spring in action 学习十一：property placeholder Xml方式实现避免注入外部属性硬代码化

　　这里用到了placeholder特有的一个语言或者将表达形式：${},spring in action 描述如下：

In spring wiring ,placeholder values are property names wrapped with ${...},as an exampl,you can resolve the constructor arguments for a BlankDisc in xml like this ：

<bean id="sgtPeppers"

　　　　class="soundsystem.BlankDisc"

　　　　c:_titile="${disc.title}"

　　　　c:_artist="${disc.artist}"/>

下面这个案例用${...}从配置文件读取内容，

记得一定要在配置文件写上下面的语句：

  <!-- 加载.properties文件-->
    <context:property-placeholder location="classpath:com/advancedWiring/ambiguityIniAutowiring2/student.properties"/>

案例的目录结构如下图所示：

案例的代码如下：

Student类的代码如下：

package com.advancedWiring.ambiguityIniAutowiring2;

import org.springframework.beans.factory.BeanNameAware;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.context.annotation.Scope;
import org.springframework.context.annotation.ScopedProxyMode;
import org.springframework.stereotype.Component;
import org.springframework.web.context.WebApplicationContext;

/**
 * Created by ${秦林森} on 2017/6/9.
 */
public class Student implements BeanNameAware{
    private  String name;
    private Integer age;

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

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

    @Override
    public void setBeanName(String name) {
        System.out.println("the Student bean name is :"+name);
    }

    /**
     * write this constructor mainly to inject external property value.
     * @param name the student's name
     * @param age  the student's age
     */
    public Student(String name, Integer age) {
        this.name = name;
        this.age = age;
    }
}

student.properties文件的代码如下：

#用配置文件的形式，避免注入属性值的硬代码化。
name=AbrahamLincoln
age=21

ambiguity.xml的代码如下：

<?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:aop="http://www.springframework.org/schema/aop"
       xmlns:c="http://www.springframework.org/schema/c"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/aop
       http://www.springframework.org/schema/aop/spring-aop.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd
       http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
    <context:annotation-config/>
   <!-- 加载.properties文件-->
    <context:property-placeholder location="classpath:com/advancedWiring/ambiguityIniAutowiring2/student.properties"/>
    <bean id="student"
          class="com.advancedWiring.ambiguityIniAutowiring2.Student"
        c:name="${name}"
          c:age="${age}">
     </bean>
</beans>

测试类Test的代码如下：

package com.advancedWiring.ambiguityIniAutowiring2;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * Created by ${秦林森} on 2017/6/9.
 */
public class Test {
    public static void main(String[] args) {

        ClassPathXmlApplicationContext ac = new ClassPathXmlApplicationContext("com/advancedWiring/ambiguityIniAutowiring2/ambiguity.xml");
        Student student = ac.getBean(Student.class);
        /**
         * 输出结果是：the student name is: AbrahamLincoln and age is :19
         * 可以看出他把配置文件的值给取出来了。
         */
        System.out.println("the student name is: "+student.getName()+" and age is :"+student.getAge());
    }
}