WebSocket
Http是無狀態的，瀏覽器每次請求，都是創建一個新連接，傳輸完畢即斷開。雙方並不能感知對方的狀態。
而WebSocket是長連接，一次TCP握手，即可建立持久性的連接，並且雙方能感知到對方的狀態。
核心代碼：
// 因爲基於http，所以要添加http編碼和解碼器
pipeline.addLast(new HttpServerCodec());
// 以塊的方式寫，添加ChunkedWriteHandler
pipeline.addLast(new ChunkedWriteHandler());
// http數據傳輸過程中是分段的
// HttpObjectAggregator將多個段聚合起來
pipeline.addLast(new HttpObjectAggregator(4096));
// WebSocket以幀的方式傳遞(frame)
// 指定webSocketPath 對應瀏覽器地址ws://localhost/hello
// 將http協議升級爲WebSocket協議，保持長連接
pipeline.addLast(new WebSocketServerProtocolHandler("/hello"));
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HttpServerCodec ：Http編碼和解碼器
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ChunkedWriteHandler ：以塊的方式寫數據
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HttpObjectAggregator(4096) ：將多個段聚合起來，最大長度4096
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WebSocketServerProtocolHandler ：將http協議升級爲WebSocket協議，通過狀態碼101切換的。101（switch protocols）。構造方法參數是ws的路徑
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WebSocket傳輸數據以frame（幀）的形式傳遞：
WebSocketFrame：
附代碼
Server
NioEventLoopGroup bossGroup = new NioEventLoopGroup();
NioEventLoopGroup workGroup = new NioEventLoopGroup();
try{
ServerBootstrap serverBootstrap = new ServerBootstrap();
serverBootstrap.group(bossGroup,workGroup).channel(NioServerSocketChannel.class)
.handler(new LoggingHandler(LogLevel.INFO))
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
// 因爲基於http，所以要添加http編碼和解碼器
pipeline.addLast(new HttpServerCodec());
// 以塊的方式寫，添加ChunkedWriteHandler
pipeline.addLast(new ChunkedWriteHandler());
// http數據傳輸過程中是分段的
// HttpObjectAggregator將多個段聚合起來
pipeline.addLast(new HttpObjectAggregator(4096));
// WebSocket以幀的方式傳遞(frame)
// 指定webSocketPath 對應瀏覽器地址ws://localhost/hello
// 將http協議升級爲WebSocket協議，保持長連接
pipeline.addLast(new WebSocketServerProtocolHandler("/hello"));
// 自定義的WebSocket處理器
pipeline.addLast(new WebSocketHandler());
}
});
ChannelFuture channelFuture = serverBootstrap.bind(7000).sync();
channelFuture.channel().closeFuture().sync();
}finally {
bossGroup.shutdownGracefully();
workGroup.shutdownGracefully();
}
ServerHandler:
// 泛型表示一個文本幀
public class WebSocketHandler extends SimpleChannelInboundHandler<TextWebSocketFrame> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, TextWebSocketFrame msg) throws Exception {
System.out.println(msg.text());
ctx.writeAndFlush(new TextWebSocketFrame("服務器時間 : "+Instant.now() + msg.text()));
}
// web連接即觸發
@Override
public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
System.out.println("handler add 被觸發 " + ctx.channel().id().asLongText());
}
@Override
public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
System.out.println("handler remove被調用" + ctx.channel().id().asShortText());
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
System.out.println("異常發生");
ctx.close();
}
}
html頁面：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>hello,WebSocket</title>
</head>
<body>
<script>
var socket;
if (window.WebSocket){
socket = new WebSocket("ws://localhost:7000/hello")
socket.onmessage = function (ev) {
var text = document.getElementById('repText')
text.value = text.value +"\n" + ev.data
}
socket.onopen = function (ev) {
var text = document.getElementById('repText')
text.value = "連接開啓"
}
socket.onclose = function (ev) {
var text = document.getElementById('repText')
text.value = text.value +"\n" +"連接關閉"
}
function send(text) {
if (!window.socket){
return
}
if (socket.readyState == WebSocket.OPEN){
socket.send(text)
}else{
alert("連接未開啓")
}
}
}else {
alert("瀏覽器不辭職WebSocket")
}
</script>
<form onsubmit="return false">
<textarea name="msg" style="width: 300px;height: 300px"></textarea>
<input type="button" value="發送" onclick="send(this.form.msg.value)">
<textarea id="repText" style="width: 300px;height: 300px"></textarea>
<input type="button" value="清空" onclick="document.getElementById('repText').value=''">
</form>
</body>
</html>