1.TCP

1.客户端：
    1.1:创建一个socket对象，指定ip和端口
    1.2： 通过socket.getOutputStream()获取输出流，来发送数据
    1.3：如果服务器有返回信息，则通过socket.getInputStream(),来获取信息。在此之前，客户端在发送完数据之后，需要通过socket.shutdownOutput()将输出流关闭，否则服务器端会一直等待客户端发送消息
2.服务端：
    2.1：创建一个serverSocket
    2.2:通过serverSocket.accept()来获取客户端的socket
    2.3:通过客户端的socket来接收、发送数据

public class SocketTest {

    @Test
    public void client(){
        try {
            Client yang = new Client("yang");
            InetAddress inetAddress = InetAddress.getByName("127.0.0.1");
            yang.sentMsg(inetAddress,8000,"你好啊");
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }
    }

    @Test
    public void server(){
        Server server = new Server(8000);
        server.getMsg();
    }
}

class Client{
    private String name;
    private Socket socket;

    public Client(String name) {
        this.name = name;
        this.socket = null;
    }

    public void sentMsg(InetAddress inetAddress,int port,String msg){
        OutputStream os = null;
        try {
            //创建socket对象，指定ip和端口
            socket = new Socket(inetAddress,port);
            //获取输出流，用于输出数据
            os = socket.getOutputStream();
            os.write(msg.getBytes());

            System.out.println("发送成功");
            System.out.println("Client1:"+socket.isOutputShutdown());
            socket.shutdownOutput(); //关闭socket的输出，否则服务器端会一直等待着接受数据
            System.out.println("Client2:"+socket.isOutputShutdown());

            //获取服务端返回的信息
            InputStream inputStream = socket.getInputStream();
            byte[] bytes = new byte[1024];
            int len;
            ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
            while((len = inputStream.read(bytes)) != -1){
                byteArrayOutputStream.write(bytes,0,len);
            }
            System.out.println(byteArrayOutputStream.toString());
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //关闭流和socket
            try {
                if(os != null)
                os.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                if(socket != null)
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Socket getSocket() {
        return socket;
    }

    public void setSocket(Socket socket) {
        this.socket = socket;
    }
}

class Server{
    private ServerSocket serverSocket;

    public Server(int port) {
        try {
            this.serverSocket = new ServerSocket(8000);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void getMsg(){
        Socket accept = null;
        ByteArrayOutputStream baos = null;
        OutputStream os = null;
        try {
            //获取客户端的socket
            accept = serverSocket.accept();
            //获取输入流
            InputStream is = accept.getInputStream();
            //读取输入流
            byte[] bytes = new byte[1024];
            int len;
            baos = new ByteArrayOutputStream();
            System.out.println("Server1:"+accept.isOutputShutdown());
            while((len = is.read(bytes)) != -1){
                System.out.println("Server3:"+accept.isOutputShutdown());
                baos.write(bytes,0,len);
            }
            System.out.println("Server2:"+accept.isOutputShutdown());
            System.out.println("收到"+accept.getInetAddress()+"的消息");
            System.out.println(baos.toString());

            //返回给客户端消息
            System.out.println("开始回复");
            os = accept.getOutputStream();
            os.write("我已经收到了".getBytes());

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if(baos != null)
                baos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                if(os != null)
                os.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

2.UDP

1.客户端：
    1.1:创建一个socket对象
    1.2： 创建一个packet对象，存放数据，ip和端口
    1.3：通过socket.send()发送数据包
2.服务端：
    2.1：创建一个socket对象，指定端口
    2.2:通过socket.receive(packet)来接收数据包并保存在packet中

public class SocketTest2 {
    @Test
    public void sender(){
        try {
            //创建一个socket
            DatagramSocket socket = new DatagramSocket();
            //创建一个packet，存放数据
            byte[]  bytes = "你好啊".getBytes();
            DatagramPacket packet = new DatagramPacket(bytes,bytes.length,
                    InetAddress.getByName("127.0.0.1"),
                    8000);
            socket.send(packet);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    @Test
    public void reciver(){
        try {
            DatagramSocket socket = new DatagramSocket(8000);
            byte[] bytes = new byte[100];
            DatagramPacket packet = new DatagramPacket(bytes,bytes.length);
            socket.receive(packet);
            System.out.println(new String(packet.getData(),0,packet.getLength()));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

3.URL

   3.1:创建URL对象
   3.2：创建urlConnection对象
   3.3：连接
   3.4：通过urlConnection对象获取数据

public class URLTest {
    @Test
    public void test1(){
        try {
            URL url = new URL("https://www.baidu.com");

            URLConnection urlConnection = url.openConnection();

            urlConnection.connect();

            InputStream is = urlConnection.getInputStream();

            FileOutputStream fos = new FileOutputStream("./baidu.html");
            byte[] bytes = new byte[1024];
            int len;
            while((len = is.read(bytes)) != -1){
                fos.write(bytes,0,len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }


    }
}