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：

 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：

 <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：

 <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：

 <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>

 //-------------------------------------------------------------

public interface Person {
 public static final int BOSS_LEVEL = 5;
 public static final int MANAGE_LEVEL = 2;
 public static final int STAFF_LEVEL = 1;
//以下省略
}

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<!-- 将person接口中的常量 ，赋值给相应的bean,通过引用可以获取程序中的常量 --> < bean id = "BOSS_LEVEL_BEAN" class = "org.springframework.beans.factory.config.FieldRetrievingFactoryBean" > < property name = "staticField" value = "person.member.Person.BOSS_LEVEL" /> </ bean > < bean id = "MANAGE_LEVEL_BEAN" class = "org.springframework.beans.factory.config.FieldRetrievingFactoryBean" > < property name = "staticField" value = "person.member.Person.MANAGE_LEVEL" /> </ bean > < bean id = "STAFF_LEVEL_BEAN" class = "org.springframework.beans.factory.config.FieldRetrievingFactoryBean" > < property name = "staticField" value = "person.member.Person.STAFF_LEVEL" /> </ bean > <!-- 第二种方式也可以，感觉速度有点慢 也是通过引用--> <!-- <bean id="person.member.Person.MANAGE_LEVEL" class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean" /> <bean id="person.member.Person.BOSS_LEVEL" class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean"/> <bean id="person.member.Person.STAFF_LEVEL" class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean"/> --> < bean id = "bossMessage" class = "person.attribute.BaseMessage" > < property name = "userName" value = "老板" /> < property name = "age" value = "30" /> </ bean > < bean id = "bossJob" class = "person.attribute.Job" > < property name = "jobName" value = "takeMoney" /> < property name = "salary" value = "20000" /> < property name = "level" ref = "BOSS_LEVEL_BEAN" ></ property > </ bean > < bean id = "manageMessage" class = "person.attribute.BaseMessage" scope = "prototype" > < property name = "userName" value = "管理者" /> < property name = "age" value = "25" /> </ bean > < bean id = "manageJob" class = "person.attribute.Job" scope = "prototype" > < property name = "jobName" value = "management" /> < property name = "salary" value = "10000" /> < property name = "level" ref = "MANAGE_LEVEL_BEAN" ></ property > </ bean > < bean id = "staffMessage" class = "person.attribute.BaseMessage" > < property name = "userName" value = "职员" /> < property name = "age" value = "20" /> </ bean > < bean id = "staffJob" class = "person.attribute.Job" > < property name = "jobName" value = "work" /> < property name = "salary" value = "5000" /> < property name = "level" ref = "STAFF_LEVEL_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：

 <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：

 <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：

 <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

 private static Configuration _instance = null;

 private Configuration(String configPath){
                 //执行你配置文件的加载
         System.out.println("configPath");
     }

     public static Configuration getInstance(String configPath){
         logger.info("init...");
         if(_instance == null){
             _instance = new Configuration(configPath);
         }
         return _instance;
 }