Why use jsp:useBean?

Question

I got the below sample code in sun document. Here bookId is passed as a parameter in cart.remove method and sql query. I want to know why the statement "<jsp:useBean id="bookId" type="java.lang.String" /> " is used.
<c:set var="bookId" value="${param.Remove}"/>
<jsp:useBean id="bookId" type="java.lang.String" />
<% cart.remove(bookId); %>
<sql:query var="books"
dataSource="${applicationScope.bookDS}">
select * from PUBLIC.books where id = ?
<sql:param value="${bookId}" />
</sql:query>
thanks,
Vinodh

Answer 1

The useBean tag has a side effect of creating a local scriptlet variable with the id "bookId"
This variable is then used on the next line in the scriptlet code.
In effect, it is executing the following code
<c:set var="bookId" value="${param.Remove}"/>
<%
String bookId = (String)pageContext.findAttribute("bookId");
cart.remove(bookId); %>which if you think about it, you could get rid of the <c:set> and have the scriptlet code access the variable directly.
<%
String bookId = request.getParameter("Remove");
cart.remove(bookId); %>Mixing scriptlet and JSTL code in this fashion gets confusing.
The scriptlet code here is part of the 1% of code that can't be replaced directly by JSTL (but could be replaced by a custom function/tag)
However it more probably belongs in a servlet/bean.