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：
通过持有Client对象，可以随时（使用sendObject方法）发送Object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对象给服务端，
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。
import java.io.Serializable; import java.text.SimpleDateFormat; import java.util.Date; /** * 维持连接的消息对象。 * <p> * 创建时间：2010-7-18 上午12:22:09 * @author HouLei * @since 1.0 */ 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())+" 维持连接包"; } } 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; /** * C/S架构的客户端对象，持有该对象，可以随时向服务端发送消息。 * <p> * 创建时间：2010-7-18 上午12:17:25 * @author HouLei * @since 1.0 */ 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： "+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; private long lastSendTime; 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(); new Thread(new ReceiveWatchDog()).start(); } 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： "+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： "+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(); } } } } } 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架构的服务端对象。 * <p> * 创建时间：2010-7-18 上午12:17:37 * @author HouLei * @since 1.0 */ 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); } public static final class DefaultObjectAction implements ObjectAction{ public Object doAction(Object rev) { 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： "+obj); ObjectAction oa = actionMapping.get(obj.getClass()); oa = oa==null?new DefaultObjectAction():oa; Object out = oa.doAction(obj); 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()); } } }