J2EE Bad Practices: Direct Use of Threads

Description

Thread management in a web application is forbidden by the J2EE standard in some circumstances and is always highly error prone. Managing threads is difficult and is likely to interfere in unpredictable ways with the behavior of the application container. Even without interfering with the container, thread management usually leads to bugs that are hard to detect and diagnose like deadlock, race conditions, and other synchronization errors.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

In the following example, a new Thread object is created and invoked directly from within the body of a doGet() method in a Java servlet.

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


  // Perform servlet tasks.
  ...

  // Create a new thread to handle background processing.
  Runnable r = new Runnable() {

    public void run() {


      // Process and store request statistics.
      ...

    }

  };

  new Thread(r).start();

}

See Also