Netty 4 实现一个 NettyClient

本文章为作者原创，有问题的地方请提出指正。

1、类继承Diagram

2、定义EndPoint类

目前仅仅定义了2个方法，分别用来获取本地或远程服务器的地址。

package netty;

import java.net.InetSocketAddress;

/**
 * @author xfyou
 * @date 2019/8/28
 */
public interface EndPoint {

  /**
   * Return  the local Inet address
   *
   * @return The local Inet address to which this <code>EndPoint</code> is bound, or <code>null</code>
   * if this <code>EndPoint</code> does not represent a network connection.
   */
  InetSocketAddress getLocalAddress();

  /**
   * Return the remote Inet address
   *
   * @return The remote Inet address to which this <code>EndPoint</code> is bound, or <code>null</code>
   * if this <code>EndPoint</code> does not represent a network connection.
   */
  InetSocketAddress getRemoteAddress();

}

2、定义AbstractClass类

主要是定义几个抽象方法：

doOpen - 创建引导类Bootstrap；
doConnect - 创建Channel并连接远程服务器；
getChannel - 获取已创建的Channel

另外，提供了2个公共的方法给外部调用：

send - 发送消息（OutBound）
receive - 接收消息（InBound）

内部私有的write()方法。write方法负责在connect成功后，把消息写到远程peer。翻阅源码，我们可以看到如下的调用栈：

channel.writeAndFlush
- pipeline.writeAndFlush （pipleline为channel实例所关联的pipleline实例）
  - AbstractChannelHandlerContext.writeAndFlush （每个ChannelHanlder都有一个对应的ChannelHandlerContext，可以从这个ChannelHanlderConext获取Channel、ChannelHanlder和ChannelPipeline）
    - AbstractChannelHandlerContext.write（在这个方法里面有一个executor.inEventLoop()的判断，这个地方很重要，它主要是判断当前线程是否是EventLoop分配的线程，如果是则直接使用EventLoop分配的线程执行，否则会将当前要执行的任务封装成一个Task，然后塞到一个LinkedBlockQueue里面去等待后续的调度执行。这样做的目的主要是就是把用户线程的操作封装成Task放入队列，统一由I/O线程来处理）

package netty;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import lombok.*;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang.NotImplementedException;

import java.net.InetSocketAddress;
import java.nio.charset.StandardCharsets;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

/**
 * @author xfyou
 * @date 2019/8/29
 */
@Slf4j
@RequiredArgsConstructor
abstract class AbstractClient implements EndPoint {

  @NonNull
  private String hostName;

  @NonNull
  private int port;

  @NonNull
  @Getter(value = AccessLevel.PROTECTED)
  private int connectionTimeout;

  protected final CountDownLatch countDownLatch = new CountDownLatch(1);
  protected String respMsg;

  @SneakyThrows
  public void send(Object message) {
    doOpen();
    doConnect();
    write(message);
  }

  @SneakyThrows
  public String receive() {
    boolean b = countDownLatch.await(getConnectionTimeout(), TimeUnit.MILLISECONDS);
    if (!b) {
      log.error("Timeout(" + getConnectionTimeout() + "ms) when receiving response message");
    }
    return respMsg;
  }

  private void write(Object message) {
    Channel channel = getChannel();
    if (null != channel) {
      ChannelFuture f = channel.writeAndFlush(byteBufferFrom(message)).syncUninterruptibly();
      if (!f.isSuccess()) {
        log.error("Failed to send message to " + getRemoteAddress() + f.cause().getMessage());
      }
    }
  }

  private ByteBuf byteBufferFrom(Object message) {
    return message instanceof String ? Unpooled.copiedBuffer((String) message, StandardCharsets.UTF_8) : Unpooled.copiedBuffer((byte[]) message);
  }

  @Override
  public InetSocketAddress getRemoteAddress() {
    return new InetSocketAddress(hostName, port);
  }

  @Override
  public InetSocketAddress getLocalAddress() {
    throw new NotImplementedException("This method is not need to be implemented");
  }

  /**
   * Open client.
   *
   * @throws Throwable
   */
  protected abstract void doOpen() throws Throwable;

  /**
   * Connect to server.
   *
   * @throws Throwable
   */
  protected abstract void doConnect() throws Throwable;

  /**
   * Get the connected channel.
   *
   * @return channel
   */
  protected abstract Channel getChannel();

