Socket class understanding and learning about TCP character stream programming

Basic introduction

Socket （socket）： Is the cornerstone of communication , It's supporting TCP/IP Basic operation unit of network communication of protocol . It is an abstract representation of the endpoint in the process of network communication , Contains five kinds of information necessary for network communication ： The protocol used for the connection , localhost IP Address , Protocol port of local process , Remote host's IP Address , Protocol port of remote process

1. socket Is the cornerstone of communication , It's supporting TCP/IP Basic operation unit of network communication of protocol .
2. socket To put it simply , from port , agreement , Address three components .
3. The connection process between sockets is divided into three steps ： Server listening , Client request , Connect to confirm .
4. Because usually Socket The connection is TCP Connect , therefore Socket Once the connection is established , Both sides of the communication can start sending data content to each other , Until both sides are disconnected .
5. But in actual network applications , Communication between client and server often needs to go through multiple intermediate nodes , For example, router 、 gateway 、 Firewall, etc , Most firewalls default to closing connections that are inactive for a long time Socket The connection is broken , So you need to tell the network by polling , The connection is active .

• Socket It is mainly used to develop network applications , Its back is widely used

• Both ends of the communication need Socket, It is the breakpoint of communication between two machines

• Network communication is actually Socket Communication for

• Socket Allows programs to treat network connections as a stream , The data is in two Socket Interpass IO transmission

• commonly The application that initiates communication actively belongs to the client , The server waiting for the communication request

Sketch Map ：

Code implementation

Be sure to pay attention to , You must first open the server , Starting the client , Otherwise, an error will be reported

** Be careful ：** The code examples here are all about sending and receiving information , If you need to send or receive pictures, it's almost the same , Only byte stream must be used instead of character stream , The basic process is to use IO Knowledge in .

demand 1：

1. Write a server and a client
2. The service side in 9999 Port listening
3. Client connects to server , send out "hello,server", sign out
4. The server receives the information sent by the client and outputs , sign out

Server side

/** * *  Server side  *  demand ： Receive the information sent from the client and output  * * @author: Lei Zijie  * @date:2022/7/27 */
public class ScoketTCP01Server {
    
    public static void main(String[] args) throws IOException {
    

        // newly build serverSocket object , Realization 9999 Port listening 
        ServerSocket serverSocket = new ServerSocket(9999);

        // The pipeline will be generated after the client connects 
        Socket socket = serverSocket.accept();

        // Get the input stream of the pipeline 
        InputStream inputStream = socket.getInputStream();
        byte[] buf=new byte[1024];
        int len = 0;

        while ((len = inputStream.read(buf))!=-1){
    
            System.out.println(new String(buf,0,len));
        }

        // Closed flow 
        inputStream.close();
        socket.close();
        serverSocket.close();


    }
}

client

After the output stream writes data, it must be flush(), At the same time, mark the end

/** * *  client  *  demand ： Send a message to the server  * * @author: Lei Zijie  * @date:2022/7/27 */
public class ScoketTCP01Client {
    
    public static void main(String[] args) throws IOException {
    
        // obtain socket Connect 
        Socket socket = new Socket(InetAddress.getLocalHost(),9999);

        // Get output stream object 
        OutputStream outputStream = socket.getOutputStream();
        // Write information to the output stream 
        outputStream.write("hello,server".getBytes());

        // Closed flow 
        outputStream.close();
        socket.close();
    }
}

test result

The server receives the message

demand 2

1. Write a server and a client
2. The service side in 9999 Port listening
3. Client connects to server , send out "hello,server", And receive the data sent back by the server "hello,client", sign out
4. The server receives the information output sent by the client , And send the "hello,client", sign out

Server side

After the output stream writes data, it must be flush(), At the same time, mark the end

/** * *  Server side  *  demand ： Receive the information output sent from the client , And return a message to the client  * * * @author: Lei Zijie  * @date:2022/7/27 */
public class ScoketTCP02Server {
    
    public static void main(String[] args) throws IOException {
    

        // newly build serverSocket object , Realization 9999 Port listening 
        ServerSocket serverSocket = new ServerSocket(9999);

        // The pipeline will be generated after the client connects 
        Socket socket = serverSocket.accept();

