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Java Netty如何实现心跳检测 Java Netty实现心跳检测代码解析

时间:2020-03-03 编辑:袖梨 来源:一聚教程网

本篇文章小编给大家分享一下Java Netty实现心跳检测代码解析,小编觉得挺不错的,现在分享给大家供大家参考,有需要的小伙伴们可以来看看。

心跳检测的逻辑

服务端启动后,等待客户端连接,客户端连接之后,向服务端发送消息。如果客户端在“干活”那么服务端必定会收到数据,如果客户端“闲下来了”那么服务端就接收不到这个客户端的消息,既然客户端闲下来了,不干事,那么何必浪费连接资源呢?所以服务端检测到一定时间内客户端不活跃的时候,将客户端连接关闭。本文要实现的逻辑步骤为:

启动服务端,启动客户端

客户端向服务端发送"I am alive",并sleep随机时间,用来模拟空闲。

服务端接收客户端消息,并返回"copy that",客户端空闲时 计数+1.

服务端客户端继续通信

服务端检测客户端空闲太多,关闭连接。客户端发现连接关闭了,就退出了。

有了这个思路,我们先来编写服务端。

心跳检测服务端代码

public class HeartBeatServer {

  int port ;
  public HeartBeatServer(int port){
    this.port = port;
  }

  public void start(){
    ServerBootstrap bootstrap = new ServerBootstrap();
    EventLoopGroup boss = new NioEventLoopGroup();
    EventLoopGroup worker = new NioEventLoopGroup();
    try{
      bootstrap.group(boss,worker)
          .handler(new LoggingHandler(LogLevel.INFO))
          .channel(NioServerSocketChannel.class)
          .childHandler(new HeartBeatInitializer());

      ChannelFuture future = bootstrap.bind(port).sync();
      future.channel().closeFuture().sync();
    }catch(Exception e){
      e.printStackTrace();
    }finally {
      worker.shutdownGracefully();
      boss.shutdownGracefully();
    }
  }
  public static void main(String[] args) throws Exception {
    HeartBeatServer server = new HeartBeatServer(8090);
    server.start();
  }
}

熟悉netty的同志,对于上面的模板一样的代码一定是在熟悉不过了。啥都不用看,只需要看childHandler(new HeartBeatInitializer()) 这一句。HeartBeatInitializer就是一个ChannelInitializer顾名思义,他就是在初始化channel的时做一些事情。我们所需要开发的业务逻辑Handler就是在这里添加的。其代码如下:

public class HeartBeatInitializer extends ChannelInitializer {

  @Override
  protected void initChannel(Channel channel) throws Exception {
    ChannelPipeline pipeline = channel.pipeline();
    pipeline.addLast("decoder", new StringDecoder());
    pipeline.addLast("encoder", new StringEncoder());
    pipeline.addLast(new IdleStateHandler(2,2,2, TimeUnit.SECONDS));
    pipeline.addLast(new HeartBeatHandler());
  }
}

代码很简单,我们先添加了StringDecoder,和StringEncoder。这两个其实就是编解码用的,下面的IdleStateHandler才是本次心跳的核心组件。我们可以看到IdleStateHandler的构造函数中接收了4个参数,其定义如下:

public IdleStateHandler(long readerIdleTime, long writerIdleTime, long allIdleTime, TimeUnit unit);

三个空闲时间参数,以及时间参数的格式。我们的例子中设置的是2,2,2,意思就是客户端2秒没有读/写,这个超时时间就会被触发。超时事件触发就需要我们来处理了,这就是上的HeartBeatInitializer中最后一行的HeartBeatHandler所做的事情。代码如下:

public class HeartBeatHandler extends SimpleChannelInboundHandler {

  int readIdleTimes = 0;

  @Override
  protected void channelRead0(ChannelHandlerContext ctx, String s) throws Exception {
    System.out.println(" ====== > [server] message received : " + s);
    if("I am alive".equals(s)){
      ctx.channel().writeAndFlush("copy that");
    }else {
      System.out.println(" 其他信息处理 ... ");
    }
  }

  @Override
  public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
    IdleStateEvent event = (IdleStateEvent)evt;

