Jsp Parameter Standard Actions

Consider the following code : (an Employee is a Person who has an empID)
public class Person { private String name; public Person() { super(); } public String getName() { return name; } public void setName(String name) { this.name = name; } } public class Employee extends Person { private String empID; public Employee() { super(); } public String getEmpID() { return empID; } public void setEmpID(String id) { empID = id; } }

Both JSP's standard actions getParameter and setParameter use introspection to find the getter/setter of a property, so accessing the following page displays the employee's id correctly, even if the bean is a Person:

http://localhost:8080/jspaction/getter.jsp?name=doraemon&empID=12345 <jsp:useBean id="per" type="bean.Person" class="bean.Employee" scope = "page"> <jsp:setProperty name="per" property = "*"/> </jsp:useBean> Person Name:<jsp:getProperty name="per" property="name"/> Employee ID:<jsp:getProperty name="per" property="empID"/>

The following code illustrates what introspection is :
public class Reflection { public static void main(String[] args) { // Notice that per is a Person here Person per = new Employee(); // display all methods try { BeanInfo beanInfo = Introspector.getBeanInfo(per.getClass()); MethodDescriptor[] methodDescriptors = beanInfo.getMethodDescriptors(); for ( int i = 0; i < methodDescriptors.length; i++ ) { Method method = methodDescriptors[i].getMethod(); System.out.println("Method : " + method.getName() ); } } catch ( IntrospectionException e ) { e.printStackTrace(); } // another test Method[] methods = per.getClass().getMethods(); for ( int i = 0; i < methods.length; i++ ) { System.out.println("ClassMethod : " + methods[i].getName() ); } // another test try { PropertyDescriptor descriptor = new PropertyDescriptor("empID", per.getClass()); Method getter = descriptor.getReadMethod(); Method setter = descriptor.getWriteMethod(); System.out.println("Getter: " + getter.getName() + " Setter: " + setter.getName()); } catch( IntrospectionException e ) { e.printStackTrace(); } } }

Refer also to the following thread :

Bryan Basham about setProperty