Netty对WebSocket的支持(五)
一.WebSocket简介
在Http1.0和Http1.1协议中，我们要实现服务端主动的发送消息到网页或者APP上，是比较困难的，尤其是现在IM(即时通信)几乎是很多APP都需要实现的功能，我们往往采用一种轮询的方式让终端去请求服务器获取对应的数据，相信很多做过IM通信的朋友应该深有感触，其实大多数的轮询都是无效的(即没有获得到任何的数据)；另外一个方面，每一次轮询都是一个完整的Http请求，而根据Http协议，每一次请求都要在Header中携带大量的参数，这无疑对带宽也是一种极大的消耗。
html5的诞生为我们带来的WebSocket，这是一个振奋人心的事情，WebSocket是基于Http协议的一种长连接协议，有了这种协议，我们就可以实现服务端主动往客户端发送消息的功能。有关WebSocket协议的相关信息请读者查询相关的文档，在笔者的博文中不再作过多的赘述。因为我们讲的是Netty, 所以今天我们就来说说Netty对WebSocket的支持。
二.Netty实现WebSocket
2.1 服务端启动程序
public class WebsocketServer {
public static void main(String[] args) throws InterruptedException {
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
try{
ServerBootstrap serverBootstrap = new ServerBootstrap();
serverBootstrap.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)
.handler(new LoggingHandler(LogLevel.INFO))
.childHandler(new WebSocketChannelInitializer());
ChannelFuture channelFuture = serverBootstrap.bind(8989).sync();
channelFuture.channel().closeFuture().sync();
}finally{
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
}2.2 服务端通道初始化
public class WebSocketChannelInitializer extends ChannelInitializer<SocketChannel>{
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
//HttpServerCodec: 针对http协议进行编解码
pipeline.addLast("httpServerCodec", new HttpServerCodec());
//ChunkedWriteHandler分块写处理，文件过大会将内存撑爆
pipeline.addLast("chunkedWriteHandler", new ChunkedWriteHandler());
/**
* 作用是将一个Http的消息组装成一个完成的HttpRequest或者HttpResponse，那么具体的是什么
* 取决于是请求还是响应, 该Handler必须放在HttpServerCodec后的后面
*/
pipeline.addLast("httpObjectAggregator", new HttpObjectAggregator(8192));
//用于处理websocket, /ws为访问websocket时的uri
pipeline.addLast("webSocketServerProtocolHandler", new WebSocketServerProtocolHandler("/ws"));
pipeline.addLast("myWebSocketHandler", new MyWebSocketHandler());
}
}2.3 服务端Handler
public class WebSocketHandler extends SimpleChannelInboundHandler<TextWebSocketFrame>{
@Override
protected void channelRead0(ChannelHandlerContext ctx, TextWebSocketFrame msg) throws Exception {
Channel channel = ctx.channel();
System.out.println(channel.remoteAddress() + ": " + msg.text());
ctx.channel().writeAndFlush(new TextWebSocketFrame("来自服务端: " + LocalDateTime.now()));
}
@Override
public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
System.out.println("ChannelId" + ctx.channel().id().asLongText());
}
@Override
public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
System.out.println("用户下线: " + ctx.channel().id().asLongText());
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
ctx.channel().close();
}
}2.4 网页端的实现
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Socket</title>
<script type="text/javascript">
var websocket; //如果浏览器支持WebSocket
if(window.WebSocket){
websocket = new WebSocket("ws://localhost:8989/ws"); //获得WebSocket对象 //当有消息过来的时候触发
websocket.onmessage = function(event){
var respMessage = document.getElementById("respMessage");
respMessage.value = respMessage.value + "\n" + event.data;
} //连接关闭的时候触发
websocket.onclose = function(event){
var respMessage = document.getElementById("respMessage");
respMessage.value = respMessage.value + "\n断开连接";
} //连接打开的时候触发
websocket.onopen = function(event){
var respMessage = document.getElementById("respMessage");
respMessage.value = "建立连接";
}
}else{
alert("浏览器不支持WebSocket");
} function sendMsg(msg) { //发送消息
if(window.WebSocket){
if(websocket.readyState == WebSocket.OPEN) { //如果WebSocket是打开状态
websocket.send(msg); //send()发送消息
}
}else{
return;
}
}
</script>
</head>
<body>
<form onsubmit="return false">
<textarea style="width: 300px; height: 200px;" name="message"></textarea>
<input type="button" onclick="sendMsg(this.form.message.value)" value="发送"><br>
<h3>信息</h3>
<textarea style="width: 300px; height: 200px;" id="respMessage"></textarea>
<input type="button" value="清空" onclick="javascript:document.getElementById('respMessage').value = ''">
</form>
</body>
</html>
2.5 测试
首先运行服务端启动程序，然后打开网页，发送“Hello world!”，如下图：