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




JSP Web Hosting JavaServer Pages Specifications JSP Hosting




 
TotalRoute.net Business web hosting division of Vision Web Hosting Inc. All rights reserved.