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 {
}