        // Get the input stream of the pipeline , Get the information sent by the client 
        InputStream inputStream = socket.getInputStream();
        byte[] buf=new byte[1024];
        int len = 0;

        while ((len = inputStream.read(buf))!=-1){
    
            System.out.println(new String(buf,0,len));
        }
        // Close the read 
        socket.shutdownInput();

        // Get output stream object 
        OutputStream outputStream = socket.getOutputStream();
        // Write information to the output stream , Send it to the server 
        outputStream.write("hello,client".getBytes());
        // Close the write 
        socket.shutdownOutput();

        // Closed flow 
        outputStream.close();
        inputStream.close();
        socket.close();
        serverSocket.close();


    }
}

client

After the output stream writes data, it must be flush(), At the same time, mark the end

/** * *  client  *  demand ： Send a message to the server , And receive a message returned from the server  * * @author: Lei Zijie  * @date:2022/7/27 */
public class ScoketTCP02Client {
    
    public static void main(String[] args) throws IOException {
    
        // obtain socket Connect 
        Socket socket = new Socket(InetAddress.getLocalHost(),9999);

        // Get output stream object 
        OutputStream outputStream = socket.getOutputStream();
        // Write information to the output stream , Send it to the server 
        outputStream.write("hello,server".getBytes());
        // Close the write 
        socket.shutdownOutput();

        // Get the input stream of the pipeline , Get the information sent by the server 
        InputStream inputStream = socket.getInputStream();
        byte[] buf=new byte[1024];
        int len = 0;

        while ((len = inputStream.read(buf))!=-1){
    
            System.out.println(new String(buf,0,len));
        }

        // Closed flow 
        inputStream.close();
        outputStream.close();
        socket.close();
    }
}

test result

The server receives the message

Client receives message

demand 3

Use character stream to complete , The previous two requirements are completed by using byte stream

1. Write a server and a client
2. The service side in 9999 Port listening
3. Client connects to server , send out "hello,server", And receive the data sent back by the server "hello,client", sign out
4. The server receives the information output sent by the client , And send the "hello,client", sign out

Server side

After the output stream writes data, it must be flush(), At the same time, mark the end

/** * *  Server side  *  demand ： Use character stream , Receive the information output sent from the client , And return a message to the client  * * @author: Lei Zijie  * @date:2022/7/27 */
public class ScoketTCP03Server {
    
    public static void main(String[] args) throws IOException {
    

        // newly build serverSocket object , Realization 9999 Port listening 
        ServerSocket serverSocket = new ServerSocket(9999);

        // The pipeline will be generated after the client connects 
        Socket socket = serverSocket.accept();

        // Get the input stream of the pipeline , Get the information sent by the client 
        InputStream inputStream = socket.getInputStream();
        // Transfer byte stream input to character stream input 
        InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
        char[] cbuf=new char[1024];
        int len;
        while ((len = inputStreamReader.read(cbuf))!=-1){
    
            System.out.println(new String(cbuf,0,len));
        }
        // Close the read 
        socket.shutdownInput();

        // Get output stream object 
        OutputStream outputStream = socket.getOutputStream();
        // Convert byte stream output stream to character stream output stream 
        OutputStreamWriter outputStreamWriter = new OutputStreamWriter(outputStream);
        // Write information to the output stream , Send it to the server 
        outputStreamWriter.write("hello,client");
        // You need to brush a new stream before writing 
        outputStreamWriter.flush();
        // Close the write 
        socket.shutdownOutput();

        // Closed flow 
        outputStreamWriter.close();
        inputStreamReader.close();
        socket.close();
        serverSocket.close();


    }
}

client

After the output stream writes data, it must be flush(), At the same time, mark the end

/** * *  client  *  demand ： Use character stream , Send a message to the server , And receive a message returned from the server  * * @author: Lei Zijie  * @date:2022/7/27 */
public class ScoketTCP03Client {
    
    public static void main(String[] args) throws IOException {
    
        // obtain socket Connect 
        Socket socket = new Socket(InetAddress.getLocalHost(),9999);

        // Get output stream object 
        OutputStream outputStream = socket.getOutputStream();
        // Convert byte stream output stream to character stream output stream 
        OutputStreamWriter outputStreamWriter = new OutputStreamWriter(outputStream);
        // Write information to the output stream , Send it to the server 
        outputStreamWriter.write("hello,server");
        // You need to brush a new stream before writing 
        outputStreamWriter.flush();

