Implemented "NotChangedException" when detecting that no response is …

…required #77

agent/core/src/main/java/org/jolokia/backend/BackendManager.java

@@ -7,6 +7,7 @@
 
 import javax.management.*;
 
+import org.jolokia.backend.executor.NotChangedException;
 import org.jolokia.config.ConfigKey;
 import org.jolokia.config.Configuration;
 import org.jolokia.converter.Converters;
@@ -144,11 +145,21 @@ public JSONObject handleRequest(JmxRequest pJmxReq) throws InstanceNotFoundExcep
         if (debug) {
             time = System.currentTimeMillis();
         }
-        JSONObject json = callRequestDispatcher(pJmxReq);
-
-        // Update global history store
-        historyStore.updateAndAdd(pJmxReq,json);
-        json.put("status",200 /* success */);
+        JSONObject json = null;
+        try {
+            json = callRequestDispatcher(pJmxReq);
+
+            // Update global history store, add timestamp and possibly history information to the request
+            historyStore.updateAndAdd(pJmxReq,json);
+            json.put("status",200 /* success */);
+        } catch (NotChangedException exp) {
+            // A handled indicates that its value hasn't changed. We return an status with
+            //"304 Not Modified" similar to the HTTP status code (http://en.wikipedia.org/wiki/HTTP_status)
+            json = new JSONObject();
+            json.put("request",pJmxReq.toJSON());
+            json.put("status",304);
+            json.put("timestamp",System.currentTimeMillis() / 1000);
+        }
 
         if (debug) {
             debug("Execution time: " + (System.currentTimeMillis() - time) + " ms");
@@ -368,7 +379,7 @@ private RequestDispatcher createDispatcher(String pDispatcherClass,
 
     // call the an appropriate request dispatcher
     private JSONObject callRequestDispatcher(JmxRequest pJmxReq)
-            throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException, IOException {
+            throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException, IOException, NotChangedException {
         Object retValue = null;
         boolean useValueWithPath = false;
         boolean found = false;

agent/core/src/main/java/org/jolokia/backend/LocalRequestDispatcher.java

@@ -20,6 +20,7 @@
 
 import javax.management.*;
 
+import org.jolokia.backend.executor.NotChangedException;
 import org.jolokia.config.ConfigKey;
 import org.jolokia.config.Configuration;
 import org.jolokia.converter.Converters;
@@ -85,7 +86,7 @@ public boolean useReturnValueWithPath(JmxRequest pJmxRequest) {
 
     /** {@inheritDoc} */
     public Object dispatchRequest(JmxRequest pJmxReq)
-            throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException {
+            throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException, NotChangedException {
         JsonRequestHandler handler = requestHandlerManager.getRequestHandler(pJmxReq.getType());
         return mBeanServerHandler.dispatchRequest(handler, pJmxReq);
     }

agent/core/src/main/java/org/jolokia/backend/MBeanServerExecutorLocal.java

@@ -22,6 +22,7 @@
 import javax.management.*;
 
 import org.jolokia.backend.executor.AbstractMBeanServerExecutor;
+import org.jolokia.backend.executor.NotChangedException;
 import org.jolokia.detector.ServerDetector;
 import org.jolokia.handler.JsonRequestHandler;
 import org.jolokia.request.JmxRequest;
@@ -99,7 +100,7 @@ private synchronized void init(List<ServerDetector> pDetectors) {
      * @throws InstanceNotFoundException
      */
     public <R extends JmxRequest> Object handleRequest(JsonRequestHandler<R> pRequestHandler, R pJmxReq)
-            throws MBeanException, ReflectionException, AttributeNotFoundException, InstanceNotFoundException {
+            throws MBeanException, ReflectionException, AttributeNotFoundException, InstanceNotFoundException, NotChangedException {
         AttributeNotFoundException attrException = null;
         InstanceNotFoundException objNotFoundException = null;
 

agent/core/src/main/java/org/jolokia/backend/MBeanServerHandler.java

@@ -7,6 +7,7 @@
 import javax.management.*;
 
 import org.jolokia.backend.executor.MBeanServerExecutor;
+import org.jolokia.backend.executor.NotChangedException;
 import org.jolokia.config.ConfigKey;
 import org.jolokia.config.Configuration;
 import org.jolokia.detector.*;
@@ -89,7 +90,7 @@ private void initServerHandle(Configuration pConfig, LogHandler pLogHandler, Lis
      * @return the result of the request
      */
     public Object dispatchRequest(JsonRequestHandler pRequestHandler, JmxRequest pJmxReq)
-            throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException {
+            throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException, NotChangedException {
         serverHandle.preDispatch(mBeanServerManager,pJmxReq);
         if (pRequestHandler.handleAllServersAtOnce(pJmxReq)) {
             try {

agent/core/src/main/java/org/jolokia/backend/RequestDispatcher.java

@@ -4,6 +4,7 @@
 
 import javax.management.*;
 
+import org.jolokia.backend.executor.NotChangedException;
 import org.jolokia.request.JmxRequest;
 
