In this article we will discuss Constructor Injection and Setter Injection. These are two ways to define the dependency injection in the spring application. Spring Dependency Injection (DI) design pattern is used to define the object dependencies between each other. There are following two types in dependency-injection:
Popular Tutorials
Constructor Injection
Triangle.java
package com.dineshonjava.sdnext.constructorInjection.tutorial; /** * @author Dinesh Rajput * */ public class Triangle { private String type; private int height; /** * @param type the type to set */ /*public void setType(String type) { this.type = type; }*/ public Triangle(String type) { this.type = type; } public Triangle(int height) { this.height = height; } public Triangle(String type, int height) { this.type = type; this.height = height; } public void draw() { System.out.println(this.type+" triangle is drawn of height "+this.height); } }
The Triangle bean class has two attributes viz. type and height. All the two attributes are set using the constructor injection.
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 http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd http://www.springframework.org/schema/security http://www.springframework.org/schema/security/spring-security-2.0.4.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd"> <bean class="com.dineshonjava.sdnext.constructorInjection.tutorial.Triangle" id="triangle"> <constructor-arg index="0" type="java.lang.String" value="Equilateral"></constructor-arg><constructor-arg index="1" type="int" value="20"></constructor-arg></bean> </beans>
such as..
Triangle(String type, int height)
at index = 0 argument is type;
and at index = 1 argument is height;
and so on.
If any class has one argument constructor then there are no need to specify the index attribute of the bean in the bean configuration in spring. i.e. We can say index attribute used to distinguished to arguments of the constructor. Now second attribute is type of the constructor-arg it is used for type of the arguments of the constructor.
Such as..
Triangle(String type, int height)
then type = “java.lang.String”
and type = “int”
and the value attribute specifies the corresponding property value.
DrawingApp.java
package com.dineshonjava.sdnext.constructorInjection.tutorial; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; /** * @author Dinesh Rajput * */ public class DrawingApp { /** * @param args */ public static void main(String[] args) { //Triangle triangle = new Triangle(); //BeanFactory factory =new XmlBeanFactory(new FileSystemResource("spring.xml")); ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml"); Triangle triangle = (Triangle) context.getBean("triangle"); triangle.draw(); } }
Equilateral triangle is drawn of height 20
Setter Injection
Triangle.java
package com.sdnext.constructorInjection.tutorial; /** * @author Dinesh Rajput * */ public class Triangle { private String type; private int height; /** * @param type the type to set */ public void setType(String type) { this.type = type; } /** * @param height the height to set */ public void setHeight(String height) { this.height= height; } public void draw() { System.out.println(this.type+" triangle is drawn of height "+this.height); } }
The Triangle bean class has two attributes viz. type and height. All the two attributes are set using the setter injection.
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 http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd http://www.springframework.org/schema/security http://www.springframework.org/schema/security/spring-security-2.0.4.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd"> <bean class="com.dineshonjava.sdnext.constructorInjection.tutorial.Triangle" id="triangle"> <property name="type" value="Equilateral"> <property name="height" value="20"> </property></property></bean> </beans>
DrawingApp.java
package com.dineshonjava.sdnext.constructorInjection.tutorial; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; /** * @author Dinesh Rajput * */ public class DrawingApp { /** * @param args */ public static void main(String[] args) { //Triangle triangle = new Triangle(); //BeanFactory factory =new XmlBeanFactory(new FileSystemResource("spring.xml")); ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml"); Triangle triangle = (Triangle) context.getBean("triangle"); triangle.draw(); } }
Equilateral triangle is drawn of height 20
Injecting Object(User define) to the Bean
pubic class Triangle{ private int height; private String type; private double area; ... ... }
pubic class Triangle{ private Point pointA; private Point pointB; private Point pointC; ... ... }
pubic class Point{ private int X; private int Y; ... ... }
Lets see with the example.
Triangle.java
package com.dineshonjava.sdnext.injectingObject.tutorial; public class Triangle { 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("PointA is ("+pointA.getX()+", "+pointA.getY()+")"); System.out.println("PointB is ("+pointB.getX()+", "+pointB.getY()+")"); System.out.println("PointC is ("+pointC.getX()+", "+pointC.getY()+")"); } }
Point.java
package com.dineshonjava.sdnext.injectingObject.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; } }
Here we define the Point class with two properties int x, int y. Actually Point class is also a bean which is as a property of the Triangle bean. Now we will configure both beans to the configuration file(spring.xml).
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 http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd http://www.springframework.org/schema/security http://www.springframework.org/schema/security/spring-security-2.0.4.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd"> <bean class="com.dineshonjava.sdnext.injectingObject.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.injectingObject.tutorial.Point" id="pointA"> <property name="x" value="0"></property> <property name="y" value="0"></property> </bean> <bean class="com.dineshonjava.sdnext.injectingObject.tutorial.Point" id="pointB"> <property name="x" value="-20"></property> <property name="y" value="0"></property> </bean> <bean class="com.dineshonjava.sdnext.injectingObject.tutorial.Point" id="pointC"> <property name="x" value="20"></property> <property name="y" value="0"></property> </bean> </beans>
DrawingApp.java
package com.dineshonjava.sdnext.injectingObject.tutorial; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; /** * @author Dinesh Rajput * */ public class DrawingApp { /** * @param args */ public static void main(String[] args) { //BeanFactory factory =new XmlBeanFactory(new FileSystemResource("spring.xml")); ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml"); Triangle triangle = (Triangle) context.getBean("triangle"); triangle.draw(); } }
PointA is (0, 0)
PointB is (-20, 0)
PointC is (20, 0)
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In Next Chapter we will discuss about Injecting Inner Beans in Spring with Example in Application.
good one..
very nice.,