Spring为属性注入某个类的常量或方法的返回值

spring提供了filed的值注入和method的返回值注入。

1、Field值的注入

filed值注入需要使用org.springframework.beans.factory.config.FieldRetrievingFactoryBean来获取类的静态变量。

例如，我们通常在接口中定义常量：

[java] view plaincopyprint?

1. package com.baobaotao.fb; 
2. public interface CarBrandType { 
3.     String HONG_QI = "红旗"; 
4.     String JI_LI = "吉利"; 
5. } 

package com.baobaotao.fb;public interface CarBrandType { String HONG_QI = "红旗"; String JI_LI = "吉利";}

下面利用FieldRetrievingFactoryBean获取CarBandType接口中定义的常量，并注入到某个bean的属性中：

[xhtml] view plaincopyprint?

1. <beanid="car"class="com.baobaotao.fb.Car"> 
2.     <propertyname="brand"ref="hongQi"/> 
3. </bean> 
4. <bean id="hongQi"class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean" 
5.     <propertyname="staticField"value="com.baobaotao.fb.CarBrandType.HONG_QI"/> 
6. </bean> 

<bean id="car" class="com.baobaotao.fb.Car"> <property name="brand" ref="hongQi"/></bean><bean id="hongQi" class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean" <property name="staticField" value="com.baobaotao.fb.CarBrandType.HONG_QI"/></bean>

Spring还允许用户用常量的全限定名作为FieldRetrievingFactoryBean的id，其效果和通过配置staticField属性是一样的：

[xhtml] view plaincopyprint?

1. <beanid="car"class="com.baobaotao.fb.Car"> 
2.     <propertyname="brand"ref="com.baobaotao.fb.CarBrandType.HONG_QI"/> 
3. </bean> 
4. <bean id="com.baobaotao.fb.CarBrandType.HONG_QI"class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean"/> 

<bean id="car" class="com.baobaotao.fb.Car"> <property name="brand" ref="com.baobaotao.fb.CarBrandType.HONG_QI"/></bean><bean id="com.baobaotao.fb.CarBrandType.HONG_QI" class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean" />

当然，也可以直接将FieldRetrievingFactoryBean以内置bean的方式对brand属性进行赋值，这样在配置上更紧凑一些：

[xhtml] view plaincopyprint?

1. <beanid="car"class="com.baobaotao.fb.Car"> 
2.     <propertyname="brand"> 
3.         <beanid="com.baobaotao.fb.CarBrandType.HONG_QI"class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean"> 
4.         </bean> 
5.     </property> 
6. </bean> 

<bean id="car" class="com.baobaotao.fb.Car"> <property name="brand"> <bean id="com.baobaotao.fb.CarBrandType.HONG_QI" class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean"> </bean> </property></bean>

2、Method返回值的注入
Method返回值的注入需要使用MethodInvokingFactoryBean来完成。

在xml配置中，需要设定targetObject和targetMethod来指定目标bean和方法。如果使用静态方法，则需要指定targetClass和targetMethod

配置文件如下：

[xhtml] view plaincopyprint?

1. <beanid="bdog"class="com.baobaotao.fb.Dog"> 
2.   <propertyname="age"> 
3.     <beanclass="org.springframework.beans.factory.config.MethodInvokingFactoryBean"> 
4.       <propertyname="targetObject"> 
5.         <reflocal="randomAge"/> 
6.       </property> 
7.       <propertyname="targetMethod"> 
8.         <value>getAge</value> 
9.       </property> 
10.     </bean> 
11.   </property> 
12. </bean> 
13. <beanid="randomAge"class="com.baobaotao.fd.RandomAge"/> 

<bean id="bdog" class="com.baobaotao.fb.Dog"> <property name="age"> <bean class="org.springframework.beans.factory.config.MethodInvokingFactoryBean"> <property name="targetObject"> <ref local="randomAge"/> </property> <property name="targetMethod"> <value>getAge</value> </property> </bean> </property></bean><bean id="randomAge" class="com.baobaotao.fd.RandomAge" />

对于静态方法：

[xhtml] view plaincopyprint?

1. <beanid="bdog"class="com.baobaotao.fb.Dog"> 
2.   <propertyname="age"> 
3.     <beanclass="org.springframework.beans.factory.config.MethodInvokingFactoryBean"> 
4.       <propertyname="targetClass"> 
5.         <value>com.baobaotao.fb.RandomAge</value> 
6.       </property> 
7.       <propertyname="targetMethod"> 
8.         <!-- getAge必须是静态方法 --> 
9.         <value>getAges</value> 
10.       </property> 
11.     </bean> 
12.   </property> 
13. </bean> 

<bean id="bdog" class="com.baobaotao.fb.Dog"> <property name="age"> <bean class="org.springframework.beans.factory.config.MethodInvokingFactoryBean"> <property name="targetClass"> <value>com.baobaotao.fb.RandomAge</value> </property> <property name="targetMethod"> <!-- getAge必须是静态方法 --> <value>getAges</value> </property> </bean> </property></bean>

使用静态方法的返回值注入的另一种方式：

[html] view plaincopyprint?

1. <beanid="config"   
2.         class="Configuration"factory-method="getInstance">   
3.         <!-- 配置文件路径 -->   
4.         <constructor-argtype="java.lang.String"value="config.properties"/>   
5. </bean>  

<bean id="config" class="Configuration" factory-method="getInstance"> <!-- 配置文件路径 --> <constructor-arg type="java.lang.String" value="config.properties"/> </bean>
运用 factory-method创建单例 ,getInstance指定的是静态方法，而不是使用构造函数来创建类的实例

[java] view plaincopyprint?

1. private static Configuration _instance =null;   
2.    
3. private Configuration(String configPath){   
4.                 //执行你配置文件的加载   
5.         System.out.println("configPath");   
6.     }   
7.        
8.     public static Configuration getInstance(String configPath){   
9.         logger.info("init...");   
10.         if(_instance == null){   
11.             _instance = new Configuration(configPath);   
12.         }   
13.         return _instance;   
14. }