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
