Spring笔记2——Spring中Bean的装配

1、引言  

　　Spring中，对象无需自己负责查找或创建与其关联的其他对象，而是由容器负责把需要相互协作的对象引用赋予各个对象。创建应用对象之间的协作关系的行为通常称为装配（Wiring），这也是依赖注入的本质。

2、声明Bean

　　配置Bean的方式主要有两种：基于XML文件的配置方式和基于Java注解的配置方式。传统的基于XML文件的配置方式在声明Bean时，Spring配置文件的根元素来源于Spring beans命名空间所定义的<beans>元素。除了beans命名空间外，Java自带了多种XML命名空间，通过这些命名空间可以配置Spring容器 。

　　下图为一些常见的Spring命名空间：

 

简单声明Bean的实例：

     Bean类：

 package com.springinaction.springidol;
public class Juggler implements Performer {
     private int beanBags = 3;
 
     public Juggler(){
     }
 
     public Juggler( int beanBags){
            this. beanBags = beanBags;
     }
     
     public void perform() throws PerformanceException {
           System. out.println( "抛掷 "+ beanBags + "个豆袋子" );
     }
 }

     配置文件：

<?xml version="1.0" encoding= "UTF-8"?>
     <beans xmlns= "http://www.springframework.org/schema/beans"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd" >
 
     <bean id ="duke" class= "com.springinaction.springidol.Juggler" >
            <constructor-arg value ="15" />
     </bean >         
</beans>

3、Spring的常用装配Bean值的方法     

<?xml version="1.0" encoding= "UTF-8"?>
  <beans xmlns= "http://www.springframework.org/schema/beans"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://www.springframework.org/schema/beans     http://www.springframework.org/schema/beans/spring-beans.xsd">
 
     <!--构造器注入值 -->
     <bean id ="duke" class= "com.springinaction.springidol.Juggler" >
            <constructor-arg value ="15" />
     </bean >
     <bean id ="sonnet29" class= "com.springinaction.springidol.Sonnet29" >
     </bean >
     <bean id ="poeticDuke" class= "com.springinaction.springidol.PoeticJuggler" >
            <constructor-arg  value ="15" />
            <!--构造器注入对象引用 -->
            <constructor-arg  ref ="sonnet29" />
     </bean >
     <!--通过工厂方法创建Bean,适合单例设计模式 -->
     <bean id ="theStage" class= "com.springinaction.springidol.Stage"
            factory-method= "getInstance">
     </bean >
 
     <!--初始化和销毁Bean -->
     <bean id ="auditorium" class= "com.springinaction.springidol.Auditorium"
            init-method= "turnOnLights" destroy-method="turnOffLights" >
     </bean >
     <!--注入属性值 -->
     <bean id ="kenny" class= "com.springinaction.springidol.Instrumentalist" >
            <!--注入简单值 -->
            <property name ="song" value="Jingle Bells" />
            <!--注入引用 -->
            <property name ="instrument" ref="pinao" />
            <!-- 内部Bean（inner bean） -->
            <!-- <property name="instrument"> <bean class="com.springinaction.springidol.Saxophone"></bean>
                </property> -->
     </bean >
     <!--装配集合 -->
     <bean id ="hank" class= "com.springinaction.springidol.OneManBand" >
            <property name ="instruments">
                 <list >
                      <ref bean ="pinao" />
                      <ref bean ="saxophon" />
                 </list >
            </property >
     </bean >
     <!--装配Map集合 -->
     <bean id ="hank2" class= "com.springinaction.springidol.OneManBand2" >
            <property name ="instruments">
                 <map >
                      <entry key ="PINAO" value-ref="pinao" />
                      <entry key ="SAXOPHON" value-ref="saxophon" />
                 </map >
            </property >
     </bean >
     <!--装配Properties集合 -->
     <bean id ="hank3" class= "com.springinaction.springidol.OneManBand3" >
            <property name ="instruments">
                 <props >
                      <prop key ="PINAO">TOOT TOOT TOOT</ prop>
                      <prop key ="SAXOPHON">PLINK PLINK PLINK</prop>
                 </props >
            </property >
     </bean >
     <!--装配空值 -->
     <bean id="example" class="com.springinaction.springidol.OneManBand2">
           <property name="someNonNullProperty">
                <null />
           </property>
     </bean> 
     <bean id ="saxophon" class= "com.springinaction.springidol.Saxophone" ></bean >
     <bean id ="pinao" class= "com.springinaction.springidol.Pinao" ></bean >
</beans>

