4、Channel简介

1 public interface Channel extends AttributeMap, ChannelOutboundInvoker, Comparable<Channel>

public interface ChannelOutboundInvoker {
    //绑定本地地址
    ChannelFuture bind(SocketAddress localAddress);
    ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise);
    
    //连接远程地址
    ChannelFuture connect(SocketAddress remoteAddress);
    ChannelFuture connect(SocketAddress remoteAddress, ChannelPromise promise);
    ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress);
    ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise);
    
    //解除连接
    ChannelFuture disconnect();
    ChannelFuture disconnect(ChannelPromise promise);
    
    //关闭Channel
    ChannelFuture close();
    ChannelFuture close(ChannelPromise promise);
    //与EventLoop解除注册
    ChannelFuture deregister();
    ChannelFuture deregister(ChannelPromise promise);
    /**
     * Request to Read data from the {@link Channel} into the first inbound buffer, 
     * triggers an {@link ChannelInboundHandler#channelRead(ChannelHandlerContext, Object)} event if data was read, 
     * and triggers a {@link ChannelInboundHandler#channelReadComplete(ChannelHandlerContext) channelReadComplete} event so the
     * handler can decide to continue reading.  If there‘s a pending read operation already, this method does nothing.
     * This will result in having the
     * {@link ChannelOutboundHandler#read(ChannelHandlerContext)}
     * method called of the next {@link ChannelOutboundHandler} contained in the {@link ChannelPipeline} of the
     * {@link Channel}.
     */
    /**
     * 从channel中读取数据到第一个 InboundBuffer，
     * 1、触发 ChannelInboundHandler#channelRead(ChannelHandlerContext, Object)事件，在有数据的情况下
     * 2、触发ChannelInboundHandler#channelReadComplete(ChannelHandlerContext)事件，handler继续读取
     * 如果有read操作已经挂起，则不执行任何操作
     * 实际调用：Channel——>ChannelPipeline——>ChannelOutboundHandler——>ChannelOutboundHandler#read(ChannelHandlerContext)——>read()
     * ChannelHandlerContext继承了ChannelOutboundInvoker，它的子类实现read()方法，最后ctx.read()。
     * */
    ChannelOutboundInvoker read();
    //写
    ChannelFuture write(Object msg);
    ChannelFuture write(Object msg, ChannelPromise promise);
    
    //将数据冲刷到Channel
    ChannelOutboundInvoker flush();
    //write + flush
    ChannelFuture writeAndFlush(Object msg);
    ChannelFuture writeAndFlush(Object msg, ChannelPromise promise);
    ChannelPromise newPromise();
    ChannelProgressivePromise newProgressivePromise();
    ChannelFuture newSucceededFuture();
    ChannelFuture newFailedFuture(Throwable cause);
    ChannelPromise voidPromise();
}

public interface Channel extends AttributeMap, ChannelOutboundInvoker, Comparable<Channel> {
    //get属性
    ChannelId id(); //获得一个唯一的channelId
    EventLoop eventLoop();//获得关联的EventLoop
    Channel parent();//父Channel
    ChannelConfig config();//获得配置参数
    ChannelMetadata metadata();//获得元数据
    SocketAddress localAddress();//获得本地地址
    SocketAddress remoteAddress();//获得远端地址
    ChannelFuture closeFuture();//获得Channel关闭时的异步结果
    ChannelPipeline pipeline();//获得事件管道，用于处理IO事件
    ByteBufAllocator alloc();//获得字节缓存分配器
    Unsafe unsafe();//获得Unsafe对象
    
    //状态查询
    boolean isOpen();//是否开放
    boolean isRegistered();// 是否注册到一个EventLoop
    boolean isActive();// 是否激活
    boolean isWritable();// 是否可写
    
    long bytesBeforeUnwritable();
    long bytesBeforeWritable();
    @Override
    Channel read();
    @Override
    Channel flush();
}