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This article mainly shows you "what is Java Socket programming", the content is easy to understand, clear, hope to help you solve your doubts, the following let the editor lead you to study and learn "what is Java Socket programming" this article.

1. What is socket?

The so-called socket, also known as a "socket", is used to describe the IP address and port, and is a handle to a communication chain. Applications usually send requests to or respond to network requests through "sockets".

Take J2SDK-1.3 as an example, the Socket and ServerSocket class libraries are located in the java.net package. ServerSocket is used on the server side, and Socket is used when establishing network connections. When the connection is successful, an Socket instance is generated at both ends of the application, and the instance is manipulated to complete the required session. For a network connection, sockets are equal, there is no difference, and there are no different levels on the server side or on the client side. Both Socket and ServerSocket do their work through the SocketImpl class and its subclasses.

Important Socket API:

Java.net.Socket inherits from java.lang.Object and has eight constructors, but there are not many methods. Here are the three most frequently used methods, and others can be found in the JDK-1.3 documentation.

The .accept method is used to generate "blocking" until a connection is received and an instance of the client's Socket object is returned. "blocking" is a term that causes a program to run temporarily "stay" at this place until a session is generated, and then the program continues; usually "blocking" is caused by a loop.

The. GetInputStream method takes the network connection input and returns an instance of the IutputStream object.

The other end of the .getOutputStream method connection gets the input and returns an instance of the OutputStream object.

Note: both the getInputStream and getOutputStream methods produce an IOException that must be captured because the stream object they return is usually used by another stream object.

two。 How to develop a program of Server-Client model

Development principles:

The server uses ServerSocket to listen on the specified port, and the port can be specified at will (since the port below 1024 is usually reserved and cannot be used at will in some operating systems, it is recommended to use a port greater than 1024). Wait for the customer connection request, and the session occurs after the client connection is completed. After the session is completed, close the connection.

The client uses Socket to make a connection request to a port of a server on the network, once the connection is successful, open the session; after the session is completed, close the Socket. The client does not need to specify an open port, and usually temporarily and dynamically assigns a port of more than 1024.

{build server} import java.net.*;import java.io.*;public class Server {private ServerSocket ss;private Socket socket;private BufferedReader in;private PrintWriter out;public Server () {try {ss = new ServerSocket (10000); while (true) {socket = ss.accept (); in = new BufferedReader (new InputStreamReader (socket.getInputStream (); out = new PrintWriter (socket.getOutputStream (), true); String line = in.readLine (); out.println ("you input is:" + line); out.close () In.close (); socket.close ();} ss.close ();} catch (IOException e) {}} public static void main (String [] args) {new Server ();}}

This program sets up a server that has been listening to port 10000, waiting for users to connect. Return a piece of information to the client after the connection is established, and then end the session. This program can only accept one customer connection at a time.

{build client} import java.io.*;import java.net.*;public class Client {Socket socket;BufferedReader in;PrintWriter out;public Client () {try {socket = new Socket ("xxx.xxx.xxx.xxx", 10000); in = new BufferedReader (new InputStreamReader (socket.getInputStream (); out = new PrintWriter (socket.getOutputStream (), true); BufferedReader line = new BufferedReader (new InputStreamReader (System.in)); out.println (line.readLine ()); line.close (); out.close () In.close (); socket.close ();} catch (IOException e) {}} public static void main (String [] args) {new Client ();}}

This client connects to the server with the address xxx.xxx.xxx.xxx, port 10000, and enters a line of information from the keyboard, sends it to the server, then accepts the return message from the server, and ends the session.

The second step is to connect multiple customers at the same time

In the actual network environment, it is not feasible to serve only one user at a time. In addition to processing the input information of users, an excellent network service program must also be able to respond to connection requests from multiple clients at the same time. In java, it is very easy to achieve the above features.

Design principle:

The main program listens on a port and waits for the customer to access; at the same time, it constructs a thread class, ready to take over the session. When a Socket session is generated, the session is handed over to the thread, and the main program continues to listen. It is a good idea to use the Thread class or Runnable interface to implement it.

