引用網址：http://基于Chrome、Java、WebSocket、WebRTC实现浏览器视频通话

介绍

 
        最近这段时间折腾了一下WebRTC，看了网上的https://apprtc.appspot.com/的例子（可能需要翻墙访问），这个例子是部署在Google App Engine上的应用程序，依赖GAE的环境，后台的语言是python，而且还依赖Google App Engine Channel API，所以无法在本地运行，也无法扩展。费了一番功夫研读了例子的python端的源代码，决定用Java实现，Tomcat7之后开始支持WebSocket，打算用WebSocket代替Google App Engine Channel API实现前后台的通讯，在整个例子中Java+WebSocket起到的作用是负责客户端之间的通信，并不负责视频的传输，视频的传输依赖于WebRTC。
 
实例的特点是：
  1. HTML5
  2. 不需要任何插件
  3. 资源占用不是很大，对服务器的开销比较小，只要客户端建立连接，视频传输完全有浏览器完成
  4. 通过JS实现，理论上只要浏览器支持WebSocket，WebRTC就能运行（目前只在Chrome测试通过，Chrome版本24.0.1312.2 dev-m）

实现

 
对于前端JS代码及用到的对象大家可以访问http://www.html5rocks.com/en/tutorials/webrtc/basics/查看详细的代码介绍。我在这里只介绍下我改动过的地方，首先建立一个客户端实时获取状态的连接，在GAE的例子上是通过GAE Channel API实现，我在这里用WebSocket实现，代码：
		function openChannel() {
			console.log("Opening channel.");
			socket = new WebSocket(
					"ws://192.168.1.102:8080/RTCApp/websocket?u=${user}");
			socket.onopen = onChannelOpened;
			socket.onmessage = onChannelMessage;
			socket.onclose = onChannelClosed;
		}
建立一个WebSocket连接，并注册相关的事件。这里通过Java实现WebSocket连接：
package org.rtc.servlet;

import java.io.IOException;

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

import org.apache.catalina.websocket.StreamInbound;
import org.apache.catalina.websocket.WebSocketServlet;
import org.rtc.websocket.WebRTCMessageInbound;

@WebServlet(urlPatterns = { "/websocket"})
public class WebRTCWebSocketServlet extends WebSocketServlet {

	private static final long serialVersionUID = 1L;

	private String user;
	
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.user = request.getParameter("u");
		super.doGet(request, response);
	}

    @Override
    protected StreamInbound createWebSocketInbound(String subProtocol) {
        return new WebRTCMessageInbound(user);
    }
}
如果你想实现WebSocket必须得用Tomcat7及以上版本，并且引入：catalina.jar，tomcat-coyote.jar两个JAR包，部署到Tomcat7之后得要去webapps/应用下面去删除这两个AR包否则无法启动，WebSocket访问和普通的访问最大的不同在于继承了WebSocketServlet，关于WebSocket的详细介绍大家可以访问http://redstarofsleep.iteye.com/blog/1488639，在这里就不再赘述。大家可以看看WebRTCMessageInbound这个类的实现：
package org.rtc.websocket;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;

import org.apache.catalina.websocket.MessageInbound;
import org.apache.catalina.websocket.WsOutbound;

public class WebRTCMessageInbound extends MessageInbound {

    private final String user;

    public WebRTCMessageInbound(String user) {
        this.user = user;
    }
    
    public String getUser(){
    	return this.user;
    }

    @Override
    protected void onOpen(WsOutbound outbound) {
    	//触发连接事件，在连接池中添加连接
    	WebRTCMessageInboundPool.addMessageInbound(this);
    }

    @Override
    protected void onClose(int status) {
    	//触发关闭事件，在连接池中移除连接
    	WebRTCMessageInboundPool.removeMessageInbound(this);
    }

    @Override
    protected void onBinaryMessage(ByteBuffer message) throws IOException {
        throw new UnsupportedOperationException(
                "Binary message not supported.");
    }

    @Override
    protected void onTextMessage(CharBuffer message) throws IOException {
    	
