PostConstruct注解

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 {

}