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());
     }
 }