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