<Long, ConfigurationAttribute> getAttributes(final ConfigurationAttribute attribute) {
-        return this.configurationAttributeDAO
-                .allMatching(new FilterMap().putIfAbsent(
-                        ConfigurationAttribute.FILTER_ATTR_PARENT_ID,
-                        attribute.getModelId()))
-                .getOrThrow()
-                .stream()
-                .collect(Collectors.toMap(
-                        attr -> attr.id,
-                        Function.identity()));
-
-    }
-
     private void writeRows(
             final OutputStream out,
             final Map<Long, ConfigurationAttribute> attributeMap,
             final List<List<ConfigurationValue>> values,
-            final XMLValueConverterService xmlValueConverterService) throws IOException {
+            final AttributeValueConverterService attributeValueConverterService,
+            final boolean xml) throws IOException {
 
-        for (final List<ConfigurationValue> rowValues : values) {
+        final Iterator<List<ConfigurationValue>> irows = values.iterator();
-            out.write(DICT_START);
+
-            for (final ConfigurationValue value : rowValues) {
+        while (irows.hasNext()) {
+            final List<ConfigurationValue> rowValues = irows.next();
+            out.write((xml) ? XML_DICT_START : JSON_DICT_START);
+
+            final Iterator<ConfigurationValue> ivalue = rowValues.iterator();
+
+            while (ivalue.hasNext()) {
+                final ConfigurationValue value = ivalue.next();
                 final ConfigurationAttribute attr = attributeMap.get(value.attributeId);
-                final XMLValueConverter converter = xmlValueConverterService.getXMLConverter(attr);
+                final AttributeValueConverter converter =
-                converter.convertToXML(out, attr, value);
+                        attributeValueConverterService.getAttributeValueConverter(attr);
+
+                if (xml) {
+                    converter.convertToXML(out, attr, a -> value);
+                } else {
+                    converter.convertToJSON(out, attr, a -> value);
+                }
+
+                if (!xml && ivalue.hasNext()) {
+                    out.write(Utils.toByteArray(Constants.LIST_SEPARATOR));
+                }
             }
-            out.write(DICT_END);
+            out.write((xml) ? XML_DICT_END : JSON_DICT_END);
+
+            if (!xml && irows.hasNext()) {
+                out.write(Utils.toByteArray(Constants.LIST_SEPARATOR));
+            }
+
             out.flush();
         }
     }
 
+    private Map<Long, ConfigurationAttribute> getSortedChildAttributes(final ConfigurationAttribute attribute) {
+        return this.configurationAttributeDAO
+                .allMatching(new FilterMap().putIfAbsent(
+                        ConfigurationAttribute.FILTER_ATTR_PARENT_ID,
+                        attribute.getModelId()))
+                .getOrThrow()
+                .stream()
+                .sorted()
+                .collect(Collectors.toMap(
+                        attr -> attr.id,
+                        Function.identity()));
+    }
+
 }

src/main/java/ch/ethz/seb/sebserver/webservice/weblayer/api/APIExceptionHandler.java

@@ -31,6 +31,7 @@ import org.springframework.web.servlet.mvc.method.annotation.ResponseEntityExcep
 import ch.ethz.seb.sebserver.gbl.api.APIMessage;
 import ch.ethz.seb.sebserver.gbl.api.APIMessage.APIMessageException;
 import ch.ethz.seb.sebserver.gbl.api.APIMessage.FieldValidationException;
+import ch.ethz.seb.sebserver.gbl.util.Utils;
 import ch.ethz.seb.sebserver.webservice.servicelayer.authorization.PermissionDeniedException;
 import ch.ethz.seb.sebserver.webservice.servicelayer.dao.ResourceNotFoundException;
 import ch.ethz.seb.sebserver.webservice.servicelayer.validation.BeanValidationException;
@@ -51,7 +52,10 @@ public class APIExceptionHandler extends ResponseEntityExceptionHandler {
 
         log.error("Unexpected generic error catched at the API endpoint: ", ex);
         final List<APIMessage> errors = Arrays.asList(APIMessage.ErrorMessage.GENERIC.of(ex.getMessage()));
-        return new ResponseEntity<>(errors, status);
+        return new ResponseEntity<>(
+                errors,
+                Utils.createJsonContentHeader(),
+                status);
     }
 