}

4、定义NettyClient类

NettyClient类继承了AbstractClient类，主要是实现了doOpen、doConnect、getChannel类；同时实现了一个自定义的ChannelHander用来在ChannelActive时获取Channel以及有消息返回时读取消息。

doOpen方法的实现。创建引导类并在引导类上注册相关属性；
- 注册NioEventLoopGroup，基于java NIO传输的一个线程池，线程池的默认大小为：CPU核数*2。当一个新的Channel被创建后，Netty会从这个NioEventLoopGroup中选择一个线程来为此Channel创建一个关联的EventLoop（用来监听关联Channel的所有的I/O事件，比如连接、断开连接、读、写等）；
- 注册NioSocketChannel类类型，这个类型说明将要创建的Channel的实例的类型，客户端为：NioSocketChannel，服务器端为：NioServerSocketChannel；Bootstrap会根据这个class来创建一个BootstrapChannelFactory<NioSocketChannel>实例（Channel工厂类，用于将来在connect时创建Channel）；
- 设置相关Option选项
- 注册自定义的ChannelHandler，这些ChannelHandler会被注册到与Channel相关联的ChannelPipleline中，用来拦截消息并做相应的处理。
doConnect方法的实现。通过已创建的Channel来连接到远程服务器。前面我们已经在Bootstrap中设置的超时时间，所以connect时可以使用忽略线程中断阻塞的方式去连接，直到超时。connect时会先通过BootstrapChannelFactory<NioSocketChannel>来创建一个NioSocketChannel实例，并把这个NioSocketChannel实例注册到NioEventGroup中去（从线程池中按某种算法选择一个EventLoop来和当前的Channel建立对应关系，可以是1:N，即一个EventLoop可以对应多个Channel ）。EventLoop同时也是一个EventLoopExecutor，EventLoop和Channel对应起来后就可以处理所有这个Channel的I/O操作了。一句话，某个Channel的所有I/O操作都是线程池（NioEventGroup）中的某个I/O线程（EventLoopExecutor）来异步处理的。

package netty;

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import lombok.extern.slf4j.Slf4j;

import java.nio.charset.StandardCharsets;

/**
 * @author xfyou
 * @date 2019/8/28
 */
@Slf4j
public class NettyClient extends AbstractClient {

  private Bootstrap bootstrap;

  private volatile Channel channel;

  private static final NioEventLoopGroup NIO_GROUP = new NioEventLoopGroup();

  public NettyClient(String hostName, int port, int connectionTimeout) {
    super(hostName, port, connectionTimeout);
  }

  private class ClientHandler extends SimpleChannelInboundHandler<ByteBuf> {

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
      super.channelActive(ctx);
      channel = ctx.channel();
    }

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
      try {
        respMsg = msg.toString(StandardCharsets.UTF_8);
      } finally {
        countDownLatch.countDown();
        ctx.close();
      }
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
      log.error("An exception was thrown, cause:" + cause.getMessage());
      ctx.close();
    }
  }

  @Override
  protected void doOpen() throws Throwable {
    bootstrap = new Bootstrap();
    bootstrap
        .group(NIO_GROUP)
        .remoteAddress(getRemoteAddress())
        .channel(NioSocketChannel.class)
        .option(ChannelOption.TCP_NODELAY, true)
        .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, getConnectionTimeout())
        .handler(new ChannelInitializer<SocketChannel>() {
          @Override
          protected void initChannel(SocketChannel ch) throws Exception {
            ch.pipeline().addLast(new ClientHandler());
          }
        });
  }

  @Override
  public void doConnect() {
    ChannelFuture f = bootstrap.connect().syncUninterruptibly();
    if (!f.isSuccess() && null != f.cause()) {
      log.error("The client failed to connect the server:" + getRemoteAddress() + ",error message is:" + f.cause().getMessage());
    }
  }

  @Override
  protected Channel getChannel() {
    return channel;
  }

}

5、测试类

package netty;

import lombok.SneakyThrows;

/**
 * Test
 *
 * @author xfyou
 */
public class Test {

  @SneakyThrows
  public static void main(String[] args) {
    NettyClient client = new NettyClient("127.0.0.1", 8080, 45000);
    client.send("aaa".getBytes());
    // maybe do something else
    System.out.println(client.receive());
  }
  
}

posted @ 2019-08-29 15:44 FrankYou 阅读(10347) 评论(1) 编辑收藏举报

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FrankYou

"If I had eight hours to chop down a tree, I would spend six hours sharpening my axe." A. Lincoln