Spring : Creating custom factory-bean

Because of the complexity involved, we tend to write our own factory classes to initialize complex beans. There are couple of ways :

• Traditional way of writing factory classes
• Using FactoryBean Api for writing a factory class

example :

Suppose we have a bean called MyService. Likewise there can be many other beans, and there is a factory class to which contain multiple methods to return these different type of beans. So based on the parameter of the function, it generates a bean of different type.

Consider the bean class:

package ex3;

public class MyService {

   //some bean components
}

Consider the factory class :

import javax.sql.DataSource;

public class MyServiceLocator {

    public MyService createMyService() {
        //we assume there is some complex code to initialize MyService bean
        return new MyService();
    }
    
    public MyService createMyService(DataSource dataSource) {
        //some database specific code to fetch values required for instantiating the bean
        return new MyService();
    }
}

Describing the factory class:

<!-- define the bean of type factory-class -->
<bean id="serviceLocator" class="ex3.MyServiceLocator" />
<!-- Now get the bean created by factory class by factory-bean -->
<bean id="myService" factory-bean="serviceLocator" factory-method="createMyService" />

Creating the beans from factory class:

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

public class MyServiceLocatorTest {

    public void testMyServiceLocator() {
        ApplicationContext container = new ClassPathXmlApplicationContext("/sompath/config.xml");
        //getbean of type myservice from factory class inside containter
        MyService myService = container.getBean("myService", MyService.class);
}

Now this will call factory-method of type with no arguments, but when factory-method has argument then we can do this by these 2 methods. See here.