public class SocketServer {
 public static void main(String[] args) throws IOException {
  //1.创建一个服务器端Socket，即ServerSocket，指定绑定的端口，并监听此端口
  ServerSocket serverSocket = new ServerSocket(12345);
  InetAddress address = InetAddress.getLocalHost();
  String ip = address.getHostAddress();
  Socket socket = null;
  //2.调用accept()等待客户端连接
  System.out.println("~~~服务端已就绪，等待客户端接入~，服务端ip地址: " + ip);
  socket = serverSocket.accept();
  //3.连接后获取输入流，读取客户端信息
  InputStream is=null;
  InputStreamReader isr=null;
  BufferedReader br=null;
  OutputStream os=null;
  PrintWriter pw=null;
  is = socket.getInputStream();  //获取输入流
  isr = new InputStreamReader(is,"UTF-8");
  br = new BufferedReader(isr);
  String info = null;
  while((info=br.readLine())!=null){//循环读取客户端的信息
   System.out.println("客户端发送过来的信息" + info);
  }
  socket.shutdownInput();//关闭输入流
  socket.close();
 }
}

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  Button btn_accept = (Button) findViewById(R.id.btn_accept);
  btn_accept.setOnClickListener(this);
 }

 @Override
 public void onClick(View v) {
  new Thread() {
   @Override
   public void run() {
    try {
     acceptServer();
    } catch (IOException e) {
     e.printStackTrace();
    }
   }
  }.start();
 }

 private void acceptServer() throws IOException {
  //1.创建客户端Socket，指定服务器地址和端口
  Socket socket = new Socket("172.16.2.54", 12345);
  //2.获取输出流，向服务器端发送信息
  OutputStream os = socket.getOutputStream();//字节输出流
  PrintWriter pw = new PrintWriter(os);//将输出流包装为打印流
  //获取客户端的IP地址
  InetAddress address = InetAddress.getLocalHost();
  String ip = address.getHostAddress();
  pw.write("客户端：~" + ip + "~ 接入服务器！！");
  pw.flush();
  socket.shutdownOutput();//关闭输出流
  socket.close();
 }
}

public class Server {
 //定义相关的参数,端口,存储Socket连接的集合,ServerSocket对象
 //以及线程池
 private static final int PORT = 12345;
 private List<Socket> mList = new ArrayList<Socket>();
 private ServerSocket server = null;
 private ExecutorService myExecutorService = null;
 
 
 public static void main(String[] args) {
  new Server();
 }

 public Server()
 {
  try
  {
   server = new ServerSocket(PORT);
   //创建线程池
   myExecutorService = Executors.newCachedThreadPool();
   System.out.println("服务端运行中...\n");
   Socket client = null;
   while(true)
   {
    client = server.accept();
    mList.add(client);
    myExecutorService.execute(new Service(client));
   }
   
  }catch(Exception e){e.printStackTrace();}
 }
 
 class Service implements Runnable
 {
  private Socket socket;
  private BufferedReader in = null;
  private String msg = "";
  
  public Service(Socket socket) {
   this.socket = socket;
   try
   {
    in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
     msg = "用户:" +this.socket.getInetAddress() + "~加入了聊天室" 
       +"当前在线人数:" +mList.size(); 
    this.sendmsg();
   }catch(IOException e){e.printStackTrace();}
  }
  
  
  
  @Override
  public void run() {
   try{
    while(true)
    {
     if((msg = in.readLine()) != null)
     {
      if(msg.equals("bye"))
      {
       System.out.println("~~~~~~~~~~~~~");
       mList.remove(socket);
       in.close();
       msg = "用户:" + socket.getInetAddress() 
         + "退出:" +"当前在线人数:"+mList.size(); 
       socket.close(); 
       this.sendmsg(); 
       break;
      }else{
       msg = socket.getInetAddress() + " 说: " + msg; 
       this.sendmsg(); 
      }
     }
    }
   }catch(Exception e){e.printStackTrace();}
  }
  
  //为连接上服务端的每个客户端发送信息
  public void sendmsg()
  {
   System.out.println(msg);
   int num = mList.size();
   for(int index = 0;index < num;index++)
   {
    Socket mSocket = mList.get(index); 
    PrintWriter pout = null; 
    try { 
     pout = new PrintWriter(new BufferedWriter( 
       new OutputStreamWriter(mSocket.getOutputStream(),"UTF-8")),true); 
     pout.println(msg); 
    }catch (IOException e) {e.printStackTrace();} 
   }
  }
  
 }
}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:orientation="vertical" >

