2.13

Standard Actions

The JSP 1.1 specification defines some standard action types that are always available, 

regardless of the version of the JSP container or Web server the developer uses. The standard 

action types are in addition to any custom types specific to a given JSP container 

implementation.

2.13.1

A

 jsp:useBean

 action associates an instance of a Java programming language object 

defined within a given 

scope

 available with a given 

id 

via a newly declared scripting 

variable of the same 

id

.

The 

jsp:useBean

 action is quite flexible; its exact semantics depends on the attributes 

given.  The basic semantic tries to find an existing object using 

id

 and 

scope

; if it is not 

found it will attempt to create the object using the other attributes.  It is also possible to use 

this action only to give a local name to an object define elsewhere, as in another JSP page or 

in a Servlet; this can be done by using the 

type

 attribute and not providing neither 

class

nor 

beanName

 attributes.

At least one of 

type

 and 

class

 must be present, and it is not valid to provide both 

class

and 

beanName

. If 

type

 and 

class

 are present, 

class

 must be assignable (in the Java 

platform sense) to 

type; 

failure to do so is a translation time error.

The attribute 

beanName

 is the name of a Bean, as specified in the JavaBeans specification 

for an argument to the instantiate() method in java.beans.Beans. I.e. it is of the form  a.b.c , 

which may be either a class, or the name of a resource of the form  a/b/c.ser  that will be 

resolved in the current ClassLoader. If this is not true, a request time exception, as indicated 

in the semantics of instantiate() will be raised. The value of this attribute can be a request 

time attribute expression.

The actions performed are:

1. Attempt to locate an object based on the attribute values (

id,

scope

). The inspection is 

done appropriately synchronized per scope namespace to avoid non deterministic 

behavior.

2.  Define a scripting language variable with the given 

id

 in the current lexical scope of the 

scripting language of the specified 

type

 (if given) or 

class

 (if type is not given).

3.  If the object is found, the variable's value is initialized with a reference to the located 

object, cast to the specified 

type

. If the cast fails, a 

java.lang.ClassCastException

 shall occur. This completes the processing of 

this 

useBean

 action.

61

JavaServer Pages 1.1 Specification  

November 30, 1999