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New features added to Servlet 2.5

Servlets updated with annotations, web.xml conveniences, and more

By Jason Hunter, JavaWorld.com, 01/02/06

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Page 5 of 5

Still on the wish list

Because of the maintenance review nature of the Servlet 2.5 release, several larger ideas had to be postponed until the next review phase. Among the ideas postponed:

  • New Input/Output (NIO) support: It's possible NIO Channels would be a more efficient way for servlets to communicate with clients.
  • Filter wrap-under or wrap-over semantics: People sometimes use filters to wrap the request and/or response objects to alter method behavior or expose new methods. When this wrapping is combined with a server's need to wrap the request and response as part of a request dispatch, how do the wraps fit together?
  • Servlets as welcome files: Should an index.do be able to act as a welcome file? Historically, the answer has been yes. But the specification doesn't clarify how to allow that functionality, especially if no index.do is on the filesystem, but a *.do mapping is, which would always exist virtually and shadow other welcome files.
  • Welcome file dispatch rules: The details on how to dispatch to welcome files have not been exhaustively specified and leave open cracks for incompatibility.
  • Selecting a default page after login: If users visit a servlet's form-based login page from their bookmarks, where should they be sent after a successful login? It's unspecified today.
  • Programmatically log in a user: Right after a user registers with a site, there's no way to inform the servlet environment about the user's credentials without the user performing a traditional login.

Update: March 6, 2006

After this article was first published, Sun issued a Servlets 2.5 MR2 (second manufacturing release) that includes a few changes from the first manufacturing release:

  • The attribute full on the <web-app> root was renamed to the more descriptive metadata-complete. This change has been incorporated into the above text.
  • A new method getContextPath() was added to ServletContext. Formerly context path information was only available in the request object, following the logic that the same context object might be bound to multiple paths so you'd only know the path at request time. However, no known servers have utilized the multiple path binding option, and a context being able to report its path is often convenient, so the method got the green light. Should it ever happen that a context be bound to multiple paths, it will return its "preferred" path.


Conclusion

If you look at the Servlet 2.5 changes apart from annotations, the new release does a nice job of giving web.xml a little syntactic sugar, of removing a few restrictions that were getting in the way, and of clarifying edge case behavior to enable more powerful and portable component-based Webpages.

The effect of annotations in Servlet 2.5 looks more dramatic. It's important to remember that servlets themselves don't define any new annotation types, and simple servlet containers don't even have to support annotations. Yet servlets authored for a JEE 5 environment will see their code change a lot from the annotation types introduced by common annotations and the EJB 3.0 and JAX-WS 2.0 specifications, and these will have a big impact on how servlets manage external resources, object persistence, and EJB components.

About the author

Jason Hunter is author of the book Java Servlet Programming, 2nd Edition (O'Reilly, 2001; ISBN: 0596000405) and coauthor of Java Enterprise Best Practices (O'Reilly, 2002; ISBN: 0596003846). He's an Apache Member and, as Apache's representative to the Java Community Process Executive Committee, he established a landmark agreement for open source Java. He's publisher of Servlets.com, an original contributor to Apache Tomcat, and cocreated the open source JDOM library to enable optimized Java and XML integration. He also designed and developed CountryHawk, a product that quickly determines a user's country based on their IP address.

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