Doubt about instance creation by using Spring framework ???
- by Arthur Ronald F D Garcia
Here goes a command object which needs to be populated from a Spring form
public class Person {
private String name;
private Integer age;
/**
* on-demand initialized
*/
private Address address;
// getter's and setter's
}
And Address
public class Address {
private String street;
// getter's and setter's
}
Now suppose the following MultiActionController
@Component
public class PersonController extends MultiActionController {
@Autowired
@Qualifier("personRepository")
private Repository<Person, Integer> personRepository;
/**
* mapped To /person/add
*/
public ModelAndView add(HttpServletRequest request, HttpServletResponse response, Person person) throws Exception {
personRepository.add(person);
return new ModelAndView("redirect:/home.htm");
}
}
Because Address attribute of Person needs to be initialized on-demand, i need to override newCommandObject to create an instance of Person to initiaze address property. Otherwise, i will get NullPointerException
@Component
public class PersonController extends MultiActionController {
/**
* code as shown above
*/
@Override
public Object newCommandObject(Class clazz) thorws Exception {
if(clazz.isAssignableFrom(Person.class)) {
Person person = new Person();
person.setAddress(new Address());
return person;
}
}
}
Ok, Expert Spring MVC and Web Flow says
Options for alternate object creation include pulling an instance from a BeanFactory or using method injection to transparently return a new instance.
First option
pulling an instance from a BeanFactory
can be written as
@Override
public Object newCommandObject(Class clazz) thorws Exception {
/**
* Will retrieve a prototype instance from ApplicationContext whose name matchs its clazz.getSimpleName()
*/
getApplicationContext().getBean(clazz.getSimpleName());
}
But what does he want to say by using method injection to transparently return a new instance ??? Can you show how i implement what he said ???
ATT: I know this funcionality can be filled by a SimpleFormController instead of MultiActionController. But it is shown just as an example, nothing else
