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：
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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";
}
}
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服务端
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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());
}
}
}
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客户端
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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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以上就是Java如何实现长连接的详细内容，更多关于java实现长连接的资料请关注快网idc其它相关文章！
原文链接：https://cloud.tencent.com/developer/article/1640058
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