前言

看過dubbo源碼的同學(xué)應(yīng)該都清楚，使用dubbo協(xié)議的底層通信是使用的netty進(jìn)行交互，而最近看了dubbo的Netty部分后，自己寫了個(gè)簡(jiǎn)單的Netty通信例子。

準(zhǔn)備

工程截圖

模塊詳解

rpc-common

rpc-common作為各個(gè)模塊都需使用的模塊，工程中出現(xiàn)的是一些通信時(shí)請(qǐng)求的參數(shù)以及返回的參數(shù)，還有一些序列化的工具。

rpc-client

rpc-client中目前只是單單的一個(gè)NettyClient啟動(dòng)類。

rpc-server

rpc-client中目前也只是單單的一個(gè)NettyServer服務(wù)啟動(dòng)類。

需要的依賴

目前所有的依賴項(xiàng)都出現(xiàn)在 rpc-common 下的 pom.xml中。

<dependencies> <!-- Netty --> <dependency> <groupId>io.netty</groupId> <artifactId>netty-all</artifactId> <version>4.1.10.Final</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-log4j12</artifactId> <version>1.7.25</version> </dependency> <!-- Protostuff --> <dependency> <groupId>com.dyuproject.protostuff</groupId> <artifactId>protostuff-core</artifactId> <version>1.0.9</version> </dependency> <dependency> <groupId>com.dyuproject.protostuff</groupId> <artifactId>protostuff-runtime</artifactId> <version>1.0.9</version> </dependency> <!-- Objenesis --> <dependency> <groupId>org.objenesis</groupId> <artifactId>objenesis</artifactId> <version>2.1</version> </dependency> <!-- fastjson --> <dependency> <groupId>com.alibaba</groupId> <artifactId>fastjson</artifactId> <version>1.2.38</version> </dependency></dependencies>

實(shí)現(xiàn)

首先我們?cè)赾ommon中先定義本次的Request和Response的基類對(duì)象。

public class Request { private String requestId; private Object parameter; public String getRequestId() { return requestId; } public void setRequestId(String requestId) { this.requestId = requestId; } public Object getParameter() { return parameter; } public void setParameter(Object parameter) { this.parameter = parameter; }}public class Response { private String requestId; private Object result; public String getRequestId() { return requestId; } public void setRequestId(String requestId) { this.requestId = requestId; } public Object getResult() { return result; } public void setResult(Object result) { this.result = result; }}

使用fastJson進(jìn)行本次序列化

Netty對(duì)象的序列化轉(zhuǎn)換很好懂， ByteToMessageDecoder 和 MessageToByteEncoder 分別只要繼承它們，重寫方法后，獲取到Object和Byte，各自轉(zhuǎn)換就OK。

不過如果是有要用到生產(chǎn)上的同學(xué)，建議不要使用 fastJson，因?yàn)樗穆┒囱a(bǔ)丁真的是太多了，可以使用google的 protostuff。

public class RpcDecoder extends ByteToMessageDecoder { // 目標(biāo)對(duì)象類型進(jìn)行解碼 private Class<?> target; public RpcDecoder(Class target) { this.target = target; } @Override protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception { if (in.readableBytes() < 4) { // 不夠長(zhǎng)度丟棄 return; } in.markReaderIndex(); // 標(biāo)記一下當(dāng)前的readIndex的位置 int dataLength = in.readInt(); // 讀取傳送過來的消息的長(zhǎng)度。ByteBuf 的readInt()方法會(huì)讓他的readIndex增加4 if (in.readableBytes() < dataLength) { // 讀到的消息體長(zhǎng)度如果小于我們傳送過來的消息長(zhǎng)度，則resetReaderIndex. 這個(gè)配合markReaderIndex使用的。把readIndex重置到mark的地方 in.resetReaderIndex(); return; } byte[] data = new byte[dataLength]; in.readBytes(data); Object obj = JSON.parseObject(data, target); // 將byte數(shù)據(jù)轉(zhuǎn)化為我們需要的對(duì)象 out.add(obj); }}public class RpcEncoder extends MessageToByteEncoder { //目標(biāo)對(duì)象類型進(jìn)行編碼 private Class<?> target; public RpcEncoder(Class target) { this.target = target; } @Override protected void encode(ChannelHandlerContext ctx, Object msg, ByteBuf out) throws Exception { if (target.isInstance(msg)) { byte[] data = JSON.toJSONBytes(msg); // 使用fastJson將對(duì)象轉(zhuǎn)換為byte out.writeInt(data.length); // 先將消息長(zhǎng)度寫入，也就是消息頭 out.writeBytes(data); // 消息體中包含我們要發(fā)送的數(shù)據(jù) } }}

