How can read input from a Client in a simple HTTP Web Server in Java?

Question

I am trying to create a simple HTTP web server in Java. I'm just taking this in baby steps so it's super simplistic. I'm trying to make it so I can read simple input from the Client and output anything from the Server when they are both connected.

After searching around on tutorials on websites, this is what I've done so far:

public class Server
{
    public static void main(String[] args) throws Exception
    {
        boolean listening = true;
        ServerSocket server = null;
        int port = 2222;
        try
        {
            System.out.println("Server binding to port " + port);
            server = new ServerSocket(port);
        }
        catch(Exception e)
        {
            System.out.println("Error: " + e);
            System.exit(1);
        }

        System.out.println("Server successfully binded to port " + port);

        while(listening)
        {
            System.out.println("Attempting to connect to client");
            Socket client = server.accept();
            System.out.println("Successfully connected to client");
            new ServerThread(client).start() ;
        }

        server.close();
    }
}

public class ServerThread extends Thread
{
    private Socket socket = null ;
    public ServerThread(Socket s)
    {
        this.socket = s ;
    }

    public void run()
    {       
        InputStream in = socket.getInputStream() ;
        OutputStream out = socket.getOutputStream() ;
        byte [] message, reply;
        while((in.read(message))
        {
            out.write(reply) ;
        }
        in.close() ;
        out.close() ;
        socket.close() ;    
    }
}

It binds and then hangs after attempting to connect to the client. This is because I'm not sure what you do in the while loop in the ServerThread and what you do with the message and reply variables >_< It's been a long time since I've done Java so take it easy on me!

PbxMan · Accepted Answer · 2012-12-20 09:49:27Z

I have only use this kind of server as a "curiosity", to learn new stuff nothing more because you are reinventing the wheel, security reasons etc... I only had to use it once because I had to communicate a server with a JSON code and no server could be installed. This code needs more work such us creating a new thread for each request, a better RCF HTTP implementation but it works with your ordinary browser.

I hope this helps.

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class MiniPbxManServer extends Thread {
    private final int PORT = 2222;    
    public static void main(String[] args) {
        MiniPbxManServer gtp = new MiniPbxManServer();
        gtp.start();
    }    
    public void run() {
        try {
            ServerSocket server = new ServerSocket(PORT);
            System.out.println("MiniServer active "+PORT);
            boolean shudown = true;
            while (shudown) {               
                Socket socket = server.accept();                
                InputStream is = socket.getInputStream();
                PrintWriter out = new PrintWriter(socket.getOutputStream());            
                BufferedReader in = new BufferedReader(new InputStreamReader(is));              
                String line;
                line = in.readLine();
                String auxLine = line;
                line = "";
                // looks for post data
                int postDataI = -1;
                while ((line = in.readLine()) != null && (line.length() != 0)) {
                    System.out.println(line);
                    if (line.indexOf("Content-Length:") > -1) {
                        postDataI = new Integer(line
                                .substring(
                                        line.indexOf("Content-Length:") + 16,
                                        line.length())).intValue();
                    }
                }
                String postData = "";
                for (int i = 0; i < postDataI; i++) {
                    int intParser = in.read();
                    postData += (char) intParser;
                }                               
                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 PbxMan server</H1>");
                out.println("<H2>GET->"+auxLine+ "</H2>");        
                out.println("<H2>Post->"+postData+ "</H2>");
                out.println("<form name=\"input\" action=\"imback\" method=\"post\">");
                out.println("Username: <input type=\"text\" name=\"user\"><input type=\"submit\" value=\"Submit\"></form>");                 
                //if your get parameter contains shutdown it will shutdown
                if(auxLine.indexOf("?shutdown")>-1){
                    shudown = false;
                }
                out.close();
                socket.close();
            }
            server.close();            
        } catch (Exception e) {
            e.printStackTrace();
        }
    }    
}

url: localhost:2222/whatever

Chris Gerken · Accepted Answer · 2012-10-07 15:45:16Z

0

I think you're going the right way at a high level. The difference between what you've got and production systems is that they do their polling for input on a socket is done in a different thread so as not to halt the system while waiting for input.

In fact, one of the configuration parameters for a web server is how many clients (threads) to have up and running.

answered Oct 7, 2012 at 15:45

Chris Gerken

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2 Comments

Johnathan Au Over a year ago

On that note, how would you handle multiple threads, let's say 10 clients? Is that done with new ServerThread(client).start() or is this very limited?

Chris Gerken Over a year ago

Yes. Start a new thread for each client. You may need some kind of semaphore to make sure that common resources (across the threads) are accesses in a serialized way. This approach is limited, but only in that if you want a production-ready multi-client server than you might be better of going with an open source web server like tomcat/jetty as a base for your application. If you're just playing around, though, then you could go quite far with your approach.

Reimeus · Accepted Answer · 2012-10-07 15:51:05Z

0

You should always flush data from the server's output stream. The client response may depend on this:

out.flush();

To check for the end of stream, you could use:

int result = 0;
while ((result = in.read(message)) != -1) {
...

Also your reply message does not appear to be initialized, you probably want to resend the client data initially:

reply = message;

answered Oct 7, 2012 at 15:51

Reimeus

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Comments

Alex · Accepted Answer · 2012-10-07 16:29:30Z

0

The jdk has a simplistic http server included to build embedded http servers. Take a look at this link.

edited Oct 7, 2012 at 16:29

answered Oct 7, 2012 at 16:18

Alex

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