實現原理：
長連線的維持，是要客戶端程式，定時向服務端程式，傳送一個維持連線包的。
如果，長時間未傳送維持連線包，服務端程式將斷開連線。

客戶端：
Client通過持有Socket的物件，可以隨時（使用sendObject方法）傳送Massage Object(訊息)給服務端。
如果keepAliveDelay毫秒（程式中是2秒）內未傳送任何資料，則自動傳送一個KeepAlive Object(心跳)給服務端，用於維持連線。
由於，我們向服務端，可以傳送很多不同的訊息物件，服務端也可以返回不同的物件。所以，對於返回物件的處理，要編寫具體的ObjectAction實現類進行處理。通過Client.addActionMap方法進行新增。這樣，程式會回撥處理。

服務端：
由於客戶端會定時（keepAliveDelay毫秒）傳送維持連線的資訊過來，所以，服務端要有一個檢測機制。
即當服務端receiveTimeDelay毫秒（程式中是3秒）內未接收任何資料，則自動斷開與客戶端的連線。
ActionMapping的原理與客戶端相似（相同）。

通過新增相應的ObjectAction實現類，可以實現不同物件的響應、應答過程。

Demo:

package socket.keepalive.test;
 
 
import java.io.Serializable;
import java.text.SimpleDateFormat;
import java.util.Date;
 
/**
 * 
 * 維持連線的訊息物件（心跳物件）
 */
public class KeepAlive implements Serializable{
 
 private static final long serialVersionUID = -2813120366138988480L;
 
 /* 覆蓋該方法，僅用於測試使用。
 * @see java.lang.Object#toString()
 */
 @Override
 public String toString() {
 return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date())+"\t維持連線包";
 }
 
}

package socket.keepalive.test;
 
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.Collections;
import java.util.concurrent.ConcurrentHashMap;
 
/**
 * C/S架構的客戶端物件，持有該物件，可以隨時向服務端傳送訊息。
 * <p>
 * 建立時間：2010-7-18 上午12:17:25
 * @author HouLei
 * @since 1.0
 */
public class Client {
 
 /**
 * 處理服務端發回的物件，可實現該介面。
 */
 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; //連線狀態
 
 private long lastSendTime; //最後一次傳送資料的時間
 
 //用於儲存接收訊息物件型別及該型別訊息處理的物件
 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("本地埠："+socket.getLocalPort());
 lastSendTime=System.currentTimeMillis();
 running=true;
 new Thread(new KeepAliveWatchDog()).start(); //保持長連線的執行緒，每隔2秒項伺服器發一個一個保持連線的心跳訊息
 new Thread(new ReceiveWatchDog()).start();  //接受訊息的執行緒，處理訊息
 }
 
 public void stop(){
 if(running)running=false;
 }
 
 /**
 * 新增接收物件的處理物件。
 * @param cls 待處理的物件，其所屬的類。
 * @param action 處理過程物件。
 */
 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("傳送：\t"+obj);
 oos.flush();
 }
 
 class KeepAliveWatchDog implements Runnable{
 long checkDelay = 10;
 long keepAliveDelay = 2000;
 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();
  } 
  }
 }
 }
 
}

package socket.keepalive.test;
 
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;
 
/**
 * C/S架構的服務端物件。
 * <p>
 * 建立時間：2010-7-18 上午12:17:37
 * @author HouLei
 * @since 1.0
 */
public class Server {
 
 /**
 * 要處理客戶端發來的物件，並返回一個物件，可實現該介面。
 */
 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("處理並返回："+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("關閉："+s.getRemoteSocketAddress());
 }
 
 }
 
}

以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支援碼農教程。