应用场景：当你需要往Bean里注入一个其父类中定义的属性，而你又无法复写父类的属性或属性的setter方法时
public class UserDaoImpl extends HibernateDaoSupport implements UserDao {
private SessionFactory mySessionFacotry;
@Resource
public void setMySessionFacotry(SessionFactory sessionFacotry) {
this.mySessionFacotry = sessionFacotry;
}
@PostConstruct
public void injectSessionFactory() {
super.setSessionFactory(mySessionFacotry);
}
...
}
这里通过@PostConstruct，为UserDaoImpl的父类里定义的一个sessionFactory私有属性，注入了我们自己定义的sessionFactory（父类的setSessionFactory方法为final，不可复写），之后我们就可以通过调用 super.getSessionFactory()来访问该属性了。
Java源码：
//Copyright Sun Microsystems Inc. 2004 - 2005. package javax.annotation; import java.lang.annotation.*;
import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.*; /**
* The PostConstruct annotation is used on a method that needs to be executed
* after dependency injection is done to perform any initialization. This
* method MUST be invoked before the class is put into service. This
* annotation MUST be supported on all classes that support dependency
* injection. The method annotated with PostConstruct MUST be invoked even
* if the class does not request any resources to be injected. Only one
* method can be annotated with this annotation. The method on which the
* PostConstruct annotation is applied MUST fulfill all of the following
* criteria -
- The method MUST NOT have any parameters except in the case of EJB
* interceptors in which case it takes an InvocationC ontext object as
* defined by the EJB specification.
* - The return type of the method MUST be void.
* - The method MUST NOT throw a checked exception.
* - The method on which PostConstruct is applied MAY be public, protected,
* package private or private.
* - The method MUST NOT be static except for the application client.
* - The method MAY be final.
* - If the method throws an unchecked exception the class MUST NOT be put into
* service except in the case of EJBs where the EJB can handle exceptions and
* even recover from them.
* @since Common Annotations 1.0
* @see javax.annotation.PreDestroy
* @see javax.annotation.Resource
*/
@Documented
@Retention (RUNTIME)
@Target(METHOD)
public @interface PostConstruct {
}