spring Creating and using beans Using FactoryBean for dynamic bean instantiation
Example
In order to dynamically decide what beans to inject, we can use FactoryBeans. These are classes which implement the factory method pattern, providing instances of beans for the container. They are recognized by Spring and can be used transparently, without need to know that the bean comes from a factory. For example:
public class ExampleFactoryBean extends AbstractFactoryBean<String> {
// This method determines the type of the bean for autowiring purposes
@Override
public Class<?> getObjectType() {
return String.class;
}
// this factory method produces the actual bean
@Override
protected String createInstance() throws Exception {
// The thing you return can be defined dynamically,
// that is read from a file, database, network or just
// simply randomly generated if you wish.
return "Something from factory";
}
}
Configuration:
@Configuration
public class ExampleConfig {
@Bean
public FactoryBean<String> fromFactory() {
return new ExampleFactoryBean();
}
}
Getting the bean:
AbstractApplicationContext context = new AnnotationConfigApplicationContext(ExampleConfig.class);
String exampleString = (String) context.getBean("fromFactory");
To get the actual FactoryBean, use the ampersand prefix before the bean's name:
FactoryBean<String> bean = (FactoryBean<String>) context.getBean("&fromFactory");
Please note that you can only use prototype or singleton scopes - to change the scope to prototype override isSingleton method:
public class ExampleFactoryBean extends AbstractFactoryBean<String> {
@Override
public boolean isSingleton() {
return false;
}
// other methods omitted for readability reasons
}
Note that scoping refers to the actual instances being created, not the factory bean itself.
