详解Java的Spring框架中bean的注入集合

 更新时间:2015年12月05日 17:15:10   投稿:goldensun   我要评论
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:

2015125170730018.png (578×174)

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:

2015125170747225.png (589×320)

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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