JavaServer Pages Pocket Reference

Actions Creating Objects

Actions can cooperate through objects available in the standard JSP scopes (page, request, session, and application). One example of this type of cooperation is illustrated by the three standard JSP actions: <jsp:useBean>, <jsp:setProperty>, and <jsp:getProperty>. The <jsp:useBean> action creates a new object and makes it available in one of the JSP scopes. The other two actions can then access the properties of the object by searching for it in the scopes. Besides making the object available in one of the scopes, the <jsp:useBean> action also makes it available as a scripting variable, so it can be accessed by scripting elements in the page.

The JSP 1.1 specification states that an attribute named id must be used to name a variable created by an action. The value of the id attribute must be unique within the page. Since it’s used as a scripting variable name, it must also follow the variable-name rules for the scripting language. For Java, this means it must start with a letter followed by a combination of letters and digits and must not contain special characters, such as a dot or a plus sign. An attribute used in another action to refer to the variable can be named anything, but the convention established by the standard actions is to call it name.

To create a scripting variable, a custom action must cooperate with the web container. To understand how this works, recall that the JSP page is turned into a servlet by the web container. First, the container ...