What's a FactoryBean?
In this post, I'll look at Spring's org.springframework.beans.factory.FactoryBean<T> interface. The definition of this interface is:
public interface FactoryBean<T> {
T getObject() throws Exception;
Class<T> getObjectType();
boolean isSingleton();
}
A FactoryBean is a pattern to encapsulate interesting object construction logic in a class. It might be used, for example, to encode the construction of a complex object graph in a reusable way. Often this is used to construct complex objects that have many dependencies. It might also be used when the construction logic itself is highly volatile and depends on the configuration. A FactoryBean is also useful to help Spring construct objects that it couldn't easily construct itself. For example, in order to inject a reference to a bean that was obtained from JNDI, the reference must first be obtained. You can use the JndiFactoryBean to obtain this reference in a consistent way. You may inject the result of a FactoryBean's getObject() method into any other property.
Suppose you have a Person class whose definition is thus:
public class Person {
private Car car ;
private void setCar(Car car){ this.car = car; }
}
and a FactoryBean whose definition is thus:
public class MyCarFactoryBean implements FactoryBean<Car>{
private String make;
private int year ;
public void setMake(String m){ this.make =m ; }
public void setYear(int y){ this.year = y; }
public Car getObject(){
// wouldn't be a very useful FactoryBean
// if we could simply instantiate the object…
