Chapter 16. Using Scripting Elements

Before reading this book, you may have heard that JSP is all about including Java code in web pages. If so, you may wonder why you haven't seen any Java code in the examples so far. That's because there's really no reason to embed raw Java code in JSP pages anymore. With JSP 1.0, it was the only way to do anything interesting. JSP 1.1 removed most reasons by introducing custom actions, but many developers figured developing custom actions for simple conditionals and loops was not worth the trouble and continued to embed Java code snippets for these things. Even with JSP 1.2, you still had to use Java code to assign dynamic values to JSP action element attributes, but JSTL 1.0 (and the EL it introduced) removed these excuses for most cases. With JSP 2.0, where the EL is part of the JSP specification so it can be used for all attributes and the greatly simplified mechanisms for developing custom actions, there are really no good reasons for embedding Java in your JSP pages.

JSP continues to support the scripting elements for putting code in JSP pages—even though their use is now discouraged—because all Java specifications go to great lengths to be backward compatible. There are three types of scripting elements: scriptlets for a block of code to be executed, expressions for a single statement to be evaluated with its result added to the response, and declarations for declaring variables and methods. In this chapter we look at how to use all of them, and the type of problems you should be prepared to encounter if you do.

Because using scripting elements means writing Java code, you should know how to program in Java before you read this chapter. If you don't know Java programming, my advice is that you steer clear from the scripting elements altogether and use the EL, JSTL and other custom actions exclusively.