Package org.apache.commons.collections4

Class FactoryUtils

java.lang.Object

org.apache.commons.collections4.FactoryUtils

public class FactoryUtils
extends Object

FactoryUtils provides reference implementations and utilities for the Factory functor interface. The supplied factories are:

• Prototype - clones a specified object
• Instantiate - creates objects using reflection
• Constant - always returns the same object
• Null - always returns null
• Exception - always throws an exception

Since v4.1 only factories which are considered to be safe are Serializable. Factories considered to be unsafe for serialization are:

• Prototype
• Instantiate

Since:

3.0

Method Summary

Modifier and Type	Method	Description
static <T> Factory<T>	constantFactory(T constantToReturn)	Creates a Factory that will return the same object each time the factory is used.
static <T> Factory<T>	exceptionFactory()	Gets a Factory that always throws an exception.
static <T> Factory<T>	instantiateFactory(Class<T> classToInstantiate)	Creates a Factory that can create objects of a specific type using a no-args constructor.
static <T> Factory<T>	instantiateFactory(Class<T> classToInstantiate, Class<?>[] paramTypes, Object[] args)	Creates a Factory that can create objects of a specific type using the arguments specified to this method.
static <T> Factory<T>	nullFactory()	Gets a Factory that will return null each time the factory is used.
static <T> Factory<T>	prototypeFactory(T prototype)	Creates a Factory that will return a clone of the same prototype object each time the factory is used.

Methods inherited from class java.lang.Object

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

Method Details

constantFactory

public static <T> Factory<T> constantFactory(T constantToReturn)

Creates a Factory that will return the same object each time the factory is used. No check is made that the object is immutable. In general, only immutable objects should use the constant factory. Mutable objects should use the prototype factory.

Type Parameters:

T - the type that the factory creates

Parameters:

constantToReturn - the constant object to return each time in the factory

Returns:

the constant factory.

See Also:

• ConstantFactory

exceptionFactory

public static <T> Factory<T> exceptionFactory()

Gets a Factory that always throws an exception. This could be useful during testing as a placeholder.

Type Parameters:

T - the type that the factory creates

Returns:

the factory

See Also:

• ExceptionFactory

instantiateFactory

public static <T> Factory<T> instantiateFactory(Class<T> classToInstantiate)

Creates a Factory that can create objects of a specific type using a no-args constructor.

Type Parameters:

T - the type that the factory creates

Parameters:

classToInstantiate - the Class to instantiate each time in the factory

Returns:

the reflection factory

Throws:

NullPointerException - if the classToInstantiate is null

See Also:

• InstantiateFactory

instantiateFactory

public static <T> Factory<T> instantiateFactory(Class<T> classToInstantiate,
 Class<?>[] paramTypes,
 Object[] args)

Creates a Factory that can create objects of a specific type using the arguments specified to this method.

Type Parameters:

T - the type that the factory creates

Parameters:

classToInstantiate - the Class to instantiate each time in the factory

paramTypes - parameter types for the constructor, can be null

args - the arguments to pass to the constructor, can be null

Returns:

the reflection factory

Throws:

NullPointerException - if the classToInstantiate is null

IllegalArgumentException - if the paramTypes and args don't match

IllegalArgumentException - if the constructor doesn't exist

See Also:

• InstantiateFactory

nullFactory

public static <T> Factory<T> nullFactory()

Gets a Factory that will return null each time the factory is used. This could be useful during testing as a placeholder.

Type Parameters:

T - the "type" of null object the factory should return.

Returns:

the factory

See Also:

• ConstantFactory

prototypeFactory

public static <T> Factory<T> prototypeFactory(T prototype)

Creates a Factory that will return a clone of the same prototype object each time the factory is used. The prototype will be cloned using one of these techniques (in order):

• public clone method
• public copy constructor
• serialization clone

Type Parameters:

T - the type that the factory creates

Parameters:

prototype - the object to clone each time in the factory

Returns:

the prototype factory, or a ConstantFactory.NULL_INSTANCE if the prototype is null

Throws:

IllegalArgumentException - if the prototype cannot be cloned

See Also:

• PrototypeFactory