Dependency Injection with Factory Method in Spring

Spring framework provides facility to inject bean using factory method. To do so, we can use two attributes of bean element.

factory-method: represents the factory method that will be invoked to inject the bean.
factory-bean: represents the reference of the bean by which factory method will be invoked. It is used if factory method is non-static.

A method that returns instance of a class is called factory method.

Factory Method Types

There can be three types of factory method:

1) A static factory method that returns instance of its own class. It is used in singleton design pattern.

 <bean id=”a” class=”com.tutoraspire.A” factory-method=”getA”></bean> 

2) A static factory method that returns instance of another class. It is used instance is not known and decided at runtime.

 <bean id=”b” class=”com.tutoraspire.A” factory-method=”getB”></bean> 

3) A non-static factory method that returns instance of another class. It is used instance is not known and decided at runtime.

 <bean id=”a” class=”com.tutoraspire.A”></bean> <bean id=”b” class=”com.tutoraspire.A” factory-method=”getB” factory-bean=”a”></bean> 

Type 1

Let’s see the simple code to inject the dependency by static factory method.

 <bean id=”a” class=”com.tutoraspire.A” factory-method=”getA”></bean> 

Let’s see the full example to inject dependency using factory method in spring. To create this example, we have created 3 files.

A.java
applicationContext.xml
Test.java

A.java

This class is a singleton class.

 package com.tutoraspire; public class A { private static final A obj=new A(); private A(){System.out.println(“private constructor”);} public static A getA(){ System.out.println(“factory method “); return obj; } public void msg(){ System.out.println(“hello user”); } } 

applicationContext.xml

 <?xml version=”1.0″ encoding=”UTF-8″?> <beans xmlns=”http://www.springframework.org/schema/beans” xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance” xmlns:p=”http://www.springframework.org/schema/p” xsi:schemaLocation=”http://www.springframework.org/schema/beans  http://www.springframework.org/schema/beans/spring-beans-3.0.xsd”>  <bean id=”a” class=”com.tutoraspire.A” factory-method=”getA”></bean>  </beans> 

Test.java

This class gets the bean from the applicationContext.xml file and calls the msg method.

 package org.sssit; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class Test { public static void main(String[] args) { ApplicationContext context=new ClassPathXmlApplicationContext(“applicationContext.xml”); A a=(A)context.getBean(“a”); a.msg(); } } 

Output:

private constructor factory method hello user

Type 2

Let’s see the simple code to inject the dependency by static factory method that returns the instance of another class.

To create this example, we have created 6 files.

Printable.java
A.java
B.java
PrintableFactory.java
applicationContext.xml
Test.java

Printable.java

A.java

 package com.tutoraspire; public class A implements Printable{ @Override public void print() { System.out.println(“hello a”); }  } 

B.java

 package com.tutoraspire; public class B implements Printable{ @Override public void print() { System.out.println(“hello b”); } } 

PrintableFactory.java

 package com.tutoraspire; public class PrintableFactory { public static Printable getPrintable(){ //return new B();           return new A();//return any one instance, either A or B } } 

applicationContext.xml

 <?xml version=”1.0″ encoding=”UTF-8″?> <beans xmlns=”http://www.springframework.org/schema/beans” xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance” xmlns:p=”http://www.springframework.org/schema/p” xsi:schemaLocation=”http://www.springframework.org/schema/beans  http://www.springframework.org/schema/beans/spring-beans-3.0.xsd”>  <bean id=”p” class=”com.tutoraspire.PrintableFactory” factory-method=”getPrintable”></bean>  </beans> 

Test.java

This class gets the bean from the applicationContext.xml file and calls the print() method.

 package org.sssit; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class Test { public static void main(String[] args) { ApplicationContext context=new ClassPathXmlApplicationContext(“applicationContext.xml”); Printable p=(Printable)context.getBean(“p”); p.print(); } } 

Output:

hello a

Type 3

Let’s see the example to inject the dependency by non-static factory method that returns the instance of another class.

To create this example, we have created 6 files.

Printable.java
A.java
B.java
PrintableFactory.java
applicationContext.xml
Test.java

All files are same as previous, you need to change only 2 files: PrintableFactory and applicationContext.xml.

PrintableFactory.java

 package com.tutoraspire; public class PrintableFactory { //non-static factory method public Printable getPrintable(){ return new A();//return any one instance, either A or B } } 

applicationContext.xml

 <?xml version=”1.0″ encoding=”UTF-8″?> <beans xmlns=”http://www.springframework.org/schema/beans” xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance” xmlns:p=”http://www.springframework.org/schema/p” xsi:schemaLocation=”http://www.springframework.org/schema/beans  http://www.springframework.org/schema/beans/spring-beans-3.0.xsd”>  <bean id=”pfactory” class=”com.tutoraspire.PrintableFactory”></bean> <bean id=”p” class=”com.tutoraspire.PrintableFactory” factory-method=”getPrintable”  factory-bean=”pfactory”></bean>  </beans> 

Output:

hello a

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