spring中PropertyPlaceholderConfigurer的运用---使用${property-name}取值

代码如下：

配置文件：

jdbc.properties的代码如下：

 jdbc.driverClassName=org.hsqldb.jdbcDriver
 jdbc.url=jdbc:hsqldb:hsql://production:9002
 jdbc.username=sa
 jdbc.password=root

applicationContext-properties-placeholder.xml 代码如下：

 <?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:p="http://www.springframework.org/schema/p"
        xmlns:c="http://www.springframework.org/schema/c"
        xmlns:aop="http://www.springframework.org/schema/aop"
        xsi:schemaLocation="http://www.springframework.org/schema/beans
                 http://www.springframework.org/schema/beans/spring-beans.xsd
 http://www.springframework.org/schema/aop
 http://www.springframework.org/schema/aop/spring-aop.xsd">

     <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
         <property name="locations" value="classpath:jdbc.properties"/>
     </bean>
     <bean id="dataSource" destroy-method="close"
           class="org.apache.commons.dbcp.BasicDataSource">
         <property name="driverClassName" value="${jdbc.driverClassName}"/>
         <property name="url" value="${jdbc.url}"/>
         <property name="username" value="${jdbc.username}"/>
         <property name="password" value="${jdbc.password}"/>
     </bean>
 </beans>

上面的红色部分均按照：${property-name}取值.

测试类的代码如下：

package com.timo.test;

import org.apache.commons.dbcp.BasicDataSource;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test19 {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext-properties-placeholder.xml");
        BasicDataSource dataSource = applicationContext.getBean(BasicDataSource.class);
        System.out.println("driverClassName="+dataSource.getDriverClassName());
    }
}

上面xml配置文件中

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="locations" value="classpath:jdbc.properties"/>
    </bean>
等效于

<context:property-placeholder location="classpath:jdbc.properties"/>