Netty-Channel

Channel的常用操作(与网络通信相关)

• Channel read()
  从当前的Channel中读取数据到第一个缓冲区中，如果数据被成功读取，触发ChannelHandler.channelRead()事件，读取操作调用完成后，紧接着会触发ChannelHandler.channelReadComplete事件，这样业务的ChannelHandler可以决定是否需要继续读取数据
• Channel write(Object msg)
  请求将当前的msg通过ChannelPipeline写入到目标Channel中。注意，write操作只是将消息存入到消息发送环形数组中，并没有被真正发送，只有调用flush操作才会被写入到Channel中，发送给对方。
• Channel write(Object msg，ChannelPromise promise)
  功能与write(Object msg)相同，多携带了ChannelPromise参数负责写入操作的结果
• ChannelFuture writeAndFlush(Object msg，ChannelPromise promise)
  功能与上相同，不同之处在于会将消息写入到Channel中发送，等价于write + flush
• Channel flush()
  将之前写入到发送环形数组中的消息全部写入到目标Channel中，发送给通信对方
• ChannelFuture close(ChannelPromise promise)
  主动关闭当前连接，通过ChannelPromise设置操作结果并进行结果通知，无论是否操作成功，都可以通过ChannelPromise获取操作结果。该操作会级联触发ChannelPipeline中所有的ChannelHandler的close事件
• ChannelFuture disconnect(ChannelPromise promise)
  请求断开与远程通信对端的链接并使用ChannelPromise获取操作结果的通知消息，级联触发ChannelHandler的disconnect事件
• ChannelFuture connect(SocketAddress remoteAddress)
  客户端发起连接请求，如果连接请求因为超时而失败，ChannelFuture中的操作结果就是ConnectTimeoutException异常，如果连接被拒绝，就是ConnectException异常。该方法会级联触发ChannelHandler的connect事件

Channel的其他常用操作

• EventLoop eventLoop()–获取Channel对应的eventLoop()
  Channel需要注册到EventLoop的多路复用器上，用于处理IO事件。EventLoop本质上就是处理网络读写事件的Reactor线程
• ChannelMetadata metadata()–获取当前Chanel的TCP参数配置

Channel源码分析

服务端NioServerSocketChannel

客户端NioSocketChannel

NioServerSocketChannel

public class NioServerSocketChannel extends AbstractNioMessageServerChannel implements ServerSocketChannel {
    private static final ChannelMetadata METADATA = new ChannelMetadata(false);
    private static final InternalLogger logger = InternalLoggerFactory.getInstance(NioServerSocketChannel.class);
    private final ServerSocketChannelConfig config = new DefaultServerSocketChannelConfig(this, this.javaChannel().socket());

    //静态方法调用jdk下的NIO生成ServerSocketChannel
    private static java.nio.channels.ServerSocketChannel newSocket() {
        try {
            return java.nio.channels.ServerSocketChannel.open();
        } catch (IOException var1) {
            throw new ChannelException("Failed to open a server socket.", var1);
        }
    }

    public NioServerSocketChannel(EventLoop eventLoop, EventLoopGroup childGroup) {
        super((Channel)null, eventLoop, childGroup, newSocket(), 16);
    }

    public InetSocketAddress localAddress() {
        return (InetSocketAddress)super.localAddress();
    }

    public ChannelMetadata metadata() {
        return METADATA;
    }

    public ServerSocketChannelConfig config() {
        return this.config;
    }

    public boolean isActive() {
        return this.javaChannel().socket().isBound();
    }

    public InetSocketAddress remoteAddress() {
        return null;
    }

    protected java.nio.channels.ServerSocketChannel javaChannel() {
        return (java.nio.channels.ServerSocketChannel)super.javaChannel();
    }

    protected SocketAddress localAddress0() {
        return this.javaChannel().socket().getLocalSocketAddress();
    }

    protected void doBind(SocketAddress localAddress) throws Exception {
        this.javaChannel().socket().bind(localAddress, this.config.getBacklog());
    }

    protected void doClose() throws Exception {
        this.javaChannel().close();
    }

    protected int doReadMessages(List<Object> buf) throws Exception {
	    //接收新的客户端连接
        SocketChannel ch = this.javaChannel().accept();

        try {
            if (ch != null) {//SocketChannel不空，则利用当前的NioServerSocketChannel、EventLoop和SocketChannel创建新的NioSocketChannel，并加入List