     @Override
@@ -67,7 +71,10 @@ public class APIExceptionHandler extends ResponseEntityExceptionHandler {
                 .map(field -> APIMessage.fieldValidationError(field))
                 .collect(Collectors.toList());
 
-        return new ResponseEntity<>(valErrors, HttpStatus.BAD_REQUEST);
+        return new ResponseEntity<>(
+                valErrors,
+                Utils.createJsonContentHeader(),
+                HttpStatus.BAD_REQUEST);
     }
 
     @ExceptionHandler(OAuth2Exception.class)
@@ -77,7 +84,10 @@ public class APIExceptionHandler extends ResponseEntityExceptionHandler {
 
         log.error("OAuth2Exception: ", ex);
         final APIMessage message = APIMessage.ErrorMessage.UNAUTHORIZED.of(ex.getMessage());
-        return new ResponseEntity<>(message, HttpStatus.UNAUTHORIZED);
+        return new ResponseEntity<>(
+                message,
+                Utils.createJsonContentHeader(),
+                HttpStatus.UNAUTHORIZED);
     }
 
     @ExceptionHandler(BeanValidationException.class)
@@ -91,7 +101,10 @@ public class APIExceptionHandler extends ResponseEntityExceptionHandler {
                 .map(field -> APIMessage.fieldValidationError(field))
                 .collect(Collectors.toList());
 
-        return new ResponseEntity<>(valErrors, HttpStatus.BAD_REQUEST);
+        return new ResponseEntity<>(
+                valErrors,
+                Utils.createJsonContentHeader(),
+                HttpStatus.BAD_REQUEST);
     }
 
     @ExceptionHandler(ResourceNotFoundException.class)
@@ -149,6 +162,7 @@ public class APIExceptionHandler extends ResponseEntityExceptionHandler {
 
         return new ResponseEntity<>(
                 ex.getAPIMessages(),
+                Utils.createJsonContentHeader(),
                 HttpStatus.BAD_REQUEST);
     }
 
@@ -159,6 +173,7 @@ public class APIExceptionHandler extends ResponseEntityExceptionHandler {
 
         return new ResponseEntity<>(
                 Arrays.asList(ex.apiMessage),
+                Utils.createJsonContentHeader(),
                 HttpStatus.BAD_REQUEST);
     }
 

src/test/java/ch/ethz/seb/sebserver/webservice/servicelayer/sebconfig/impl/ConfigAttributeSortOrderTest.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2019 ETH Zürich, Educational Development and Technology (LET)
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+package ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.impl;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.junit.Test;
+
+import ch.ethz.seb.sebserver.gbl.model.sebconfig.AttributeType;
+import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationAttribute;
+
+public class ConfigAttributeSortOrderTest {
+
+    @Test
+    public void testSortOrder() throws Exception {
+        // test example from: https://www.safeexambrowser.org/developer/seb-config-key.html
+        // For example the key <key>allowWlan</key> comes before <key>allowWLAN</key>
+
+        final ConfigurationAttribute aa = new ConfigurationAttribute(
+                1L,
+                null,
+                "aa",
+                AttributeType.CHECKBOX,
+                null, null, null, "false");
+
+        final ConfigurationAttribute allowWlan = new ConfigurationAttribute(
+                1L,
+                null,
+                "allowWlan",
+                AttributeType.CHECKBOX,
+                null, null, null, "false");
+        final ConfigurationAttribute allowWLAN = new ConfigurationAttribute(
+                1L,
+                null,
+                "allowWLAN",
+                AttributeType.CHECKBOX,
+                null, null, null, "false");
+
+        final ConfigurationAttribute zz = new ConfigurationAttribute(
+                1L,
+                null,
+                "zz",
+                AttributeType.CHECKBOX,
+                null, null, null, "false");
+
+        final List<ConfigurationAttribute> list = Arrays.asList(zz, allowWLAN, aa, allowWlan);
+        Collections.sort(list);
+
+        assertEquals(
+                "[aa, allowWlan, allowWLAN, zz]",
+                list.stream()
+                        .map(ConfigurationAttribute::getName)
+                        .collect(Collectors.toList())
+                        .toString());
+    }
+
+}

src/test/java/ch/ethz/seb/sebserver/webservice/servicelayer/sebconfig/impl/converter/ArrayOfStringConverterTest.java

