Mini Java Socket Server Example

This Example shows how to create a small HTTP server using Java Sockets. It can be useful to communicate with Cron jobs, to test whether Java is working, check out HTTP communications with a specific port, see all the headers sent by the web browser, or to verify that the post data is being sent to a specific port.

It is also useful when you need a web interface are you are not allowed to install an application server or you just don't want to use and embedded server such us Jetty.

It has the following features.

• Doesn't need external libraries.
• Retrieves post data from the request.
• Uses one thread per request.
• Retrieves all the post data into a char array.

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
public class MiniServerSocketExample {
    private static final int PORT = 8080;
    public static void main(String[] args) {
        try {
            ServerSocket server = new ServerSocket(PORT);
            System.out.println("MiniServer active " + PORT);
            while (true) {
                new ThreadSocket(server.accept());
            }
        } catch (Exception e) {
        }
    }
}
class ThreadSocket extends Thread {
    private Socket insocket;
    ThreadSocket(Socket insocket) {
        this.insocket = insocket;
        this.start();
    }
    @Override
    public void run() {
        try {
            InputStream is = insocket.getInputStream();
            PrintWriter out = new PrintWriter(insocket.getOutputStream());
            BufferedReader in = new BufferedReader(new InputStreamReader(is));
            String line;
            line = in.readLine();
            String request_method = line;
            System.out.println("HTTP-HEADER: " + line);
            line = "";
            // looks for post data
            int postDataI = -1;
            while ((line = in.readLine()) != null && (line.length() != 0)) {
                System.out.println("HTTP-HEADER: " + line);
                if (line.indexOf("Content-Length:") > -1) {
                    postDataI = new Integer(
                            line.substring(
                                    line.indexOf("Content-Length:") + 16,
                                    line.length())).intValue();
                }
            }
            String postData = "";
            // read the post data
            if (postDataI > 0) {
                char[] charArray = new char[postDataI];
                in.read(charArray, 0, postDataI);
                postData = new String(charArray);
            }
            out.println("HTTP/1.0 200 OK");
            out.println("Content-Type: text/html; charset=utf-8");
            out.println("Server: MINISERVER");
            // this blank line signals the end of the headers
            out.println("");
            // Send the HTML page
            out.println("<H1>Welcome to the Mini Server</H1>");
            out.println("<H2>Request Method->" + request_method + "</H2>");
            out.println("<H2>Post->" + postData + "</H2>");
            out.println("<form name=\"input\" action=\"form_submited\" method=\"post\">");
            out.println("Username: <input type=\"text\" name=\"user\"><input type=\"submit\" value=\"Submit\"></form>");
            out.close();
            insocket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

To verify that It's working

Type http://localhost:8080 in your webbrowser:

Possible Errors

• If the port is already being used you will get a  java.net.BindException: Address already in use
• If you are using a firewall or the user you used to run the java sample doesn't have enough privileges you will get a java.net.BindException: Permission denied

Notes

• I have tested it with over 2 million requests over 5 months with no problems.
• Change the Content type header if you wish to use it to serve other contents such us JSON, MP3, JPEGs, etc. ex. for mp3 files "Content-Type: audio/mpeg, audio/x-mpeg, audio/x-mpeg-3, audio/mpeg3"