com.opensymphony.xwork2.util
Class InstantiatingNullHandler

java.lang.Object
  com.opensymphony.xwork2.util.InstantiatingNullHandler

All Implemented Interfaces:

ognl.NullHandler

public class InstantiatingNullHandler
extends Object
implements ognl.NullHandler

Provided that the key CREATE_NULL_OBJECTS is in the action context with a value of true (this key is set only during the execution of the 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.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.

Field Summary

static String	CREATE_NULL_OBJECTS
private static Log	LOG

Constructor Summary

InstantiatingNullHandler()

Method Summary

private Object	createObject(Class clazz, Object target, String property, Map context)
Object	nullMethodResult(Map context, Object target, String methodName, Object[] args)
Object	nullPropertyValue(Map context, Object target, Object property)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

CREATE_NULL_OBJECTS

public static final String CREATE_NULL_OBJECTS

See Also:

Constant Field Values

LOG

private static final Log LOG

Constructor Detail

InstantiatingNullHandler

public InstantiatingNullHandler()

Method Detail

nullMethodResult

public Object nullMethodResult(Map context,
                               Object target,
                               String methodName,
                               Object[] args)

Specified by:

nullMethodResult in interface ognl.NullHandler

nullPropertyValue

public Object nullPropertyValue(Map context,
                                Object target,
                                Object property)

Specified by:

nullPropertyValue in interface ognl.NullHandler

createObject

private Object createObject(Class clazz,
                            Object target,
                            String property,
                            Map context)
                     throws Exception

Throws:

Exception