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Netty组件之Channel实例化

Netty

一、Channel概述Channel即Socket封装 ， 提供了I/O的基本操作 。从以下子接口中可以看出Netty对不同的底层协议提供了对应的channel来处理 ， 例如：TCP/IP、UDP/IP、SCTP/IP、HTTP2等 。

Netty组件之Channel实例化

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Channel类图

Netty组件之Channel实例化

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Channel子接口
二、实例化流程从客户端引导类示例中查看Channel初始化过程 。示例中使用NIOSocketChannel作为通信通道 ， 在JAVA中通信中会建立socket连接 。
【Netty组件之Channel实例化】EventLoopGroup workerGroup = new NioEventLoopGroup();Http2ClientInitializer initializer = new Http2ClientInitializer(sslCtx, Integer.MAX_VALUE);Bootstrap b = new Bootstrap();b.group(workerGroup);b.channel(NioSocketChannel.class);b.option(ChannelOption.SO_KEEPALIVE, true);b.remoteAddress(HOST, PORT);b.handler(initializer);Channel channel = b.connect().syncUninterruptibly().channel();Channel通过ChannelFactory创建 ， 下面看一下ChannelFactory类图 。
Netty组件之Channel实例化

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ChannelFactory类图
ReflectiveChannelFactory提供了newChannel()方法通过反射实例化 。示例中通过b.channel(NioSocketChannel.class)将NioSocketChannel.class赋值给ReflectiveChannelFactory的成员变量Constructor<? extends T> constructor ， Channel在connect的时候实例化 ， 下面为实例化调用链路 。
Netty组件之Channel实例化

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Channel实例化链路
三、实例化过程1.客户端实例化过程了解了Channel初始化调用链 ， 再来看下以NioSocketChannel为例初始化做了哪些事情 。下面是NioSocketChannel的四个构造重载方法 。
public NioSocketChannel() {this(DEFAULT_SELECTOR_PROVIDER); // @1}public NioSocketChannel(SelectorProvider provider) {this(newSocket(provider)); // @2}public NioSocketChannel(SocketChannel socket) {this(null, socket);}public NioSocketChannel(Channel parent, SocketChannel socket) {super(parent, socket);config = new NioSocketChannelConfig(this, socket.socket());}protected AbstractNioChannel(Channel parent, SelectableChannel ch, int readInterestOp) {super(parent);this.ch = ch;this.readInterestOp = readInterestOp;ch.configureBlocking(false); // @3}}代码解读
@1 默认使用SelectorProvider.provider()
@2 使用Provider创建SocketChannel 。provider.openSocketChannel()->new SocketChannelImpl(this) 。
@3 设置NioChannel非阻塞模式
小结：客户端NioSocketChannel实例化过程中已经回到所熟悉的java nio 。创建了通道SocketChannel ， 并设置为非阻塞 。
2.服务端实例化过程Channel服务端的实例化流程与客户端是相同的 ， 下面以NioServerSocketChannel为例走查实例化过程 。服务端引导初始化示例代码如下 。
EventLoopGroup group = new NioEventLoopGroup();ServerBootstrap b = new ServerBootstrap();b.option(ChannelOption.SO_BACKLOG, 1024);b.group(group) .channel(NioServerSocketChannel.class) .handler(new LoggingHandler(LogLevel.INFO)) .childHandler(new Http2ServerInitializer(sslCtx));Channel ch = b.bind(PORT).sync().channel();NioServerSocketChannel的构造方法 。
public NioServerSocketChannel() {this(newSocket(DEFAULT_SELECTOR_PROVIDER)); // @1}public NioServerSocketChannel(SelectorProvider provider) {this(newSocket(provider)); // @2} public NioServerSocketChannel(ServerSocketChannel channel) {super(null, channel, SelectionKey.OP_ACCEPT);config = new NioServerSocketChannelConfig(this, javaChannel().socket());}protected AbstractNioChannel(Channel parent, SelectableChannel ch, int readInterestOp) {super(parent);this.ch = ch;this.readInterestOp = readInterestOp;ch.configureBlocking(false); // @3}代码解读
@1 使用默认Provider类SelectorProvider
@2 开启服务端通道ServerSocketChannel 。provider.openServerSocketChannel()->new ServerSocketChannelImpl(this)
@3 将ServerSocketChanne设置为非阻塞
小结：服务端NioServerSocketChannel的实例化过程同样回到熟悉的Java NIO ， 创建非阻塞ServerSocketChanne通道 。
3.实例化其他事项在实例化的过程中 ， 会调父类的构造方法super(parent) 。
protected AbstractChannel(Channel parent) {this.parent = parent;id = newId(); // @1unsafe = newUnsafe(); // @2pipeline = newChannelPipeline(); // @3}@1 ChannelId初始化
ChannelId是Channel的唯一标识 ， 下面看下DefaultChannelId的生成规则 。
private DefaultChannelId() {data = https://www.isolves.com/it/cxkf/bk/2020-07-05/new byte[macHINE_ID.length + PROCESS_ID_LEN + SEQUENCE_LEN + TIMESTAMP_LEN + RANDOM_LEN];int i = 0;// machineIdSystem.arraycopy(MACHINE_ID, 0, data, i, MACHINE_ID.length);i += MACHINE_ID.length;// processIdi = writeInt(i, PROCESS_ID);// sequencei = writeInt(i, nextSequence.getAndIncrement());// timestamp (kind of)i = writeLong(i, Long.reverse(System.nanoTime()) ^ System.currentTimeMillis());// randomint random = PlatformDependent.threadLocalRandom().nextInt();i = writeInt(i, random);assert i == data.length;hashCode = Arrays.hashCode(data);}


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