ManyHandlers.java

//
//  ========================================================================
//  Copyright (c) 1995-2017 Mort Bay Consulting Pty. Ltd.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
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//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
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package org.eclipse.jetty.embedded;

import java.io.File;
import java.io.IOException;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.eclipse.jetty.server.Handler;
import org.eclipse.jetty.server.NCSARequestLog;
import org.eclipse.jetty.server.Request;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.server.handler.AbstractHandler;
import org.eclipse.jetty.server.handler.DefaultHandler;
import org.eclipse.jetty.server.handler.HandlerCollection;
import org.eclipse.jetty.server.handler.HandlerList;
import org.eclipse.jetty.server.handler.HandlerWrapper;
import org.eclipse.jetty.server.handler.RequestLogHandler;
import org.eclipse.jetty.server.handler.gzip.GzipHandler;
import org.eclipse.jetty.util.ajax.JSON;

/**
 * Frequently many handlers are combined together to handle different aspects of
 * a request. A handler may:
 * <ul>
 * <li>handle the request and completely generate the response
 * <li>partially handle the request, but defer response generation to another
 * handler.
 * <li>select another handler to pass the request to.
 * <li>use business logic to decide to do one of the above.
 * </ul>
 * Multiple handlers may be combined with:
 * <ul>
 * <li>{@link HandlerWrapper} which will nest one handler inside another. In
 * this example, the HelloHandler is nested inside a HandlerWrapper that sets
 * the greeting as a request attribute.
 * <li>{@link HandlerList} which will call a collection of handlers until the
 * request is marked as handled. In this example, a list is used to combine the
 * param handler (which only handles the request if there are parameters) and
 * the wrapper handler. Frequently handler lists are terminated with the
 * {@link DefaultHandler}, which will generate a suitable 404 response if the
 * request has not been handled.
 * <li>{@link HandlerCollection} which will call each handler regardless if the
 * request has been handled or not. Typically this is used to always pass a
 * request to the logging handler.
 * </ul>
 */
public class ManyHandlers
{
    /**
     * Produce output that lists all of the request parameters
     */
    public static class ParamHandler extends AbstractHandler
    {
        public void handle( String target,
                            Request baseRequest,
                            HttpServletRequest request,
                            HttpServletResponse response ) throws IOException,
                                                          ServletException
        {
            Map<String, String[]> params = request.getParameterMap();
            if (params.size() > 0)
            {
                response.setContentType("text/plain");
                response.getWriter().println(JSON.toString(params));
                baseRequest.setHandled(true);
            }
        }
    }

    /**
     * Add a request attribute, but produce no output.
     */
    public static class WelcomeWrapHandler extends HandlerWrapper
    {
        @Override
        public void handle( String target,
                            Request baseRequest,
                            HttpServletRequest request,
                            HttpServletResponse response ) throws IOException,
                                                          ServletException
        {
            request.setAttribute("welcome", "Hello");
            super.handle(target, baseRequest, request, response);
        }
    }

    public static void main( String[] args ) throws Exception
    {
        Server server = new Server(8080);

        // create the handlers
        Handler param = new ParamHandler();
        HandlerWrapper wrapper = new WelcomeWrapHandler();
        Handler hello = new HelloHandler();
        Handler dft = new DefaultHandler();
        RequestLogHandler requestLog = new RequestLogHandler();

        // configure request logging
        File requestLogFile = File.createTempFile("demo", "log");
        NCSARequestLog ncsaLog = new NCSARequestLog(
                requestLogFile.getAbsolutePath());
        requestLog.setRequestLog(ncsaLog);

        // create the handler collections
        HandlerCollection handlers = new HandlerCollection();
        HandlerList list = new HandlerList();

        // link them all together
        wrapper.setHandler(hello);
        list.setHandlers(new Handler[] { param, new GzipHandler(), dft });
        handlers.setHandlers(new Handler[] { list, requestLog });

        // Handler tree looks like the following
        // <pre>
        // Server
        // + HandlerCollection
        // . + HandlerList
        // . | + param (ParamHandler)
        // . | + wrapper (WelcomeWrapHandler)
        // . | | \ hello (HelloHandler)
        // . | \ dft (DefaultHandler)
        // . \ requestLog (RequestLogHandler)
        // </pre>

        server.setHandler(handlers);

        server.start();
        server.join();
    }
}