Solutions to the Programming Assignments|Programming Assignment 1

Solutions for Programming Assignment 1

Below are the solutions for the Web Server lab. There are two classes, HttpRequest and WebServer.

HttpRequest.java

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

final class HttpRequest implements Runnable {
    final static String CRLF = "\r\n";
    Socket socket;
    
    // Constructor
    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 a reference to the socket's input and output streams.
	InputStream is = socket.getInputStream();
	DataOutputStream os = new DataOutputStream(socket.getOutputStream());
	
	// Set up input stream filters.
	BufferedReader br = new BufferedReader(new InputStreamReader(is));

        // Get the request line of the HTTP request message.
        String requestLine = br.readLine();

        // Extract the filename from the request line.
        StringTokenizer tokens = new StringTokenizer(requestLine);
        tokens.nextToken();  // skip over the method, which should be "GET"
        String fileName = tokens.nextToken();
	
        // Prepend a "." so that file request is within the current directory.
        fileName = "." + fileName ;
	
	// Open the requested file.
        FileInputStream fis = null ;
        boolean fileExists = true ;
        try {
	    fis = new FileInputStream(fileName);
        } catch (FileNotFoundException e) {
	    fileExists = false ;
        }

	// Debug info for private use
	System.out.println("Incoming!!!");
	System.out.println(requestLine);
	String headerLine = null;
	while ((headerLine = br.readLine()).length() != 0) {
	    System.out.println(headerLine);
	}
	
	// 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 = "Content-Type: text/html" + CRLF;
	    entityBody = "<HTML>" + 
		"<HEAD><TITLE>Not Found</TITLE></HEAD>" +
		"<BODY>Not Found</BODY></HTML>";
        }
	// 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 streams and socket.
        os.close();
        br.close();
        socket.close();
    }

    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);
	}
    }

    private static String contentType(String fileName) {
	if(fileName.endsWith(".htm") || fileName.endsWith(".html")) {
	    return "text/html";
	}
	if(fileName.endsWith(".ram") || fileName.endsWith(".ra")) {
	    return "audio/x-pn-realaudio";
	}
	return "application/octet-stream" ;
    }
}

WebServer.java

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

public final class WebServer {
    public static void main(String argv[]) throws Exception {
	// Get the port number from the command line.
	int port = (new Integer(argv[0])).intValue();
	
	// Establish the listen socket.
	ServerSocket socket = new ServerSocket(port);
	
	// Process HTTP service requests in an infinite loop.
	while (true) {
	    // Listen for a TCP connection request.
	    Socket connection = socket.accept();
	    
	    // Construct an object to process the HTTP request message.
	    HttpRequest request = new HttpRequest(connection);
	    
	    // Create a new thread to process the request.
	    Thread thread = new Thread(request);
	    
	    // Start the thread.
	    thread.start();
	}
    }
}