Java如何实现长连接

实现原理：

长连接的维持，是要客户端程序，定时向服务端程序，发送一个维持连接包的。
如果，长时间未发送维持连接包，服务端程序将断开连接。

客户端：

Client通过持有Socket的对象，可以随时（使用sendObject方法）发送Massage Object(消息)给服务端。
如果keepAliveDelay毫秒（程序中是2秒）内未发送任何数据，则自动发送一个KeepAlive Object(心跳)给服务端，用于维持连接。
由于，我们向服务端，可以发送很多不同的消息对象，服务端也可以返回不同的对象。所以，对于返回对象的处理，要编写具体的ObjectAction实现类进行处理。通过Client.addActionMap方法进行添加。这样，程序会回调处理。

服务端：

由于客户端会定时（keepAliveDelay毫秒）发送维持连接的信息过来，所以，服务端要有一个检测机制。
即当服务端receiveTimeDelay毫秒（程序中是3秒）内未接收任何数据，则自动断开与客户端的连接。
ActionMapping的原理与客户端相似（相同）。
通过添加相应的ObjectAction实现类，可以实现不同对象的响应、应答过程。

心跳反映的代码：

package com.java.excel.keepalive;

import java.io.Serializable;
import java.text.SimpleDateFormat;
import java.util.Date;
/**
    *
    * 维持连接的消息对象（心跳对象）
    */
public class KeepAlive implements Serializable {

  private static final long serialVersionUID = -2813120366138988480L;

  /* 覆盖该方法，仅用于测试使用。
   * @see java.lang.Object#toString()
   */
  @Override
  public String toString() {
    return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date())+"\t维持连接包";
  }

}

服务端

package com.java.excel.keepalive;

import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.concurrent.ConcurrentHashMap;

public class Server {

  /**
   * 要处理客户端发来的对象，并返回一个对象，可实现该接口。
   */
  public interface ObjectAction{
    Object doAction(Object rev, Server server);
  }

  public static final class DefaultObjectAction implements ObjectAction{
    public Object doAction(Object rev,Server server) {
      System.out.println("处理并返回："+rev);
      return rev;
    }
  }

  public static void main(String[] args) {
    int port = 65432;
    Server server = new Server(port);
    server.start();
  }

  private int port;
  private volatile boolean running=false;
  private long receiveTimeDelay=3000;
  private ConcurrentHashMap<Class, ObjectAction> actionMapping = new ConcurrentHashMap<Class,ObjectAction>();
  private Thread connWatchDog;

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

  public void start(){
    if(running)return;
    running=true;
    connWatchDog = new Thread(new ConnWatchDog());
    connWatchDog.start();
  }

  @SuppressWarnings("deprecation")
  public void stop(){
    if(running)running=false;
    if(connWatchDog!=null)connWatchDog.stop();
  }

  public void addActionMap(Class<Object> cls,ObjectAction action){
    actionMapping.put(cls, action);
  }

  class ConnWatchDog implements Runnable{
    public void run(){
      try {
        ServerSocket ss = new ServerSocket(port,5);
        while(running){
          Socket s = ss.accept();
          new Thread(new SocketAction(s)).start();
        }
      } catch (IOException e) {
        e.printStackTrace();
        Server.this.stop();
      }

    }
  }

  class SocketAction implements Runnable{
    Socket s;
    boolean run=true;
    long lastReceiveTime = System.currentTimeMillis();
    public SocketAction(Socket s) {
      this.s = s;
    }
    public void run() {
      while(running && run){
        if(System.currentTimeMillis()-lastReceiveTime>receiveTimeDelay){
          overThis();
        }else{
          try {
            InputStream in = s.getInputStream();
            if(in.available()>0){
              ObjectInputStream ois = new ObjectInputStream(in);
              Object obj = ois.readObject();
              lastReceiveTime = System.currentTimeMillis();
              System.out.println("接收：\t"+obj);
              ObjectAction oa = actionMapping.get(obj.getClass());
              oa = oa==null?new DefaultObjectAction():oa;
              Object out = oa.doAction(obj,Server.this);
              if(out!=null){
                ObjectOutputStream oos = new ObjectOutputStream(s.getOutputStream());
                oos.writeObject(out);
                oos.flush();
              }
            }else{
              Thread.sleep(10);
            }
          } catch (Exception e) {
            e.printStackTrace();
            overThis();
          }
        }
      }
    }

