Java Server Pages

Creating New Variables Through Actions

Actions can also 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 <jspUseBean> 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 defines that an attribute named id typically is used to name a variable created by an action.^[8] The value of the id attribute must be unique within the page. Because 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. The 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.

When a custom action creates a variable, it must cooperate with the JSP container to make it happen. To understand how this works, recall that the JSP page is turned into ...