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Spring注入集合

   

您已经看到了如何配置基本数据类型使用value属性和使用<property>标签的ref属性在你的bean配置文件中的对象引用。这两种情况下处理过单值到一个bean。

现在什么样,如果你想通过多元价值,如Java Collection类型List, Set, Map 及 Properties。要处理这种情况,Spring提供了四种类型的如下集合的配置元素:

元素 描述
<list> 这有助于注入值列表List配线,使重复。
<set> 这有助于在配线的一组值,但不能重复。
<map> 这可用于注入的名称 - 值对,其中名称和值可以是任何类型的集合。
<props> 这可以用来注入的名称 - 值对,其中名称和值都是字符串的集合。

可以使用<list> 或<set> 来连接任何实现java.util.Collection或数组。

会遇到两种情况(a)将收集的直接的值及(b)传递一个bean的引用作为集合的元素之一。

例子:

我们使用Eclipse IDE,然后按照下面的步骤来创建一个Spring应用程序:

步骤 描述
1 Create a project with a name SpringExample and create a package com.yiibai under the src folder in the created project.
2 Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter.
3 Create Java classes JavaCollection, and MainApp under the com.yiibai package.
4 Create Beans configuration file Beans.xml under the src folder.
5 The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below.

这里是JavaCollection.java文件的内容:

 package com.yiibai; import java.util.*;  public class JavaCollection {    List addressList;    Set  addressSet;    Map  addressMap;    Properties addressProp;     // a setter method to set List    public void setAddressList(List addressList) {       this.addressList = addressList;    }    // prints and returns all the elements of the list.    public List getAddressList() {       System.out.println("List Elements :"  + addressList);       return addressList;    }     // a setter method to set Set    public void setAddressSet(Set addressSet) {       this.addressSet = addressSet;    }     // prints and returns all the elements of the Set.    public Set getAddressSet() {       System.out.println("Set Elements :"  + addressSet);       return addressSet;    }     // a setter method to set Map    public void setAddressMap(Map addressMap) {       this.addressMap = addressMap;    }    // prints and returns all the elements of the Map.    public Map getAddressMap() {       System.out.println("Map Elements :"  + addressMap);       return addressMap;    }     // a setter method to set Property    public void setAddressProp(Properties addressProp) {       this.addressProp = addressProp;    }    // prints and returns all the elements of the Property.    public Properties getAddressProp() {       System.out.println("Property Elements :"  + addressProp);       return addressProp;    } }

以下是MainApp.java文件的内容:

 package com.yiibai;  import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext;  public class MainApp {    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();    } }

以下是配置文件beans.xml文件里面有配置的集合的所有类型:

 <?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-3.0.xsd">     <!-- Definition for javaCollection -->    <bean id="javaCollection" class="com.yiibai.JavaCollection">        <!-- results in a setAddressList(java.util.List) call -->       <property name="addressList">         <list>            <value>INDIA</value>            <value>Pakistan</value>            <value>USA</value>            <value>USA</value>         </list>       </property>       <!-- results in a setAddressSet(java.util.Set) call -->      <property name="addressSet">         <set>            <value>INDIA</value>            <value>Pakistan</value>            <value>USA</value>            <value>USA</value>         </set>       </property>       <!-- results in a setAddressMap(java.util.Map) call -->      <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>       <!-- results in a setAddressProp(java.util.Properties) call -->      <property name="addressProp">         <props>            <prop key="one">INDIA</prop>            <prop key="two">Pakistan</prop>            <prop key="three">USA</prop>            <prop key="four">USA</prop>         </props>       </property>     </bean>  </beans>

创建源代码和bean配置文件完成后,让我们运行应用程序。如果应用程序一切顺利,这将打印以下信息:

 List Elements :[INDIA, Pakistan, USA, USA] Set Elements :[INDIA, Pakistan, USA] Map Elements :{1=INDIA, 2=Pakistan, 3=USA, 4=USA} Property Elements :{two=Pakistan, one=INDIA, three=USA, four=USA} 

注入Bean引用:

下面bean定义将帮助您了解如何注入bean的引用作为集合的元素之一。甚至可以混合引用和值都在一起,如下图所示:

 <?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-3.0.xsd">     <!-- Bean Definition to handle references and values -->    <bean id="..." class="...">        <!-- Passing bean reference  for java.util.List -->       <property name="addressList">         <list>            <ref bean="address1"/>            <ref bean="address2"/>            <value>Pakistan</value>         </list>       </property>       <!-- Passing bean reference  for java.util.Set -->      <property name="addressSet">         <set>            <ref bean="address1"/>            <ref bean="address2"/>            <value>Pakistan</value>         </set>       </property>       <!-- Passing bean reference  for java.util.Map -->      <property name="addressMap">         <map>            <entry key="one" value="INDIA"/>            <entry key ="two" value-ref="address1"/>            <entry key ="three" value-ref="address2"/>         </map>       </property>     </bean>  </beans>

使用上面的bean定义,需要定义这样一种方式,他们应该能够处理的参考,以及setter方法。

注入null和空字符串的值

如果需要传递一个空字符串作为值,如下所示:

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

前面的例子等同于Java代码: exampleBean.setEmail("")

如果需要传递一个null值,如下所示:

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

前面的例子等同于Java代码:exampleBean.setEmail(null)

   
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