Working with variables by using c:set and c:remove actions
JSTL provides c:set action to allow you to init or set a variable of the web application in a specific scope. The usage of the c:set is as follows:
<c:set var = "variable"
value = "value"
scope = "scope" />
In the var attribute you can declare or refer to a variable. The value attribute specify the value of the variable. If you want to set the scope of the varible, you can use the scope attribute. The scope attribute accepts any valid JSP variable scopes such as page, request, session and application. Let's take a look at an example of using c:set action.
<c:set var = "userid"
value = "10"
scope = "session" />
<c:out value="${userid}" />
In the example, we set the variable userid to 10 with the session scope. Then we print it out using c:out action.
The other usage of c:set action is used to set the value of a property of an object:
<c:set target= "object"
property = "property name"
value = "value of property" />
You assign object to the target attribute, property name to the property attribute and value of that property in the value attribute. Let's take a look at an example of using c:set for setting property of an object.
package com.jsptutorial;
public class Person {
private String firstName;
private String lastName;
public Person() {
this.firstName = "";
this.lastName = "";
}
/**
* @return the firstName
*/
public String getFirstName() {
return firstName;
}
/**
* @param firstName the firstName to set
*/
public void setFirstName(String firstName) {
this.firstName = firstName;
}
/**
* @return the lastName
*/
public String getLastName() {
return lastName;
}
/**
* @param lastName the lastName to set
*/
public void setLastName(String lastName) {
this.lastName = lastName;
}
}
In the above code we have a person class. We will use this person class as a JavaBean in a JSP page.
<%@page contentType="text/html"
pageEncoding="UTF-8"
import="com.jsptutorial.*"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core"
prefix="c" %>
<html>
<head>
<title>JSTL demo</title>
</head>
<body>
<jsp:useBean id="person"
class="com.jsptutorial.Person" />
<c:set target="${person}"
property="firstName"
value="Jack" />
<c:set target="${person}"
property="lastName"
value="Daniel" />
<c:out value="${person.fullName}" />
</body>
</html>
In the code above, we use standard action useBean to initialize an object person. Then we use c:set to set the firstName and lastName property of that object. finally we output the fullName of that object person to the web browser. Be noted that in the target attribute, only object not object name is accepted therefore you should never forget the expression ${object_name}
Beside c:set action, JSTL also provides c:remove action to allow you to remove a variable from a particular scope. The usage of c:remove is as follows:
<c:remove var = "variable name"
scope = "scope" />
For example, if you want to remove the userid session variable you can use c:remove below:
<c:remove var="userid" scope="variable" />