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 actionMapping = new ConcurrentHashMap();

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 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 actionMapping = new ConcurrentHashMap();

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 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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