J2EE Bad Practices: Non-serializable Object Stored in Session

Description

A J2EE application can make use of multiple JVMs in order to improve application reliability and performance. In order to make the multiple JVMs appear as a single application to the end user, the J2EE container can replicate an HttpSession object across multiple JVMs so that if one JVM becomes unavailable another can step in and take its place without disrupting the flow of the application. This is only possible if all session data is serializable, allowing the session to be duplicated between the JVMs.

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

The following class adds itself to the session, but because it is not serializable, the session can no longer be replicated.

public class DataGlob {

  String globName;
  String globValue;

  public void addToSession(HttpSession session) {
    session.setAttribute("glob", this);
  }

}

See Also