public class FileServer {


    public boolean connectedClient() throws Exception{
        ServerSocket serverSocket = new ServerSocket(8899);
        Socket socket = null;
        int count = 0;
        System.out.println("服务器已启动,正在等待客户端的连接。。。");
        try {
            while (true) {
                socket = serverSocket.accept();
                ServerThread st = new ServerThread(socket);
                st.start();
                count++;
                InetAddress ia = InetAddress.getLocalHost();
                System.out.println("这是第"+count+"个客户！");
                System.out.println("连接主机的地址："+ia.getHostAddress());
            }
        }catch (Exception e){
            e.printStackTrace();
        }
        return true;
    }

    public static void main(String[] args) throws Exception {
        FileServer fs = new FileServer();
        fs.connectedClient();
    }
}

public class ServerThread extends Thread {
        private Socket socket;

        public ServerThread(Socket socket){
            this.socket = socket;
        }

        public void run() {

                InputStream is = null;
//                OutputStream os = null;
                InputStreamReader isr = null;
                BufferedReader br = null;
                PrintWriter pw = null;
                String s = null;
                int count = 0;
            try {
                is = socket.getInputStream();
                isr = new InputStreamReader(is);
                br = new BufferedReader(isr);
                while ((s=br.readLine())!=null){
                    System.out.print(s);
                }
                socket.shutdownInput();
                pw = new PrintWriter(socket.getOutputStream());
                pw.write("服务器欢迎您");
                pw.flush();
                socket.shutdownOutput();
            } catch (Exception e) {
                e.printStackTrace();
            }finally {
                try {
                    if (is!=null)
                        is.close();
                    if (isr!=null)
                        isr.close();
                    if (br!=null)
                        br.close();
                    if(pw!=null)
                        pw.close();
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        }
}

public class FileClient {

    public static void main(String[] args) throws Exception{
        Socket socket = null;
        OutputStream os = null;
        PrintWriter pw = null;
        InputStream is = null;
        InputStreamReader isr = null;
        BufferedReader br = null;
        String serverInfo = null;
        socket = new Socket("localhost",8800);
        try {
            os = socket.getOutputStream();
            pw = new PrintWriter(os);
            pw.write("账号：admin  密码：123");
            pw.flush();
            socket.shutdownOutput();
            is = socket.getInputStream();
            isr = new InputStreamReader(is);
            br = new BufferedReader(isr);
            while ((serverInfo=br.readLine())!=null){
                System.out.println("服务器说："+serverInfo);
            }
            socket.shutdownInput();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            try {
                if (is != null) {
                    is.close();
                }
                if (isr != null)
                    isr.close();
                if (br != null)
                    br.close();
                if (pw != null)
                    pw.close();
                socket.close();
            }catch (Exception e){
                e.printStackTrace();
            }
        }
    }
}

Exception in thread "main" java.net.ConnectException: Connection refused: connect
    at java.net.DualStackPlainSocketImpl.connect0(Native Method)
    at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79)
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
    at java.net.Socket.connect(Socket.java:579)
    at java.net.Socket.connect(Socket.java:528)
    at java.net.Socket.<init>(Socket.java:425)
    at java.net.Socket.<init>(Socket.java:208)
    at com.com.filetest.FileClient.main(FileClient.java:19)