说明

io.netty.channel.ChannelInitializer是一个特殊的ChannelInboundHandler。它的主要作用是向 Channel对应的ChannelPipeline中增加ChannelHandler。执行完ChannelInitializer的initChannel(C ch)函数以后，ChannelInitializer就会从ChannelPipeline自动删除自己，防止重复进入。
一般是通过Bootstrap.handler(ChannelHandler) 、ServerBootstrap.childHandler(ChannelHandler)的方式分别在客户端、服务端中将ChannelInitializer这个ChannelHandler增加到ChannelPipeline中。

示例

思路

我们来验证下ChannelInitializer是否会被自动删除。我们在ChannelInitializer的initChannel(C ch)函数末尾打印出来当前ChannelPipeline中已经添加的ChannelHandler名称；在Channel连接成功以后，再打印出来当前ChannelPipeline中已经添加的ChannelHandler名称，两者对照下，就能看出来是否被自动删除了。

代码片段

package com.thb.power.terminal;import java.io.BufferedReader;
import java.io.InputStreamReader;import com.thb.power.packet.register.RegisterRequestPacket;import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;/*** 主函数* @author thb**/
public class Terminal {// 要连接的服务端的host static final String HOST = System.getProperty("host", "127.0.0.1"); // 要连接的服务端的端口号 static final int PORT = Integer.parseInt(System.getProperty("port", "22335"));public static void main(String[] args) throws Exception {// 配置客户端EventLoopGroup group = new NioEventLoopGroup();try {Bootstrap b = new Bootstrap();b.group(group).channel(NioSocketChannel.class).option(ChannelOption.TCP_NODELAY, true).handler(new TerminalInitializer());// 启动客户端Channel ch = b.connect(HOST, PORT).sync().channel();		// 查看ChannelPipeline添加的ChannelHandler名称System.out.println("after channel connected:");for (String name : ch.pipeline().names()) {System.out.println("handler name: " + name);} ChannelFuture lastWriteFuture = null;BufferedReader in = new BufferedReader(new InputStreamReader(System.in));System.out.println("please input(register):");for (;;) {String line = in.readLine();if (line == null) {break;}				// 如果用户输入register，表示命令客户端发送注册请求给服务器if (line.toLowerCase().equals("register")) {RegisterRequestPacket registerRequest = new RegisterRequestPacket();// 返回的ByteBuf存放着注册请求的数据ByteBuf buf = registerRequest.build(ch);lastWriteFuture = ch.writeAndFlush(buf);						}}if (lastWriteFuture != null) {lastWriteFuture.sync();}} finally {// 关闭event loop以便终止所有的线程group.shutdownGracefully();}}}// ChannelInitializer的子类
package com.thb.power.terminal;import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;public class TerminalInitializer extends ChannelInitializer<SocketChannel> {@Overridepublic void initChannel(SocketChannel ch) throws Exception {ChannelPipeline p = ch.pipeline();p.addLast(new LoggingHandler(LogLevel.INFO));// 查看ChannelPipeline添加的ChannelHandler名称System.out.println("in initChannel(SocketChannel ch) method of TerminalInitializer:");for (String name : ch.pipeline().names()) {System.out.println("handler name: " + name);} }
}

运行输出

从上面输出可以看出，ChannelInitializer开始被添加到ChannelPipeline中，后来又被自动删除了。