 /*
@@ -42,7 +43,7 @@ public interface RequestDispatcher {
      * @throws MBeanException
      */
     Object dispatchRequest(JmxRequest pJmxReq)
-            throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException, IOException;
+            throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException, IOException, NotChangedException;
 
     /**
      * Check whether current dispatcher can handle the given request

agent/core/src/main/java/org/jolokia/backend/executor/AbstractMBeanServerExecutor.java

@@ -32,7 +32,7 @@
 public abstract class AbstractMBeanServerExecutor implements MBeanServerExecutor, NotificationListener {
 
     // Timestamp of last MBeanServer change in milliseconds
-    private long lastMBeanServerChange;
+    private long lastMBeanRegistrationChange;
 
     /**
      * Get all MBeanServers
@@ -118,9 +118,6 @@ public Set<ObjectName> queryNames(ObjectName pObjectName) throws IOException {
     /**
      * Add this executor as listener for MBeanServer notification so that we can update
      * the local timestamp for when the set of registered MBeans has changed last.
-     *
-     * @throws IOException
-     * @throws InstanceNotFoundException
      */
     protected void registerForMBeanNotifications() {
         Set<MBeanServerConnection> servers = getMBeanServers();
@@ -139,7 +136,7 @@ protected void registerForMBeanNotifications() {
     }
 
     /**
-     * Deregister ourself as listener from every registered server
+     * Unregister us as listener from every registered server
      */
     public void destroy() {
         Set<MBeanServerConnection> servers = getMBeanServers();
@@ -157,34 +154,21 @@ public void destroy() {
         }
     }
 
-    private Exception updateErrorMsg(StringBuilder pErrors, Exception exp) {
-        pErrors.append(exp.getClass()).append(": ").append(exp.getMessage()).append("\n");
-        return exp;
-    }
-
     /** {@inheritDoc} */
     // Remember current timestamp
     public void handleNotification(Notification pNotification, Object pHandback) {
         // Update timestamp
-        lastMBeanServerChange = System.currentTimeMillis();
+        lastMBeanRegistrationChange = System.currentTimeMillis();
     }
 
-    /**
-     * Check whether the set of MBeans in all managed MBeanServer has been changed
-     * since the given time. The input is the epoch time in seconds, however, milliseconds
-     * would be much more appropriate. However, the Jolokia responses contain
-     * currently time measured in seconds. This should be changed in a future version,
-     * but this implies a quite heavy API changed (and if this is changed, the key 
-     * "timestamp" should be changed to "time", too, in order to fail early in case of
-     * problems).
-     *
-     * In order to avoid inconsistencies for sub-second updates, we are comparing
-     * conservatively (so hasBeenUpdated might return "true" more often than required).
-     *
-     * @param pTimestamp seconds since 1.1.1970
-     * @return true if the MBeans has been updated since this time, false otherwise
-     */
-    public boolean hasBeenUpdatedSince(long pTimestamp) {
-        return (lastMBeanServerChange / 1000) >= pTimestamp;
+    /** {@inheritDoc} */
+    public boolean hasMBeansListChangedSince(long pTimestamp) {
+        return (lastMBeanRegistrationChange / 1000) >= pTimestamp;
+    }
+
+    // Helper method for adding the exception for an appropriate error message
+    private Exception updateErrorMsg(StringBuilder pErrors, Exception exp) {
+        pErrors.append(exp.getClass()).append(": ").append(exp.getMessage()).append("\n");
+        return exp;
     }
 }

agent/core/src/main/java/org/jolokia/backend/executor/MBeanServerExecutor.java

@@ -85,6 +85,23 @@ <R> R call(ObjectName pObjectName, MBeanAction<R> pMBeanAction, Object... pExtra
      */
     void destroy();
 
+    /**
+     * Check whether the set of MBeans in all managed MBeanServer has been changed
+     * since the given time. The input is the epoch time in seconds, however, milliseconds
+     * would be much more appropriate. However, the Jolokia responses contain
+     * currently time measured in seconds. This should be changed in a future version,
+     * but this implies a quite heavy API changed (and if this is changed, the key
+     * "timestamp" should be changed to "time", too, in order to fail early in case of
+     * problems).
+     *
+     * In order to avoid inconsistencies for sub-second updates, we are comparing
+     * conservatively (so hasBeenUpdated might return "true" more often than required).
+     *
+     * @param pTimestamp seconds since 1.1.1970
+     * @return true if the MBeans has been updated since this time, false otherwise
+     */
+    boolean hasMBeansListChangedSince(long pTimestamp);
+
     /**
      * This callback is used together with {@link #each(ObjectName, MBeanEachCallback)} for iterating over all
      * active MBeanServers. The callback is responsible on its own to collect the information queried.

