org.directwebremoting.guice.DwrGuiceUtil 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 2007 Tim Peierls
 *
 * 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.guice;

import java.util.LinkedList;
import java.util.concurrent.Callable;

import javax.servlet.ServletContext;

import org.directwebremoting.WebContext;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.ServerContext;
import org.directwebremoting.impl.StartupUtil;

import com.google.inject.Injector;

/**
 * Utilities for making Injector and ServletContext instances available.
 * @author Tim Peierls [tim at peierls dot net]
 */
public class DwrGuiceUtil
{
    /**
     * The key under which a provided Injector is stashed in a ServletContext.
     * The name is prefixed by the package to avoid conflicting with other
     * listeners using the same technique.
     */
    public static final String INJECTOR = "org.directwebremoting.guice.Injector";


    /**
     * Returns the Injector instance published in the current servlet context.
     */
    public static Injector getInjector()
    {
        return AbstractDwrGuiceServletContextListener.getPublishedInjector(getServletContext());
    }

    /**
     * Gets the servlet context from the thread-local stash, if any,
     * otherwise from the current web context, if one exists,
     * otherwise from the singleton server context, if it exists,
     * otherwise from the first of all server contexts, if there are any,
     * otherwise null.
     */
    public static ServletContext getServletContext()
    {
        LinkedList sclist = servletContexts.get();
        if (!sclist.isEmpty())
        {
            return sclist.getFirst();
        }

        WebContext webcx = WebContextFactory.get();
        if (webcx != null)
        {
            return webcx.getServletContext();
        }

        ServerContext serverContext = StartupUtil.getSingletonServerContext();
        if (serverContext != null)
        {
            return serverContext.getServletContext();
        }

        for (ServerContext sc : StartupUtil.getAllServerContexts())
        {
            // Use the ServletContext of the first ServerContext we see.
            return sc.getServletContext();
        }

        return null;
    }

    /**
     * Executes the given Runnable with the thread-locally stashed servlet context
     * set to the given value.
     */
    public static void withServletContext(ServletContext servletContext, Runnable runnable)
    {
        pushServletContext(servletContext);
        try
        {
            runnable.run();
        }
        finally
        {
            popServletContext();
        }
    }

    /**
     * Executes the given Callable with the thread-locally stashed servlet context
     * set to the given value, and returns the result.
     */
    public static  T withServletContext(ServletContext servletContext, Callable callable) throws Exception
    {
        pushServletContext(servletContext);
        try
        {
            return callable.call();
        }
        finally
        {
            popServletContext();
        }
    }

    /**
     * Thread-locally pushes a servlet context. Call {@link #popServletContext}
     * in a finally block when calling this method.
     */
    private static void pushServletContext(ServletContext context)
    {
        servletContexts.get().addFirst(context);
    }

    /**
     * Pops a thread-locally stashed servlet context. Call this in
     * a finally block when {@link #pushServletContext} is called.
     */
    private static void popServletContext()
    {
        servletContexts.get().removeFirst();
    }

    private static final ThreadLocal> servletContexts =
        new ThreadLocal>()
        {
            @Override
            protected LinkedList initialValue()
            {
                return new LinkedList();
            }
        };
}