Recipe 23.10 Accessing Request Parameters with the EL

Problem

You want to access a request parameter using the EL in a JSP.

Solution

Use the param implicit object in your JSP code.

Discussion

The JSTL provides an implicit object named param that you can use to get a request parameter. Simply follow the term "param" with a period and the parameter name . Use this terminology with the EL to output the value of a request parameter with the c:out tag. Example 23-11 displays a greeting with the visitor's name. The request might look like:

 http://localhost:8080/home/welcome.jsp?name=Bruce%20Perry

If the URL does not include the "name" parameter, the JSP displays the message "Hello Esteemed Visitor."

Example 23-11. Using the JSTL in a JSP to display the result of a request parameter

  <%@ taglib uri="http://java.sun.com/jstl/core" prefix="c" %>  <html> <head><title>Accessing a Scoped Value</title></head> <body> <h2>Hello  <c:choose> <c:when test="${empty param.name}">  Esteemed Visitor  </c:when> <c:otherwise> <c:out value="${param.name}" /> </c:otherwise> </c:choose>  </h2> </body> </html>

The code tests whether the request contains a value for name by using the empty EL keyword:

 <c:when test="${empty param.name}">

The c:choose , c:when , and c:otherwise tags are like if/then/else statements in Java code. If the request parameter name does not have a value, the browser will display "Esteemed Visitor". Otherwise, it displays the value of name .

Figure 23-6 shows a JSP displaying the message, including the parameter value.

Figure 23-6. Humble output of a JSP using the param JSTL implicit object