Java: How To Create A Simple Web Server Using HttpServer

To program a web or HTTP server from nothing could be very difficult. It’s gonna to take you to write thousands of source instructions. The HTTP protocol it self is pretty to understand but it complicated to implement them in programming language. It involves a lot of parsing and need a lot of understanding how the HTTP requests and HTTP responses work together.

In Java SDK, you can use the HttpServer class in com.sun.net.httpserver.HttpServer package. It is pretty simple to use HttpServer to create a simple web server, what you need to do is to implement a HttpHandler for a specific URL/context.

Below is a sample of simple HTTP server that send files sit on the web server to client when user request the file via web browser.

import java.io.*;
import java.net.*;
import java.text.*;
import java.util.*;
import com.sun.net.httpserver.*;

public class TimeServer
{
    private static int SERVER_PORT = 3000;

    private class FileDownloadHandler
	implements HttpHandler
    {
	public void
	handle (
	    HttpExchange	httpExc)
	    throws IOException 
	{
	    String		filename;
	    String		contentType;
	    OutputStream	out;
	    long		rspLen;
	    int			len;
	    byte[]		buffer;
	    File		file;
	    FileInputStream	in;

	    filename = httpExc.getRequestURI ().getPath ();
	    if (filename == null || filename.isEmpty ())
		filename = "TimeClient.html";
	    if (filename.startsWith ("/"))
		filename = filename.substring (1);

	    file = new File (filename);
	    if (!file.isFile ()) {
		sendResponse (httpExc, 404, 
		    "Not found: " + filename + "");
		System.err.println ("Not found: " + filename);
	    	return;
	    }

	    in = null;
	    buffer = new byte[4096];
	    out = httpExc.getResponseBody ();
	    rspLen = file.length ();
	    httpExc.sendResponseHeaders (200, rspLen);
	    try {
	    	in = new FileInputStream (file);
	    } catch (IOException e) {
		sendResponse (httpExc, 500, 
		    "Error reading file: " + 
		    	filename + "");
		System.err.println ("Error reading file: " + filename);
	    	return;
	    }
	    try {
		while ((len = in.read(buffer)) != -1)
		    out.write (buffer, 0, len);
	    } catch (IOException e) {
		sendResponse (httpExc, 500, 
		    "Error writing file: " + 
		    	filename + "");
		System.err.println ("Error writing file: " + filename);
	    }
	    try {
	    	in.close ();
	    } catch (IOException e) {
		// DO NOTHING
	    }
	    try {
	    	out.close ();
	    } catch (IOException e) {
		// DO NOTHING
	    }
	}
    }

    public void
    sendResponse (
	HttpExchange		httpExc,
	int 			responseCode,	// Response code
	String 			responseBody)	// Response body
    	throws IOException
    {
	byte[]			data;		// Data
	OutputStream		out;		// Output stream

	data = responseBody.getBytes ();
	httpExc.sendResponseHeaders (responseCode, data.length);
	out = httpExc.getResponseBody ();
	out.write (data, 0, data.length);
	out.close ();
    }

    public void
    main ()
    	throws IOException
    {
	HttpServer		server;

	// Create and start the http server instance

	server = HttpServer.create (new InetSocketAddress(SERVER_PORT), 0);
	server.createContext ("/", new FileDownloadHandler());
	server.setExecutor (null);
	server.start ();
    }

    public static void 
    main (
	String[]		args)
    throws Exception 
    {
	(new WebServer()).main ();
    }
}

The example above is just a very simple web server that allow user to download files. If you need a more comprehensive one, you may want to look into the packages in J2EE (Servlet and JSP).