jsp:useBean

The jsp:useBean Action This action load in a JavaBean to be used in the JSP page. The simplest syntax for specifying that a bean should be used is:

<jsp:useBean id="name" class="package.class" />

This usually means "instantiate an object of the class specified by class, and bind it to a variable with the name specified by id." You can specify a scope attribute that makes the bean associated with more than just the current page. In that case, it is useful to obtain references to existing beans, and the jsp:useBean action specifies that a new object is instantiated only if there is no existing one with the same id and scope. Now, once you have a bean,you can modify its properties via jsp:setProperty, or by using a scriptlet and calling a method explicitly on the object with the variable name specified earlier via the id attribute. You read existing properties in a JSP expression or scriptlet by calling the appropriate getYYY method, or more commonly, by using the jsp:getProperty action.

Here is a very simple example that loads a bean and sets/gets a simple String parameter.

test.jsp

<HTML>
<HEAD>
<TITLE> JavaBeans in JSP</TITLE>
</HEAD>
<BODY>
<jsp:useBean id="test" class="com.EmpBean" />
<jsp:setProperty name="test" property="name" value="Das" />
Name is : <jsp:getProperty name="test" property="name" />
</BODY>
</HTML>
Output is :
Name is : Das

EmpBean.java

Here's the source code for the bean used in the test.jsp page. package com;
public class EmpBean {
private String name = "";
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
The below code
<jsp:useBean id="test" class="com.EmpBean" />
is equivalent to
com.EmpBean test = new com.EmpBean();
and
<jsp:setProperty name="test" property="name" value="Das" />
is equivalent to
test.setName("Das"); and
<jsp:getProperty name="test" property="name" />
is equivalent to
out.println(test.getName());

Atribute	Usage
`id`	Gives a name to the variable that will reference the bean. A previous bean object is used instead of instantiating a new one if one can be found with the same `id` and `scope`.
`class`	Designates the full package name of the bean.
`scope`	Indicates the context in which the bean should be made available. There are four possible values: `page`, `request`, `session`, and `application`. The default, `page`, indicates that the bean is only available on the current page (stored in the `PageContext` of the current page). A value of `request` indicates that the bean is only available for the current client request (stored in the `ServletRequest` object). A value of `session` indicates that the object is available to all pages during the life of the current `HttpSession`. Finally, a value of `application` indicates that it is available to all pages that share the same `ServletContext`. The reason that the scope matters is that a `jsp:useBean` entry will only result in a new object being instantiated if there is no previous object with the same `id` and `scope`. Otherwise the previously existing object is used, and any `jsp:setParameter` elements or other entries between the `jsp:useBean` start and end tags will be ignored.
`type`	Specifies the type of the variable that will refer to the object. This must match the classname or be a superclass or an interface that the class implements. Remember that the name of the variable is designated via the `id` attribute.
`beanName`	Gives the name of the bean, as you would supply it to the `instantiate` method of `Beans`. It is permissible to supply a `type` and a `beanName`, and omit the `class` attribute.