/**
* Copyright 2011 ArcBees Inc.
*
* 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 com.gwtplatform.dispatch.client.actionhandler.caching;
import java.util.ArrayList;
import java.util.HashMap;
import com.google.gwt.user.client.rpc.AsyncCallback;
import com.gwtplatform.dispatch.client.CallbackDispatchRequest;
import com.gwtplatform.dispatch.client.CompletedDispatchRequest;
import com.gwtplatform.dispatch.client.DefaultCallbackDispatchRequest;
import com.gwtplatform.dispatch.client.DelagatingCallbackDispatchRequest;
import com.gwtplatform.dispatch.client.actionhandler.AbstractClientActionHandler;
import com.gwtplatform.dispatch.client.actionhandler.ExecuteCommand;
import com.gwtplatform.dispatch.client.actionhandler.UndoCommand;
import com.gwtplatform.dispatch.shared.Action;
import com.gwtplatform.dispatch.shared.DispatchRequest;
import com.gwtplatform.dispatch.shared.Result;
/**
* Abstract base class for client-side action handlers with caching support.
* <p>
* Supported features include:
* </p>
* <p>
* 1. {@link #prefetch}/{@link #postfetch} perform the cache lookup and the
* cache store. You can use this to customize the caching logic.
* </p>
* <p>
* 2. Automatic action queuing so that calls in quick succession result in a
* single trip to the server.
* </p>
* <p>
* 3. Flexibility of cache implementation to support custom caching
* </p>
*
* @param <A> The type of the action extending {@link Action}.
* @param <R> The type of the result extending {@link Result}.
* @author Sunny Gupta
* @author David M. Chandler
* @author Christian Goudreau
*/
public abstract class AbstractCachingClientActionHandler<A extends Action<R>, R extends Result>
extends AbstractClientActionHandler<A, R> {
private final Cache cache;
// Holds callbacks, so that for multiple requests before the first returns (is
// served), we save round trips as well
private HashMap<A, ArrayList<CallbackDispatchRequest<R>>> pendingRequestCallbackMap = new HashMap<A,
ArrayList<CallbackDispatchRequest<R>>>();
public AbstractCachingClientActionHandler(Class<A> actionType, Cache cache) {
super(actionType);
this.cache = cache;
}
public DispatchRequest execute(final A action,
final AsyncCallback<R> resultCallback, ExecuteCommand<A, R> executeCommand) {
// First check if any pending callbacks for this action
ArrayList<CallbackDispatchRequest<R>> pendingRequestCallbacks = pendingRequestCallbackMap.get(action);
if (pendingRequestCallbacks != null) {
CallbackDispatchRequest<R> callbackDispatchRequest = new DefaultCallbackDispatchRequest<R>(resultCallback);
// Add callback to pending list and return
pendingRequestCallbacks.add(callbackDispatchRequest);
return callbackDispatchRequest;
}
// Prefetch to see if result is cached
R prefetchResult = prefetch(action);
if (prefetchResult != null) {
// Return the cached result
resultCallback.onSuccess(prefetchResult);
return new CompletedDispatchRequest();
} else {
// Execute
DispatchRequest request = executeCommand.execute(action,
new AsyncCallback<R>() {
@Override
public void onFailure(Throwable caught) {
// Call postfetch with null result
postfetch(action, null);
resultCallback.onFailure(caught);
// Callback onFailure
ArrayList<CallbackDispatchRequest<R>> pendingRequestCallbacks = pendingRequestCallbackMap
.remove(action);
for (CallbackDispatchRequest<R> pendingRequestCallback : pendingRequestCallbacks) {
if (pendingRequestCallback.isPending()) {
pendingRequestCallback.onFailure(caught);
}
}
}
@Override
public void onSuccess(R result) {
// Postfetch
postfetch(action, result);
resultCallback.onSuccess(result);
// Callback onSuccess
ArrayList<CallbackDispatchRequest<R>> pendingRequestCallbacks = pendingRequestCallbackMap
.remove(action);
for (CallbackDispatchRequest<R> pendingRequestCallback : pendingRequestCallbacks) {
if (pendingRequestCallback.isPending()) {
pendingRequestCallback.onSuccess(result);
}
}
}
});
// Add pending callback
ArrayList<CallbackDispatchRequest<R>> resultRequestCallbacks = new ArrayList<CallbackDispatchRequest<R>>();
CallbackDispatchRequest<R> callbackDispatchRequest = new DelagatingCallbackDispatchRequest<R>(request,
resultCallback);
resultRequestCallbacks.add(callbackDispatchRequest);
pendingRequestCallbackMap.put(action, resultRequestCallbacks);
return callbackDispatchRequest;
}
}
@Override
public DispatchRequest undo(A action, R result, AsyncCallback<Void> callback,
UndoCommand<A, R> undoCommand) {
// Remove the cached entry
getCache().remove(action);
// Undo the previous action
return undoCommand.undo(action, result, callback);
}
/**
* Override this method to perform an action before the call is sent to the
* server. If the call returns a non-{@code null} result then the action is
* never executed on the server and the returned value is used. If the call
* returns {@code null} then the action is executed on the server.
* <p/>
* You can use this method to fetch the {@code action} from the cache.
*
* @param action The action to be prefetched
* @return The prefetched result. If not found, return {@code null}.
*/
protected abstract R prefetch(A action);
/**
* Override this method to perform an action after the call to the server
* returns successfully or not. If the call succeeded, the result will be
* passed, if it failed {@code null} will be passed in the {@code result}
* parameter.
* <p/>
* You can use this method to add the result to cache, if it is {@code null}
* you should remove the {@code action} from the cache.
*
* @param action The action that just finished execution on the server.
* @param result The result after the server call, or {@code null} if the
* server call failed.
*/
protected abstract void postfetch(A action, R result);
/**
* @return the cache
*/
protected Cache getCache() {
return cache;
}
}