org.directwebremoting.extend.CallbackHelper Maven / Gradle / Ivy

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DWR is easy Ajax for Java. It makes it simple to call Java code directly from Javascript. It gets rid of almost all the boiler plate code between the web browser and your Java code.
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/*
 * Copyright 2005 Joe Walker
 *
 * 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.directwebremoting.extend;

import java.lang.reflect.Method;
import java.util.Map;

import org.directwebremoting.ScriptSession;
import org.directwebremoting.WebContext;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.io.RawData;
import org.directwebremoting.proxy.Callback;
import org.directwebremoting.util.IdGenerator;

/**
 * A class to help with the use of {@link Callback}s
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public class CallbackHelper
{
    /**
     * Used by the many proxy classes to record a callback for later calling
     * @param callback The callback that acts on the type
     * @param type The type of the data that we are recording
     * @return A key under which the data is stored
     */
    @SuppressWarnings("unchecked")
    public static  String saveCallback(Callback callback, Class type)
    {
        String key = createUniqueId();

        for (ScriptSession session : callback.getScriptSessions())
        {
            // Save the callback itself
            Map> callbackMap = (Map>) session.getAttribute(KEY_CALLBACK);
            callbackMap.put(key, callback);
            session.setAttribute(KEY_CALLBACK, callbackMap);

            // And save the type of the callback
            Map> typeMap = (Map>) session.getAttribute(KEY_TYPE);
            typeMap.put(key, type);
            session.setAttribute(KEY_TYPE, typeMap);
        }

        return key;
    }

    /**
     * The reverse of {@link #saveCallback(Callback, Class)}
     * which executes a {@link Callback} which has been 
     * @param key
     * @param data
     * @throws MarshallException
     */
    @SuppressWarnings("unchecked")
    public static  void executeCallback(String key, RawData data) throws MarshallException
    {
        WebContext webContext = WebContextFactory.get();
        ScriptSession session = webContext.getScriptSession();
        ConverterManager converterManager = webContext.getContainer().getBean(ConverterManager.class);

        Map> typeMap = (Map>) session.getAttribute(KEY_TYPE);
        Class type = typeMap.remove(key);
        session.removeAttribute(KEY_TYPE);
        session.setAttribute(KEY_TYPE, typeMap);

        try
        {
            Method method = Callback.class.getMethod("dataReturned", type);

            InboundContext inctx = data.getInboundContext();
            TypeHintContext incc = new TypeHintContext(converterManager, method, 0);
            InboundVariable iv = data.getInboundVariable();
            Object callbackData  = converterManager.convertInbound(type, iv, inctx, incc);

            Map> callbackMap = (Map>) session.getAttribute(KEY_TYPE);
            Callback callback = callbackMap.remove(key);
            session.removeAttribute(KEY_TYPE);
            session.setAttribute(KEY_CALLBACK, callbackMap);

            callback.dataReturned((T) callbackData);
        }
        catch (Exception ex)
        {
            throw new MarshallException(type, ex);
        }
    }

    /**
     * Callbacks need a unique ID
     */
    public static String createUniqueId()
    {
        return idGenerator.generateId(16);
    }

    /**
     * Callbacks need a unique ID
     */
    private static IdGenerator idGenerator = new IdGenerator();

    /**
     * The key that we use in a script session to store Callbacks
     */
    public static final String KEY_CALLBACK = "org.directwebremoting.callback";

    /**
     * The key that we use in a script session to store Callbacks
     */
    public static final String KEY_TYPE = "org.directwebremoting.type";
}