1、实现：实现服务端与客户端一对多的关系；服务端关闭则客户端等待服务端启动后重连，客户端关闭则服务端关闭与服务端的socket连接，如果所有客户端关闭，则服务端等待客户端连接。

                实现客户端向服务端单向发送数据（服务端向客户端发送数据同理）。

2、服务端：

A、服务器端创建ServerSocket，循环调用accept()等待客户端连接

B、客户端创建一个socket并请求和服务器端连接

C、服务器端接受客户端请求，创建socket与该客户建立专线连接

D、建立连接的两个socket在一个单独的线程上对话

E、服务器端继续等待新的连接

代码：

import java.io.IOException;
import java.io.ObjectInputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.concurrent.ConcurrentHashMap;

public class SocketServer {

    private static ServerSocket serverSocket = null;
    private static Map<String, ModelClass> info = new ConcurrentHashMap<>();
    
    static {
        try {
            serverSocket = new ServerSocket(9090);
        } catch (IOException e) {
            System.out.println("create serverSocket error: " + e.getMessage());
        }
    }
    
    public static void main(String[] args) throws IOException {
        
        // 定时打印接收到的数据
        new Thread(new Runnable( ) {
            @Override
            public void run() {
                while (true) {
                    Iterator<Map.Entry<String, ModelClass>> it = info.entrySet().iterator();
                    while(it.hasNext()) {
                        Entry<String, ModelClass> entry = it.next();
                        ModelClass mc = entry.getValue();
                        System.out.println(mc.name);
                        System.out.println(mc.m1.get(0));
                        System.out.println(mc.m2.get(0).value);
                        System.out.println();
                    }
                    
                    try {
                        Thread.sleep(5000);
                    } catch (InterruptedException e) {
                        System.out.println(e.getMessage());
                    }
                }
            }
            
        }).start();
        
        // 等待客户端连接
        new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    try {
                        System.out.println("*****服务器已启动，等待客户端连接*****");
                        Socket socket = serverSocket.accept();
                        System.out.println("*****已连接客户端*****");
                        new SST(socket).start();
                    } catch (Exception e) {
                        System.out.println("socket accept error: " + e.getMessage());
                    } 
                }
            }
        }).start();
    }
    
    static class SST extends Thread {
        private Socket socket;
        private String key;
        
        public SST(Socket socket) {
            this.socket = socket;
            key = socket.getInetAddress().toString() + "/" + socket.getPort();
        }
        
        @Override
        public void run() {
//            BufferedReader br = null; // 读取客户端输入的文件流
            ObjectInputStream ois = null; // 读取客户端输入的对象流
            try {
                while (true) {
//                    br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
//                    String msg = null;
//                    while((msg = br.readLine()) != null) {
//                        System.out.println("get msg---" + socket.getInetAddress() + "/" + socket.getPort());
//                        System.out.println("client msg: " + msg);
//                    }
                    
                    ois = new ObjectInputStream(socket.getInputStream());
                    Object obj = ois.readObject();
                    ModelClass mc = (ModelClass)obj;
                    info.put(key, mc);
                }
            } catch (Exception e) {
                System.out.println("get msg error: " + e.getMessage());
            } finally {
                if (info.containsKey(key)) {
                    info.remove(key);
                }
                try {
//                    if (br != null) {
//                        br.close();
//                    }
                    if (ois != null) {
                        ois.close();
                    }
                } catch (IOException e) {
                    System.out.println("br close error: " + e.getMessage());
                } finally {
                    if (socket != null) {
                        try {
                            socket.close();
                        } catch (IOException e) {
                            System.out.println(e.getMessage());
                        }
                    }
                }
            }
        }
    }
}

3、客户端：

A、用服务器的IP地址和端口号实例化Socket对象。

B、获得Socket上的流，以进行读写。

C、关闭打开的流和Socket。

代码：

import java.io.ObjectOutputStream;
import java.net.Socket;

public class SocketClient {
    ModelClass mc;
    
    public SocketClient() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    client();
                } catch (Exception e) {
                    System.out.println(e.getMessage());
                }
            }
        }).start();
    }
    
    public void send(ModelClass mc) {
        this.mc = mc;
    }

    private void client() throws Exception {
        Socket socket = null;
        ObjectOutputStream oos = null;
        try {
            while(true) {
                System.out.println("create new socket!");
                try {
                    socket = new Socket("127.0.0.1", 9090);
                    while (true) {
                        if (mc == null) {
                            Thread.sleep(1000);
                            continue;
                        }
                        System.out.println("out object!");
                        oos = new ObjectOutputStream(socket.getOutputStream());
                        oos.writeObject(mc);
                        
                        mc = null;
                    }
                } catch (Exception e) {
                    System.out.println("socket error: " + e.getMessage());
                } 
                
                Thread.sleep(5000);
            }
        } finally {
            if (socket != null) {
                socket.close();
            }
            
            if (oos != null) {
                oos.close();
            }
        }
    }
}

4、客户端实例：

import socket.ModelClass.InnerModel;
import socket.ModelClass.Status;

public class Client2 {
    private static SocketClient client;
    public static void main(String[] args) throws Exception {
        client = new SocketClient();
        new Client2().func();
    }
    
    public void func() throws InterruptedException {
        ModelClass mc = new ModelClass();
        mc.name = "client2";
        mc.m1.add(Status.NA);
        mc.m2.clear();
        InnerModel im = new InnerModel();
        while(true) {
            im.value = "client2: " + System.currentTimeMillis();
            mc.m2.add(im);
            
            client.send(mc);
            Thread.sleep(2000);
        }
    }
}

5、对象model：

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

public class ModelClass implements Serializable {
    private static final long serialVersionUID = 1000L;

    String name;
    List<Status> m1 = new ArrayList<>();
    List<InnerModel> m2 = new ArrayList<>();
    
    static class InnerModel implements Serializable {
        private static final long serialVersionUID = 1001L;
        String value;
    }
    
    public enum Status {
        OK,
        ERROR,
        NA,
        WARNING,
        FATAL;
    }
}