一、前言

上篇博客介绍了服务端的启动源码,这篇就开始介绍客户端

二、源码分析

首先贴上客户端的简单代码~

public class SocketClient {
    public static void main(String[] args) throws InterruptedException {
        EventLoopGroup eventLoopGroup = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(eventLoopGroup).channel(NioSocketChannel.class).handler(new LoggingHandler(LogLevel.INFO))
                    .handler(new SocketClientInitializer());
            ChannelFuture channelFuture = bootstrap.connect("localhost", 7878).sync();
            channelFuture.channel().closeFuture().sync();
        } finally {
            eventLoopGroup.shutdownGracefully();
        }
    }
}

设置group和server端不同的是,这里这设置一个group

public B group(EventLoopGroup group) {
    if (group == null) {
        throw new NullPointerException("group");
    }
    if (this.group != null) {
        throw new IllegalStateException("group set already");
    }
    this.group = group;
    return (B) this;
}

设置channel

public B channel(Class<? extends C> channelClass) { 
    if (channelClass == null) {
        throw new NullPointerException("channelClass");
    }
    // server端使用的是ReflectiveChannelFactory
    // 最后newChannel()后面也是通过反射来实现的了
    return channelFactory(new BootstrapChannelFactory<C>(channelClass));
}

设置handler

@SuppressWarnings("unchecked")
public B handler(ChannelHandler handler) {
    if (handler == null) {
        throw new NullPointerException("handler");
    }
    this.handler = handler;
    return (B) this;
}

