j2ee: Using JavaBeans in JSPs [17/20]

Declaring the Bean

<jsp:useBean> action

Locates or instantiates a bean with a specified name and scope.

Syntax:

        <jsp:useBean id="name" scope="page|request|session|application" typeSpec />
        
        typeSpec ::= class="className" |
        class="className" type="typeName" |
        type="typeName" class="className" |
        beanName="beanName" type="typeName" |
        type="typeName" beanName="beanName" |
        type="typeName" 
        

class must be assignable to type if both are declared

If the useBean has a body, it is of the form:

        <jsp:useBean id="name" scope="page|request|session|application" typeSpec >
        body
        </jsp:useBean>
        

The body will be invoked if the Bean is created.

Typically, the body will contain either scriptlets or jsp:setProperty tags that will modify the object created in the useBean tag

The contents of the body are not restricted.

Semantics:

1. Attempt to locate a bean based on id and scope.
2. Define a variable with the given id in the current scope of the specified type or class.
3. If the bean is found in the specified scope
   • The variable is initialized with a reference to the bean
   • End of action. The body is skipped.
4. If the bean is not found in the specified scope
   • Instantiate a new instance of bean using either the specified class or beanName.
   • The variable is initialized with a reference to the newly instantiated bean.
   • If the <jsp:useBean> element has a non-empty body, the body is processed.