Spring在Bean中注入集合

以下内容引用自http://wiki.jikexueyuan.com/project/spring/injecting-collection.html：

如果你想传递多个值，如Java Collection类型List、Set、Map和Properties，Spring 提供了四种类型的集合的配置元素，如下所示：

元素	描述
<list>	它有助于连线，如注入一列值，允许重复。
<set>	它有助于连线一组值，但不能重复。
<map>	它可以用来注入键值对的集合，其中键和值可以是任何类型。
<props>	它可以用来注入键值对的集合，其中键和值都是字符串类型。

您可以使用<list>或<set>来连接java.util.Collection的任何实现或数组。您将遇到两种情况（a）传递集合的直接值，（b）将bean的引用作为集合元素之一传递。

例子：

pom.xml：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.jsoft.testspring</groupId>
  <artifactId>testinjectioncollection</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>testinjectioncollection</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    
    <!-- Spring Core -->
    <!-- http://mvnrepository.com/artifact/org.springframework/spring-core -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>4.1.4.RELEASE</version>
    </dependency>
     
    <!-- Spring Context -->
    <!-- http://mvnrepository.com/artifact/org.springframework/spring-context -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>4.1.4.RELEASE</version>
    </dependency>
    
  </dependencies>
</project>

JavaCollection.java：

package com.jsoft.testspring.testinjectioncollection;

import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set;

public class JavaCollection {
       private List addressList;
       private Set  addressSet;
       private Map  addressMap;
       private Properties addressProp;

       public void setAddressList(List addressList) {
          this.addressList = addressList;
       }
       
       public List getAddressList() {
          System.out.println("List :"  + addressList);
          return addressList;
       }
       
       public void setAddressSet(Set addressSet) {
          this.addressSet = addressSet;
       }
       
       public Set getAddressSet() {
          System.out.println("Set :"  + addressSet);
          return addressSet;
       }
       
       public void setAddressMap(Map addressMap) {
          this.addressMap = addressMap;
       }
       
       public Map getAddressMap() {
          System.out.println("Map :"  + addressMap);
          return addressMap;
       }
       
       public void setAddressProp(Properties addressProp) {
          this.addressProp = addressProp;
       }
       
       public Properties getAddressProp() {
          System.out.println("Property :"  + addressProp);
          return addressProp;
       }
}

beans.xml：

<?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="javaCollection" class="com.jsoft.testspring.testinjectioncollection.JavaCollection">
      
      <!-- list -->
      <property name="addressList">
         <list>
            <value>INDIA</value>
            <value>Pakistan</value>
            <value>USA</value>
            <value>USA</value>
         </list>
      </property>

      <!-- set -->
      <property name="addressSet">
         <set>
            <value>INDIA</value>
            <value>Pakistan</value>
            <value>USA</value>
            <value>USA</value>
         </set>
      </property>

      <!-- map -->
      <property name="addressMap">
         <map>
            <entry key="1" value="INDIA"/>
            <entry key="2" value="Pakistan"/>
            <entry key="3" value="USA"/>
            <entry key="4" value="USA"/>
         </map>
      </property>
      
      <!-- property -->
      <property name="addressProp">
         <props>
            <prop key="one">INDIA</prop>
            <prop key="one">INDIA</prop>
            <prop key="two">Pakistan</prop>
            <prop key="three">USA</prop>
            <prop key="four">USA</prop>
         </props>
      </property>
   </bean>

</beans>

App.java：

package com.jsoft.testspring.testinjectioncollection;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * Hello world!
 *
 */
public class App 
{
    public static void main( String[] args )
    {
        ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        JavaCollection jc=(JavaCollection)context.getBean("javaCollection");

        jc.getAddressList();
        jc.getAddressSet();
        jc.getAddressMap();
        jc.getAddressProp();
    }
}

运行结果：

注入Bean引用：

下面的Bean定义将展示如何注入bean的引用作为集合的元素。甚至可以将引用和值混合在一起，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">


    <bean id="address1" class="com.jsoft.testspring.testinjectioncollection.Address"></bean>
    <bean id="address2" class="com.jsoft.testspring.testinjectioncollection.Address"></bean>
    <bean id="javaCollection" class="com.jsoft.testspring.testinjectioncollection.JavaCollection">

        <!-- list -->
        <property name="addressList">
            <list>
                <value>INDIA</value>
                <value>Pakistan</value>
                <value>USA</value>
                <value>USA</value>
                <ref bean="address1"/>
                <ref bean="address2"/>
            </list>
        </property>

        <!-- set -->
        <property name="addressSet">
            <set>
                <value>INDIA</value>
                <value>Pakistan</value>
                <value>USA</value>
                <value>USA</value>
                <ref bean="address1"/>
                <ref bean="address2"/>
            </set>
        </property>

        <!-- map -->
        <property name="addressMap">
            <map>
                <entry key="1" value="INDIA" />
                <entry key="2" value="Pakistan" />
                <entry key="3" value="USA" />
                <entry key="4" value="USA" />
                <entry key="5" value-ref="address1" />
                <entry key="6" value-ref="address2" />
            </map>
        </property>

        <!-- property -->
        <property name="addressProp">
            <props>
                <prop key="one">INDIA</prop>
                <prop key="one">INDIA</prop>
                <prop key="two">Pakistan</prop>
                <prop key="three">USA</prop>
                <prop key="four">USA</prop>
            </props>
        </property>
        
    </bean>

</beans>

可以看出，除了property类型外，全部都可以注入bean。因为property类型键值都只能是字符串类型，所以没办法使用对象。

注入null或空字符串的值：

如果你需要传递一个空字符串作为值，那么你可以传递它，如下所示：

<bean id="..." class="exampleBean">
   <property name="email" value=""/>
</bean>

前面的例子相当于Java代码：exampleBean.setEmail("")。

如果你需要传递一个NULL值，那么你可以传递它，如下所示：

<bean id="..." class="exampleBean">
   <property name="email"><null/></property>
</bean>

前面的例子相当于Java代码：exampleBean.setEmail(null)。

测试工程：https://github.com/easonjim/5_java_example/tree/master/springtest/test10/testinjectioncollection