NetyServer

public class NettyServerHandler extends ChannelInboundHandlerAdapter { @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { Request request = (Request) msg; System.out.println('Client Data:' + JSON.toJSONString(request)); Response response = new Response(); response.setRequestId(request.getRequestId()); response.setResult('Hello Client !'); // client接收到信息后主動(dòng)關(guān)閉掉連接 ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE); } @Override public void channelReadComplete(ChannelHandlerContext ctx) throws Exception { ctx.flush(); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { ctx.close(); }}public class NettyServer { private static final Logger logger = LoggerFactory.getLogger(NettyServer.class); private String ip; private int port; public NettyServer(String ip, int port) { this.ip = ip; this.port = port; } public void server() throws Exception { EventLoopGroup bossGroup = new NioEventLoopGroup(); EventLoopGroup workerGroup = new NioEventLoopGroup(); try { final ServerBootstrap serverBootstrap = new ServerBootstrap(); serverBootstrap.group(bossGroup, workerGroup) .channel(NioServerSocketChannel.class) .option(ChannelOption.SO_BACKLOG, 1024) .option(ChannelOption.SO_SNDBUF, 32 * 1024) .option(ChannelOption.SO_RCVBUF, 32 * 1024) .option(ChannelOption.SO_KEEPALIVE, true) .childHandler(new ChannelInitializer<SocketChannel>() { protected void initChannel(SocketChannel socketChannel) throws Exception { socketChannel.pipeline().addLast(new RpcDecoder(Request.class)) .addLast(new RpcEncoder(Response.class)) .addLast(new NettyServerHandler()); } }); serverBootstrap.childOption(ChannelOption.SO_KEEPALIVE, true); // 開啟長(zhǎng)連接 ChannelFuture future = serverBootstrap.bind(ip, port).sync();// if (future.isSuccess()) {////new Register().register('/yanzhenyidai/com.yanzhenyidai.server', ip + ':' + port);// } future.channel().closeFuture().sync(); } finally { bossGroup.shutdownGracefully(); workerGroup.shutdownGracefully(); } } public static void main(String[] args) throws Exception { new NettyServer('127.0.0.1', 20000).server(); }}

關(guān)鍵名詞：

EventLoopGroup workerGroup bossGroup Server端的EventLoopGroup分為兩個(gè)，一般workerGroup作為處理請(qǐng)求，bossGroup作為接收請(qǐng)求。 ChannelOption SO_BACKLOG SO_SNDBUF SO_RCVBUF SO_KEEPALIVE 以上四個(gè)常量作為TCP連接中的屬性。 ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);

NettyServerHandler中出現(xiàn)的 ChannelFutureListener.CLOSE ，作為Server端主動(dòng)關(guān)閉與Client端的通信，如果沒有主動(dòng)Close，那么NettyClient將會(huì)一直處于阻塞狀態(tài)，得不到NettyServer的返回信息。

NettyClient

public class NettyClient extends SimpleChannelInboundHandler<Response> { private final String ip; private final int port; private Response response; public NettyClient(String ip, int port) { this.ip = ip; this.port = port; } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { ctx.close(); } @Override protected void channelRead0(ChannelHandlerContext channelHandlerContext, Response response) throws Exception { this.response = response; } public Response client(Request request) throws Exception { EventLoopGroup group = new NioEventLoopGroup(); try { // 創(chuàng)建并初始化 Netty 客戶端 Bootstrap 對(duì)象 Bootstrap bootstrap = new Bootstrap(); bootstrap.group(group); bootstrap.channel(NioSocketChannel.class); bootstrap.handler(new ChannelInitializer<SocketChannel>() {@Overridepublic void initChannel(SocketChannel channel) throws Exception { ChannelPipeline pipeline = channel.pipeline(); pipeline.addLast(new RpcDecoder(Response.class)); pipeline.addLast(new RpcEncoder(Request.class)); pipeline.addLast(NettyClient.this);} }); bootstrap.option(ChannelOption.TCP_NODELAY, true);// String[] discover = new Discover().discover('/yanzhenyidai/com.yanzhenyidai.server').split(':'); // 連接 RPC 服務(wù)器 ChannelFuture future = bootstrap.connect(ip, port).sync(); // 寫入 RPC 請(qǐng)求數(shù)據(jù)并關(guān)閉連接 Channel channel = future.channel(); channel.writeAndFlush(request).sync(); channel.closeFuture().sync(); return response; } finally { group.shutdownGracefully(); } } public static void main(String[] args) throws Exception { Request request = new Request(); request.setRequestId(UUID.randomUUID().toString()); request.setParameter('Hello Server !'); System.out.println(JSON.toJSONString(new NettyClient('127.0.0.1', 30000).client(request))); }}

測(cè)試

如果以上所有內(nèi)容都準(zhǔn)備就緒，那么就可以進(jìn)行調(diào)試了。

啟動(dòng)順序，先啟動(dòng)NettyServer，再啟動(dòng)NettyClient。

總結(jié)

記得剛出來工作時(shí)，有工作很多年的同事問我了不了解Netty，當(dāng)時(shí)工作太短，直說聽過Putty，現(xiàn)在回想起來真的挺丟人的，哈哈。😋

Netty作為通信框架，如果你了解TCP，而且項(xiàng)目中有類似傳輸信息的需求，又不想集成HTTP或者Socket，那么Netty真的挺實(shí)用的。

參考資料：

Dubbo-Netty Netty.io

本項(xiàng)目Github地址：Netty-RPC

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