    }
}
WebRTCMessageInbound继承了MessageInbound，并绑定了两个事件，关键的在于连接事件，将连接存放在连接池中，等客户端A发起发送信息的时候将客户端B的连接取出来发送数据，看看WebRTCMessageInboundPool这个类：
package org.rtc.websocket;

import java.io.IOException;
import java.nio.CharBuffer;
import java.util.HashMap;
import java.util.Map;

public class WebRTCMessageInboundPool {

	private static final Map<String,WebRTCMessageInbound > connections = new HashMap<String,WebRTCMessageInbound>();
	
	public static void addMessageInbound(WebRTCMessageInbound inbound){
		//添加连接
		System.out.println("user : " + inbound.getUser() + " join..");
		connections.put(inbound.getUser(), inbound);
	}
	
	public static void removeMessageInbound(WebRTCMessageInbound inbound){
		//移除连接
		connections.remove(inbound.getUser());
	}
	
	public static void sendMessage(String user,String message){
		try {
			//向特定的用户发送数据
			System.out.println("send message to user : " + user + " message content : " + message);
			WebRTCMessageInbound inbound = connections.get(user);
			if(inbound != null){
				inbound.getWsOutbound().writeTextMessage(CharBuffer.wrap(message));
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
}
WebRTCMessageInboundPool这个类中最重要的是sendMessage方法，向特定的用户发送数据。
大家可以看看这段代码：
		function openChannel() {
			console.log("Opening channel.");
			socket = new WebSocket(
					"ws://192.168.1.102:8080/RTCApp/websocket?u=${user}");
			socket.onopen = onChannelOpened;
			socket.onmessage = onChannelMessage;
			socket.onclose = onChannelClosed;
		}
${user}是怎么来的呢？其实在进入这个页面之前是有段处理的：
package org.rtc.servlet;

import java.io.IOException;
import java.util.UUID;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.lang.StringUtils;
import org.rtc.room.WebRTCRoomManager;

@WebServlet(urlPatterns = {"/room"})
public class WebRTCRoomServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;
	
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.doPost(request, response);
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String r = request.getParameter("r");
		if(StringUtils.isEmpty(r)){
			//如果房间为空，则生成一个新的房间号
			r = String.valueOf(System.currentTimeMillis());
			response.sendRedirect("room?r=" + r);
		}else{
			Integer initiator = 1;
			String user = UUID.randomUUID().toString().replace("-", "");//生成一个用户ID串
			if(!WebRTCRoomManager.haveUser(r)){//第一次进入可能是没有人的，所以就要等待连接，如果有人进入了带这个房间好的页面就会发起视频通话的连接
				initiator = 0;//如果房间没有人则不发送连接的请求
			}
			WebRTCRoomManager.addUser(r, user);//向房间中添加一个用户
			String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort() +  request.getContextPath() +"/";
			String roomLink = basePath + "room?r=" + r;
			String roomKey = r;//设置一些变量
			request.setAttribute("initiator", initiator);
			request.setAttribute("roomLink", roomLink);
			request.setAttribute("roomKey", roomKey);
			request.setAttribute("user", user);
			request.getRequestDispatcher("index.jsp").forward(request, response);
		}
	}
}
这个是进入房间前的处理，然而客户端是怎么发起视频通话的呢？
function initialize() {
			console.log("Initializing; room=${roomKey}.");
			card = document.getElementById("card");
			localVideo = document.getElementById("localVideo");
			miniVideo = document.getElementById("miniVideo");
			remoteVideo = document.getElementById("remoteVideo");
			resetStatus();
			openChannel();
			getUserMedia();
		}
		
		function getUserMedia() {
			try {
				navigator.webkitGetUserMedia({
					'audio' : true,
					'video' : true
				}, onUserMediaSuccess, onUserMediaError);
				console.log("Requested access to local media with new syntax.");
			} catch (e) {
				try {
					navigator.webkitGetUserMedia("video,audio",
							onUserMediaSuccess, onUserMediaError);
					console
							.log("Requested access to local media with old syntax.");
				} catch (e) {
					alert("webkitGetUserMedia() failed. Is the MediaStream flag enabled in about:flags?");
					console.log("webkitGetUserMedia failed with exception: "
							+ e.message);
				}
			}
		}
		
