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spring-扩展点-BeanFactoryPostProcessor

BeanFactoryPostProcessor：允许自定义对ApplicationContext的 bean definitions 进行修饰，扩展功能。

1、实现BeanFactoryPostProcessor 接口，会被Application contexts自动发现

2、BeanFactoryPostProcessor 仅仅对 bean definitions 发生关系，不能对bean instances 交互，对bean instances 的交互，由BeanPostProcessor的实现来处理

3、PropertyResourceConfigurer 是一个典型的实现

举例：

有这样的也个业务场景：

<bean id="user" class="com.gym.UserServiceImpl" >        <property name="username" value="${username_}"/>        <property name="password" value="${password_}"/> </bean>

spring支持系统对username_进行占位符的配置为properties文件配置，试想如果我们有个配置中心，我们希望spring启动的时候，从配置中心取数据，而非本地文件，这里就需要我们自定义一个实现BeanFactoryPostProcessor的PropertyResourceConfigurer 实例。

看下面的例子：

xml配置：

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans"  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"  xsi:schemaLocation="http://www.springframework.org/schema/beans   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd  http://www.springframework.org/schema/context   http://www.springframework.org/schema/context/spring-context-3.0.xsd"  default-autowire="byName">       <bean id="user" class="com.gym.UserServiceImpl" >        <property name="username" value="${username_}"/>        <property name="password" value="${password_}"/>      </bean>            <bean id="myFactoryPostProcessor" class="com.gym.MyFilePlaceHolderBeanFactoryPostProcessor"/> </beans>

模拟从远程取文件：

import org.springframework.beans.factory.InitializingBean; import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer; import org.springframework.core.io.support.PropertiesLoaderUtils;  /**  * @author xinchun.wang  */ public class MyFilePlaceHolderBeanFactoryPostProcessor      extends PropertyPlaceholderConfigurer implements InitializingBean{    public void afterPropertiesSet() throws Exception {   List<Properties> list = new ArrayList<Properties>();   Properties p = PropertiesLoaderUtils.loadAllProperties("config.properties");   list.add(p);   //这里是关键，这就设置了我们远程取得的List<Properties>列表   setPropertiesArray(list.toArray(new Properties[list.size()]));  }   }

javaBean配置：

public class UserServiceImpl implements IUserService{  private static final Logger logger = LoggerFactory.getLogger(UserServiceImpl.class);   public UserServiceImpl(){   logger.info("UserServiceImpl 构造函数 ");  }    private String username;  private String password;   public String getUsername() {   return username;  }   public String getPassword() {   return password;  }   public void setUsername(String username) {   logger.info("UserServiceImpl setUsername {}",username);   this.username = username;  }   public void setPassword(String password) {   logger.info("UserServiceImpl setPassword {}",password);   this.password = password;  }   @Override  public String toString() {   return "UserServiceImpl [username=" + username + ", password="     + password + "]";  }   }

测试：

public class TestApplicationContext {  public static void main(String[] args) {   ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext(     "classpath:spring/applicationContext.xml");   IUserService userService = applicationContext.getBean(IUserService.class);   String password = userService.getPassword();   applicationContext.destroy();   System.out.println(password);  }  }

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调用入口：