 <TextView
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:text="小猪简易聊天室" />
 <TextView
  android:id="@+id/txtshow"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  />
 <EditText
  android:id="@+id/editsend"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  />
 <Button
  android:id="@+id/btnsend"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:text="发送"
  />
</LinearLayout>

public class MainActivity extends AppCompatActivity implements Runnable {

 //定义相关变量,完成初始化
 private TextView txtshow;
 private EditText editsend;
 private Button btnsend;
 private static final String HOST = "172.16.2.54";
 private static final int PORT = 12345;
 private Socket socket = null;
 private BufferedReader in = null;
 private PrintWriter out = null;
 private String content = "";
 private StringBuilder sb = null;

 //定义一个handler对象,用来刷新界面
 public Handler handler = new Handler() {
  public void handleMessage(Message msg) {
   if (msg.what == 0x123) {
    sb.append(content);
    txtshow.setText(sb.toString());
   }
  }

  ;
 };


 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  sb = new StringBuilder();
  txtshow = (TextView) findViewById(R.id.txtshow);
  editsend = (EditText) findViewById(R.id.editsend);
  btnsend = (Button) findViewById(R.id.btnsend);

  //当程序一开始运行的时候就实例化Socket对象,与服务端进行连接,获取输入输出流
  //因为4.0以后不能再主线程中进行网络操作,所以需要另外开辟一个线程
  new Thread() {

   public void run() {
    try {
     socket = new Socket(HOST, PORT);
     in = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
     out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(
       socket.getOutputStream())), true);
    } catch (IOException e) {
     e.printStackTrace();
    }
   }
  }.start();

  //为发送按钮设置点击事件
  btnsend.setOnClickListener(new View.OnClickListener() {

   @Override
   public void onClick(View v) {
    String msg = editsend.getText().toString();
    if (socket.isConnected()) {
     if (!socket.isOutputShutdown()) {
      out.println(msg);
     }
    }
   }
  });
  new Thread(MainActivity.this).start();
 }

 //重写run方法,在该方法中输入流的读取
 @Override
 public void run() {
  try {
   while (true) {
    if (socket.isConnected()) {
     if (!socket.isInputShutdown()) {
      if ((content = in.readLine()) != null) {
       content += "\n";
       handler.sendEmptyMessage(0x123);
      }
     }
    }
   }
  } catch (Exception e) {
   e.printStackTrace();
  }
 }
}

public class UPDServer {
 public static void main(String[] args) throws IOException {
  /*
   * 接收客户端发送的数据
   */
  // 1.创建服务器端DatagramSocket，指定端口
  DatagramSocket socket = new DatagramSocket(12345);
  // 2.创建数据报，用于接收客户端发送的数据
  byte[] data = new byte[1024];// 创建字节数组，指定接收的数据包的大小
  DatagramPacket packet = new DatagramPacket(data, data.length);
  // 3.接收客户端发送的数据
  System.out.println("****服务器端已经启动，等待客户端发送数据");
  socket.receive(packet);// 此方法在接收到数据报之前会一直阻塞
  // 4.读取数据
  String info = new String(data, 0, packet.getLength());
  System.out.println("我是服务器，客户端说：" + info);

  /*
   * 向客户端响应数据
   */
  // 1.定义客户端的地址、端口号、数据
  InetAddress address = packet.getAddress();
  int port = packet.getPort();
  byte[] data2 = "欢迎您!".getBytes();
  // 2.创建数据报，包含响应的数据信息
  DatagramPacket packet2 = new DatagramPacket(data2, data2.length, address, port);
  // 3.响应客户端
  socket.send(packet2);
  // 4.关闭资源
  socket.close();
 }
}

public class UDPClient {
 public static void main(String[] args) throws IOException {
  /*
   * 向服务器端发送数据
   */
  // 1.定义服务器的地址、端口号、数据
  InetAddress address = InetAddress.getByName("localhost");
  int port = 8800;
  byte[] data = "用户名：admin;密码：123".getBytes();
  // 2.创建数据报，包含发送的数据信息
  DatagramPacket packet = new DatagramPacket(data, data.length, address, port);
  // 3.创建DatagramSocket对象
  DatagramSocket socket = new DatagramSocket();
  // 4.向服务器端发送数据报
  socket.send(packet);

  /*
   * 接收服务器端响应的数据
   */
  // 1.创建数据报，用于接收服务器端响应的数据
  byte[] data2 = new byte[1024];
  DatagramPacket packet2 = new DatagramPacket(data2, data2.length);
  // 2.接收服务器响应的数据
  socket.receive(packet2);
  // 3.读取数据
  String reply = new String(data2, 0, packet2.getLength());
  System.out.println("我是客户端，服务器说：" + reply);
  // 4.关闭资源
  socket.close();
 }
}