ActiveMQ example source code file (HttpTunnelServlet.java)

This example ActiveMQ source code file (HttpTunnelServlet.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - ActiveMQ tags/keywords

blockingqueuetransport, blockingqueuetransport, command, hashmap, httpservletresponse, io, ioexception, ioexception, no, no, override, request, response, servlet, servletexception, servletexception, string, threading, threads, wireformatinfo

The ActiveMQ HttpTunnelServlet.java source code

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.activemq.transport.http;

import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.activemq.Service;
import org.apache.activemq.command.Command;
import org.apache.activemq.command.WireFormatInfo;
import org.apache.activemq.transport.Transport;
import org.apache.activemq.transport.TransportAcceptListener;
import org.apache.activemq.transport.util.TextWireFormat;
import org.apache.activemq.transport.xstream.XStreamWireFormat;
import org.apache.activemq.util.IOExceptionSupport;
import org.apache.activemq.util.ServiceListener;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * A servlet which handles server side HTTP transport, delegating to the
 * ActiveMQ broker. This servlet is designed for being embedded inside an
 * ActiveMQ Broker using an embedded Jetty or Tomcat instance.
 * 
 * 
 */
public class HttpTunnelServlet extends HttpServlet {
    private static final long serialVersionUID = -3826714430767484333L;
    private static final Logger LOG = LoggerFactory.getLogger(HttpTunnelServlet.class);

    private TransportAcceptListener listener;
    private HttpTransportFactory transportFactory;
    private TextWireFormat wireFormat;
    private ConcurrentMap<String, BlockingQueueTransport> clients = new ConcurrentHashMap();
    private final long requestTimeout = 30000L;
    private HashMap transportOptions;

    @Override
    public void init() throws ServletException {
        super.init();
        listener = (TransportAcceptListener)getServletContext().getAttribute("acceptListener");
        if (listener == null) {
            throw new ServletException("No such attribute 'acceptListener' available in the ServletContext");
        }
        transportFactory = (HttpTransportFactory)getServletContext().getAttribute("transportFactory");
        if (transportFactory == null) {
            throw new ServletException("No such attribute 'transportFactory' available in the ServletContext");    
        }
        transportOptions = (HashMap)getServletContext().getAttribute("transportOptions");
        wireFormat = (TextWireFormat)getServletContext().getAttribute("wireFormat");
        if (wireFormat == null) {
            wireFormat = createWireFormat();
        }
    }

    @Override
    protected void doHead(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        createTransportChannel(request, response);
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // lets return the next response
        Command packet = null;
        int count = 0;
        try {
            BlockingQueueTransport transportChannel = getTransportChannel(request, response);
            if (transportChannel == null) {
                return;
            }

            packet = (Command)transportChannel.getQueue().poll(requestTimeout, TimeUnit.MILLISECONDS);

            DataOutputStream stream = new DataOutputStream(response.getOutputStream());
            // while( packet !=null ) {
            wireFormat.marshal(packet, stream);
            count++;
            // packet = (Command) transportChannel.getQueue().poll(0,
            // TimeUnit.MILLISECONDS);
            // }

        } catch (InterruptedException ignore) {
        }
        if (count == 0) {
            response.setStatus(HttpServletResponse.SC_REQUEST_TIMEOUT);
        }
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException,
            IOException {

        // Read the command directly from the reader, assuming UTF8 encoding
        ServletInputStream sis = request.getInputStream();
        Command command = (Command) wireFormat.unmarshalText(new InputStreamReader(sis, "UTF-8"));

        if (command instanceof WireFormatInfo) {
            WireFormatInfo info = (WireFormatInfo) command;
            if (!canProcessWireFormatVersion(info.getVersion())) {
                response.sendError(HttpServletResponse.SC_NOT_FOUND, "Cannot process wire format of version: "
                        + info.getVersion());
            }

        } else {

            BlockingQueueTransport transport = getTransportChannel(request, response);
            if (transport == null) {
                return;
            }

            transport.doConsume(command);
        }
    }

    private boolean canProcessWireFormatVersion(int version) {
        // TODO:
        return true;
    }

    protected String readRequestBody(HttpServletRequest request) throws IOException {
        StringBuffer buffer = new StringBuffer();
        BufferedReader reader = request.getReader();
        while (true) {
            String line = reader.readLine();
            if (line == null) {
                break;
            } else {
                buffer.append(line);
                buffer.append("\n");
            }
        }
        return buffer.toString();
    }

    protected BlockingQueueTransport getTransportChannel(HttpServletRequest request, HttpServletResponse response) throws IOException {
        String clientID = request.getHeader("clientID");
        if (clientID == null) {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST, "No clientID header specified");
            LOG.warn("No clientID header specified");
            return null;
        }
        BlockingQueueTransport answer = clients.get(clientID);
        if (answer == null) {
            LOG.warn("The clientID header specified is invalid. Client sesion has not yet been established for it: " + clientID);
            return null;
        }
        return answer;
    }

    protected BlockingQueueTransport createTransportChannel(HttpServletRequest request, HttpServletResponse response) throws IOException {
        final String clientID = request.getHeader("clientID");

        if (clientID == null) {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST, "No clientID header specified");
            LOG.warn("No clientID header specified");
            return null;
        }

        // Optimistically create the client's transport; this transport may be thrown away if the client has already registered.
        BlockingQueueTransport answer = createTransportChannel();

        // Record the client's transport and ensure that it has not already registered; this is thread-safe and only allows one 
        // thread to register the client
        if (clients.putIfAbsent(clientID, answer) != null) {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST, "A session for clientID '" + clientID + "' has already been established");
            LOG.warn("A session for clientID '" + clientID + "' has already been established");
            return null;
        }

        // Ensure that the client's transport is cleaned up when no longer
        // needed.
        answer.addServiceListener(new ServiceListener() {
            public void started(Service service) {
                // Nothing to do.
            }

            public void stopped(Service service) {
                clients.remove(clientID);
            }
        });

        // Configure the transport with any additional properties or filters.  Although the returned transport is not explicitly
        // persisted, if it is a filter (e.g., InactivityMonitor) it will be linked to the client's transport as a TransportListener
        // and not GC'd until the client's transport is disposed.
        Transport transport = answer;
        try {
            // Preserve the transportOptions for future use by making a copy before applying (they are removed when applied).
            HashMap options = new HashMap(transportOptions);
            transport = transportFactory.serverConfigure(answer, null, options);
        } catch (Exception e) {
            IOExceptionSupport.create(e);
        }

        // Wait for the transport to be connected or disposed.
        listener.onAccept(transport);
        while (!transport.isConnected() && !transport.isDisposed()) {
            try {
                Thread.sleep(100);
            } catch (InterruptedException ignore) {
            }
        }

        // Ensure that the transport was not prematurely disposed.
        if (transport.isDisposed()) {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST, "The session for clientID '" + clientID + "' was prematurely disposed");
            LOG.warn("The session for clientID '" + clientID + "' was prematurely disposed");
            return null;
        }

        return answer;
    }

    protected BlockingQueueTransport createTransportChannel() {
       return new BlockingQueueTransport(new LinkedBlockingQueue<Object>());
    }

    protected TextWireFormat createWireFormat() {
        return new XStreamWireFormat();
    }
}