服务器：

public class Chat {

public static void main(String[]args) throws IOException

{

System.out.println("服务器启动中...");

//创建服务器

ServerSocket server=new ServerSocket(9999);

//阻塞式等待连接，当客户端Socket创建好以后才开启

while(true)

{

Socket client=server.accept();

System.out.println("一个客户端建立了连接");

new Thread(()->{

DataInputStream dis = null;

DataOutputStream dos = null;

try {

dis = new DataInputStream(client.getInputStream());

dos = new DataOutputStream(client.getOutputStream());

} catch (IOException e1) {

e1.printStackTrace();

}

boolean flag=true;

while(flag) {

String msg = null;

try {

msg = dis.readUTF();

dos.writeUTF(msg);

dos.flush();

} catch (IOException e) {

//当断掉客户端连接时，不用循环再读取数据

flag=false;

}

//返回消息

}

try {

if(null!=dos)

{

dos.close();

}

} catch (IOException e) {

e.printStackTrace();

}

try {

if(null!=dis)

{

dis.close();

}

} catch (IOException e) {

e.printStackTrace();

}

try {

if(null!=client)

{

client.close();

}

} catch (IOException e) {

e.printStackTrace();

}

}).start();

}

}

}

客户端：

public class Client {

public static void main(String[]args) throws UnknownHostException, IOException

{

System.out.println("客户端启动中...");

Socket client=new Socket("localhost",9999);

//客户端发送消息

BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

DataOutputStream dos=new DataOutputStream(client.getOutputStream());

DataInputStream dis =new DataInputStream(client.getInputStream());

boolean flag=true;

while(flag) {

System.out.println("请输入消息");

String msg=br.readLine();

dos.writeUTF(msg);

dos.flush();

//获取消息

msg=dis.readUTF();

System.out.println(msg);

}

dos.close();

dis.close();

client.close();

}

}