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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 boilerplate code between the web browser and your Java code. This version 4.0.2 works with Jakarta Servlet 4.0.2.

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package org.directwebremoting.impl;

import java.util.ArrayList;

import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletContext;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.directwebremoting.Container;
import org.directwebremoting.WebContext;
import org.directwebremoting.WebContextFactory.WebContextBuilder;

/**
 * A WebContextBuilder that creates DefaultWebContexts.
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public class DefaultWebContextBuilder implements WebContextBuilder
{
    /* (non-Javadoc)
     * @see org.directwebremoting.WebContextBuilder#get()
     */
    public WebContext get()
    {
        ArrayList stack = contextStack.get();
        if (stack == null || stack.size() == 0)
        {
            return null;
        }
        return stack.get(stack.size() - 1);
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.WebContextBuilder#set(jakarta.servlet.http.HttpServletRequest, jakarta.servlet.http.HttpServletResponse, jakarta.servlet.ServletConfig, jakarta.servlet.ServletContext, org.directwebremoting.Container)
     */
    public void engageThread(Container container, HttpServletRequest request, HttpServletResponse response)
    {
        try
        {
            ServletConfig servletConfig = container.getBean(ServletConfig.class);
            ServletContext servletContext = container.getBean(ServletContext.class);

            WebContext ec = new DefaultWebContext(container, request, response, servletConfig, servletContext);
            engageThread(ec);
        }
        catch (Exception ex)
        {
            log.fatal("Failed to create an ExecutionContext", ex);
        }
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.WebContextFactory.WebContextBuilder#engageThread(org.directwebremoting.WebContext)
     */
    public void engageThread(WebContext webContext)
    {
        ArrayList stack = contextStack.get();
        if (stack == null)
        {
            stack = new ArrayList();
            contextStack.set(stack);
        }
        stack.add(webContext);
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.WebContextBuilder#unset()
     */
    public void disengageThread()
    {
        // null check for DWR-426 - DefaultWebContextBuilder disengageThread throws null pointer exception.
        if (contextStack != null)
        {
            ArrayList stack = contextStack.get();
            if (stack != null)
            {
                if (stack.size() > 0)
                {
                    stack.remove(stack.size() - 1);
                }
                if (stack.size() == 0)
                {
                    contextStack.set(null);
                }
            }
        }
    }

    /**
     * The storage of thread based data as a stack
     */
    private static ThreadLocal> contextStack = new ThreadLocal>();

    /**
     * The log stream
     */
    private static final Log log = LogFactory.getLog(DefaultWebContextBuilder.class);
}