@@ -0,0 +1,161 @@
+/*
+ * Copyright (c) 2019 ETH Zürich, Educational Development and Technology (LET)
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+package ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.impl.converter;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.ByteArrayOutputStream;
+
+import org.junit.Test;
+
+import ch.ethz.seb.sebserver.gbl.model.sebconfig.AttributeType;
+import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationAttribute;
+import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationValue;
+
+public class ArrayOfStringConverterTest {
+
+    @Test
+    public void testXML() throws Exception {
+        final ArrayOfStringConverter arrayOfStringConverter = new ArrayOfStringConverter();
+        final ConfigurationAttribute attribute = new ConfigurationAttribute(
+                1L,
+                null,
+                "attribute",
+                AttributeType.CHECKBOX,
+                null, null, null, "defaultValue");
+
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        arrayOfStringConverter.convertToXML(
+                out,
+                attribute,
+                attr -> new ConfigurationValue(1l, 1l, 1l, 1l, 1, "one,two,tree"));
+
+        final String xmlString = new String(out.toByteArray());
+        assertEquals(
+                "<key>attribute</key><array><string>one</string><string>two</string><string>tree</string></array>",
+                xmlString);
+    }
+
+    @Test
+    public void testEmptyXML() throws Exception {
+        final ArrayOfStringConverter arrayOfStringConverter = new ArrayOfStringConverter();
+        final ConfigurationAttribute attribute = new ConfigurationAttribute(
+                1L,
+                null,
+                "attribute",
+                AttributeType.CHECKBOX,
+                null, null, null, "defaultValue");
+
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        arrayOfStringConverter.convertToXML(
+                out,
+                attribute,
+                attr -> new ConfigurationValue(1l, 1l, 1l, 1l, 1, ""));
+
+        final String xmlString = new String(out.toByteArray());
+        assertEquals(
+                "<key>attribute</key><array></array>",
+                xmlString);
+    }
+
+    @Test
+    public void testNullXML() throws Exception {
+        final ArrayOfStringConverter arrayOfStringConverter = new ArrayOfStringConverter();
+        final ConfigurationAttribute attribute = new ConfigurationAttribute(
+                1L,
+                null,
+                "attribute",
+                AttributeType.CHECKBOX,
+                null, null, null, "defaultValue");
+
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        arrayOfStringConverter.convertToXML(
+                out,
+                attribute,
+                attr -> new ConfigurationValue(1l, 1l, 1l, 1l, 1, null));
+
+        final String xmlString = new String(out.toByteArray());
+        assertEquals(
+                "<key>attribute</key><array><string>defaultValue</string></array>",
+                xmlString);
+    }
+
+    @Test
+    public void testJSON() throws Exception {
+        final ArrayOfStringConverter arrayOfStringConverter = new ArrayOfStringConverter();
+        final ConfigurationAttribute attribute = new ConfigurationAttribute(
+                1L,
+                null,
+                "attribute",
+                AttributeType.CHECKBOX,
+                null, null, null, "defaultValue");
+
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        arrayOfStringConverter.convertToJSON(
+                out,
+                attribute,
+                attr -> new ConfigurationValue(1l, 1l, 1l, 1l, 1, "one,two,tree"));
+
+        final String xmlString = new String(out.toByteArray());
+        assertEquals(
+                "\"attribute\":[\"one\",\"two\",\"tree\"]",
+                xmlString);
+    }
+
+    @Test
+    public void testEmptyJSON() throws Exception {
+        final ArrayOfStringConverter arrayOfStringConverter = new ArrayOfStringConverter();
+        final ConfigurationAttribute attribute = new ConfigurationAttribute(
+                1L,
+                null,
+                "attribute",
+                AttributeType.CHECKBOX,
+                null, null, null, "defaultValue");
+
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        arrayOfStringConverter.convertToJSON(
+                out,
+                attribute,
+                attr -> new ConfigurationValue(1l, 1l, 1l, 1l, 1, ""));
+
+        final String xmlString = new String(out.toByteArray());
+        assertEquals(
+                "\"attribute\":[]",
+                xmlString);
+    }
+
+    @Test
+    public void testNullJSON() throws Exception {
+        final ArrayOfStringConverter arrayOfStringConverter = new ArrayOfStringConverter();
+        final ConfigurationAttribute attribute = new ConfigurationAttribute(
+                1L,
+                null,
+                "attribute",
+                AttributeType.CHECKBOX,
+                null, null, null, "defaultValue");
+
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        arrayOfStringConverter.convertToJSON(
+                out,
+                attribute,
+                attr -> new ConfigurationValue(1l, 1l, 1l, 1l, 1, null));
+
+        final String xmlString = new String(out.toByteArray());
+        assertEquals(
+                "\"attribute\":[\"defaultValue\"]",
+                xmlString);
+    }
+
+}

