Institute of Inf. Tech. - Informatikai intézet

'My own HTTP' server sample

Let's create an empty Java project, Then create files called 404.html and an index.html with the following content. Let's note that the error handling is redundant, i.e. the handling of errors 404 and 501 is written twice.

Task: create a generic error handling function to return errors to the client side.

Content of 404.html:

    <html>
        <body>
        <h1>File not found error</h1>
        </body>
    </html>

Content of index.html:

    <html>
    <body>
    <h1>My HTTP server works</h1>
    <a href="/dead_link.html">Link not working</a>
    </body>
    </html>

Content of JavaHTTPServer.java:

import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Date;
import java.util.StringTokenizer;

public class JavaHTTPServer implements Runnable {

	static final File WEB_ROOT = new File(".");
	static final String DEFAULT_FILE = "index.html";
	static final String FILE_NOT_FOUND = "404.html";

	private Socket connect;

	public JavaHTTPServer(Socket c) {
		connect = c;
	}

	public static void main(String[] args) {
		try {
			ServerSocket serverConnect = new ServerSocket(8080);
			System.out.println("Server started.\nListening for connections on port : 8080 ...\n");

			while (true) {
				JavaHTTPServer myServer = new JavaHTTPServer(serverConnect.accept());

				Thread thread = new Thread(myServer);
				thread.start();
			}
		} catch (IOException e) {
			System.err.println("Server Connection error : " + e.getMessage());
		}
	}

	@Override
	public void run() {
		BufferedReader in = null;
		PrintWriter out = null;
		BufferedOutputStream dataOut = null;
		String fileRequested = null;

		try {
			in = new BufferedReader(new InputStreamReader(connect.getInputStream()));
			out = new PrintWriter(connect.getOutputStream());
			dataOut = new BufferedOutputStream(connect.getOutputStream());

			String input = in.readLine();

			StringTokenizer parse = new StringTokenizer(input);
			String method = parse.nextToken().toUpperCase(); // we get the HTTP method of the client
			
			// we get file requested
			fileRequested = parse.nextToken().toLowerCase();

			// we support only GET and HEAD methods, we check
			if (method.equals("GET") || method.equals("HEAD")) {
				// GET or HEAD method
				if (fileRequested.endsWith("/")) {
					fileRequested += DEFAULT_FILE;
				}

				File file = new File(WEB_ROOT, fileRequested);
				int fileLength = (int) file.length();
				String content = getContentType(fileRequested);

				if (method.equals("GET")) { // GET method so we return content
					byte[] fileData = readFileData(file, fileLength);

					// send HTTP Headers
					out.println("HTTP/1.1 200 OK");
					out.println("Server: Java HTTP Server v1.0");
					out.println("Date: " + new Date());
					out.println("Content-type: " + content);
					out.println("Content-length: " + fileLength);
					out.println(); // blank line between headers and content, very important !
					out.flush(); // flush character output stream buffer

					dataOut.write(fileData, 0, fileLength);
					dataOut.flush();
				}
			}

		} catch (FileNotFoundException fnfe) {
			try {
				fileNotFound(out, dataOut, fileRequested);
			} catch (IOException ioe) {
				System.err.println("Error with file not found exception : " + ioe.getMessage());
			}

		} catch (IOException ioe) {
			System.err.println("Server error : " + ioe);
		} finally {
			try {
				in.close();
				out.close();
				dataOut.close();
				connect.close(); // we close socket connection
			} catch (Exception e) {
				System.err.println("Error closing stream : " + e.getMessage());
			}
		}

	}

	private byte[] readFileData(File file, int fileLength) throws IOException {
		FileInputStream fileIn = null;
		byte[] fileData = new byte[fileLength];

		try {
			fileIn = new FileInputStream(file);
			fileIn.read(fileData);
		} finally {
			if (fileIn != null)
				fileIn.close();
		}

		return fileData;
	}

	// return supported MIME Types
	private String getContentType(String fileRequested) {
		if (fileRequested.endsWith(".htm") || fileRequested.endsWith(".html"))
			return "text/html";
		else
			return "text/plain";
	}

	private void fileNotFound(PrintWriter out, OutputStream dataOut, String fileRequested) throws IOException {
		File file = new File(WEB_ROOT, FILE_NOT_FOUND);
		int fileLength = (int) file.length();
		String content = "text/html";
		byte[] fileData = readFileData(file, fileLength);

		out.println("HTTP/1.1 404 File Not Found");
		out.println("Server: Java HTTP Server v1.0");
		out.println("Date: " + new Date());
		out.println("Content-type: " + content);
		out.println("Content-length: " + fileLength);
		out.println(); // blank line between headers and content, very important !
		out.flush(); // flush character output stream buffer

		dataOut.write(fileData, 0, fileLength);
		dataOut.flush();
	}

}

Task: refactor the code and eliminate duplicate parts. Let's create a separate function to return a general HTTP response::

out.println("HTTP/1.1 200 OK");
out.println("Server: Java HTTP Server v1.0");
out.println("Date: " + new Date());
out.println("Content-type: " + content);
out.println("Content-length: " + fileLength);
out.println(); // blank line between headers and content, very important !
out.flush(); // flush character output stream buffer

Task: modify the source code so that it can also return images. To do this, first add <img src=„…> to index.html and copy an arbitrary image next to the html-s..

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