对Bean和Bean工厂进行后处理

1.对Bean进行后处理，必须实现BeanPostProcessor接口，后处理是在Bean实例化以及装配完成之后发生的。
下面是一个简单的例子：
先来创建一个实现了BeanPostProcessor接口的类，此类功能是把Bean中的所有String属性的值的r,l或R,L换成w或W，代码如下：
package cn.itcast;

import java.lang.reflect.Field;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;

public class Fuddifier implements BeanPostProcessor {

 public Object postProcessBeforeInitialization(Object arg0, String arg1)
   throws BeansException {
  Field[] fields = arg0.getClass().getDeclaredFields();
  try {
   for (int i = 0; i < fields.length; i++) {
    if (fields[i].getType().equals(java.lang.String.class)) {
     fields[i].setAccessible(true);
     String original = (String) fields[i].get(arg0);
     fields[i].set(arg0, fuddify(original));
    }
   }
  } catch (Exception ex) {
   ex.printStackTrace();
  }
  return arg0;
 }

 private String fuddify(String orig) {
  if (orig == null)
   return orig;
  return orig.replaceAll("(r|l)", "w").replaceAll(" (R|L) ", "W");
 }

 public Object postProcessAfterInitialization(Object arg0, String arg1)
   throws BeansException {
  return arg0;
 }
}

再来创建一个简单的javaBean：
package cn.itcast;

public class Rabbit {
 private String description;

 private String address;

 public String getAddress() {
  return address;
 }

 public void setAddress(String address) {
  this.address = address;
 }

 public String getDescription() {
  return description;
 }

 public void setDescription(String description) {
  this.description = description;
 }
}

XML配置文件：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">

<beans>
  <bean id="fuddifier" class="cn.itcast.Fuddifier" />
  
  <bean id="rabbit" class="cn.itcast.Rabbit">
   <property name="description">
    <value>That rascally rabbit!</value>
   </property>
   <property name="address">
    <value>Dalian</value>
   </property>
  </bean>
</beans>

写个主函数来测试一下：
package cn.itcast;

import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.ClassPathResource;

public class MainClass {
 public static void main(String[] args) {
  // 第一种方法，如果只用上下文容器就只需在xml文件中加入这句就可以了：
  //<bean id="fuddifier" class="cn.itcast.Fuddifier" />
  
  // ApplicationContext factory = new ClassPathXmlApplicationContext(
  // "/applicationContext.xml");

  // 第二种方法,使用Bean工厂必须得调用工厂的addBeanPostProcessor()方法来注册BeanPostProcessor，
  //这样就不需要上面那句：<bean id="fuddifier" class="cn.itcast.Fuddifier" />
  ConfigurableBeanFactory factory = new XmlBeanFactory(
    new ClassPathResource("/applicationContext.xml"));
  BeanPostProcessor fuddifier = new Fuddifier();
  factory.addBeanPostProcessor(fuddifier);

  Rabbit rabbit = (Rabbit) factory.getBean("rabbit");
  System.out.println(rabbit.getDescription());
  System.out.println(rabbit.getAddress());
 }
}
两种方法的运行结果都一样：
That wascawwy wabbit!
Dawian

可以看出两个属性的值都改变了。

2.Bean工厂后处理，必须实现接口BeanFactoryPostProcessor，此接口的功能是在Bean工厂载入所有Bean的定义后，实例化Bean之前，对Bean工厂做一些后处理工作。
来看一个简单的例子：
先创建一个实现了BeanFactoryPostProcessor的类，此类记录了容器中的Bean总数还把rabbit1的address值改变了。
package cn.it315;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;

import cn.itcast.Rabbit;

public class BeanCounter implements BeanFactoryPostProcessor {

 public void postProcessBeanFactory(ConfigurableListableBeanFactory arg0)
   throws BeansException {
  System.out.println("Bean count: " + arg0.getBeanDefinitionCount());
  Rabbit rabbit = (Rabbit)arg0.getBean("rabbit1");
  rabbit.setAddress("湖南");
 }
}

XMl配置文件：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">

 <bean id="beanCounter" class="cn.it315.BeanCounter" />

 <bean id="rabbit1" class="cn.itcast.Rabbit">
  <property name="description">
   <value>That rascally rabbit!</value>
  </property>
  <property name="address">
   <value>Dalian</value>
  </property>
 </bean>
 
 <bean id="rabbit2" class="cn.itcast.Rabbit">
  <property name="description">
   <value>That rascally rabbit!</value>
  </property>
  <property name="address">
   <value>Shenyang</value>
  </property>
 </bean>
 
</beans>

javaBean用的还是上面那个Rabbit。

来写一个主函数测试一下：
package cn.it315;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import cn.itcast.Rabbit;

public class MainClass {
 public static void main(String[] args) {
 //使用应用上下文容器，只需在xml文件中注册就行了：
 // <bean id="beanCounter" class="cn.it315.BeanCounter" />
  ApplicationContext factory = new ClassPathXmlApplicationContext(
    "/applicationContext.xml");

  Rabbit rabbit = (Rabbit) factory.getBean("rabbit1");
  System.out.print(rabbit.getAddress());
 }
}

运行结果：
Bean count: 3
湖南

注意：在Bean工厂容器中无法使用BeanFactoryPostProcessor

3.分散配置，使用Spring的PropertyPlaceholderConfigurer告诉Spring从外部属性文件中装载一些配置信息。

写一个属性文件：
url=jdbc:odbc:test
driver=sun.jdbc.odbc.JdbcOdbcDriver
username=sa
password=

XML文件就象下面这样配置：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">

<beans>

 <bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
  <property name="location">location属性告诉Spring从哪找到属性文件
   <value>jdbc.properties</value>
  </property>
 </bean>

下面的<value>就是从属性文件中读取出来的。
 <bean id="dataSource" class="cn.itcast.DriverManagerDataSource">
  <property name="url">
   <value>${url}</value>
  </property>
  <property name="driver">
   <value>${driver}</value>
  </property>
  <property name="username">
   <value>${username}</value>
  </property>
  <property name="password">
   <value>${password}</value>
  </property>
 </bean>

</beans>

DriverManagerDataSource的内容如下：
package cn.itcast;

public class DriverManagerDataSource {
 private String url;

 private String driver;

 private String username;

 private String password;

 public String getDriver() {
  return driver;
 }

 public void setDriver(String driver) {
  this.driver = driver;
 }

 public String getPassword() {
  return password;
 }

 public void setPassword(String password) {
  this.password = password;
 }

 public String getUrl() {
  return url;
 }

 public void setUrl(String url) {
  this.url = url;
 }

 public String getUsername() {
  return username;
 }

 public void setUsername(String username) {
  this.username = username;
 }
}

测试一下：
package cn.itcast;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainClass {

 public static void main(String[] args) throws SQLException,
   ClassNotFoundException {

  ApplicationContext factory = new ClassPathXmlApplicationContext(
    "applicationContext.xml");
  DriverManagerDataSource dataSource = (DriverManagerDataSource) factory
    .getBean("dataSource");
  Class.forName(dataSource.getDriver());
  Connection conn = DriverManager.getConnection(dataSource.getUrl(),
    dataSource.getUsername(), dataSource.getPassword());
  System.out.println(conn);
 }
}
运行结果：
sun.jdbc.odbc.JdbcOdbcConnection@efd552
可以看出上面已经从属性文件中读取出相应的属性建立好数据库的连接了。