You need to retrieve values from a bean property of type Map.

Use PropertyUtils.getMappedProperty() to obtain values from a map property. The code here retrieves the value corresponding to the key "Dining Room" from the room map property of the Apartment bean:

import org.apache.commons.beanutils.PropertyUtils;
Room dining = new Room( );
dining.setArea( 20 );
dining.setCarpeted( true );
dining.setFurnished( true );
Map rooms = new HashMap( );
rooms.put( "Dining Room", dining );
Apartment apartment = new Apartment( );
apartment.setRooms( rooms );
// Retrieve the Dining Room object
               Room room = 
                   PropertyUtils.getMappedProperty( apartment, "rooms(Dining Room)" );
            

The code shown in the Solution section retrieves the value from the rooms map corresponding to the key "Dining Room"—rooms(Dining Room). The call to getMappedProperty( ) is the equivalent of calling apartment.getRooms( ).get("Dining Room"). Figure 3-4 illustrates the structure and relationship of these two beans used, Apartment and Room.

Figure 3-4. Diagram of the Apartment and Room beans

getMappedProperty( ) works only if the specified Map has String keys. getMappedProperty( ) takes the string between ( and ) and retrieves the value corresponding to this string.

There is another version of PropertyUtils.getMappedProperty() that takes a third argument, allowing you to specify the map property in the second argument and the key in the third argument. The code here uses two different versions of getMappedProperty( ) to retrieve the same value from the rooms map property:

import java.util.Map;
import java.util.HashMap;
import org.apache.commons.beanutils.PropertyUtils;
Room dining = new Room( );
dining.setArea( 20 );
dining.setCarpeted( true );
dining.setFurnished( true );
Map rooms = new HashMap( );
rooms.put( "Dining Room", dining );
Apartment apartment = new Apartment( );
apartment.setRooms( rooms );
// Retrieve the livingRoom key
Room room = 
                   (Room) PropertyUtils.getMappedProperty( apartment, 
     "rooms(Dining Room)" );
// Or.. retrieve the livingRoom key with 3 parameters - 
// equivalent to previous
room = 
    (Room) PropertyUtils.getMappedProperty( apartment, "rooms", 
   "Dining Room" ); 
            

What was true for getIndexedProperty( ) is also true for getMappedProperty( ). In the previous example, the first call to getMappedProperty( ) specifies a key with a string—rooms(Dining Room). If getMappedProperty( ) is unable to parse this string, an IllegalArgumentException will be thrown; rooms[DiningRoom) and rooms((DiningRoom) will both throw IllegalArgumentException because the property string is not well-formed. The second call to getMappedProperty( ) reduces the risk of a property string parsing error because the key is specified in a third parameter.