One way in which database information can be displayed in a JSP is through the use of JavaBeans. What support do JSPs provide for JavaBeans with multi-value properties (for example a property called "Students" that returns a list of users)? Such values are often encountered in J2EE applications that pull records from a database. What are the different approaches you might take to display property values such as this in a page, and what problems could you possibly encounter?

The depth of the candidate's answer will show their familiarity with not only the JSP API, but also their general level of experience in working with data-driven J2EE applications. JSP's built in action tags do not provide the ability to access multiple values from a single property. The
< jsp:getProperty > tag can only access single, scalar bean properties such as a String or int value. To access multi-value properties, also known as indexed properties, the developer can employ one of several approaches.

The easiest, and most straightforward approach is to use scriptlets (in-line snippets of Java code) to loop through the property's values. This is the approach most JSP developers will be familiar with.

Another option is to use custom tags. Custom tags extend the JSP tag set to include such activities as iteration, and can deal with multi-value properties quite easily. A number of 3rd party tag libraries are available; including several good open source ones. One of the open source tag library projects, Jakarta-Taglibs, will become part of Sun's JSP Standard Tag Library. Alternatively, a developer may point out that they could write their own custom tags specific to the application in question. While this is often a good approach, it does require a higher degree of development skills.

A third approach that a creative candidate might propose is designing the beans such that they no longer have multi-value properties, such as by employing a cursor scheme where a bean uses a single property to rotate through all of the values.

An experienced candidate will point out that if the data is coming from a database, it may need to employ pagination strategies - exposing a subset of the results spread over several screens - in order to not overload the browser. Familiarity with the J2EE Page-by-Page Iterator (or Value List Handler) design pattern would help to indicate that the candidate is well versed in solving this problem.

About the author

Duane Fields is a Java developer, author, and Internet technologist with nearly a decade of professional experience in the design and development of leading edge Internet products and services. Duane is also a respected member of the Java development community and is frequently invited to speak at industry conferences and events. He has co-authored two books and published numerous articles on many aspects of web application development from Java to Relational Databases. The newly expanded, second edition of his best selling book "Web Development with JavaServer Pages" was released in December of 2001.