Head First Servlets and JSP, 2nd Edition

Bean-related standard action review

Bullet Points

• The <jsp:useBean> standard action defines a variable that holds a reference to either an existing bean attribute or, if the bean doesn’t already exist, a new bean.

• The <jsp:useBean> MUST have an “id” attribute which declares the variable name that’ll be used in this JSP to refer to the bean.

• If you don’t include a “scope” attribute with <jsp:useBean>, the scope defaults to page scope.

• The “class” attribute is optional, and it declares the class type that will be used if a new bean is created. The type must be public, non-abstract, and have a public no-arg constructor.

• If you put a “type” attribute in <jsp:useBean>, it must be a type to which the bean can be cast.

• If you have a “type” attribute but do NOT have a “class” attribute, the bean must already exist, since you haven’t specified the class type that should be instantiated for the new bean.

• The <jsp:useBean> tag can have a body, and anything in the body runs ONLY if a new bean is created as a result of <jsp:useBean> (which means that no bean with that “id” was found in the specified (or default) scope).

• The main purpose of the body of <jsp:useBean> is to set the new bean’s properties, using <jsp:setProperty>.

• <jsp:setProperty> must have a name attribute (which will match the “id” from <jsp:useBean>), and a “property” attribute. The “property” attribute must be either an actual property name or the wildcard “*”.

• If you don’t include a “value” attribute, the Container will set the property ...