    private void overThis() {
      if(run)run=false;
      if(s!=null){
        try {
          s.close();
        } catch (IOException e) {
          e.printStackTrace();
        }
      }
      System.out.println("关闭："+s.getRemoteSocketAddress());
    }

  }

}

客户端

package com.java.excel.keepalive;

import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.concurrent.ConcurrentHashMap;

public class Client {

  /**
   * 处理服务端发回的对象，可实现该接口。
   */
  public static interface ObjectAction{
    void doAction(Object obj,Client client);
  }

  public static final class DefaultObjectAction implements ObjectAction{
    public void doAction(Object obj,Client client) {
      System.out.println("处理：\t"+obj.toString());
    }
  }

  public static void main(String[] args) throws UnknownHostException, IOException {
    String serverIp = "127.0.0.1";
    int port = 65432;
    Client client = new Client(serverIp,port);
    client.start();
  }

  private String serverIp;
  private int port;
  private Socket socket;
  private boolean running=false; //连接状态

  private long lastSendTime; //最后一次发送数据的时间

  //用于保存接收消息对象类型及该类型消息处理的对象
  private ConcurrentHashMap<Class, ObjectAction> actionMapping = new ConcurrentHashMap<Class,ObjectAction>();

  public Client(String serverIp, int port) {
    this.serverIp=serverIp;
    this.port=port;
  }

  public void start() throws UnknownHostException, IOException {
    if(running)return;
    socket = new Socket(serverIp,port);
    System.out.println("本地端口："+socket.getLocalPort());
    lastSendTime=System.currentTimeMillis();
    running=true;
    new Thread(new KeepAliveWatchDog()).start(); //保持长连接的线程，每隔2秒项服务器发一个一个保持连接的心跳消息
    new Thread(new ReceiveWatchDog()).start();  //接受消息的线程，处理消息
  }

  public void stop(){
    if(running)running=false;
  }

  /**
   * 添加接收对象的处理对象。
   * @param cls 待处理的对象，其所属的类。
   * @param action 处理过程对象。
   */
  public void addActionMap(Class<Object> cls,ObjectAction action){
    actionMapping.put(cls, action);
  }

  public void sendObject(Object obj) throws IOException {
    ObjectOutputStream oos = new ObjectOutputStream(socket.getOutputStream());
    oos.writeObject(obj);
    System.out.println("发送：\t"+obj);
    oos.flush();
  }

  class KeepAliveWatchDog implements Runnable{
    long checkDelay = 10;
    long keepAliveDelay = 1000;
    public void run() {
      while(running){
        if(System.currentTimeMillis()-lastSendTime>keepAliveDelay){
          try {
            Client.this.sendObject(new KeepAlive());
          } catch (IOException e) {
            e.printStackTrace();
            Client.this.stop();
          }
          lastSendTime = System.currentTimeMillis();
        }else{
          try {
            Thread.sleep(checkDelay);
          } catch (InterruptedException e) {
            e.printStackTrace();
            Client.this.stop();
          }
        }
      }
    }
  }

  class ReceiveWatchDog implements Runnable{
    public void run() {
      while(running){
        try {
          InputStream in = socket.getInputStream();
          if(in.available()>0){
            ObjectInputStream ois = new ObjectInputStream(in);
            Object obj = ois.readObject();
            System.out.println("接收：\t"+obj);
            ObjectAction oa = actionMapping.get(obj.getClass());
            oa = oa==null?new DefaultObjectAction():oa;
            oa.doAction(obj, Client.this);
          }else{
            Thread.sleep(10);
          }
        } catch (Exception e) {
          e.printStackTrace();
          Client.this.stop();
        }
      }
    }
  }

}

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