src/test/java/ch/ethz/seb/sebserver/webservice/servicelayer/sebconfig/impl/converter/TableConverterTest.java

@@ -0,0 +1,329 @@
+/*
+ * Copyright (c) 2019 ETH Zürich, Educational Development and Technology (LET)
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+package ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.impl.converter;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.ByteArrayOutputStream;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+
+import org.junit.Test;
+import org.mockito.Mockito;
+
+import ch.ethz.seb.sebserver.gbl.model.sebconfig.AttributeType;
+import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationAttribute;
+import ch.ethz.seb.sebserver.gbl.model.sebconfig.ConfigurationValue;
+import ch.ethz.seb.sebserver.gbl.util.Result;
+import ch.ethz.seb.sebserver.webservice.servicelayer.dao.ConfigurationAttributeDAO;
+import ch.ethz.seb.sebserver.webservice.servicelayer.dao.ConfigurationValueDAO;
+import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.AttributeValueConverter;
+import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.AttributeValueConverterService;
+import ch.ethz.seb.sebserver.webservice.servicelayer.sebconfig.impl.AttributeValueConverterServiceImpl;
+
+public class TableConverterTest {
+
+    // ********************************
+    // **** table
+    // ********************************
+    private final ConfigurationAttribute TABLE_ATTR =
+            new ConfigurationAttribute(1L, null, "table", AttributeType.TABLE, null, null, null, null);
+    private final ConfigurationValue TABLE_VALUE =
+            new ConfigurationValue(1L, 1L, 1L, 1L, 0, null);
+
+    private final ConfigurationAttribute COLUMN_ATTR_1 =
+            new ConfigurationAttribute(2L, 1L, "attr1", AttributeType.TEXT_FIELD, null, null, null, null);
+    private final ConfigurationAttribute COLUMN_ATTR_2 =
+            new ConfigurationAttribute(3L, 1L, "attr2", AttributeType.TEXT_FIELD, null, null, null, null);
+
+    private final ConfigurationValue ROW_1_ATTR_1 =
+            new ConfigurationValue(2L, 1L, 1L, 2L, 0, "1");
+    private final ConfigurationValue ROW_1_ATTR_2 =
+            new ConfigurationValue(3L, 1L, 1L, 3L, 0, "2");
+
+    private final ConfigurationValue ROW_2_ATTR_1 =
+            new ConfigurationValue(4L, 1L, 1L, 2L, 1, "3");
+    private final ConfigurationValue ROW_2_ATTR_2 =
+            new ConfigurationValue(5L, 1L, 1L, 3L, 1, "4");
+
+    private final Collection<ConfigurationAttribute> TABLE_COLUMNS = Arrays.asList(
+            this.COLUMN_ATTR_1,
+            this.COLUMN_ATTR_2);
+
+    private final List<List<ConfigurationValue>> TABLE_VALUES = Arrays.asList(
+            Arrays.asList(this.ROW_1_ATTR_1, this.ROW_1_ATTR_2),
+            Arrays.asList(this.ROW_2_ATTR_1, this.ROW_2_ATTR_2));
+
+    // ********************************
+    // **** Composite table
+    // ********************************
+    private final ConfigurationAttribute COMPOSITE_TABLE_ATTR =
+            new ConfigurationAttribute(1L, null, "table", AttributeType.COMPOSITE_TABLE, null, null, null, null);
+    private final ConfigurationValue COMPOSITE_TABLE_VALUE =
+            new ConfigurationValue(1L, 1L, 1L, 1L, 0, null);
+
+    private final ConfigurationAttribute COMPOSITE_COLUMN_ATTR_1 =
+            new ConfigurationAttribute(2L, 1L, "attr1", AttributeType.TEXT_FIELD, null, null, null, null);
+    private final ConfigurationAttribute COMPOSITE_COLUMN_ATTR_2 =
+            new ConfigurationAttribute(3L, 1L, "attr2", AttributeType.TEXT_FIELD, null, null, null, null);
+
+    private final ConfigurationValue COMPOSITE_ROW_1_ATTR_1 =
