Java cleanup code

Java shutdown hook guarantee that clean-up code is always run, regardless of how the user terminates the application.

Here is an example from Hadoop:

java 代码

/**
 * A class to track the list of DFS clients, so that they can be closed
 * on exit.
 * @author Owen O'Malley
 */
private static class ClientFinalizer extends Thread {
  private List clients = new ArrayList();

  public synchronized void addClient(DFSClient client) {
    clients.add(client);
  }

  public synchronized void run() {
    Iterator itr = clients.iterator();
    while (itr.hasNext()) {
      DFSClient client = (DFSClient) itr.next();
      if (client.running) {
        try {
          client.close();
        } catch (IOException ie) {
          System.err.println("Error closing client");
          ie.printStackTrace();
        }
      }
    }
  }
}

// add a cleanup thread
private static ClientFinalizer clientFinalizer = new ClientFinalizer();
static {
  Runtime.getRuntime().addShutdownHook(clientFinalizer);
}

Elegant and useful!!!