一对一通信：

服务器端：

public class ServerDemo {
    public static void main(String[] args) {
        ServerSocket serverSocket = null;
        Socket socket = null;
        BufferedReader reader = null;
        try {
            //设置服务端的端口号
            serverSocket = new ServerSocket(8081);
            //等待客户端发送请求
            socket = serverSocket.accept();
            //接收客户端发来的请求
            reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            boolean flag = true;
            while (flag){
                String read = reader.readLine();
                if("结束".equals(read)){
                    flag = false;
                }
                System.out.println("服务器接收消息："+read);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                reader.close();
                socket.close();
                serverSocket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}


客户端：

public class ClientDemo {
    public static void main(String[] args) {
        Socket socket = null;
        //使用PrintWriter时，调用println、print的方法时，可以不再调用flush方法进行刷新
        PrintWriter writer = null;
        try {
            //客户端socket指定服务器的地址和端口号
            socket = new Socket("127.0.0.1", 8081);
            //发送消息到服务器
            writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(
                    socket.getOutputStream())));
            for (int i = 0; i < 10; i++) {
                writer.println("发送消息 " + i);
            }
            writer.println("结束");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                System.out.println("close......");
                writer.close();
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

多客户端通信
服务端1：

public class ServerDouble {
    public static void main(String[] args) {
        ServerSocket serverSocket = null;
        Socket socket = null;
        try {
            //设置服务端的端口号
            serverSocket = new ServerSocket(8081);
            //等待客户端发送请求
            System.out.println("正在等待连接……");
            while (true){
                socket = serverSocket.accept();
                System.out.println("连接上了："+socket.getPort());
                new ServerDoubleDemo(socket);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                socket.close();
                serverSocket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}
服务端2：

public class ServerDoubleDemo extends Thread {
    Socket socket = null;
    BufferedReader reader = null;
    public ServerDoubleDemo(Socket socket) {
        this.socket = socket;
        try {
            reader = new BufferedReader(new InputStreamReader( socket.getInputStream()));
            start();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void run() {
        try {
            boolean flag = true;
            while (flag){
                String str = reader.readLine();
                if("结束".equals(str)){
                    flag = false;
                }
                System.out.println("接收消息："+str);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                reader.close();
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

客户端同上：

public class ClientDemo {
    public static void main(String[] args) {
        Socket socket = null;
        //使用PrintWriter时，调用println、print的方法时，可以不再调用flush方法进行刷新
        PrintWriter writer = null;
        try {
            //客户端socket指定服务器的地址和端口号
            socket = new Socket("127.0.0.1", 8081);
            //发送消息到服务器
            writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(
                    socket.getOutputStream())));
            for (int i = 0; i < 10; i++) {
                writer.println("发送消息 " + i);
            }
            writer.println("结束");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                System.out.println("close......");
                writer.close();
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Java实现Socket通信