Coding To Interfaces in Spring

In last couple of tutorials we have seen that the basic features about spring framework as like Spring IoC Container, Dependency Injection, ApplicationContext, BeanFactory etc. In first chapter we have discussed about Dependency Injection using an Example of Drawing Class and Shape class. As given below in picture-
Coding To Interfaces in Spring

In above picture we will see that second part name Drawing Class Dependent on Shape Class Actually shape is not a class Its an interface which implemented by three classes as Triangle, Circle & Rectangle.

In our Drawing Application class(DrawingApp.java) we are using draw() method of the Triangle class. As below-

ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
Triangle triangle = (Triangle) context.getBean("triangle");
triangle.draw();

Here Drawing Application knows that it using draw() method of Triangle bean. If we want to use the draw() method of the circle class then we have to write the following code in the Drawing Application-

ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
Circle circle= (Circle) context.getBean("circle");
circle.draw();
If want to use the true power of spring framework then we have to use the coding to interface technique. In coding to interface Drawing Application(DrawingApp.java) does not care about that the draw() method of which classes is called. Both classes just implements the Shape interface with one method draw(). And after that Drawing Class have the following code-

ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
Shape shape = (Shape) context.getBean("shape");
shape.draw();

Lets see the full running example about the Coding to interface.

Shape.java

package com.dineshonjava.sdnext.interfaceCoding.tutorial;

public interface Shape
{
   void draw();
}


Triangle.java

package com.dineshonjava.sdnext.interfaceCoding.tutorial;

public class Triangle implements Shape
{
 private Point pointA;
 private Point pointB;
 private Point pointC;
 
 /**
  * @param pointA the pointA to set
  */
 public void setPointA(Point pointA) {
  this.pointA = pointA;
 }

 /**
  * @param pointB the pointB to set
  */
 public void setPointB(Point pointB) {
  this.pointB = pointB;
 }

 /**
  * @param pointC the pointC to set
  */
 public void setPointC(Point pointC) {
  this.pointC = pointC;
 }

 public void draw()
 {
System.out.println("Drawing Triangle");
System.out.println("PointA is ("+pointA.getX()+", "+pointA.getY()+")");
System.out.println("PointB is ("+pointB.getX()+", "+pointB.getY()+")");
System.out.println("PointC is ("+pointC.getX()+", "+pointC.getY()+")");
 }
}


Circle.java

package com.dineshonjava.sdnext.interfaceCoding.tutorial;

public class Circle implements Shape
{
 private Point center;

 /**
  * @param center the center to set
  */
 public void setCenter(Point center) 
 {
  this.center = center;
 }

 @Override
 public void draw() 
 {
System.out.println("Circle is drawn of center ("+center.getX()+", "+center.getY()+")");
 }
}


Point.java

package com.dineshonjava.sdnext.interfaceCoding.tutorial;

public class Point
{
 private int x;
 private int y;
 /**
  * @return the x
  */
 public int getX() {
  return x;
 }
 /**
  * @param x the x to set
  */
 public void setX(int x) {
  this.x = x;
 }
 /**
  * @return the y
  */
 public int getY() {
  return y;
 }
 /**
  * @param y the y to set
  */
 public void setY(int y) {
  this.y = y;
 }
}


Spring.xml

<beans xmlns:aop="http://www.springframework.org/schema/aop" xmlns:p="http://www.springframework.org/schema/p" xmlns:security="http://www.springframework.org/schema/security" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.springframework.org/schema/beans" xsi:schemalocation="http://www.springframework.org/schema/beans">
  
<bean class="com.dineshonjava.sdnext.interfaceCoding.tutorial.Triangle" id="triangle">
 <property name="pointA" ref="pointA"></property>
 <property name="pointB" ref="pointB"></property>
 <property name="pointC" ref="pointC"></property>
</bean>
  
<bean class="com.dineshonjava.sdnext.interfaceCoding.tutorial.Circle" id="circle">
 <property name="center" ref="center"></property>
</bean>
  
<bean class="com.dineshonjava.sdnext.interfaceCoding.tutorial.Point" id="pointA">
 <property name="x" value="0"></property>
 <property name="y" value="0"></property>
</bean>
  
<bean class="com.dineshonjava.sdnext.interfaceCoding.tutorial.Point" id="pointB">
 <property name="x" value="-20"></property>
 <property name="y" value="0"></property>
</bean>
  
<bean class="com.dineshonjava.sdnext.interfaceCoding.tutorial.Point" id="pointC">
 <property name="x" value="20"></property>
 <property name="y" value="0"></property>
</bean>
  
<bean class="com.dineshonjava.sdnext.interfaceCoding.tutorial.Point" id="center">
 <property name="x" value="10"></property>
 <property name="y" value="10"></property>
</bean>
</beans>

If every thing is OK then run the following Drawing Application draw a shape using draw() method of shape interface.

DrawingApp.java

package com.dineshonjava.sdnext.interfaceCoding.tutorial;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @author Dinesh
 *
 */
public class DrawingApp {

 /**
  * @param args
  */
 public static void main(String[] args)
 {
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
Shape shape = (Shape) context.getBean("triangle");
shape.draw();
 }
}

Its draw a triangle.

Output:
Jul 8, 2012 7:02:58 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@ab50cd: startup date [Sun Jul 08 19:02:57 IST 2012]; root of context hierarchy
Jul 8, 2012 7:02:58 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [spring.xml]
Jul 8, 2012 7:02:59 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@14c1103: defining beans [triangle,circle,pointA,pointB,pointC,center]; root of factory hierarchy

Drawing Triangle
PointA is (0, 0)
PointB is (-20, 0)
PointC is (20, 0)


If we want draw a circle the execute the following Drawing Application.


DrawingApp.java

package com.dineshonjava.sdnext.interfaceCoding.tutorial;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @author Dinesh
 *
 */
public class DrawingApp {

 /**
  * @param args
  */
 public static void main(String[] args)
 {
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
Shape shape = (Shape) context.getBean("circle");
shape.draw();
 }
}

Its draw a circle.
Output:
Jul 8, 2012 7:05:11 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@ab50cd: startup date [Sun Jul 08 19:05:11 IST 2012]; root of context hierarchy
Jul 8, 2012 7:05:11 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [spring.xml]
Jul 8, 2012 7:05:11 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@14c1103: defining beans [triangle,circle,pointA,pointB,pointC,center]; root of factory hierarchy

Circle is drawn of center (10, 10)

In our enterprise application the coding to interface very necessary & useful. We are using DAO & Service layers as interfaces in the enterprise application but its business logic implement these interfaces. If in future you want to change or adding new business logic of enterprise application you does not need to change in the view layer(DAO & Service layers). You just need add one more class that implements that interface and rewired with spring dependency injection.
In Next Chapter we will discuss about the Using Annotation in Spring.

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