接着就是核心代码连接了

public ChannelFuture connect(String inetHost, int inetPort) {
    return connect(new InetSocketAddress(inetHost, inetPort));
}
public ChannelFuture connect(SocketAddress remoteAddress) {
    if (remoteAddress == null) {
        throw new NullPointerException("remoteAddress");
    }
    validate();
    return doConnect(remoteAddress, localAddress());
}
// 这部分代码和server绑定类似
private ChannelFuture doConnect(final SocketAddress remoteAddress, final SocketAddress localAddress) {
    // 初始化和注册channel
    final ChannelFuture regFuture = initAndRegister();
    // 获取channel
    final Channel channel = regFuture.channel();
    if (regFuture.cause() != null) {
        return regFuture;
    }
    final ChannelPromise promise = channel.newPromise();
    if (regFuture.isDone()) {
        doConnect0(regFuture, channel, remoteAddress, localAddress, promise);
    } else {
        // 为future添加一个监听器
        regFuture.addListener(new ChannelFutureListener() {
            @Override
            public void operationComplete(ChannelFuture future) throws Exception {
                doConnect0(regFuture, channel, remoteAddress, localAddress, promise);
            }
        });
    }
    return promise;
}
final ChannelFuture initAndRegister() {
    // 创建channel
    final Channel channel = channelFactory().newChannel();
    try {
        // 初始化channel
        init(channel);
    } catch (Throwable t) {
        channel.unsafe().closeForcibly();
        return channel.newFailedFuture(t);
    }
    // 注册channel
    ChannelFuture regFuture = group().register(channel);
    if (regFuture.cause() != null) {
        if (channel.isRegistered()) {
            channel.close();
        } else {
            channel.unsafe().closeForcibly();
        }
    }
    return regFuture;
}
//Bootstrap channel初始化部分
void init(Channel channel) throws Exception {
    // 获取通道
    ChannelPipeline p = channel.pipeline();
    // 为通道添加handler,这里的handler就是我们添加的ChannelInitializer类
    p.addLast(handler());
    // 下面的一些配置就不是很重要的了
    final Map<ChannelOption<?>, Object> options = options();
    synchronized (options) {
        for (Entry<ChannelOption<?>, Object> e: options.entrySet()) {
            try {
                if (!channel.config().setOption((ChannelOption<Object>) e.getKey(), e.getValue())) {
                    logger.warn("Unknown channel option: " + e);
                }
            } catch (Throwable t) {
                logger.warn("Failed to set a channel option: " + channel, t);
            }
        }
    }
    final Map<AttributeKey<?>, Object> attrs = attrs();
    synchronized (attrs) {
        for (Entry<AttributeKey<?>, Object> e: attrs.entrySet()) {
            channel.attr((AttributeKey<Object>) e.getKey()).set(e.getValue());
        }
    }
}
// MultithreadEventLoopGroup类 
// group().register(channel)对应的注册
@Override
public ChannelFuture register(Channel channel) {
    return next().register(channel);
}
// SingleThreadEventLoop 类
@Override
public ChannelFuture register(Channel channel) {
    return register(channel, new DefaultChannelPromise(channel, this));
}
// AbstractChannel 类
@Override
public final void register(EventLoop eventLoop, final ChannelPromise promise) {
    if (eventLoop == null) {
        throw new NullPointerException("eventLoop");
    }
    if (isRegistered()) {
        promise.setFailure(new IllegalStateException("registered to an event loop already"));
        return;
    }
    if (!isCompatible(eventLoop)) {
        promise.setFailure(
                new IllegalStateException("incompatible event loop type: " + eventLoop.getClass().getName()));
        return;
    }
    AbstractChannel.this.eventLoop = eventLoop;
    if (eventLoop.inEventLoop()) {
        register0(promise);
    } else {
        try {
            eventLoop.execute(new Runnable() {
                @Override
                public void run() {
                    register0(promise);
                }
            });
        } catch (Throwable t) {
            logger.warn(
                    "Force-closing a channel whose registration task was not accepted by an event loop: {}",
                    AbstractChannel.this, t);
            closeForcibly();
            closeFuture.setClosed();
            promise.setFailure(t);
        }
    }
}
// 再看register0()吧
private void register0(ChannelPromise promise) {
    try {
        // check if the channel is still open as it could be closed in the mean time when the register
        // call was outside of the eventLoop
        if (!ensureOpen(promise)) {
            return;
        }
        // 真正执行注册
        doRegister();
        registered = true;
        promise.setSuccess();
        pipeline.fireChannelRegistered();
        if (isActive()) {
            pipeline.fireChannelActive();
        }
    } catch (Throwable t) {
        // Close the channel directly to avoid FD leak.
        closeForcibly();
        closeFuture.setClosed();
        if (!promise.tryFailure(t)) {
            logger.warn(
                    "Tried to fail the registration promise, but it is complete already. " +
                            "Swallowing the cause of the registration failure:", t);
        }
    }
}
@Override
protected void doRegister() throws Exception {
    boolean selected = false;
    for (;;) {
        try {
            // 这里的javaChannel()是:java.nio.channels.SocketChannel,很明显这里的channel就是jdk中的channel
            selectionKey = javaChannel().register(eventLoop().selector, 0, this);
            return;
        } catch (CancelledKeyException e) {
            if (!selected) {
                // Force the Selector to select now as the "canceled" SelectionKey may still be
                // cached and not removed because no Select.select(..) operation was called yet.
                eventLoop().selectNow();
                selected = true;
            } else {
                // We forced a select operation on the selector before but the SelectionKey is still cached
                // for whatever reason. JDK bug ?
                throw e;
            }
        }
    }
}

ok,到了channel的初始化和注册完成了。继续看注册完了之后

private ChannelFuture doConnect(final SocketAddress remoteAddress, final SocketAddress localAddress) {
    final ChannelFuture regFuture = initAndRegister();
    final Channel channel = regFuture.channel();
    if (regFuture.cause() != null) {
        return regFuture;
    }
    final ChannelPromise promise = channel.newPromise();
    if (regFuture.isDone()) {
        doConnect0(regFuture, channel, remoteAddress, localAddress, promise);
    } else {
        // 添加监听器
        regFuture.addListener(new ChannelFutureListener() {
            // 将会在调用sync之后调用此方法
            @Override
            public void operationComplete(ChannelFuture future) throws Exception {
                doConnect0(regFuture, channel, remoteAddress, localAddress, promise);
            }
        });
    }
    return promise;
}
// 调用sync()之后
private static void doConnect0(
            final ChannelFuture regFuture, final Channel channel,
            final SocketAddress remoteAddress, final SocketAddress localAddress, final ChannelPromise promise) {
    channel.eventLoop().execute(new Runnable() {
        @Override
        public void run() {
            if (regFuture.isSuccess()) {
                if (localAddress == null) {
                    //channel: java.nio.channels.SocketChannel
                    // 真正连接了
                    channel.connect(remoteAddress, promise);
                } else {
                    channel.connect(remoteAddress, localAddress, promise);
                }
                promise.addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
            } else {
                promise.setFailure(regFuture.cause());
            }
        }
    });
}