ONOS-2124 Improved web-exception handling when an anonymous exception, i.e. one …

…without a message, is raised.

Top stack-frame will be used as a message if exception has no message of its own.

Change-Id: I28d68e05a0d805c7320e133d8e17081513cb503c

@@ -21,6 +21,8 @@ import com.fasterxml.jackson.databind.node.ObjectNode;
 import javax.ws.rs.core.Response;
 import javax.ws.rs.ext.ExceptionMapper;
 
+import static com.google.common.base.Strings.isNullOrEmpty;
+
 /**
  * Base exception mapper implementation.
  */
@@ -49,9 +51,27 @@ public abstract class AbstractMapper<E extends Throwable> implements ExceptionMa
     protected Response.ResponseBuilder response(Response.Status status,
                                                 Throwable exception) {
         ObjectMapper mapper = new ObjectMapper();
+        String message = messageFrom(exception);
         ObjectNode result = mapper.createObjectNode()
                 .put("code", status.getStatusCode())
-                .put("message", exception.getMessage());
+                .put("message", message);
         return Response.status(status).entity(result.toString());
     }
+
+    /**
+     * Produces a response message from the supplied exception. Either it will
+     * use the exception message, if there is one, or it will use the top
+     * stack-frame message.
+     *
+     * @param exception exception from which to produce a message
+     * @return response message
+     */
+    protected String messageFrom(Throwable exception) {
+        if (isNullOrEmpty(exception.getMessage())) {
+            StackTraceElement[] trace = exception.getStackTrace();
+            return trace.length == 0 ? "Unknown error" : trace[0].toString();
+        }
+        return exception.getMessage();
+    }
+
 }

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.rest.exceptions;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+/**
+ * Set of tests for the various exception mappers.
+ */
+public class ExceptionMapperTest {
+
+    @Test
+    public void emptyMessage() {
+        RuntimeException exception = new NullPointerException();
+        ServerErrorMapper mapper = new ServerErrorMapper();
+        Object response = mapper.toResponse(exception).getEntity();
+        assertTrue("incorrect response",
+                   response.toString().contains("ExceptionMapperTest.emptyMessage("));
+    }
+}
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