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WebWork supports ways to determine the object type found in collections. This is done via an ObjectTypeDetermine ObjectTypeDeterminer. The default implementation is provided. The JavaDocs explain how map and colelction support is determined in the DefaultObjectTypeDeterminer:

{snippet:id=javadoc|javadoc=true|url=com.opensymphony.xwork.util.DefaultObjectTypeDeterminer}

Additionally, you can create your own custom ObjectTypeDeterminer by implementing the ObjectTypeDeterminer interface. There is also an optional ObjectTypeDeterminer that utilizes Java 5 generics. See the J2SE 5 Support page for more information.

Indexing a collection by a property of that collection

It is also possible using webwork to get a unique element of a collection, by passing the value of a given property of that element. By default, the property of the element of the collection is determined in Class-conversion.properties using KeyProperty_xxx=yyy where xxx is the property of the bean 'Class' that returns the collection and yyy is the property of the collection element that we want to index on. Here is an example with the following two classes:

/**
 * @return a Collection of Foo objects
 */
public Collection getFooCollection()
{
    return foo;
}

/**
 * @return a unique identifier
 */
public Long getId()
{
    return id;
}

Then put KeyProperty_fooCollection=id in my MyAction-conversion.properties file. This would allow to the use of fooCollection(someIdValue) to get the Foo object with value someIdValue in the Set fooSet. For example, fooSet(22) would return the Foo object in the fooCollection collection whose id property value was 22.

This is useful, because it ties a collection element directly to its unique identifier and therefore does not force you to use an index and thus allows you to edit the elements of a collection associated to a bean without any additional code. For example, parameter name fooCollection(22).name and value Phil would set name the Foo object in the fooCollection collection whose id property value was 22 to be Phil.

Webwork automatically converts the type of the parameter sent in to the type of the key property using type conversion.

Unlike Map and List element properties, if fooCollection(22) does not exist it will not be created. To do that, use the notation *fooCollection.makeNew\[index\]* where index is an integer 0, 1, and so on. Thus, parameter value pairs *fooCollection.makeNew\[0\]=Phil* and *fooSet.makeNew\[1\]=John* would add two new Foo objects to fooCollection one with name property value Phil and the other with name property value Bar. Note, however, that in the case of a Set, the equals and hashCode methods should be defined such that they don't only include the id property. That will cause one element of the null id propertied Foos to be removed from the Set.

Type Conversion Error Handling

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