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。
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 −
Sr.No |
Element & Description |
1 |
<list> 这有助于进行接线,即注入一个值列表,同时允许重复。 |
2 |
<set> 这有助于接线一组值,但没有任何重复。 |
您可以使用 <list> 或 <set> 来接线任何 java.util.Collection 的实现或 array 。
在此示例中,我们展示了使用 ref 传递集合元素。
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。
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 −
-
Address.java - 用于作为依赖项的类。
-
JavaCollection.java - 包含依赖项集合的类。
-
MainApp.java - 要运行和测试的主应用。
以下是 Address.java 文件的内容 −
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−
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−
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 −
<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>