Setting and Getting JavaBean's Properties

JSP Tutorials - Herong's Tutorial Examples

∟JavaBean Objects and "useBean" Action Elements

∟Setting and Getting JavaBean's Properties

This section provides a tutorial example on how to use 'setProperty' and 'getProperty' action elements to to save and retrieve values of JavaBean properties.

As you can see from previous sections, a JavaBean is just a regular Java object. Once a JavaBean is created in a JSP, you can use JSP setProperty and getProperty action elements to set and retrieve values of its properties. To support these action elements, a JavaBean class must implement set and get methods based on some rules.

In this section, let's look at some of the basic rules about setting and getting JavaBean properties:

The setProperty element must be supported by at least one set method in the JavaBean class.
The set method name must be the property name with the first lower case letter being translated to upper case, and prefixed with "set". For example, "setAuthor" is a good method name to support the setProperty action element for property name "author".
The return type of the set method should be void.
The set method should take only one input parameter.
If there are multiple set methods, there must be one that takes String as the input parameter type, and this will be the one to be used by the setProperty action element.
If there is only one set method, the input parameter type should be a primitive type.
The get method name must be the property name with the first lower case letter being translated to upper case, and prefixed with "get". For example, "getAuthor" is a good method name to support the getProperty action element for property name "author".
The get method should take no input parameter.
The return type of the get method can be String or any primitive type.
JavaBean property names must be started with a lower case letter.

To validate above rules, I wrote the following sample JavaBean class:

/* DemoBean.java
 * Copyright (c) 2002 HerongYang.com. All Rights Reserved.
 */
package herong;
public class DemoBean {
   private String author = "Herong";
   private int count = 0;
   private boolean status = true;
   private String total = "1";
   private String size = "2";
   public void setAuthor(String a) {
      author = a;
   }
   public String getAuthor() {
      return author;
   }
   public void setCount(int c) {
      count = c;
   }
   public int getCount() {
      return count;
   }
   public void setStatus(boolean s) {
      status = s;
   }
   public boolean getStatus() {
      return status;
   }
   public void setTotal(int t) {
      total = "int: "+t;
   }
   public void setTotal(double t) {
      total = "double: "+t;
   }
   public String getTotal() {
      return total;
   }
   public void setSize(int s) {
      size = "int: "+s;
   }
   public void setSize(String s) {
      size = "String: "+s;
   }
   public String getSize() {
      return size;
   }
   public void setX(String x) {
      author = x;
   }
   public String getY() {
      return author;
   }
}

Compile this JavaBean code and deploy the class file to the Tomcat class folder:

herong> javac herong\DemoBean.java

herong> xcopy herong \local\tomcat\webapps\ROOT\WEB-INF\classes\herong

Now we are ready to test this JavaBean with a JSP page, DemoBean.jspx:

<?xml version="1.0"?>
<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="2.3">
<!-- DemoBean.jspx
 - Copyright (c) 2006 HerongYang.com. All Rights Reserved.
-->
<jsp:directive.page contentType="text/html"/>
<html><body>
<jsp:useBean id="b" class="herong.DemoBean"/>
<jsp:setProperty name="b" property="author" value="Nobody"/>
Line 1: author =
<jsp:getProperty name="b" property="author"/><br/>
<!-- <jsp:getProperty name="b" property="Author"/><br/> -->
<!-- <jsp:getProperty name="b" property="AUTHOR"/><br/> -->

<jsp:setProperty name="b" property="status" value="false"/>
Line 2: status =
<jsp:getProperty name="b" property="status"/><br/>

<jsp:setProperty name="b" property="count" value="5"/>
Line 3: count =
<jsp:getProperty name="b" property="count"/><br/>

<!-- <jsp:setProperty name="b" property="total" value="9"/> -->
Line 4: total =
<jsp:getProperty name="b" property="total"/><br/>

<jsp:setProperty name="b" property="size" value="14"/>
Line 5: size =
<jsp:getProperty name="b" property="size"/><br/>

<jsp:setProperty name="b" property="x" value="Herong"/>
Line 6: size =
<jsp:getProperty name="b" property="y"/><br/>
</body></html>
</jsp:root>

Deploy this JSP to Tomcat server. Then open this JSP page with a Web browser, you will get:

Line 1: author = Nobody
Line 2: status = false
Line 3: count = 5
Line 4: total = 1
Line 5: size = String: 14
Line 6: y = Herong

Note that:

Property names are case sensitive. Property name "Author" can not be mapped to "getAuthor" method.
For the "total" property, I have two set methods. But none of them is taking String as the input parameter. So the "setProperty" action element will not work on "total".
For the "size" property, I also have two set methods. But one of them is taking String as the input parameter. So the "setProperty" action element will work on "size". Output line 5 is the proof.