+            new ConfigurationValue(2L, 1L, 1L, 2L, 0, "1");
+    private final ConfigurationValue COMPOSITE_ROW_1_ATTR_2 =
+            new ConfigurationValue(3L, 1L, 1L, 3L, 0, "2");
+
+    private final Collection<ConfigurationAttribute> COMPOSITE_TABLE_ENTRIES = Arrays.asList(
+            this.COMPOSITE_COLUMN_ATTR_1,
+            this.COMPOSITE_COLUMN_ATTR_2);
+
+    private final List<List<ConfigurationValue>> COMPOSITE_TABLE_VALUES = Arrays.asList(
+            Arrays.asList(this.COMPOSITE_ROW_1_ATTR_1, this.COMPOSITE_ROW_1_ATTR_2));
+
+    @Test
+    public void testXMLNormalTable() throws Exception {
+
+        final ConfigurationAttributeDAO configurationAttributeDAO =
+                Mockito.mock(ConfigurationAttributeDAO.class);
+        Mockito.when(configurationAttributeDAO.allMatching(Mockito.any()))
+                .thenReturn(Result.of(this.TABLE_COLUMNS));
+
+        final ConfigurationValueDAO configurationValueDAO =
+                Mockito.mock(ConfigurationValueDAO.class);
+        Mockito.when(configurationValueDAO.getOrderedTableValues(1L, 1L, 1L))
+                .thenReturn(Result.of(this.TABLE_VALUES));
+
+        final TableConverter tableConverter = new TableConverter(configurationAttributeDAO, configurationValueDAO);
+        tableConverter.init(createAttributeValueConverterService());
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        tableConverter.convertToXML(out, this.TABLE_ATTR, attr -> this.TABLE_VALUE);
+
+        final String xmlString = new String(out.toByteArray());
+        assertEquals(
+                "<key>table</key>"
+                        + "<array>"
+                        + "<dict>"
+                        + "<key>attr1</key>"
+                        + "<string>1</string>"
+                        + "<key>attr2</key>"
+                        + "<string>2</string>"
+                        + "</dict>"
+                        + "<dict>"
+                        + "<key>attr1</key>"
+                        + "<string>3</string>"
+                        + "<key>attr2</key>"
+                        + "<string>4</string>"
+                        + "</dict>"
+                        + "</array>",
+                xmlString);
+
+    }
+
+    @Test
+    public void testXMLNormalTableNoValues() throws Exception {
+
+        final ConfigurationAttributeDAO configurationAttributeDAO =
+                Mockito.mock(ConfigurationAttributeDAO.class);
+        Mockito.when(configurationAttributeDAO.allMatching(Mockito.any()))
+                .thenReturn(Result.of(this.TABLE_COLUMNS));
+
+        final ConfigurationValueDAO configurationValueDAO =
+                Mockito.mock(ConfigurationValueDAO.class);
+        Mockito.when(configurationValueDAO.getOrderedTableValues(1L, 1L, 1L))
+                .thenReturn(Result.of(Collections.emptyList()));
+
+        final TableConverter tableConverter = new TableConverter(configurationAttributeDAO, configurationValueDAO);
+        tableConverter.init(createAttributeValueConverterService());
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        tableConverter.convertToXML(out, this.TABLE_ATTR, attr -> this.TABLE_VALUE);
+
+        final String xmlString = new String(out.toByteArray());
+        assertEquals(
+                "<key>table</key><array />",
+                xmlString);
+
+    }
+
+    @Test
+    public void testXMLCompositeTable() throws Exception {
+
+        final ConfigurationAttributeDAO configurationAttributeDAO =
+                Mockito.mock(ConfigurationAttributeDAO.class);
+        Mockito.when(configurationAttributeDAO.allMatching(Mockito.any()))