        // Close the write 
        socket.shutdownOutput();

        // Get the input stream of the pipeline , Get the information sent by the server 
        InputStream inputStream = socket.getInputStream();
        // Transfer byte stream input to character stream input 
        InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
        char[] cbuf=new char[1024];
        int len;
        while ((len = inputStreamReader.read(cbuf))!=-1){
    
            System.out.println(new String(cbuf,0,len));
        }

        // Closed flow 
        inputStreamReader.close();
        outputStreamWriter.close();
        socket.close();
    }
}

test result

The server receives the message

Client receives message

Send pictures 、 Video and other documents process description

Because it's a picture 、 Video and other documents , So we must use byte stream for transmission

demand ：

1. Write a server and a client
2. The service side in 8888 Port listening
3. The client connects to the server , Send a local picture
4. The server receives the picture sent by the client , Save to src Next , send out “ Received the picture ” To the client , And then quit
5. The client receives the “ Received the picture ”, And then quit

Process example ：

1. The client uses the byte input stream to input the pictures in the disk into the memory
2. The client uses the byte output stream to output the pictures in memory to the server
3. The server uses the byte input stream to obtain the pictures in the client byte output stream
4. The server uses byte output stream to output pictures to disk file

Server side

After the output stream writes data, it must be flush(), At the same time, mark the end

/** * *  Server side  * * @author: Lei Zijie  * @date:2022/7/27 */
public class TCPFileUploadServer {
    
    public static void main(String[] args) throws IOException {
    

        // monitor 8888 port 
        ServerSocket serverSocket = new ServerSocket(8888);
        // Waiting for the connection 
        Socket socket = serverSocket.accept();

        BufferedInputStream bufferedInputStream = new BufferedInputStream(socket.getInputStream());
        // Created byte stream output stream 
        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(new FileOutputStream("basic_review\\src\\socket_\\ picture .jpg"));
        // Read picture information 
        byte[] buf = new byte[1024];
        int len;
        while ((len = bufferedInputStream.read(buf)) != -1){
    

            bufferedOutputStream.write(buf,0,len);
        }
        bufferedOutputStream.flush();

        socket.shutdownInput();



        bufferedOutputStream = new BufferedOutputStream(socket.getOutputStream());

        bufferedOutputStream.write(" Received the picture ".getBytes());

        // Refresh stream 
        bufferedOutputStream.flush();

        socket.shutdownOutput();

        bufferedOutputStream.close();
        bufferedInputStream.close();
        socket.close();
        serverSocket.close();

    }
}

client

After the output stream writes data, it must be flush(), At the same time, mark the end

/** * *  client  * * @author: Lei Zijie  * @date:2022/7/27 */
public class TCPFileUploadClient {
    
    public static void main(String[] args) throws IOException {
    
        // Connect to the host 8888 port , obtain socket object 
        Socket socket = new Socket(InetAddress.getLocalHost(), 8888);

        // Read file address 
        String filePath ="f:\\ssm The blog system .jpg";
        // Created byte stream input stream 
        BufferedInputStream bufferedInputStream = new BufferedInputStream(new FileInputStream(filePath));
        // Created byte stream output stream 
        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(socket.getOutputStream());
        // Read picture information 
        byte[] buf = new byte[1024];
        int len;
        while ((len = bufferedInputStream.read(buf)) != -1){
    
            // Write to pipeline 
            bufferedOutputStream.write(buf,0,len);
        }
        // Refresh stream 
        bufferedOutputStream.flush();
        // Close write 
        socket.shutdownOutput();


        bufferedInputStream = new BufferedInputStream(socket.getInputStream());
        while ((len = bufferedInputStream.read(buf)) != -1){
    
            System.out.println(new String(buf,0,len));

        }

        socket.shutdownInput();

        bufferedOutputStream.close();
        bufferedInputStream.close();

        socket.close();


    }
}

summary

Current review java The basic review has reached the stage of computer network , I found myself lack of knowledge in network communication programming , This article is used to record learning java Network programming technology

Another point ！！！！！ After using the output stream to write data, be sure to flush(), At the same time, mark the end , Otherwise you may report an error