fixes and ping preformance

src/main/java/ch/ethz/seb/sebserver/gui/widget/MultiSelectionCombo.java

@@ -134,22 +134,10 @@ public final class MultiSelectionCombo extends Composite implements Selection {
 
         Arrays.asList(StringUtils.split(keys, Constants.LIST_SEPARATOR))
                 .stream()
-                .map(this::itemForName)
+                .map(this::itemForId)
                 .forEach(this::addSelection);
     }
 
-    private Tuple<String> itemForName(final String name) {
-        final Optional<Tuple<String>> findFirst = this.availableValues
-                .stream()
-                .filter(it -> it._2 != null && it._2.equals(name))
-                .findFirst();
-        if (findFirst.isPresent()) {
-            return findFirst.get();
-        }
-
-        return null;
-    }
-
     @Override
     public String getSelectionValue() {
         if (this.selectedValues.isEmpty()) {
@@ -237,4 +225,28 @@ public final class MultiSelectionCombo extends Composite implements Selection {
         }
     }
 
+    private Tuple<String> itemForName(final String name) {
+        final Optional<Tuple<String>> findFirst = this.availableValues
+                .stream()
+                .filter(it -> it._2 != null && it._2.equals(name))
+                .findFirst();
+        if (findFirst.isPresent()) {
+            return findFirst.get();
+        }
+
+        return null;
+    }
+
+    private Tuple<String> itemForId(final String id) {
+        final Optional<Tuple<String>> findFirst = this.availableValues
+                .stream()
+                .filter(it -> it._1 != null && it._1.equals(id))
+                .findFirst();
+        if (findFirst.isPresent()) {
+            return findFirst.get();
+        }
+
+        return null;
+    }
+
 }

src/main/java/ch/ethz/seb/sebserver/webservice/servicelayer/session/impl/SebInstructionServiceImpl.java

@@ -75,7 +75,8 @@ public class SebInstructionServiceImpl implements SebInstructionService {
 
         loadInstruction()
                 .onError(
-                        error -> log.error("Failed  to initialize and load persistent storage SEB client instructions: ",
+                        error -> log.error(
+                                "Failed  to initialize and load persistent storage SEB client instructions: ",
                                 error));
 
         if (this.instructions.size() > 0) {
@@ -116,6 +117,9 @@ public class SebInstructionServiceImpl implements SebInstructionService {
     @Override
     public String getInstructionJSON(final String connectionToken) {
         refreshCache();
+        if (this.instructions.isEmpty()) {
+            return null;
+        }
 
         final ClientInstructionRecord clientInstruction = this.instructions.remove(connectionToken);
         if (clientInstruction != null) {

src/main/java/ch/ethz/seb/sebserver/webservice/weblayer/api/ExamAPI_V1_Controller.java

@@ -13,7 +13,6 @@ import java.security.Principal;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
-import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.Executor;
 import java.util.stream.Collectors;
 
@@ -26,6 +25,7 @@ import org.slf4j.LoggerFactory;
 import org.springframework.beans.factory.annotation.Qualifier;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
 import org.springframework.util.MultiValueMap;
 import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RequestHeader;
@@ -129,7 +129,8 @@ public class ExamAPI_V1_Controller {
         }
 
         if (result.isEmpty()) {
-            log.warn("There are no currently running exams for institution: {}. SEB connection creation denied", institutionId);
+            log.warn("There are no currently running exams for institution: {}. SEB connection creation denied",
+                    institutionId);
             throw new IllegalStateException("There are no currently running exams");
         }
 
@@ -306,22 +307,48 @@ public class ExamAPI_V1_Controller {
         }
     }
 
+    private static final ResponseEntity<String> EMPTY_PING_RESPONSE = ResponseEntity
+            .ok()
+            .build();
+
     @RequestMapping(
             path = API.EXAM_API_PING_ENDPOINT,
             method = RequestMethod.POST,
             consumes = MediaType.APPLICATION_FORM_URLENCODED_VALUE,
             produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
-    public CompletableFuture<String> ping(
+    public ResponseEntity<String> ping(
             @RequestHeader(name = API.EXAM_API_SEB_CONNECTION_TOKEN, required = true) final String connectionToken,
             @RequestParam(name = API.EXAM_API_PING_TIMESTAMP, required = true) final long timestamp,
             @RequestParam(name = API.EXAM_API_PING_NUMBER, required = false) final int pingNumber) {
 
-        return CompletableFuture.supplyAsync(
+        final String notifyPing = this.sebClientConnectionService
-                () -> this.sebClientConnectionService
+                .notifyPing(connectionToken, timestamp, pingNumber);
-                        .notifyPing(connectionToken, timestamp, pingNumber),
+
-                this.executor);
+        if (notifyPing == null) {
+            return EMPTY_PING_RESPONSE;
+        }
+
+        return ResponseEntity
+                .ok()
+                .body(notifyPing);
     }
 
+//    @RequestMapping(
+//            path = API.EXAM_API_PING_ENDPOINT,
+//            method = RequestMethod.POST,
+//            consumes = MediaType.APPLICATION_FORM_URLENCODED_VALUE,
+//            produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
+//    public CompletableFuture<String> ping(
+//            @RequestHeader(name = API.EXAM_API_SEB_CONNECTION_TOKEN, required = true) final String connectionToken,
+//            @RequestParam(name = API.EXAM_API_PING_TIMESTAMP, required = true) final long timestamp,
+//            @RequestParam(name = API.EXAM_API_PING_NUMBER, required = false) final int pingNumber) {
+//
+//        return CompletableFuture.supplyAsync(
+//                () -> this.sebClientConnectionService
+//                        .notifyPing(connectionToken, timestamp, pingNumber),
+//                this.executor);
+//    }
+
     @RequestMapping(
             path = API.EXAM_API_EVENT_ENDPOINT,
             method = RequestMethod.POST,

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

@@ -339,6 +339,14 @@ public class ExamAdministrationController extends EntityController<Exam, Exam> {
                 .flatMap(this.examAdminService::applyAdditionalSEBRestrictions);
     }
 
+    @Override
+    protected Result<Exam> notifySaved(final Exam entity) {
+        return Result.tryCatch(() -> {
+            this.examSessionService.flushCache(entity);
+            return entity;
+        });
+    }
+
     @Override
     protected Result<Exam> validForCreate(final Exam entity) {
         return super.validForCreate(entity)