Add exception mappers for custom exceptions

* Exception mapper for TaskNotFound exceptions - returns a 404 Not Found response
* Exception mapper for InvalidTaskData exceptions - returns a 400 Bad Request response

src/main/java/taskmanagement/api/ApplicationConfig.java

@@ -18,6 +18,8 @@ public class ApplicationConfig extends ResourceConfig {
     public ApplicationConfig(ServiceLocator serviceLocator) {
         register(TaskManagementResource.class);
         register(JsonObjectMapperProvider.class);
+        register(InvalidTaskDataExceptionMapper.class);
+        register(TaskNotFoundExceptionMapper.class);
 
         // bridge the Guice container (Injector) into the HK2 container (ServiceLocator)
         Injector injector = Guice.createInjector(new ApplicationModule());

src/main/java/taskmanagement/api/ExceptionMessage.java

@@ -0,0 +1,14 @@
+package taskmanagement.api;
+
+public class ExceptionMessage {
+
+    private final String message;
+
+    public ExceptionMessage(String message) {
+        this.message = message;
+    }
+
+    public String getMessage() {
+        return message;
+    }
+}

src/main/java/taskmanagement/api/InvalidTaskDataExceptionMapper.java

@@ -0,0 +1,20 @@
+package taskmanagement.api;
+
+import taskmanagement.exceptions.InvalidTaskDataException;
+
+import javax.ws.rs.core.MediaType;
+import javax.ws.rs.core.Response;
+import javax.ws.rs.ext.ExceptionMapper;
+
+public class InvalidTaskDataExceptionMapper implements ExceptionMapper<InvalidTaskDataException> {
+
+    @Override
+    public Response toResponse(InvalidTaskDataException exception) {
+        return Response
+                .status(Response.Status.BAD_REQUEST)
+                .entity(new ExceptionMessage(exception.getMessage()))
+                .type(MediaType.APPLICATION_JSON)
+                .build();
+    }
+
+}

src/main/java/taskmanagement/api/TaskNotFoundExceptionMapper.java

@@ -0,0 +1,20 @@
+package taskmanagement.api;
+
+import taskmanagement.exceptions.TaskNotFoundException;
+
+import javax.ws.rs.core.MediaType;
+import javax.ws.rs.core.Response;
+import javax.ws.rs.ext.ExceptionMapper;
+
+public class TaskNotFoundExceptionMapper implements ExceptionMapper<TaskNotFoundException> {
+
+    @Override
+    public Response toResponse(TaskNotFoundException exception) {
+        return Response
+                .status(Response.Status.NOT_FOUND)
+                .entity(new ExceptionMessage(exception.getMessage()))
+                .type(MediaType.APPLICATION_JSON)
+                .build();
+    }
+
+}