Using Java Beans in JSP
How is Beans used in JSP?
Explanation
Java bean is nothing but a class that implements java.io.Serializable interface and uses set/get methods to project its properties. Since they are reusable instance of a class Java beans provides the flexibility to JSP pages.
There are three basic actions or tags used to embedd a java bean into a jsp page they are <jsp:useBean>, <jsp:setProperty>, <jsp:getProperty>.
This tag is used to associate a bean with the given "id" and "scope" attributes.
This tag is used to set the value for a beans property mainly with the "name" attribute which defines a object already defined with the same scope. Other attributes are "property", "param", "value"
This tag is used to get the referenced beans instance property and stores in implicit out object.
package pack;
public class Counter
{
int count = 0;
String name;
public Counter() { }
public int getCount()
{
return this.count;
}
public void setCount(int count){
this.count = count;
} public String getName(){
return this.name; } public void setName(String name){
this.name=name; }
}
<%@ page language="java" %>
<%@ page import="pack.Counter" %>
</body>
<jsp:useBean id="counter" scope="page" class="pack.Counter" />
<jsp:setProperty name="counter" property="count" value="4" />
Get Value: <jsp:getProperty name="counter" property="count" /><BR>
<jsp:setProperty name="counter" property="name" value="prasad" />
Get Name: <jsp:getProperty name="counter" property="name" /><BR>
In the above examples the bean that is being included is Counter.java, that has defined the set/get properties for the "counter", "name" objects. Using the bean.jsp page first the bean is included using the <jsp:useBean> action, using the <jsp;setProperty> we set the property of "counter" to "4" and for "name" it set to "prasad". With the <jsp:getProperty> we get the values.
There are three basic actions or tags used to embedd a java bean into a jsp page they are <jsp:useBean>, <jsp:setProperty>, <jsp:getProperty>.
<jsp:useBean>
This tag is used to associate a bean with the given "id" and "scope" attributes.
<jsp:setProperty>
This tag is used to set the value for a beans property mainly with the "name" attribute which defines a object already defined with the same scope. Other attributes are "property", "param", "value"
<jsp:getProperty>
This tag is used to get the referenced beans instance property and stores in implicit out object.
Rules for Beans:
- Package should be first line of Java bean
- Bean should have an empty constructor
- All the variables in a bean should have "get", "set" methods.
- The Property name should start with an Uppercase letter when used with "set", "get" methods.
- For example the variable "name" the get, set methods will be getName(), setName(String)
- Set method should return a void value like "return void()"
Example :
package pack;
public class Counter
{
int count = 0;
String name;
public Counter() { }
public int getCount()
{
return this.count;
}
public void setCount(int count){
this.count = count;
} public String getName(){
return this.name; } public void setName(String name){
this.name=name; }
}
Example 2 :
<%@ page language="java" %>
<%@ page import="pack.Counter" %>
</body>
<jsp:useBean id="counter" scope="page" class="pack.Counter" />
<jsp:setProperty name="counter" property="count" value="4" />
Get Value: <jsp:getProperty name="counter" property="count" /><BR>
<jsp:setProperty name="counter" property="name" value="prasad" />
Get Name: <jsp:getProperty name="counter" property="name" /><BR>
In the above examples the bean that is being included is Counter.java, that has defined the set/get properties for the "counter", "name" objects. Using the bean.jsp page first the bean is included using the <jsp:useBean> action, using the <jsp;setProperty> we set the property of "counter" to "4" and for "name" it set to "prasad". With the <jsp:getProperty> we get the values.
