public class

TransformerUtils

extends Object
java.lang.Object
   ↳ org.apache.commons.collections.TransformerUtils

Class Overview

TransformerUtils provides reference implementations and utilities for the Transformer functor interface. The supplied transformers are:

  • Invoker - returns the result of a method call on the input object
  • Clone - returns a clone of the input object
  • Constant - always returns the same object
  • Closure - performs a Closure and returns the input object
  • Predicate - returns the result of the predicate as a Boolean
  • Factory - returns a new object from a factory
  • Chained - chains two or more transformers together
  • Switch - calls one transformer based on one or more predicates
  • SwitchMap - calls one transformer looked up from a Map
  • Instantiate - the Class input object is instantiated
  • Map - returns an object from a supplied Map
  • Null - always returns null
  • NOP - returns the input object, which should be immutable
  • Exception - always throws an exception
  • StringValue - returns a java.lang.String representation of the input object
All the supplied transformers are Serializable.

Summary

Public Constructors
TransformerUtils()
This class is not normally instantiated.
Public Methods
static Transformer asTransformer(Predicate predicate)
Creates a Transformer that calls a Predicate each time the transformer is used.
static Transformer asTransformer(Factory factory)
Creates a Transformer that calls a Factory each time the transformer is used.
static Transformer asTransformer(Closure closure)
Creates a Transformer that calls a Closure each time the transformer is used.
static Transformer chainedTransformer(Collection transformers)
Create a new Transformer that calls each transformer in turn, passing the result into the next transformer.
static Transformer chainedTransformer(Transformer transformer1, Transformer transformer2)
Create a new Transformer that calls two transformers, passing the result of the first into the second.
static Transformer chainedTransformer(Transformer[] transformers)
Create a new Transformer that calls each transformer in turn, passing the result into the next transformer.
static Transformer cloneTransformer()
Gets a transformer that returns a clone of the input object.
static Transformer constantTransformer(Object constantToReturn)
Creates a Transformer that will return the same object each time the transformer is used.
static Transformer exceptionTransformer()
Gets a transformer that always throws an exception.
static Transformer instantiateTransformer()
Gets a Transformer that expects an input Class object that it will instantiate.
static Transformer instantiateTransformer(Class[] paramTypes, Object[] args)
Creates a Transformer that expects an input Class object that it will instantiate.
static Transformer invokerTransformer(String methodName)
Gets a Transformer that invokes a method on the input object.
static Transformer invokerTransformer(String methodName, Class[] paramTypes, Object[] args)
Gets a Transformer that invokes a method on the input object.
static Transformer mapTransformer(Map map)
Creates a Transformer that uses the passed in Map to transform the input object (as a simple lookup).
static Transformer nopTransformer()
Gets a transformer that returns the input object.
static Transformer nullTransformer()
Gets a transformer that always returns null.
static Transformer stringValueTransformer()
Gets a transformer that returns a java.lang.String representation of the input object.
static Transformer switchMapTransformer(Map objectsAndTransformers)
Create a new Transformer that uses the input object as a key to find the transformer to call.
static Transformer switchTransformer(Predicate predicate, Transformer trueTransformer, Transformer falseTransformer)
Create a new Transformer that calls one of two transformers depending on the specified predicate.
static Transformer switchTransformer(Predicate[] predicates, Transformer[] transformers)
Create a new Transformer that calls one of the transformers depending on the predicates.
static Transformer switchTransformer(Predicate[] predicates, Transformer[] transformers, Transformer defaultTransformer)
Create a new Transformer that calls one of the transformers depending on the predicates.
static Transformer switchTransformer(Map predicatesAndTransformers)
Create a new Transformer that calls one of the transformers depending on the predicates.
[Expand]
Inherited Methods
From class java.lang.Object

Public Constructors

public TransformerUtils ()

This class is not normally instantiated.

Public Methods

public static Transformer asTransformer (Predicate predicate)

Creates a Transformer that calls a Predicate each time the transformer is used. The transformer will return either Boolean.TRUE or Boolean.FALSE.

Parameters
predicate the predicate to run each time in the transformer, not null
Returns
  • the transformer
Throws
IllegalArgumentException if the predicate is null
See Also

public static Transformer asTransformer (Factory factory)

Creates a Transformer that calls a Factory each time the transformer is used. The transformer will return the value returned by the factory.

Parameters
factory the factory to run each time in the transformer, not null
Returns
  • the transformer
Throws
IllegalArgumentException if the factory is null
See Also

public static Transformer asTransformer (Closure closure)

Creates a Transformer that calls a Closure each time the transformer is used. The transformer returns the input object.

Parameters
closure the closure to run each time in the transformer, not null
Returns
  • the transformer
Throws
IllegalArgumentException if the closure is null
See Also

public static Transformer chainedTransformer (Collection transformers)

Create a new Transformer that calls each transformer in turn, passing the result into the next transformer. The ordering is that of the iterator() method on the collection.

Parameters
transformers a collection of transformers to chain
Returns
  • the transformer
Throws
IllegalArgumentException if the transformers collection is null
IllegalArgumentException if any transformer in the collection is null
See Also

public static Transformer chainedTransformer (Transformer transformer1, Transformer transformer2)

Create a new Transformer that calls two transformers, passing the result of the first into the second.

Parameters
transformer1 the first transformer
transformer2 the second transformer
Returns
  • the transformer
Throws
IllegalArgumentException if either transformer is null
See Also

public static Transformer chainedTransformer (Transformer[] transformers)

Create a new Transformer that calls each transformer in turn, passing the result into the next transformer.

