bean
Tag define

Define a scripting variable based on the value(s) of the specified bean property.

Create a new attribute (in the scope specified by the toScope property, if any), and a corresponding scripting variable, both of which are named by the value of the id attribute. The corresponding value to which this new attribute (and scripting variable) is set are specified via use of exactly one of the following approaches (trying to use more than one will result in a JspException being thrown):

• Specify a name attribute (plus optional property and scope attributes) - The created attribute and scripting variable will be of the type of the retrieved JavaBean property, unless it is a Java primitive type, in which case it will be wrapped in the appropriate wrapper class (i.e. int is wrapped by java.lang.Integer).
• Specify a value attribute - The created attribute and scripting variable will be of type java.lang.String, set to the value of this attribute.
• Specify nested body content - The created attribute and scripting variable will be of type java.lang.String, set to the value of the nested body content.

If a problem occurs while retrieving the specified bean property, a request time exception will be thrown.

The <bean:define> tag differs from <jsp:useBean> in several ways, including:

• Unconditionally creates (or replaces) a bean under the specified identifier.
• Can create a bean with the value returned by a property getter of a different bean (including properties referenced with a nested and/or indexed property name).
• Can create a bean whose contents is a literal string (or the result of a runtime expression) specified by the value attribute.
• Does not support nested content (such as <jsp:setProperty> tags) that are only executed if a bean was actually created.

USAGE NOTE - There is a restriction in the JSP 1.1 Specification that disallows using the same value for an id attribute more than once in a single JSP page. Therefore, you will not be able to use <bean:define> for the same bean name more than once in a single page.

USAGE NOTE - If you use another tag to create the body content (e.g. bean:write), that tag must return a non-empty String. An empty String equates to an empty body or a null String, and a new scripting variable cannot be defined as null. Your bean must return a non-empty String, or the define tag must be wrapped within a logic tag to test for an empty or null value.

USAGE NOTE - You cannot use bean:define to instantiate a DynaActionForm (type="org.apache.struts.action.DynaActionForm") with the properties specified in the struts-config. The mechanics of creating the dyna-properties is complex and cannot be handled by a no-argument constructor. If you need to create an ActionForm this way, you must use a conventional ActionForm.

See the Bean Developer's Guide section on bean creation for more information about these differences, as well as alternative approaches to introducing beans into a JSP page.