Recipe 7.3 Setting the Properties of a JavaBean in a JSP


Problem

You want to set a JavaBean's properties to the values entered in a form.

Solution

Use the jsp:setProperty standard action, with its property attribute set to "*" and its class attribute set to the fully qualified class name of the JavaBean.

Discussion

The jsp:setProperty standard action has a built-in method for automatically mapping the values submitted in a form to a JavaBean's fields or variables . The names of the submitted parameters have to correspond to the names of the JavaBean's setter methods . Example 7-5 shows a setBean.jsp page that receives data from an HTML form:

 <form method=post action="http://localhost:8080/home/setBean.jsp"> 

The JSP first instantiates an object of the type com.jspservletcookbook.UserBean using jsp:useBean . Then it sets the properties of the bean using jsp:setProperty . The name attribute of jsp:setProperty matches the id attribute of jsp:useBean . The property attribute of jsp:setProperty is simply set to "*".

Example 7-5. beanSet.jsp JSP that sets the UserBean's properties with form input
 <%@page contentType="text/html"%> <%@ taglib uri="http://java.sun.com/jstl/core" prefix="c" %>  <jsp:useBean id="userB" class="com.jspservletcookbook.UserBean" > <jsp:setProperty name="userB" property="*" /> </jsp:useBean>  <html> <head><title>Post Data Viewer</title></head> <body> <h2>Here is your posted data</h2>     <strong>User name</strong>:      <c:out value="${userB.username}" /><br><br>       <strong>Department</strong>:      <c:out value="${userB.department}" /><br><br>      <strong>Email</strong>:  <c:out value="${userB.email}" />  </body> </html> 

Example 7-5 uses the c:out element of the JSTL to display the bean's various values in a browser page. The value attribute of c:out uses the EL to acquire a property value, as in "${userB.email}". This syntax is the equivalent of calling the UserBean's getEmail( ) method. Example 7-6 shows the UserBean , which uses the JavaBean naming conventions to ensure that its properties can be properly set and accessed. Figure 7-3 shows the browser display of the values.

Figure 7-3. Displaying form input via a JavaBean
figs/jsjc_0703.gif

The jsp:setProperty action, as used in this recipe, sets the JavaBean's properties by using introspection to line up parameter names with the bean's setter methods. If the bean has a field named "Username," then the parameter name must be exactly "Username" and the setter method must be exactly "setUsername( String name )" (if the bean's field is a String ). Watch out, it's case-sensitive!


Example 7-6. Encapsulating the posted data in a JavaBean
 package com.jspservletcookbook; public class UserBean implements java.io.Serializable{ String username; String email; String department; public UserBean( ){} public void setUsername(String _username){     if(_username != null && _username.length( ) > 0)         username = _username;     else          username = "Unknown"; } public String getUsername( ){     if(username != null)         return username;     else         return "Unknown";} public void setEmail(String _email){      if(_email != null && _email.length( ) > 0)         email = _email;     else          email = "Unknown"; } public String getEmail( ){  if(_email != null)         return email;     else         return "Unknown";} public void setDepartment(String _department){      if(_department != null && _department.length( ) > 0)         department = _department;     else          department = "Unknown"; } public String getDepartment( ){     if(department != null)         return department;     else         return "Unknown";  } } 

Recipe 7.4 shows how to use a bean to validate form input, then set a scoped attribute to the input.

See Also

Recipe 7.2 on handling a POST request in a JSP; Recipe 7.4 on setting a scoped attribute to the value of a parameter; Recipe 7.6 on posting data from a JSP; Chapter 23 on using the JSTL.



Java Servlet & JSP Cookbook
Java Servlet & JSP Cookbook
ISBN: 0596005725
EAN: 2147483647
Year: 2004
Pages: 326

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