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.

1. factory-method: represents the factory method that will be invoked to inject the bean.
2. 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.

1. public class A {  
2. public static A getA(){//factory method  
3.     return new A();  
4. }  
5. }  

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.

1. <bean id="a" class="com.javatpoint.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.

1. <bean id="b" class="com.javatpoint.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.

1. <bean id="a" class="com.javatpoint.A"></bean>  
2. <bean id="b" class="com.javatpoint.A" factory-method="getB" factory-bean="a"></bean>  

---

Type 1

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

1. <bean id="a" class="com.javatpoint.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.

1. A.java
2. applicationContext.xml
3. Test.java

A.java This class is a singleton class.

1. package com.javatpoint;  
2. public class A {  
3. private static final A obj=new A();  
4. private A(){System.out.println("private constructor");}  
5. public static A getA(){  
6.     System.out.println("factory method ");  
7.     return obj;  
8. }  
9. public void msg(){  
10.     System.out.println("hello user");  
11. }  
12. }  

applicationContext.xml

1. <?xml version="1.0" encoding="UTF-8"?>  
2. <beans  
3.     xmlns="http://www.springframework.org/schema/beans"  
4.     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
5.     xmlns:p="http://www.springframework.org/schema/p"  
6.     xsi:schemaLocation="http://www.springframework.org/schema/beans   
7. http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">  
8.   
9. <bean id="a" class="com.javatpoint.A" factory-method="getA"></bean>  
10.   
11. </beans>  

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

1. package org.sssit;  
2. import org.springframework.context.ApplicationContext;  
3. import org.springframework.context.support.ClassPathXmlApplicationContext;  
4. public class Test {  
5. public static void main(String[] args) {  
6.     ApplicationContext context=new ClassPathXmlApplicationContext("applicationContext.xml");  
7.     A a=(A)context.getBean("a");  
8.     a.msg();  
9. }  
10. }  

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.

1. Printable.java
2. A.java
3. B.java
4. PrintableFactory.java
5. applicationContext.xml
6. Test.java

Printable.java

1. package com.javatpoint;  
2. public interface Printable {  
3. void print();  
4. }  

A.java

1. package com.javatpoint;  
2. public class A implements Printable{  
3.     @Override  
4.     public void print() {  
5.         System.out.println("hello a");  
6.     }  
7.   
8. }  

B.java

1. package com.javatpoint;  
2. public class B implements Printable{  
3.     @Override  
4.     public void print() {  
5.         System.out.println("hello b");  
6.     }  
7. }  

PrintableFactory.java

1. package com.javatpoint;  
2. public class PrintableFactory {  
3. public static Printable getPrintable(){  
4.     //return new B();  
5.           return new A();//return any one instance, either A or B  
6. }  
7. }  

applicationContext.xml

1. <?xml version="1.0" encoding="UTF-8"?>  
2. <beans  
3.     xmlns="http://www.springframework.org/schema/beans"  
4.     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
5.     xmlns:p="http://www.springframework.org/schema/p"  
6.     xsi:schemaLocation="http://www.springframework.org/schema/beans   
7. http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">  
8.   
9. <bean id="p" class="com.javatpoint.PrintableFactory" factory-method="getPrintable"></bean>  
10.   
11. </beans>  

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

1. package org.sssit;  
2. import org.springframework.context.ApplicationContext;  
3. import org.springframework.context.support.ClassPathXmlApplicationContext;  
4. public class Test {  
5. public static void main(String[] args) {  
6.     ApplicationContext context=new ClassPathXmlApplicationContext("applicationContext.xml");  
7.     Printable p=(Printable)context.getBean("p");  
8.     p.print();  
9. }  
10. }  

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.

1. Printable.java
2. A.java
3. B.java
4. PrintableFactory.java
5. applicationContext.xml
6. Test.java

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

1. package com.javatpoint;  
2. public class PrintableFactory {  
3. //non-static factory method  
4. public Printable getPrintable(){  
5.     return new A();//return any one instance, either A or B  
6. }  
7. }  

applicationContext.xml

1. <?xml version="1.0" encoding="UTF-8"?>  
2. <beans  
3.     xmlns="http://www.springframework.org/schema/beans"  
4.     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
5.     xmlns:p="http://www.springframework.org/schema/p"  
6.     xsi:schemaLocation="http://www.springframework.org/schema/beans   
7. http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">  
8.   
9. <bean id="pfactory" class="com.javatpoint.PrintableFactory"></bean>  
10. <bean id="p" class="com.javatpoint.PrintableFactory" factory-method="getPrintable"   
11. factory-bean="pfactory"></bean>  
12.   
13. </beans>  

Output:

hello a