Netty5客户端源码解析

Netty5客户端源码解析

今天来分析下netty5的客户端源码,示例代码如下:

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel; /**
* Created by yaojiafeng on 16/1/17.
*/
public class SimpleClient { public void connect(int port, String host) throws Exception {
// 配置客户端NIO线程组
EventLoopGroup group = new NioEventLoopGroup(1);
try {
Bootstrap b = new Bootstrap();
b.group(group).channel(NioSocketChannel.class)
.option(ChannelOption.TCP_NODELAY, true)
.handler(new ChannelInitializer<SocketChannel>() {
@Override
public void initChannel(SocketChannel ch)
throws Exception {
ch.pipeline().addLast(new SimpleClientHandler());
}
}); // 发起异步连接操作
ChannelFuture f = b.connect(host, port).sync(); // 当代客户端链路关闭
f.channel().closeFuture().sync();
} finally {
// 优雅退出,释放NIO线程组
group.shutdownGracefully();
}
} /**
* @param args
* @throws Exception
*/
public static void main(String[] args) throws Exception {
int port = 8081;
if (args != null && args.length > 0) {
try {
port = Integer.valueOf(args[0]);
} catch (NumberFormatException e) {
// 采用默认值
}
}
new SimpleClient().connect(port, "127.0.0.1");
}
} import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext; /**
* Created by yaojiafeng on 16/1/17.
*/
public class SimpleClientHandler extends ChannelHandlerAdapter { /**
* Creates a client-side handler.
*/
public SimpleClientHandler() {
} @Override
public void channelActive(ChannelHandlerContext ctx) {
ByteBuf message = Unpooled.copiedBuffer("hello world".getBytes()); ctx.writeAndFlush(message);
} @Override
public void channelRead(ChannelHandlerContext ctx, Object msg)
throws Exception {
ByteBuf body = (ByteBuf) msg; byte[] bytes = new byte[body.readableBytes()];
body.readBytes(bytes);
System.out.println(new String(bytes));
} }
  1. 构造Bootstrap对象

    设置事件循环组为NioEventLoopGroup,设置channel为NioSocketChannel,设置一些socket配置项,比如ChannelOption.TCP_NODELAY,设置自定义的ChannelHandler

  2. 发起异步连接

    // 发起异步连接操作
    ChannelFuture f = b.connect(host, port).sync();

    内部具体操作如下:

    2.1 参数校验

    执行validate方法,EventLoopGroup、channelFactory、ChannelHandler这几个基本字段不能为空

    2.2 initAndRegister方法

    异步执行初始化和注册方法,反射构造初始化构造Bootstrap时,设置的NioSocketChannel对象,NioSocketChannel包含的具体字段上篇Netty5服务端源码解析有讲解。构造NioSocketChannel后,调用init方法初始化NioSocketChannel,包括设置ChannelHandler到管道里,设置ChannelOption到socket。然后异步注册NioSocketChannel到NioEventLoopGroup里的NioEventLoop。

    2.2.1 异步注册NioSocketChannel到NioEventLoop

    最终委派调用到

    channel.unsafe().register(this, promise);

    NioSocketChannel里的内部类Unsafe的register方法,然后启动NioEventLoop单线程事件循环内部获取Task并执行,register0方法,内部会调用doRegister方法,注册SocketChannel到NioSocketChannel关联的唯一NioEventLoop的selector上,并加上att为NioSocketChannel。

                    selectionKey = javaChannel().register(((NioEventLoop) eventLoop().unwrap()).selector, 0, this);

    2.2.2 safeSetSuccess方法激活doConnect0方法

    刚开始进入的doResolveAndConnect方法会调用doConnect方法,如果异步注册已经完成则直接调用doConnect0方法,否则给ChannelFuture增加监听方法,由channel注册完成后驱动调用doConnect0方法,一般情况下都是通过监听器驱动的。接下来分析doConnect0方法。

    private static void doConnect0(
    final SocketAddress remoteAddress, final SocketAddress localAddress, final ChannelFuture regFuture,
    final ChannelPromise connectPromise) { // This method is invoked before channelRegistered() is triggered. Give user handlers a chance to set up
    // the pipeline in its channelRegistered() implementation.
    final Channel channel = connectPromise.channel();
    channel.eventLoop().execute(new Runnable() {
    @Override
    public void run() {
    if (regFuture.isSuccess()) {
    if (localAddress == null) {
    channel.connect(remoteAddress, connectPromise);
    } else {
    channel.connect(remoteAddress, localAddress, connectPromise);
    }
    connectPromise.addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
    } else {
    connectPromise.setFailure(regFuture.cause());
    }
    }
    });
    }

    这个方法也是增加task到NioEventLoop里,内部执行逻辑为,注册成功的情况下调用channel.connect(remoteAddress, connectPromise)方法,它会通过管道链,一路串行调用到unsafe.connect(remoteAddress, localAddress, promise)方法。调用doConnect方法

    protected boolean doConnect(SocketAddress remoteAddress, SocketAddress localAddress) throws Exception {
    if (localAddress != null) {
    javaChannel().socket().bind(localAddress);
    } boolean success = false;
    try {
    boolean connected = javaChannel().connect(remoteAddress);
    if (!connected) {
    selectionKey().interestOps(SelectionKey.OP_CONNECT);
    }
    success = true;
    return connected;
    } finally {
    if (!success) {
    doClose();
    }
    }
    }

    调用JDK NIO的API,因为是异步连接,返回的connected是false,所以后面会设置SelectionKey的感兴趣事件为SelectionKey.OP_CONNECT,为了后续的NioEventLoop的事件循环可以获取CONNECT激活的SelectionKey做后续的连接操作。

    2.2.3 完成连接

    从SingleThreadEventExecutor的asRunnable到processSelectedKeys到processSelectedKeysOptimized到processSelectedKey方法,判断激活的操作为SelectionKey.OP_CONNECT。

     if ((readyOps & SelectionKey.OP_CONNECT) != 0) {
    // remove OP_CONNECT as otherwise Selector.select(..) will always return without blocking
    // See https://github.com/netty/netty/issues/924
    int ops = k.interestOps();
    ops &= ~SelectionKey.OP_CONNECT;
    k.interestOps(ops); unsafe.finishConnect();
    }

    重新设置感兴趣事件为0,并且调用unsafe.finishConnect方法,内部调用doFinishConnect方法完成最终连接。

     protected void doFinishConnect() throws Exception {
    if (!javaChannel().finishConnect()) {
    throw new Error();
    }
    }

    然后再调用fulfillConnectPromise方法,内部继续调用pipeline().fireChannelActive()方法

    public ChannelPipeline fireChannelActive() {
    head.fireChannelActive(); if (channel.config().isAutoRead()) {
    channel.read();
    } return this;
    }

    head.fireChannelActive走管道链,channel.read()方法也走管道链,最终调用unsafe.beginRead()方法,然后调用doBeginRead方法,重新设置感兴趣事件为SelectionKey.OP_READ(NioSocketChannel的默认感兴趣事件),至此客户端启动完成。

  3. 自行操作channel发送消息

    客户端启动完成获取channel我们可以调用writeAndFlush发送消息。当然服务端返回的消息,NioEventLoop会感知到,并通过管道链回调到自定义的channelRead方法进行读取。

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