Ans: This was very popular JSP interview question during early 2000, it has lost some of its shine but still asked now and then on interviews.

JSP Syntax

<jsp:useBean
id="beanInstName"
scope="page  |  request  |  session  |  application"
class="package.class"  type="package.class"
</jsp:useBean>

This tag is used to create an instance of java bean, first of all, it tries to find out the bean if bean instance already exists assign stores a reference to it in the variable. If we specified the type, gives the Bean that type.otherwise instantiates it from the class we specify, storing a reference to it in the new variable.so jsp:usebean is a simple way to create a java bean.

Example:

<jsp:useBean id="stock" scope="request" class="market.Stock" />

<jsp:setProperty name="bid" property="price" value="0.0" />

a <jsp:useBean> element contains a <jsp:setProperty> 
element that sets property values in the Bean, we hava <jsp:getProperty>
element also get the value from the bean.

Explanation of Attribute:

id = "beanInstanceName"
A variable that identifies the Bean in the scope we specify. If the Bean has already been created by another < jsp:useBean > element, the value of id must match the value of id used in the original < jsp:useBean > element.

scope="page | request | session | application"

The scope in which the Bean exists and the variable named in id is available. The default value is page. The meanings of the different scopes are shown below:

class="package.class"
Instantiates a Bean from a class, using the new keyword and the class constructor. The class must not be abstract and must have a public, no-argument constructor.

type="package.class"

If the Bean already exists in the scope, gives the Bean a data type other than the class from which it was instantiated. If you use type without class or beanName, no Bean is instantiated.