Initializing Map Properties

The map-entries element is used to initialize the values of a bean property with a type of java.util.Map if the map-entries element is used within a managed-property element. A map-entries element contains an optional key-class element, an optional value-class element, and zero or more map-entry elements.

Each of the map-entry elements must contain a key element and either a null-value or value element. Here is an example that uses the map-entries element:

<managed-bean>
    ...
    <managed-property>
        <property-name>prices</property-name>
        <map-entries>
            <map-entry>
                <key>My Early Years: Growing Up on *7</key>
                <value>30.75</value>
            </map-entry>
            <map-entry>
                <key>Web Servers for Fun and Profit</key>
                <value>40.75</value>
            </map-entry>
        </map-entries>
    </managed-property>
</managed-bean>

The map that is created from this map-entries tag contains two entries. By default, all the keys and values are converted to java.lang.String. If you want to specify a different type for the keys in the map, embed the key-class element just inside the map-entries element:

<map-entries>
    <key-class>java.math.BigDecimal</key-class>
    ...
</map-entries>

This declaration will convert all the keys into java.math.BigDecimal. Of course, you must make sure that the keys can be converted to the type that you specify. The key from the example in this section cannot be converted to a java.math.BigDecimal because it is a String.

If you also want to specify a different type for all the values in the map, include the value-class element after the key-class element:

<map-entries>
    <key-class>int</key-class>
    <value-class>java.math.BigDecimal</value-class>
    ...
</map-entries>

Note that this tag sets only the type of all the value subelements.

The first map-entry in the preceding example includes a value subelement. The value subelement defines a single value, which will be converted to the type specified in the bean.

The second map-entry defines a value element, which references a property on another bean. Referencing another bean from within a bean property is useful for building a system from fine-grained objects. For example, a request-scoped form-handling object might have a pointer to an application-scoped database mapping object. Together the two can perform a form-handling task. Note that including a reference to another bean will initialize the bean if it does not already exist.

Instead of using a map-entries element, it is also possible to assign the entire map using a value element that specifies a map-typed expression.