Spring_属性占位符

忍耐和坚持虽是痛苦的事情，但却能渐渐地为你带来好处。——奥维德

属性占位符

　　Spring一直支持将属性定义到外部的属性的文件中，并使用占位符值将其插入到Spring bean中。

　　占位符的形式为使用"${}"包装的属性名称，为了使用属性占位符，我们必须配置一个PropertyPlaceholderConfigurer或PropertySourcesPlaceholderConfigurer实例，从Spring 3.0开始，推荐使用PropertySourcesPlaceholderConfigurer，因为它能够基于Spring Environment及其属性源来解析占位符。

　　1.在基于Java配置中使用属性占位符注入属性

package chapter3.prctice6;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
import org.springframework.stereotype.Component;

@Component
public class AppleMobile implements Mobile {

    private String color;

    private String type;

    public AppleMobile(@Value("${mobile.color}") String color, @Value("${mobile.type}") String type) {
        this.color = color;
        this.type = type;
    }

    @Bean
    public PropertySourcesPlaceholderConfigurer placeholderConfigurer() {
        return new PropertySourcesPlaceholderConfigurer();
    }

    public void play() {
        System.out.println(color+"-"+type);
    }

}

　　2.在基于XML配置中使用占位符注入属性

<?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:aop="http://www.springframework.org/schema/aop"
    xmlns:c="http://www.springframework.org/schema/c"
    xmlns:util="http://www.springframework.org/schema/util"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:jdbc="http://www.springframework.org/schema/jdbc"
    xmlns:jee="http://www.springframework.org/schema/jee"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/jdbc         http://www.springframework.org/schema/jdbc/spring-jdbc-4.3.xsd
        http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-4.3.xsd
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.3.xsd
        http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd
        http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.3.xsd">

        <bean id="appleMobile" class="chapter3.prctice6.AppleMobile"
        c:color="${moble.color}"
        c:type="${mobile.type}">
        </bean>
        <context:property-placeholder/>
</beans>

　　解析外部属性能够将值的处理推迟到运行时，它的关注点在于根据名称解析来自于Spring Environment和属性源的属性。

原文地址：https://www.cnblogs.com/dandelZH/p/8859090.html