    String eventType = null;
    switch (event.state()){
      case READER_IDLE:
        eventType = "读空闲";
        readIdleTimes ++; // 读空闲的计数加1
        break;
      case WRITER_IDLE:
        eventType = "写空闲";
        // 不处理
        break;
      case ALL_IDLE:
        eventType ="读写空闲";
        // 不处理
        break;
    }
    System.out.println(ctx.channel().remoteAddress() + "超时事件:" +eventType);
    if(readIdleTimes > 3){
      System.out.println(" [server]读空闲超过3次,关闭连接");
      ctx.channel().writeAndFlush("you are out");
      ctx.channel().close();
    }
  }
  @Override
  public void channelActive(ChannelHandlerContext ctx) throws Exception {
    System.err.println("=== " + ctx.channel().remoteAddress() + " is active ===");
  }

}

至此,我们的服务端写好了。

心跳检测客户端代码

netty的api设计使得编码的模式非常具有通用性,所以客户端代码和服务端的代码几乎一样:启动client端的代码几乎一样,也需要一个ChannelInitializer,也需要Handler。改动的地方很少,因此本文不对客户端代码进行详细解释。下面给出client端的完整代码:

public class HeartBeatClient {

  int port;
  Channel channel;
  Random random ;

  public HeartBeatClient(int port){
    this.port = port;
    random = new Random();
  }
  public static void main(String[] args) throws Exception{
    HeartBeatClient client = new HeartBeatClient(8090);
    client.start();
  }

  public void start() {
    EventLoopGroup eventLoopGroup = new NioEventLoopGroup();
    try{
      Bootstrap bootstrap = new Bootstrap();
      bootstrap.group(eventLoopGroup).channel(NioSocketChannel.class)
          .handler(new HeartBeatClientInitializer());

      connect(bootstrap,port);
      String text = "I am alive";
      while (channel.isActive()){
        sendMsg(text);
      }
    }catch(Exception e){
      // do something
    }finally {
      eventLoopGroup.shutdownGracefully();
    }
  }

  public void connect(Bootstrap bootstrap,int port) throws Exception{
    channel = bootstrap.connect("localhost",8090).sync().channel();
  }

  public void sendMsg(String text) throws Exception{
    int num = random.nextInt(10);
    Thread.sleep(num * 1000);
    channel.writeAndFlush(text);
  }

  static class HeartBeatClientInitializer extends ChannelInitializer {

    @Override
    protected void initChannel(Channel ch) throws Exception {
      ChannelPipeline pipeline = ch.pipeline();
      pipeline.addLast("decoder", new StringDecoder());
      pipeline.addLast("encoder", new StringEncoder());
      pipeline.addLast(new HeartBeatClientHandler());
    }
  }

  static class HeartBeatClientHandler extends SimpleChannelInboundHandler {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
      System.out.println(" client received :" +msg);
      if(msg!= null && msg.equals("you are out")) {
        System.out.println(" server closed connection , so client will close too");
        ctx.channel().closeFuture();
      }
    }
  }
}

运行代码

在上面的代码写好之后,我们先启动服务端,然后在启动客户端。运行日志如下:

server端:

=== /127.0.0.1:57700 is active ===
 ====== > [server] message received : I am alive
 ====== > [server] message received : I am alive
/127.0.0.1:57700超时事件:写空闲
/127.0.0.1:57700超时事件:读空闲
/127.0.0.1:57700超时事件:读写空闲
/127.0.0.1:57700超时事件:写空闲
/127.0.0.1:57700超时事件:读空闲
/127.0.0.1:57700超时事件:读写空闲
/127.0.0.1:57700超时事件:写空闲
 ====== > [server] message received : I am alive
/127.0.0.1:57700超时事件:写空闲
/127.0.0.1:57700超时事件:读写空闲
/127.0.0.1:57700超时事件:读空闲
/127.0.0.1:57700超时事件:写空闲
/127.0.0.1:57700超时事件:读写空闲
/127.0.0.1:57700超时事件:读空闲
 [server]读空闲超过3次,关闭连接

client端:

 client sent msg and sleep 2
 client received :copy that
 client received :copy that
 client sent msg and sleep 6
 client sent msg and sleep 6
 client received :copy that
 client received :you are out
 server closed connection , so client will close too
Process finished with exit code 0

通过上面的运行日志,我们可以看到:

1.客户端在与服务器成功建立之后,发送了3次'I am alive',服务端也回应了3次:'copy that'

2.由于客户端消极怠工,超时了多次,服务端关闭了链接。

3.客户端知道服务端抛弃自己之后,也关闭了连接,程序退出。

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