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

Posted 2020-09-22 技术让世界更精彩

　　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：

1   <!-- 加载.properties文件-->
2     <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：

 1 package com.advancedWiring.ambiguityIniAutowiring2;
 2 
 3 import org.springframework.beans.factory.BeanNameAware;
 4 import org.springframework.beans.factory.config.ConfigurableBeanFactory;
 5 import org.springframework.context.annotation.Scope;
 6 import org.springframework.context.annotation.ScopedProxyMode;
 7 import org.springframework.stereotype.Component;
 8 import org.springframework.web.context.WebApplicationContext;
 9 
10 /**
11  * Created by ${秦林森} on 2017/6/9.
12  */
13 public class Student implements BeanNameAware{
14     private  String name;
15     private Integer age;
16 
17     public String getName() {
18         return name;
19     }
20 
21     public void setName(String name) {
22         this.name = name;
23     }
24 
25     public Integer getAge() {
26         return age;
27     }
28 
29     public void setAge(Integer age) {
30         this.age = age;
31     }
32 
33     @Override
34     public void setBeanName(String name) {
35         System.out.println("the Student bean name is :"+name);
36     }
37 
38     /**
39      * write this constructor mainly to inject external property value.
40      * @param name the student\'s name
41      * @param age  the student\'s age
42      */
43     public Student(String name, Integer age) {
44         this.name = name;
45         this.age = age;
46     }
47 }

student.properties文件的代码如下：

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

ambiguity.xml的代码如下：

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <beans xmlns="http://www.springframework.org/schema/beans"
 3        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 4        xmlns:aop="http://www.springframework.org/schema/aop"
 5        xmlns:c="http://www.springframework.org/schema/c"
 6        xmlns:context="http://www.springframework.org/schema/context"
 7        xsi:schemaLocation="http://www.springframework.org/schema/aop
 8        http://www.springframework.org/schema/aop/spring-aop.xsd
 9        http://www.springframework.org/schema/context
10        http://www.springframework.org/schema/context/spring-context.xsd
11        http://www.springframework.org/schema/beans
12 http://www.springframework.org/schema/beans/spring-beans.xsd">
13     <context:annotation-config/>
14    <!-- 加载.properties文件-->
15     <context:property-placeholder location="classpath:com/advancedWiring/ambiguityIniAutowiring2/student.properties"/>
16     <bean id="student"
17           class="com.advancedWiring.ambiguityIniAutowiring2.Student"
18         c:name="${name}"
19           c:age="${age}">
20      </bean>
21 </beans>

测试类Test的代码如下：

 1 package com.advancedWiring.ambiguityIniAutowiring2;
 2 
 3 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 4 import org.springframework.context.support.ClassPathXmlApplicationContext;
 5 
 6 /**
 7  * Created by ${秦林森} on 2017/6/9.
 8  */
 9 public class Test {
10     public static void main(String[] args) {
11 
12         ClassPathXmlApplicationContext ac = new ClassPathXmlApplicationContext("com/advancedWiring/ambiguityIniAutowiring2/ambiguity.xml");
13         Student student = ac.getBean(Student.class);
14         /**
15          * 输出结果是：the student name is: AbrahamLincoln and age is :19
16          * 可以看出他把配置文件的值给取出来了。
17          */
18         System.out.println("the student name is: "+student.getName()+" and age is :"+student.getAge());
19     }
20 }