{achieve message sharing} import java.io.*;import java.net.*;public class Server extends ServerSocket {private static final int SERVER_PORT = 10000 potential public Server () throws IOException {super (SERVER_PORT); try {while (true) {Socket socket = accept (); new CreateServerThread (socket);}} catch (IOException e) {} finally {close ();}} /-- CreateServerThreadclass CreateServerThread extends Thread {private Socket client;private BufferedReader in;private PrintWriter out;public CreateServerThread (Socket s) throws IOException {client = s In = new BufferedReader (new InputStreamReader (client.getInputStream (), "GB2312"); out = new PrintWriter (client.getOutputStream (), true); out.println ("--Welcome -"); start ();} public void run () {try {String line = in.readLine (); while (! line.equals ("bye")) {String msg = createMessage (line); out.println (msg); line = in.readLine ();} out.println ("--See you, bye!--") Client.close ();} catch (IOException e) {}} private String createMessage (String line) {xxxxxxxxx;}} public static void main (String [] args) throws IOException {new Server ();}}

This program listens on port 10000 and gives the access to the CreateServer thread to run. The CreateServerThread thread accepts the input and responds to the customer until the customer enters "bye" and the thread ends. In the createMessage method, we can process the input, produce the result, and then return the result to the customer.

The third step is to realize information sharing: real-time communication on Socket.

One of the greatness of the network is information sharing. Server can actively broadcast messages to all Client, while Client can also publish messages to other Client. Let's take a look at how to develop a program that can deliver messages in real time.

Design principle:

The server accepts the connection request from the client and starts a thread to process the connection. The thread keeps reading the client input, and then adds the input to the queue and waits for processing. The thread is queued while the thread is started so that it can be located and taken out when needed.

{source code} import java.io.*;import java.net.*;import java.util.*;import java.lang.*;public class Server extends ServerSocket {private static ArrayList User_List = new ArrayList (); private static ArrayList Threader = new ArrayList (); private static LinkedList Message_Array = new LinkedList (); private static int Thread_Counter = 0th private static boolean isClear = true;protected static final int SERVER_PORT = 10000 true;protected static final int SERVER_PORT protected FileOutputStream LOG_FILE = new FileOutputStream ("d:/connect.log", true) Public Server () throws FileNotFoundException, IOException {super (SERVER_PORT); new Broadcast (); / / append connection logCalendar now = Calendar.getInstance (); String str = "[" + now.getTime (). ToString () + "] Accepted a connection1512"; byte [] tmp = str.getBytes (); LOG_FILE.write (tmp); try {while (true) {Socket socket = accept (); new CreateServerThread (socket);}} finally {close ();}} public static void main (String [] args) throws IOException {new Server () } / /-Broadcastclass Broadcast extends Thread {public Broadcast () {start ();} public void run () {while (true) {if (! isClear) {String tmp = (String) Message_Array.getFirst (); for (int I = 0; I

< Threader.size(); i++){CreateServerThread client = (CreateServerThread)Threader.get(i);client.sendMessage(tmp);}Message_Array.removeFirst();isClear = Message_Array.size() >

0? False: true;} / /-CreateServerThreadclass CreateServerThread extends Thread {private Socket client;private BufferedReader in;private PrintWriter out;private String Username;public CreateServerThread (Socket s) throws IOException {client = sbosin = new BufferedReader (new InputStreamReader (client.getInputStream (); out = new PrintWriter (client.getOutputStream (), true); out.println ("--Welcome to this chatroom -"); out.println ("Input your nickname:"); start ();} public void sendMessage (String msg) {out.println (msg) } public void run () {try {int flag = 0th Threadbasket Countermeasure playing host string line = in.readLine (); while (! line.equals ("bye")) {if (line.equals ("l")) {out.println (listOnlineUsers ()); line = in.readLine (); continue;} if (flag++ = 0) {Username = line;User_List.add (Username); out.println (listOnlineUsers ()); Threader.add (this); pushMessage ("[

< " + Username + " come on in >

] ");} else {pushMessage ("+ line);} line = in.readLine ();} out.println ("-- See you, bye!-"); client.close ();} catch (IOException e) {} finally {try {client.close ();} catch (IOException e) {} Thread_Counter--;Threader.remove (this); User_List.remove (Username); pushMessage (" [

< " + Username + " left>

]);}} private String listOnlineUsers () {String s = "- +-Online list-+-1512"; for (int I = 0; I < User_List.size (); iTunes +) {s + = "[" + User_List.get (I) + "] 1512";} s + = "- +-+ -"; return s;} private void pushMessage (String msg) {Message_Array.addLast (msg); isClear = false;}

This is the screen after the program runs and multiple users log in and enter information. The real-time broadcast of information is realized. The user enters "l" to list the online personnel table.

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