Spring - Method Replacement

It is one type of method injection, where we will give an intimation to IOC Container

about to replace the existed method implementation with some other method

implementation.

To achieve Method Replacement, we have to declare an user defined bean class with a

method whose implementation we want to replace and we will provide new

implementation for that method by declaring a class and by implementing

"MethodReplacer" interface.

MethodReplacer interface contains reimplement(-----) method, here we must provide

our new implementation in reimplement() method.

Example:

Course.java

package com.durgasoft.beans;

public class Course {

private String cid;

private String cname;

private int ccost;

setXXX()

getXXX()

public void getCourseDetails(){

System.out.println("Course Details");

System.out.println("-----------------");

System.out.println("Course Id :"+cid);

System.out.println("Course Name :"+cname);

System.out.println("Course Cost :"+ccost);

}

}

NewImpl.java

package com.durgasoft.beans;

import java.lang.reflect.Method;

import org.springframework.beans.factory.support.MethodReplacer;

public class NewImpl implements MethodReplacer {

public Object reimplement(Object arg0, Method arg1, Object[] arg2) throws Throwable

{

System.out.println("Course Details");

System.out.println("-----------------");

System.out.println("Course Id :C-222");

System.out.println("Course Name :.NET");

System.out.println("Course Cost :20000");

return null;

}

}

spring_beans_config.xml

<beans>

<bean id="newImpl" class="com.durgasoft.beans.NewImpl"/>

<bean id="course" class="com.durgasoft.beans.Course">

<property name="cid" value="C-111"/>

<property name="cname" value="Java"/>

<property name="ccost" value="10000"/>

<replaced-method name="getCourseDetails" replacer="newImpl"/>

</bean>

</beans>

Test.java

package com.durgasoft.test;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.durgasoft.beans.Course;

public class Test {

public static void main(String[] args)throws Exception {

ApplicationContext context=new

ClassPathXmlApplicationContext("/com/durgasoft/cfgs/spring_beans_config.xml");

Course crs=(Course)context.getBean("course");

crs.getCourseDetails();

}

}

Bean Validations in spring

The process of checking data validity before using data in applications is called as Data

Validations.

In Web Applications, there are two types of data validations.

1.Client Side Data Validations

2.Server Side Data Validations

1.Client Side Data Validations: The process of checking whether data is valid or not at

client browser before submitting request to the Server is called as Client Side Data Data

Validations. To perform client side data validations we will use "Java Script" Functions.

2.Server Side Data Validations: The process of checking whether data is valid or not

at server after getting request from client and before using data in application logic is

called as Server side data validations. To perform Server side data validations we have

to use Java code explicitly.

Note: If we use web Frameworks like Struts, JSF , SPring WEB MVC module then all

these frameworks are able to provide their own validations services implicitly to

perform data validations.

In Spring Core Module, to perform validations over the data after storing data in Bean

objects Spring Framework has provided a predefined interface in the form of

"org.springframework.validation.Validator" .

To perform bean validations in Spring applications then we have to use the following

steps.

1.Prepare a properties file with all validation messages:

Declare validation messages in the form of key-value pairs, where keys must be

validation message code and value must be validation message.

EX: abc.properties

error.uname= User Name is required.

error.password=User Password is required.

2.Prepare Validator class:

The main intention of Validator class is to define all data validation logic w.r.t the bean

properties.

Steps:

a)Declare an user defined class.

b)Implement org.springframework.validation.Validator interface.

c)Implement the following Validator interface provided methods.

public boolean supports(Class type)

public void validate(Object obj, Errors errors)

Where supports(--) method will check whether the Bean object is supporting data

validations or not.

Where validate(---) is able to include data validation logic inorder to perform data

validations.

Where "Errors" is able to include all validation messages in the form of Map object

inorder to display. To add an error message to Errors object we have to use

"rejectValue(----)" method.

d)Declare Resource property and its setXXX() method inorder to repersent the name

and location of the properties file where all the validation messages are existed.