agent/core/src/main/java/org/jolokia/backend/executor/NotChangedException.java

@@ -0,0 +1,30 @@
+package org.jolokia.backend.executor;
+
+import org.jolokia.request.JmxRequest;
+
+/**
+ * Exception thrown when an <code>ifModifiedSince</code> parameter was given and
+ * the requested resourced doesnt has changed
+ * @author roland
+ * @since 07.03.13
+ */
+public class NotChangedException extends Exception {
+
+    private JmxRequest request;
+
+    /**
+     * Constructor
+     * @param pRequest which lead to this exception
+     */
+    public NotChangedException(JmxRequest pRequest) {
+        request = pRequest;
+    }
+
+    /**
+     * Request which lead to this exception
+     * @return request
+     */
+    public JmxRequest getRequest() {
+        return request;
+    }
+}

agent/core/src/main/java/org/jolokia/handler/JsonRequestHandler.java

@@ -5,6 +5,7 @@
 import javax.management.*;
 
 import org.jolokia.backend.executor.MBeanServerExecutor;
+import org.jolokia.backend.executor.NotChangedException;
 import org.jolokia.request.JmxRequest;
 import org.jolokia.restrictor.Restrictor;
 import org.jolokia.util.RequestType;
@@ -81,7 +82,7 @@ public boolean handleAllServersAtOnce(R pRequest) {
      * @throws java.io.IOException
      */
     public Object handleRequest(MBeanServerConnection pServer, R pRequest)
-            throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException, IOException {
+            throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException, IOException, NotChangedException {
         checkForRestriction(pRequest);
         checkHttpMethod(pRequest);
         return doHandleRequest(pServer, pRequest);
@@ -136,7 +137,7 @@ private void checkHttpMethod(R pRequest) {
      * @throws IOException
      */
     protected abstract Object doHandleRequest(MBeanServerConnection server, R request)
-            throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException, IOException;
+            throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException, IOException, NotChangedException;
 
     /**
      * Override this if you want to have all servers at once for processing the request
@@ -154,7 +155,7 @@ protected abstract Object doHandleRequest(MBeanServerConnection server, R reques
      * @throws ReflectionException
      */
     public Object handleRequest(MBeanServerExecutor pServerManager, R request)
-            throws ReflectionException, InstanceNotFoundException, MBeanException, AttributeNotFoundException, IOException {
+            throws ReflectionException, InstanceNotFoundException, MBeanException, AttributeNotFoundException, IOException, NotChangedException {
         checkForRestriction(request);
         return doHandleRequest(pServerManager,request);
     }
@@ -174,7 +175,7 @@ public Object handleRequest(MBeanServerExecutor pServerManager, R request)
      * @throws ReflectionException
      */
     public Object doHandleRequest(MBeanServerExecutor serverManager, R request)
-                throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException, IOException {
+                throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException, IOException, NotChangedException {
         return null;
     }
 

agent/core/src/main/java/org/jolokia/handler/ListHandler.java

@@ -7,6 +7,7 @@
 import javax.management.*;
 
 import org.jolokia.backend.executor.MBeanServerExecutor;
+import org.jolokia.backend.executor.NotChangedException;
 import org.jolokia.config.ConfigKey;
 import org.jolokia.handler.list.MBeanInfoData;
 import org.jolokia.request.JmxListRequest;
@@ -73,7 +74,10 @@ protected void checkForRestriction(JmxListRequest pRequest) {
     /** {@inheritDoc} */
     @Override
     public Object doHandleRequest(MBeanServerExecutor pServerManager, JmxListRequest pRequest)
-            throws IOException {
+            throws IOException, NotChangedException {
+        // Throw an exception if list has not changed
+        checkForModifiedSince(pServerManager, pRequest);
+
         Stack<String> originalPathStack = EscapeUtil.reversePath(pRequest.getPathParts());
         int maxDepth = pRequest.getParameterAsInt(ConfigKey.MAX_DEPTH);
         boolean useCanonicalName = pRequest.getParameterAsBool(ConfigKey.CANONICAL_NAMING);
@@ -101,14 +105,15 @@ public Object doHandleRequest(MBeanServerExecutor pServerManager, JmxListRequest
     }
 
     // will not be called
+
     /** {@inheritDoc} */
     @Override
     public Object doHandleRequest(MBeanServerConnection server, JmxListRequest request)
             throws InstanceNotFoundException, AttributeNotFoundException, ReflectionException, MBeanException {
         throw new UnsupportedOperationException("Internal: Method must not be called when all MBeanServers are handled at once");
     }
-
     @Override
+
     /**
      * Path handling is done directly within this handler to avoid
      * excessive memory consumption by building up the whole list
@@ -122,6 +127,14 @@ public boolean useReturnValueWithPath() {
 
     // ==========================================================================================================
 
+    // check for freshness
+    private void checkForModifiedSince(MBeanServerExecutor pServerManager, JmxListRequest pRequest) throws NotChangedException {
+        int ifModifiedSince = pRequest.getParameterAsInt(ConfigKey.IF_MODIFIED_SINCE);
+        if (!pServerManager.hasMBeansListChangedSince(ifModifiedSince)) {
+            throw new NotChangedException(pRequest);
+        }
+    }
+
     /**
      * Prepare an objectname patttern from a path (or "null" if no path is given)
      * @param pPathStack path