Wiring Map Collections Using References
In this tutorial you will learn about how to wire Map collection Using References
In this tutorial you will learn about how to wire Map collection Using ReferencesWiring references to <set> element
The <set> element is used to store multiple unique values. Its sub element <ref> element can be used to provide values as references to other beans. Lets take an example to demonstrate how set element is used.
Product.java: The product class contains property named parts which is the collection of the values of Part type.
import java.util.*;
public class Product
{
private List<Part> parts;
public void setParts(List<Part> parts) {
this.parts = parts;
}
public List<Part> getParts() {
return parts;
}
}
Part.java: This is the class the objects of which are being used as the values for the property of List type named parts.
import java.util.*;
public class Part
{
private String name;
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
spring-beans.xml: The <set> element is used to provide unique values to the Set or List type property of the Product class. Here <ref> element provides those values as references to the Part type objects.
<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-2.5.xsd">
<bean id="product" class="Product">
<property name="parts">
<set>
<ref bean="part1"/>
<ref bean="part2"/>
<ref bean="part3"/>
</set>
</property>
</bean>
<bean id="part1" class="Part">
<property name="name" value="Part 1"/>
</bean>
<bean id="part2" class="Part">
<property name="name" value="Part 2"/>
</bean>
<bean id="part3" class="Part">
<property name="name" value="Part 3"/>
</bean>
</beans>
AppMain.java: This class loads the context configuration file spring-beans-list.xml from the class path.
import
org.springframework.context.ApplicationContext;
import
org.springframework.context.support.ClassPathXmlApplicationContext;
public class AppMain
{
public static void main( String[] args )
{
ApplicationContext appContext =
new ClassPathXmlApplicationContext(new String[]
{"spring-beans.xml"});
Product product = (Product)appContext.getBean("product");
for (Part part : product.getParts()) {
System.out.println(part.getName());
}
}
}
If we provide two same objects to the set property then it considers only one because of uniqueness feature of set type collection. For example
<bean id="product" class="Product">
<property name="parts">
<set>
<ref bean="part1"/>
<ref bean="part1"/>
<ref bean="part3"/>
</set>
</property>
</bean>
Now in this case the main class prints names of two parts part1 and part 3 only once each.