		function onUserMediaSuccess(stream) {
			console.log("User has granted access to local media.");
			var url = webkitURL.createObjectURL(stream);
			localVideo.style.opacity = 1;
			localVideo.src = url;
			localStream = stream;
			// Caller creates PeerConnection.
			if (initiator)
				maybeStart();
		}
		
		function maybeStart() {
			if (!started && localStream && channelReady) {
				setStatus("Connecting...");
				console.log("Creating PeerConnection.");
				createPeerConnection();
				console.log("Adding local stream.");
				pc.addStream(localStream);
				started = true;
				// Caller initiates offer to peer.
				if (initiator)
					doCall();
			}
		}

		function doCall() {
			console.log("Sending offer to peer.");
			if (isRTCPeerConnection) {
				pc.createOffer(setLocalAndSendMessage, null, mediaConstraints);
			} else {
				var offer = pc.createOffer(mediaConstraints);
				pc.setLocalDescription(pc.SDP_OFFER, offer);
				sendMessage({
					type : 'offer',
					sdp : offer.toSdp()
				});
				pc.startIce();
			}
		}

		function setLocalAndSendMessage(sessionDescription) {
			pc.setLocalDescription(sessionDescription);
			sendMessage(sessionDescription);
		}

		function sendMessage(message) {
			var msgString = JSON.stringify(message);
			console.log('发出信息 : ' + msgString);
			path = 'message?r=${roomKey}' + '&u=${user}';
			var xhr = new XMLHttpRequest();
			xhr.open('POST', path, true);
			xhr.send(msgString);
		}
页面加载完之后会调用initialize方法，initialize方法中调用了getUserMedia方法，这个方法是通过本地摄像头获取视频的方法，在成功获取视频之后发送连接请求，并在客户端建立连接管道，最后通过sendMessage向另外一个客户端发送连接的请求，参数为当前通话的房间号和当前登陆人，下图是连接产生的日志：
基于Chrome、Java、WebSocket、WebRTC实现浏览器视频通话
 
 
package org.rtc.servlet;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import net.sf.json.JSONObject;

import org.rtc.room.WebRTCRoomManager;
import org.rtc.websocket.WebRTCMessageInboundPool;

@WebServlet(urlPatterns = {"/message"})
public class WebRTCMessageServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		super.doPost(request, response);
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String r = request.getParameter("r");//房间号
		String u = request.getParameter("u");//通话人
	    BufferedReader br = new BufferedReader(new InputStreamReader((ServletInputStream)request.getInputStream()));
        String line = null;
        StringBuilder sb = new StringBuilder();
        while((line = br.readLine())!=null){
            sb.append(line); //获取输入流，主要是视频定位的信息
        }
		
		String message = sb.toString();
		JSONObject json = JSONObject.fromObject(message);
		if (json != null) {
			String type = json.getString("type");
			if ("bye".equals(type)) {//客户端退出视频聊天
				System.out.println("user :" + u + " exit..");
				WebRTCRoomManager.removeUser(r, u);
			}
		}
		String otherUser = WebRTCRoomManager.getOtherUser(r, u);//获取通话的对象
		if (u.equals(otherUser)) {
			message = message.replace("\"offer\"", "\"answer\"");
			message = message.replace("a=crypto:0 AES_CM_128_HMAC_SHA1_32",
					"a=xrypto:0 AES_CM_128_HMAC_SHA1_32");
			message = message.replace("a=ice-options:google-ice\\r\\n", "");
		}
		//向对方发送连接数据
		WebRTCMessageInboundPool.sendMessage(otherUser, message);
	}
}
就这样通过WebSokcet向客户端发送连接数据，然后客户端根据接收到的数据进行视频接收：
function onChannelMessage(message) {
			console.log('收到信息 : ' + message.data);
			if (isRTCPeerConnection)
				processSignalingMessage(message.data);//建立视频连接
			else
				processSignalingMessage00(message.data);
		}
		
		function processSignalingMessage(message) {
			var msg = JSON.parse(message);

			if (msg.type === 'offer') {
				// Callee creates PeerConnection
				if (!initiator && !started)
					maybeStart();

				// We only know JSEP version after createPeerConnection().
				if (isRTCPeerConnection)
					pc.setRemoteDescription(new RTCSessionDescription(msg));
				else
					pc.setRemoteDescription(pc.SDP_OFFER,
							new
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