4、SPEL(Spring表达式语言)

　　Spring还可以使用表达式进行装配，Spring使用SPEL装配的实例如下所示：     

<?xml version="1.0" encoding= "UTF-8"?>
  <beans xmlns= "http://www.springframework.org/schema/beans"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
 
     <!-- 字面值 -->
     <bean id ="duke" class= "com.springinaction.springidol.Juggler" >
            <!-- 整形 -->
            <property name ="song" value="#{5}" />
            <!-- 混合表达 -->
            <property name ="song" value="The Value is #{5}" />
            <!--浮点数 -->
            <property name ="song" value="#{89.7}" />
            <!--科学计数法 -->
            <property name ="song" value="#{1e4}" />
            <!--单引号或双引号为字符串 -->
            <property name ="song" value="#{'string'}" />
            <property name ="song" value='#{"string"}' />
            <!--布尔值 -->
            <property name ="song" value="#{false}" />
     </bean >
 
     <!-- 引用Bean、Properties和方法 -->
     <bean id ="car1" class= "com.springinaction.springidol.Instrumentalist" >
            <!-- 使用SPEL表达式装配Bean值 -->
            <property name ="instrument" value="#{saxophone}" />
            <!-- 使用SPEL表达式装配属性值 -->
            <property name ="song" value="#{kenny.song}" />
            <!-- 使用SPEL表达式调用其他Bean的方法 -->
            <property name ="song" value= "#{songSelector.selectSong()?.toUpperCase()}" />
     </bean >
 
     <!-- 操作类,T()会调用类作用域的方法和常量 -->
     <bean id ="car1" class= "com.springinaction.springidol.Instrumentalist" >
            <!-- 使用SPEL表达式获取PI值 -->
            <property name ="multiolier" value= "#{T(java.lang.Math).PI}" />
            <!-- 使用SPEL表达式获取随机数 -->
            <property name ="song" value= "#{T(java.lang.Math).random()}" />
     </bean >
 
     <!-- SPEL进行数值计算 -->
     <bean id ="car1" class= "com.springinaction.springidol.Instrumentalist" >
            <!-- 使用SPEL进行常规计算 -->
            <property name ="adjustedAmount" value= "#{counter.total+42}" />
            <!-- 使用SPEL进行乘法运算 -->
            <property name ="adjustedAmount" value="#{2 * T(java.lang.Math).PI * circle.radius}" />
            <!-- 使用SPEL进行除法运算 -->
            <property name ="adjustedAmount" value= "#{counter.total / counter.count}" />
            <!-- 使用SPEL进行求余运算 -->
            <property name ="adjustedAmount" value= "#{counter.total % counter.count}}" />
            <!-- 不同于Java，SPEL还提供乘方运算 -->
            <property name ="adjustedAmount"
                 value= "#{2 * T(java.lang.Math).PI * circle.radius ^ 2}" />
            <!-- 使用SPEL还可以使用+号进行字符串的连接 -->
            <property name ="adjustedAmount"
                 value= "#{performer.firstName + '' + performer.lastName}" />
     </bean >
 
     <!-- SPEL进行比较 -->
     <bean id ="car2" class= "com.springinaction.springidol.Instrumentalist" >
            <!-- 判断条件是否成立，进行装配布尔值属性,并且Spring中使用le和ge替代<=和>=号 -->
            <property name ="equal" value="#{counter.total == 100}" />
     </bean >
 
