詳解Java的Spring框架中bean的注入聚集

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應用value屬性和應用<property>標簽的ref屬性在你的bean設置裝備擺設文件中的對象援用，這兩種情形下可以處置單值到一個bean，假如你想經由過程多元值，如Java Collection類型List, Set, Map 及 Properties。要處置這類情形，Spring供給了四品種型的以下聚集的設置裝備擺設元素：

可使用<list> 或<set> 來銜接任何完成java.util.Collection或數組。

會碰到兩種情形（a）將搜集的直接的值及（b）傳遞一個bean的援用作為聚集的元素之一。

例子:
我們應用Eclipse IDE，然後依照上面的步調來創立一個Spring運用法式：

這裡是JavaCollection.java文件的內容：

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文件的內容：

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();
  }
}

以下是設置裝備擺設文件beans.xml文件外面有設置裝備擺設的聚集的一切類型：

<?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>

創立源代碼和bean設置裝備擺設文件完成後，讓我們運轉運用法式。假如運用法式一切順遂，這將打印以下信息：

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援用：
上面bean界說將贊助您懂得若何注入bean的援用作為聚集的元素之一。乃至可以混雜援用和值都在一路，以下圖所示：

<?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>

應用下面的bean界說，須要界說如許一種方法，他們應當可以或許處置的參考，和setter辦法。

注入null和空字符串的值
假如須要傳遞一個空字符串作為值，以下所示：

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

後面的例子同等於Java代碼： exampleBean.setEmail("")

假如須要傳遞一個null值，以下所示：

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

後面的例子同等於Java代碼：exampleBean.setEmail(null)