详解Java的Spring框架中bean的注入集合

这篇文章主要介绍了详解Java的Spring框架中bean的注入集合,Spring是Java的SSH三大web开发框架之一,需要的朋友可以参考下

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，这两种情况下可以处理单值到一个bean，如果你想通过多元值，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：

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：

这里是JavaCollection.java文件的内容：

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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：

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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：

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<? 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：

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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：

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<? 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：

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<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：

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

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