spring PropertyPlaceholderConfigurer分析，带实例

1：写在前面

该类的作用是替换配置文件中配置的占位符信息为properties文件中实际的值，原理是PropertyPlaceholderConfigurer实现了BeanFactoryPostProcessor接口，利用其在创建bean前能够修改BeanDefinition的特点，来替换修改占位符为properties文件中的实际值。另外，关于该类的源码分析可以参考这里。在spring中还一个类PropertyOverrideConfiguer,功能类似，感兴趣的朋友也可以看下。

2：例子

2.1：定义bean

public class MyPropertyPlaceholderConfigurerBean {
    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return JSON.toJSONString(this);
    }
}
           

2.2：xml和配置文件

• xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id="propertyPlaceholderConfigurer"
          class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="location"
                  value="classpath:studyhelp/testpropertyplaceholderconfigurer.properties"/>
        <property name="fileEncoding" value="UTF-8"/>
    </bean>

    <bean class="yudaosourcecode.studyhelp.MyPropertyPlaceholderConfigurerBean"
          id="myPropertyPlaceholderConfigurerBean">
        <property name="name" value="${my.name}"/>
        <property name="age" value="${my.age}"/>
    </bean>
</beans>
           

• 配置文件

my.name=张三的歌
my.age=900
           

• 测试

@Test
public void testpropertyplaceholderconfigurer() {
    ClassPathXmlApplicationContext ac
            = new ClassPathXmlApplicationContext("classpath*:studyhelp/testpropertyplaceholderconfigurer.xml");
    System.out.println(ac.getBean("myPropertyPlaceholderConfigurerBean"));
}
           

• 运行

{"age":900,"name":"张三的歌"}

Process finished with exit code 0