+                .thenReturn(Result.of(this.COMPOSITE_TABLE_ENTRIES));
+
+        final ConfigurationValueDAO configurationValueDAO =
+                Mockito.mock(ConfigurationValueDAO.class);
+        Mockito.when(configurationValueDAO.getOrderedTableValues(1L, 1L, 1L))
+                .thenReturn(Result.of(this.COMPOSITE_TABLE_VALUES));
+
+        final TableConverter tableConverter = new TableConverter(configurationAttributeDAO, configurationValueDAO);
+        tableConverter.init(createAttributeValueConverterService());
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        tableConverter.convertToXML(out, this.COMPOSITE_TABLE_ATTR, attr -> this.COMPOSITE_TABLE_VALUE);
+
+        final String xmlString = new String(out.toByteArray());
+        assertEquals(
+                "<key>table</key>"
+                        + "<dict>"
+                        + "<key>attr1</key>"
+                        + "<string>1</string>"
+                        + "<key>attr2</key>"
+                        + "<string>2</string>"
+                        + "</dict>",
+                xmlString);
+
+    }
+
+    @Test
+    public void testXMLCompositeTableEmpty() throws Exception {
+
+        final ConfigurationAttributeDAO configurationAttributeDAO =
+                Mockito.mock(ConfigurationAttributeDAO.class);
+        Mockito.when(configurationAttributeDAO.allMatching(Mockito.any()))
+                .thenReturn(Result.of(this.COMPOSITE_TABLE_ENTRIES));
+
+        final ConfigurationValueDAO configurationValueDAO =
+                Mockito.mock(ConfigurationValueDAO.class);
+        Mockito.when(configurationValueDAO.getOrderedTableValues(1L, 1L, 1L))
+                .thenReturn(Result.of(Collections.emptyList()));
+
+        final TableConverter tableConverter = new TableConverter(configurationAttributeDAO, configurationValueDAO);
+        tableConverter.init(createAttributeValueConverterService());
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        tableConverter.convertToXML(out, this.COMPOSITE_TABLE_ATTR, attr -> this.COMPOSITE_TABLE_VALUE);
+
+        final String xmlString = new String(out.toByteArray());
+        assertEquals(
+                "",
+                xmlString);
+
+    }
+
+    @Test
+    public void testJSONNormalTable() throws Exception {
+
+        final ConfigurationAttributeDAO configurationAttributeDAO =
+                Mockito.mock(ConfigurationAttributeDAO.class);
+        Mockito.when(configurationAttributeDAO.allMatching(Mockito.any()))
+                .thenReturn(Result.of(this.TABLE_COLUMNS));
+
+        final ConfigurationValueDAO configurationValueDAO =
+                Mockito.mock(ConfigurationValueDAO.class);
+        Mockito.when(configurationValueDAO.getOrderedTableValues(1L, 1L, 1L))
+                .thenReturn(Result.of(this.TABLE_VALUES));
+
+        final TableConverter tableConverter = new TableConverter(configurationAttributeDAO, configurationValueDAO);
+        tableConverter.init(createAttributeValueConverterService());
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        tableConverter.convertToJSON(out, this.TABLE_ATTR, attr -> this.TABLE_VALUE);
+
+        final String xmlString = new String(out.toByteArray());
+        // expected : "table":[{"attr1":"1","attr2":"2"},{"attr1":"3","attr2":"4"}]
+        assertEquals(
+                "\"table\":[{\"attr1\":\"1\",\"attr2\":\"2\"},{\"attr1\":\"3\",\"attr2\":\"4\"}]",
+                xmlString);
+
+    }
+
+    @Test
+    public void testJSONNormalTableEmpty() throws Exception {
+
+        final ConfigurationAttributeDAO configurationAttributeDAO =
