Channel、ChannelHandler

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;

/**
 * Netty 服務端
 */
public class NettyServerListenerSimple {

  /**
   * 創建bootstrap
   */
  private static final ServerBootstrap serverBootstrap = new ServerBootstrap();

  /**
   * Worker
   */
  private static final EventLoopGroup work = new NioEventLoopGroup();

  /**
   * 端口號
   */
  private int port = getPort();

  /**
   * 關閉服務器方法
   */
  public void close() {
    System.out.println("關閉服務器....");
    //優雅退出
    work.shutdownGracefully();
  }

  /**
   * 開啓及服務線程
   */
  public void start() {
    serverBootstrap.group(work)
        .channel(NioServerSocketChannel.class)
        .option(ChannelOption.SO_BACKLOG, 100)
        .handler(new LoggingHandler(LogLevel.INFO));
    try {
      //設置事件處理
      serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
        @Override
        protected void initChannel(SocketChannel ch) throws Exception {
          ChannelPipeline pipeline = ch.pipeline();
          pipeline.addLast(new ServerChannelHandlerSimple());
        }
      });
      System.out.println("netty服務器在[" + port + "]端口啓動監聽");
      ChannelFuture f = serverBootstrap.bind(port);
      f.channel().closeFuture();
    } catch (Exception e) {
      System.out.println("[出現異常] 釋放資源");
    } finally {
      close();
    }
  }

  private static int getPort() {
    Double port = (Math.random() + 1) * 10000;
    return port.intValue();
  }

  public static void main(String[] args) {
    NettyServerListenerSimple nsl = new NettyServerListenerSimple();
    nsl.start();
  }
}

![在這裏插入圖片描述](https://img-blog.csdnimg.cn/20191122143044930.png)

```cpp
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
import java.nio.charset.Charset;

/**
 * 服務端的通道適配器
 */
public class ServerChannelHandlerSimple extends ChannelInboundHandlerAdapter {

  @Override
  public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
    System.out.println("error.");
    cause.printStackTrace();
    ctx.close();
  }

  @Override
  public void channelRead(ChannelHandlerContext ctx, Object msg) {
    // 具體處理客戶端的數據信息
    System.out.println("receive message. ");
    ByteBuf buf = (ByteBuf) msg;
    String rev = getMessage(buf);
    System.out.println(rev);

    // 如果有多個適配器，調用此方法通知下一個適配器執行，並將處理過的數據傳遞給下一個適配器
    ctx.fireChannelRead(rev);
  }

  private String getMessage(ByteBuf buf) {
    byte[] con = new byte[buf.readableBytes()];
    buf.readBytes(con);
    try {
      return new String(con, Charset.forName("GBK"));
    } catch (Exception e) {
      System.out.println("trans bytes to string error. ");
      e.printStackTrace();
      return null;
    }
  }
}