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Provided that the key
InstantiatingNullHandler.CREATE_NULL_OBJECTS is in the action context with a value of true (this key is set
only during the execution of the
com.opensymphony.xwork.interceptor.ParametersInterceptor ), OGNL expressions
that have caused a NullPointerException will be temporarily stopped for evaluation while the system automatically
tries to solve the null references by automatically creating the object.
The following rules are used when handling null references:
- If the property is declared exactly as a
Collection or
List , then an ArrayList shall be
returned and assigned to the null references.
- If the property is declared as a
Map , then a HashMap will be returned and assigned to the null
references.
- If the null property is a simple bean with a no-arg constructor, it will simply be created using the
ObjectFactory.buildBean(java.lang.Classjava.util.Map) method.
For example, if a form element has a text field named person.name and the expression person evaluates
to null, then this class will be invoked. Because the person expression evaluates to a Person class, a
new Person is created and assigned to the null reference. Finally, the name is set on that object and the overall
effect is that the system automatically created a Person object for you, set it by calling setPerson() and then
finally called getPerson().setName() as you would typically expect.
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