httpserver.java

Java Thread Programming (Source

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

// uses ObjectFIFO from chapter 18

public class HttpServer extends Object {

	// currently available HttpWorker objects
	private ObjectFIFO idleWorkers;

	// all HttpWorker objects
	private HttpWorker[] workerList;
	private ServerSocket ss;

	private Thread internalThread;
	private volatile boolean noStopRequested;

	public HttpServer(
				File docRoot,
				int port,
				int numberOfWorkers,
				int maxPriority
			) throws IOException {

		// Allow a max of 10 sockets to queue up 
		// waiting for accpet().
		ss = new ServerSocket(port, 10); 

		if ( ( docRoot == null ) || 
			 !docRoot.exists() || 
			 !docRoot.isDirectory() 
		   ) {

			throw new IOException("specified docRoot is null " +
				"or does not exist or is not a directory");
		}

		// ensure that at least one worker is created
		numberOfWorkers = Math.max(1, numberOfWorkers);

		// Ensure: 
		// (minAllowed + 2) <= serverPriority <= (maxAllowed - 1)
		// which is generally:
		//   3 <= serverPriority <= 9
		int serverPriority = Math.max(
				Thread.MIN_PRIORITY + 2, 
				Math.min(maxPriority, Thread.MAX_PRIORITY - 1)
			);

		// Have the workers run at a slightly lower priority so 
		// that new requests are handled with more urgency than 
		// in-progress requests.
		int workerPriority = serverPriority - 1;

		idleWorkers = new ObjectFIFO(numberOfWorkers);
		workerList = new HttpWorker[numberOfWorkers];

		for ( int i = 0; i < numberOfWorkers; i++ ) {
			// Workers get a reference to the FIFO to add 
			// themselves back in when they are ready to 
			// handle a new request.
			workerList[i] = new HttpWorker(
						docRoot, workerPriority, idleWorkers);
		}

		// Just before returning, the thread should be 
		// created and started.
		noStopRequested = true;

		Runnable r = new Runnable() {
				public void run() {
					try {
						runWork();
					} catch ( Exception x ) {
						// in case ANY exception slips through
						x.printStackTrace(); 
					}
				}
			};

		internalThread = new Thread(r);
		internalThread.setPriority(serverPriority); 
		internalThread.start();
	}

	private void runWork() {
		System.out.println(
				"HttpServer ready to receive requests");

		while ( noStopRequested ) {
			try {
				Socket s = ss.accept();

				if ( idleWorkers.isEmpty() ) {
					System.out.println(
						"HttpServer too busy, denying request");

					BufferedWriter writer = 
						new BufferedWriter(
							new OutputStreamWriter(
								s.getOutputStream()));
					
					writer.write("HTTP/1.0 503 Service " +
									"Unavailable\r\n\r\n");

					writer.flush();
					writer.close();
					writer = null;
				} else {
					// No need to be worried that idleWorkers 
					// will suddenly be empty since this is the 
					// only thread removing items from the queue.
					HttpWorker worker = 
							(HttpWorker) idleWorkers.remove();

					worker.processRequest(s);
				}
			} catch ( IOException iox ) {
				if ( noStopRequested ) {
					iox.printStackTrace();
				}
			} catch ( InterruptedException x ) {
				// re-assert interrupt
				Thread.currentThread().interrupt(); 
			}
		}
	}

	public void stopRequest() {
		noStopRequested = false;
		internalThread.interrupt();

		for ( int i = 0; i < workerList.length; i++ ) {
			workerList[i].stopRequest();
		}

		if ( ss != null ) {
			try { ss.close(); } catch ( IOException iox ) { }
			ss = null;
		}
	}

	public boolean isAlive() {
		return internalThread.isAlive();
	}

	private static void usageAndExit(String msg, int exitCode) {
		System.err.println(msg);
		System.err.println("Usage: java HttpServer <port> " +
							"<numWorkers> <documentRoot>");
		System.err.println("   <port> - port to listen on " +
							"for HTTP requests");
		System.err.println("   <numWorkers> - number of " +
							"worker threads to create");
		System.err.println("   <documentRoot> - base " +
							"directory for HTML files");
		System.exit(exitCode);
	}

	public static void main(String[] args) {
		if ( args.length != 3 ) {
			usageAndExit("wrong number of arguments", 1);
		}

		String portStr = args[0];
		String numWorkersStr = args[1];
		String docRootStr = args[2];

		int port = 0;

		try {
			port = Integer.parseInt(portStr);
		} catch ( NumberFormatException x ) {
			usageAndExit("could not parse port number from '" + 
					portStr + "'", 2);
		}

		if ( port < 1 ) {
			usageAndExit("invalid port number specified: " + 
					port, 3);
		}

		int numWorkers = 0;

		try {
			numWorkers = Integer.parseInt(numWorkersStr);
		} catch ( NumberFormatException x ) {
			usageAndExit(
					"could not parse number of workers from '" + 
					numWorkersStr + "'", 4);
		}

		File docRoot = new File(docRootStr);

		try {
			new HttpServer(docRoot, port, numWorkers, 6);
		} catch ( IOException x ) {
			x.printStackTrace();
			usageAndExit("could not construct HttpServer", 5);
		}
	}
}