Handle multiple HTTP requests
Accept and Parse the HTTP request
Get the requested file from the server
Create an HTTP response message, including the requested file
Send the response to the client.

Excuse the extremely brief "discussion" on sockets, but the concept should become clearer in the code. So let's get to that.

import java.io.*;
import java.net.*;
import java.util.*;

public final class WebServer {
    public static void main(String args[]) throws Exception {

        //Establish the listen socket
        int PORT = 5306;     //select your favorite number > 1123
        ServerSocket listenSocket = new ServerSocket(PORT);

        //Process HTTP service requests in an infinite loop
        while(true) {
            //listen for TCP connection request
            //Construct an object to process the HTTP request message
            HttpRequest request = new HttpRequest(listenSocket.accept());
            Thread thread = new Thread(request);
            thread.start();
        }
    }
}

final class HttpRequest implements Runnable {

    final static String CRLF ="\r\n";
    Socket socket;

    public HttpRequest(Socket socket) throws Exception {
        this.socket = socket;
    }


    //Implement the run() method of the Runnable interface
    public void run() {
        try {
            processRequest();
        } catch (Exception e) {
            System.out.println(e);
        }
    }

    private void processRequest() throws Exception {
        //Get references to sockets input and output streams
        InputStream is = this.socket.getInputStream();
        DataOutputStream os = new DataOutputStream(this.socket.getOutputStream());
        
        //Set up input stream filter
        BufferedReader br = new BufferedReader(new InputStreamReader(is));
        
        //Get the request line of HTTP message 
        String requestLine = br.readLine();


        //...

• 200 OK
• 404 Not Found
• 400 Bad Request
• 505 HTTP Version Not Supported

• text/html
• image/jpeg
• image/gif
• text/plain

        // Extract the filename from the request line. Assume a GET command
        StringTokenizer tokens = new StringTokenizer(requestLine);
        tokens.nextToken(); //SKIP OVER THE ASSUMED 'GET' token
        String fileName = tokens.nextToken();
        // Drop the slash at the begginning. 
        if(fileName.startsWith("/"))
            fileName = fileName.substring(1,fileName.length());

        // Open the requested file.  
        FileInputStream fis = null;
        boolean fileExists = true;
        try {
            fis = new FileInputStream(fileName);
        } catch (FileNotFoundException e) {
            fileExists = false;
        }
    
        // Construct the response message.
        String statusLine = null;
        String contentTypeLine = null;
        String entityBody = null;
            
        if (fileExists) {
            statusLine = "HTTP/1.0 200 OK" + CRLF;
            contentTypeLine = "Content-type: " + contentType(fileName) + CRLF;
        } else {
            statusLine = "HTTP/1.0 404 Not Found" + CRLF; 
            contentTypeLine = "NONE";
            entityBody = "\n\n Not Found";
        }
        
        // Send the status line.
        os.writeBytes(statusLine);
        
        // Send the content type line.
        os.writeBytes(contentTypeLine);
        
        // Send a blank line to indicate the end of the header lines.
        os.writeBytes(CRLF);
        
        // Send the entity body.
        if (fileExists) {
            sendBytes(fis, os);
            fis.close();
        } else {
            os.writeBytes(entityBody);
        }
        
        //Close the streams
        os.close();
        br.close();
        socket.close();
    }

    private String contentType(String fileName) {
        if(fileName.endsWith(".htm") || fileName.endsWith(".html"))
            return "text/html";
        else if(fileName.endsWith(".jpg") || fileName.endsWith(".jpeg"))
            return "image/jpeg";
        else if(fileName.endsWith(".gif"))
            return "image/gif";
        else if(fileName.endsWith(".txt"))
            return "text/plain";
        else
            return "application/octet-stream";
    }
         
    private static void sendBytes(FileInputStream fis, OutputStream os) throws Exception {
        // Construct a 1K buffer to hold bytes on their way to the socket.
        byte[] buffer = new byte[1024];
        int bytes = 0;
        
        // Copy requested file into the socket's output stream.
        while((bytes = fis.read(buffer)) != -1 )
            os.write(buffer, 0, bytes);
    }
}