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Java如何實現(xiàn)長連接

更新時間：2020年09月08日 11:50:00 作者：崔笑顏

這篇文章主要介紹了Java如何實現(xiàn)長連接，幫助大家更好的理解和學習Java，感興趣的朋友可以了解下

實現(xiàn)原理：

長連接的維持，是要客戶端程序，定時向服務(wù)端程序，發(fā)送一個維持連接包的。
如果，長時間未發(fā)送維持連接包，服務(wù)端程序?qū)嚅_連接。

客戶端：

Client通過持有Socket的對象，可以隨時（使用sendObject方法）發(fā)送Massage Object(消息)給服務(wù)端。
如果keepAliveDelay毫秒（程序中是2秒）內(nèi)未發(fā)送任何數(shù)據(jù)，則自動發(fā)送一個KeepAlive Object(心跳)給服務(wù)端，用于維持連接。
由于，我們向服務(wù)端，可以發(fā)送很多不同的消息對象，服務(wù)端也可以返回不同的對象。所以，對于返回對象的處理，要編寫具體的ObjectAction實現(xiàn)類進行處理。通過Client.addActionMap方法進行添加。這樣，程序會回調(diào)處理。

服務(wù)端：

由于客戶端會定時（keepAliveDelay毫秒）發(fā)送維持連接的信息過來，所以，服務(wù)端要有一個檢測機制。
即當服務(wù)端receiveTimeDelay毫秒（程序中是3秒）內(nèi)未接收任何數(shù)據(jù)，則自動斷開與客戶端的連接。
ActionMapping的原理與客戶端相似（相同）。
通過添加相應(yīng)的ObjectAction實現(xiàn)類，可以實現(xiàn)不同對象的響應(yīng)、應(yīng)答過程。

心跳反映的代碼：

package com.java.excel.keepalive;

import java.io.Serializable;
import java.text.SimpleDateFormat;
import java.util.Date;
/**
    *
    * 維持連接的消息對象（心跳對象）
    */
public class KeepAlive implements Serializable {

  private static final long serialVersionUID = -2813120366138988480L;

  /* 覆蓋該方法，僅用于測試使用。
   * @see java.lang.Object#toString()
   */
  @Override
  public String toString() {
    return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date())+"\t維持連接包";
  }

}

服務(wù)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 {

  /**
   * 要處理客戶端發(fā)來的對象，并返回一個對象，可實現(xiàn)該接口。
   */
  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("處理并返回："+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("關(guān)閉："+s.getRemoteSocketAddress());
    }
    
  }
  
}

客戶端

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 {

  /**
   * 處理服務(wù)端發(fā)回的對象，可實現(xiàn)該接口。
   */
  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("處理：\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; //連接狀態(tài)
  
  private long lastSendTime; //最后一次發(fā)送數(shù)據(jù)的時間
  
  //用于保存接收消息對象類型及該類型消息處理的對象
  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(); //保持長連接的線程，每隔2秒項服務(wù)器發(fā)一個一個保持連接的心跳消息
    new Thread(new ReceiveWatchDog()).start();  //接受消息的線程，處理消息
  }
  
  public void stop(){
    if(running)running=false;
  }
  
  /**
   * 添加接收對象的處理對象。
   * @param cls 待處理的對象，其所屬的類。
   * @param action 處理過程對象。
   */
  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("發(fā)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();
        } 
      }
    }
  }
  
}