Provided that the key {@link ReflectionContextState#CREATE_NULL_OBJECTS} is in the action context with a value of true (this key is setonly during the execution of the {@link com.opensymphony.xwork2.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 {@link Collection} or {@link List}, then an ArrayList shall be returned and assigned to the null references.
- If the property is declared as a {@link 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 {@link ObjectFactory#buildBean(java.lang.Class,java.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 setUsers() and then finally called getUsers().setName() as you would typically expect.