     <!-- SPEL的逻辑表达式 and、or、not或！ -->
     <bean id ="car1" class= "com.springinaction.springidol.Instrumentalist2" >
            <property name ="largeCircle"
                 value= "#{shape.kind == 'circle' and shape.perimeter gt 1000}" />
            <property name ="outOfStock" value= "#{!product.avaliable}" />
     </bean >
 
     <!-- SPEL的条件表达式 -->
     <bean id ="car1" class= "com.springinaction.springidol.Instrumentalist2" >
            <property name ="song"
                 value= "#{kenny.song != null ? kenny.song : 'Greensleeves'}" />
            <!-- 三元运算符的简化形式 ,这被称为elvis运算符 -->
            <property name ="song" value="#{kenny.song ?: 'Greensleeves'}" />
     </bean >
 
     <!-- SPEL的正则表达式 -->
     <bean id ="car1" class= "com.springinaction.springidol.Instrumentalist2" >
            <property name ="validEmail"
                 value= "#{admin.email matches '[a-zA-Z0-9._%+-]+\.com'}" />
     </bean >
</beans>

SPEL的重要功能，筛选集合实例：    

 <?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:p= "http://www.springframework.org/schema/p"
     xmlns:util="http://www.springframework.org/schema/util"
     xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
     http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd">
 
     <!-- 使用Spring设置列表 -->
     <util:list id ="cities">
            <bean class ="com.springinaction.springidol.spel.City" p:name= "Chicage1"
                 p:state= "1L" p:population ="111111111"></ bean>
            <bean class ="com.springinaction.springidol.spel.City" p:name= "Chicage2"
                 p:state= "2L" p:population ="211111111">
            </bean >
            <bean class ="com.springinaction.springidol.spel.City" p:name= "Chicage3"
                 p:state= "3L" p:population ="311111111">
            </bean >
            <bean class ="com.springinaction.springidol.spel.City" p:name= "Chicage4"
                 p:state= "4L" p:population ="411111111">
            </bean >
            <bean class ="com.springinaction.springidol.spel.City" p:name= "Chicage5"
                 p:state= "5L" p:population ="511111111">
            </bean >
            <bean class ="com.springinaction.springidol.spel.City" p:name= "Chicage6"
                 p:state= "6L" p:population ="611111111">
            </bean >
            <bean class ="com.springinaction.springidol.spel.City" p:name= "Chicage7"
                 p:state= "7L" p:population ="711111111">
            </bean >
            <bean class ="com.springinaction.springidol.spel.City" p:name= "Chicage8"
                 p:state= "8L" p:population ="811111111">
            </bean >
     </util:list >
 
     <!-- SPEL筛选集合 -->
     <bean id ="spelSelectSet" class= "com.springinaction.springidol.spel.ChooseCity" >
            <!-- 选择第三个城市 -->
            <!-- <property name="chooseCitySet" value="#{cities[2]}"></property> -->
            <!-- 随机选择城市 -->
            <property name ="chooseCitySet"
                 value= "#{cities[T(java.lang.Math).random() * cities.size()]}"></property>
            <!-- 系统环境 -->
            <property name ="systemEnviorment" value= "#{systemEnvironment['JAVA_HOME']}" ></property >
            <!-- 系统配置信息 -->
            <property name ="systemProperties" value= "#{systemProperties['path']}"></property >
            <!-- 查询集合成员.?[]运算符 -->
            <property name ="bigCities" value= "#{cities.?[population gt 400000000]}" ></property >
            <!-- 查询第一个符合条件.^[]运算符 -->
            <property name ="firstBigCity" value= "#{cities.^[population gt 400000000]}" ></property >
            <!-- 查询最后一个符合条件.$[]运算符 -->
            <property name ="lastBigCity" value= "#{cities.$[population gt 400000000]}" ></property >
            <!-- 集合投影,即将将每一个成员中选取特有的属性放入新集合中 ,运算符.![] -->
            <property name ="cityNames" value= "#{cities.?[population gt 400000000].![name + ',' +state]}"></ property>
     </bean >
</beans>