Introduction to Spring - Spring Enterprise Recipes: A Problem Solution Approach - page 15

</entry>
</map>
</property>
</bean>
In all the collection classes seen thus far, you used values to set the properties. Sometimes the
desired goal is to configure a null value using a Map instance. Spring's XML configuration schema
includes explicit support for this. Here is a map with null values for the value of an entry:
<property name="nulledMapValue">
<map>
<entry>
<key> <value>null</value> </key>
</entry>
</map>
</property>
A java.util.Properties collection is very similar to a map. It also implements the java.util.Map
interface and stores entries in key/value pairs. The only difference is that the keys and values of a
Properties collection are always strings.
package com.apress.springenterpriserecipes.sequence;
...
public class SequenceGenerator {
...
private Properties suffixes;
public void setSuffixes( Properties suffixes) {
this.suffixes = suffixes;
}
...
}
To define a java.util.Properties collection in Spring, use the <props> tag with multiple <prop> tags
as children. Each <prop> tag must have a key attribute defined and the corresponding value enclosed.
<bean id="sequenceGenerator"
class="com.apress.springenterpriserecipes.sequence.SequenceGenerator">
...
<property name="suffixes">
<props>
<prop key="type">A</prop>
<prop key="url"> http://www.apress.com/</prop>
<prop key="null">null</prop>
</props>
</property>
</bean>
If you define your beans with inheritance, a child bean's collection can be merged with that of its
parent by setting the merge attribute to true . For a <list> collection, the child elements will be added.