Spring Dependency Injection 简明教程

Spring DI - Injecting Collections Ref Constructor

您已经看到如何使用 Bean 配置文件中的 <property> 标记的 value 属性配置原始数据类型，以及使用 ref 属性配置对象引用。这两种情况都涉及将奇异值传递给 Bean。

You have seen how to configure primitive data type using value attribute and object references using ref attribute of the <property> tag in your Bean configuration file. Both the cases deal with passing singular value to a bean.

现在，如果您想传递像 Java Collection 类型（比如 List、Set 和 Properties）这样的复数值该怎么办？为了应对这种情况，Spring 提供了以下类型的集合配置元素，如下所示 −

Now what if you want to pass plural values like Java Collection types such as List, Set, and Properties. To handle the situation, Spring offers following types of collection configuration elements which are as follows −

Sr.No

Element & Description

1

<list> This helps in wiring ie injecting a list of values, allowing duplicates.

2

<set> This helps in wiring a set of values but without any duplicates.

您可以使用 <list> 或 <set> 来接线任何 java.util.Collection 的实现或 array 。

You can use either <list> or <set> to wire any implementation of java.util.Collection or an array.

在此示例中，我们展示了使用 ref 传递集合元素。

In this example, we’re showcasing passing collection elements using ref.

Example

以下示例展示了一个 JavaCollection 类，它使用通过 setter 注入的依赖关系集合。

The following example shows a class JavaCollection that is using collection of dependencies injected using setters.

让我们更新在 Spring DI - Create Project 章节中创建的项目。我们将添加以下文件 −

Let’s update the project created in Spring DI - Create Project chapter. We’re adding following files −

  1. Address.java − A class to be used as dependency.

  2. JavaCollection.java − A class containing a collections of dependencies.

  3. MainApp.java − Main application to run and test.

以下是 Address.java 文件的内容 −

Here is the content of Address.java file −

package com.tutorialspoint;

public class Address {
   private String name;

   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
   @Override
   public String toString() {
      return name;
   }
}

以下是 JavaCollection.java 文件的内容−

Here is the content of JavaCollection.java file −

package com.tutorialspoint;
import java.util.*;

public class JavaCollection {
   List<Address> addressList;
   Set<Address>  addressSet;

   public JavaCollection(List<Address> addressList, Set<Address> addressSet) {
      this.addressList = addressList;
      this.addressSet = addressSet;
   }

   // a setter method to set List
   public void setAddressList(List<Address> addressList) {
      this.addressList = addressList;
   }

   // prints and returns all the elements of the list.
   public List<Address> getAddressList() {
      System.out.println("List Elements :"  + addressList);
      return addressList;
   }

   // a setter method to set Set
   public void setAddressSet(Set<Address> addressSet) {
      this.addressSet = addressSet;
   }

   // prints and returns all the elements of the Set.
   public Set<Address> getAddressSet() {
      System.out.println("Set Elements :"  + addressSet);
      return addressSet;
   }
}

以下是 MainApp.java 文件的内容−

Following is the content of the MainApp.java file −

package com.tutorialspoint;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("applicationcontext.xml");
      JavaCollection jc=(JavaCollection)context.getBean("javaCollection");

      jc.getAddressList();
      jc.getAddressSet();
   }
}

以下是配置文件 applicationcontext.xml ，其中包含了所有类型的集合配置 −

Following is the configuration file applicationcontext.xml which has configuration for all the type of collections −

<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 id = "address1" class = "com.tutorialspoint.Address">
      <property name="name" value="INDIA"></property>
   </bean>
   <bean id = "address2" class = "com.tutorialspoint.Address">
      <property name="name" value="JAPAN"></property>
   </bean>
   <bean id = "address3" class = "com.tutorialspoint.Address">
      <property name="name" value="USA"></property>
   </bean>
   <bean id = "address4" class = "com.tutorialspoint.Address">
      <property name="name" value="UK"></property>
   </bean>
   <!-- Definition for javaCollection -->
   <bean id = "javaCollection" class = "com.tutorialspoint.JavaCollection">
      <constructor-arg name = "addressList">
         <list>
            <ref bean="address1" />
            <ref bean="address2" />
            <ref bean="address3" />
            <ref bean="address4" />
         </list>
      </constructor-arg>
      <constructor-arg name = "addressSet">
         <set>
            <ref bean="address1" />
            <ref bean="address2" />
            <ref bean="address3" />
            <ref bean="address4" />
         </set>
      </constructor-arg>
   </bean>
</beans>

Output

完成源文件和 Bean 配置文件创建后，我们运行该应用程序。如果您的应用程序一切正常，它将打印以下消息−

Once you are done creating the source and bean configuration files, let us run the application. If everything is fine with your application, it will print the following message −

List Elements :[INDIA, JAPAN, USA, UK]
Set Elements :[INDIA, JAPAN, USA, UK]