+                Mockito.mock(ConfigurationAttributeDAO.class);
+        Mockito.when(configurationAttributeDAO.allMatching(Mockito.any()))
+                .thenReturn(Result.of(this.TABLE_COLUMNS));
+
+        final ConfigurationValueDAO configurationValueDAO =
+                Mockito.mock(ConfigurationValueDAO.class);
+        Mockito.when(configurationValueDAO.getOrderedTableValues(1L, 1L, 1L))
+                .thenReturn(Result.of(Collections.emptyList()));
+
+        final TableConverter tableConverter = new TableConverter(configurationAttributeDAO, configurationValueDAO);
+        tableConverter.init(createAttributeValueConverterService());
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        tableConverter.convertToJSON(out, this.TABLE_ATTR, attr -> this.TABLE_VALUE);
+
+        final String xmlString = new String(out.toByteArray());
+        // expected : "table":[]
+        assertEquals(
+                "\"table\":[]",
+                xmlString);
+
+    }
+
+    @Test
+    public void testJSONCompositeTable() throws Exception {
+
+        final ConfigurationAttributeDAO configurationAttributeDAO =
+                Mockito.mock(ConfigurationAttributeDAO.class);
+        Mockito.when(configurationAttributeDAO.allMatching(Mockito.any()))
+                .thenReturn(Result.of(this.COMPOSITE_TABLE_ENTRIES));
+
+        final ConfigurationValueDAO configurationValueDAO =
+                Mockito.mock(ConfigurationValueDAO.class);
+        Mockito.when(configurationValueDAO.getOrderedTableValues(1L, 1L, 1L))
+                .thenReturn(Result.of(this.COMPOSITE_TABLE_VALUES));
+
+        final TableConverter tableConverter = new TableConverter(configurationAttributeDAO, configurationValueDAO);
+        tableConverter.init(createAttributeValueConverterService());
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        tableConverter.convertToJSON(out, this.COMPOSITE_TABLE_ATTR, attr -> this.COMPOSITE_TABLE_VALUE);
+
+        final String xmlString = new String(out.toByteArray());
+        // expected : "table":{"attr1":"1","attr2":"2"}
+        assertEquals(
+                "\"table\":{\"attr1\":\"1\",\"attr2\":\"2\"}",
+                xmlString);
+
+    }
+
+    @Test
+    public void testJSONCompositeTableEmpty() throws Exception {
+
+        final ConfigurationAttributeDAO configurationAttributeDAO =
+                Mockito.mock(ConfigurationAttributeDAO.class);
+        Mockito.when(configurationAttributeDAO.allMatching(Mockito.any()))
+                .thenReturn(Result.of(this.COMPOSITE_TABLE_ENTRIES));
+
+        final ConfigurationValueDAO configurationValueDAO =
+                Mockito.mock(ConfigurationValueDAO.class);
+        Mockito.when(configurationValueDAO.getOrderedTableValues(1L, 1L, 1L))
+                .thenReturn(Result.of(Collections.emptyList()));
+
+        final TableConverter tableConverter = new TableConverter(configurationAttributeDAO, configurationValueDAO);
+        tableConverter.init(createAttributeValueConverterService());
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        tableConverter.convertToJSON(out, this.COMPOSITE_TABLE_ATTR, attr -> this.COMPOSITE_TABLE_VALUE);
+
+        final String xmlString = new String(out.toByteArray());
+        // expected :
+        assertEquals(
+                "",
+                xmlString);
+
+    }
+
+    private AttributeValueConverterService createAttributeValueConverterService() {
+        final List<AttributeValueConverter> converter = new ArrayList<>();
+        converter.add(new StringConverter());
+        return new AttributeValueConverterServiceImpl(converter);
+    }
+
+}