Parameters
transformers an array of transformers to chain
Returns
  • the transformer
Throws
IllegalArgumentException if the transformers array is null
IllegalArgumentException if any transformer in the array is null
See Also

public static Transformer cloneTransformer ()

Gets a transformer that returns a clone of the input object. The input object will be cloned using one of these techniques (in order):

  • public clone method
  • public copy constructor
  • serialization clone

Returns
  • the transformer
See Also

public static Transformer constantTransformer (Object constantToReturn)

Creates a Transformer that will return the same object each time the transformer is used.

Parameters
constantToReturn the constant object to return each time in the transformer
Returns
  • the transformer.
See Also

public static Transformer exceptionTransformer ()

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

Returns
  • the transformer
See Also

public static Transformer instantiateTransformer ()

Gets a Transformer that expects an input Class object that it will instantiate.

Returns
  • the transformer
See Also

public static Transformer instantiateTransformer (Class[] paramTypes, Object[] args)

Creates a Transformer that expects an input Class object that it will instantiate. The constructor used is determined by the arguments specified to this method.

Parameters
paramTypes parameter types for the constructor, can be null
args the arguments to pass to the constructor, can be null
Returns
  • the transformer
Throws
IllegalArgumentException if the paramTypes and args don't match
See Also

public static Transformer invokerTransformer (String methodName)

Gets a Transformer that invokes a method on the input object. The method must have no parameters. If the input object is null, null is returned.

For example, TransformerUtils.invokerTransformer("getName"); will call the getName/code> method on the input object to determine the transformer result.

Parameters
methodName the method name to call on the input object, may not be null
Returns
  • the transformer
Throws
IllegalArgumentException if the methodName is null.
See Also

public static Transformer invokerTransformer (String methodName, Class[] paramTypes, Object[] args)

Gets a Transformer that invokes a method on the input object. The method parameters are specified. If the input object is null, null is returned.

Parameters
methodName the name of the method
paramTypes the parameter types
args the arguments
Returns
  • the transformer
Throws
IllegalArgumentException if the method name is null
IllegalArgumentException if the paramTypes and args don't match
See Also

public static Transformer mapTransformer (Map map)

Creates a Transformer that uses the passed in Map to transform the input object (as a simple lookup).

Parameters
map the map to use to transform the objects
Returns
  • the transformer
Throws
IllegalArgumentException if the map is null
See Also

public static Transformer nopTransformer ()

Gets a transformer that returns the input object. The input object should be immutable to maintain the contract of Transformer (although this is not checked).

Returns
  • the transformer
See Also

public static Transformer nullTransformer ()

Gets a transformer that always returns null.

Returns
  • the transformer
See Also

public static Transformer stringValueTransformer ()

Gets a transformer that returns a java.lang.String representation of the input object. This is achieved via the toString method, null returns 'null'.

Returns
  • the transformer
See Also

public static Transformer switchMapTransformer (Map objectsAndTransformers)

Create a new Transformer that uses the input object as a key to find the transformer to call.

The Map consists of object keys and Transformer values. A transformer is called if the input object equals the key. If there is no match, the default transformer is called. The default transformer is set in the map using a null key. If no default is set, null will be returned in a default case.

Parameters
objectsAndTransformers a map of objects to transformers
Returns
  • the transformer
Throws
IllegalArgumentException if the map is null
IllegalArgumentException if the map is empty
IllegalArgumentException if any transformer in the map is null
See Also

public static Transformer switchTransformer (Predicate predicate, Transformer trueTransformer, Transformer falseTransformer)

Create a new Transformer that calls one of two transformers depending on the specified predicate.

Parameters
predicate the predicate to switch on
trueTransformer the transformer called if the predicate is true
falseTransformer the transformer called if the predicate is false
Returns
  • the transformer
Throws
IllegalArgumentException if the predicate is null
IllegalArgumentException if either transformer is null
See Also

public static Transformer switchTransformer (Predicate[] predicates, Transformer[] transformers)

Create a new Transformer that calls one of the transformers depending on the predicates. The transformer at array location 0 is called if the predicate at array location 0 returned true. Each predicate is evaluated until one returns true. If no predicates evaluate to true, null is returned.

Parameters
predicates an array of predicates to check
transformers an array of transformers to call
Returns
  • the transformer
Throws
IllegalArgumentException if the either array is null
IllegalArgumentException if the either array has 0 elements
IllegalArgumentException if any element in the arrays is null
IllegalArgumentException if the arrays are different sizes
See Also

public static Transformer switchTransformer (Predicate[] predicates, Transformer[] transformers, Transformer defaultTransformer)

Create a new Transformer that calls one of the transformers depending on the predicates. The transformer at array location 0 is called if the predicate at array location 0 returned true. Each predicate is evaluated until one returns true. If no predicates evaluate to true, the default transformer is called. If the default transformer is null, null is returned.

Parameters
predicates an array of predicates to check
transformers an array of transformers to call
defaultTransformer the default to call if no predicate matches, null means return null
Returns
  • the transformer
Throws
IllegalArgumentException if the either array is null
IllegalArgumentException if the either array has 0 elements
IllegalArgumentException if any element in the arrays is null
IllegalArgumentException if the arrays are different sizes
See Also

public static Transformer switchTransformer (Map predicatesAndTransformers)

Create a new Transformer that calls one of the transformers depending on the predicates.

The Map consists of Predicate keys and Transformer values. A transformer is called if its matching predicate returns true. Each predicate is evaluated until one returns true. If no predicates evaluate to true, the default transformer is called. The default transformer is set in the map with a null key. If no default transformer is set, null will be returned in a default case. The ordering is that of the iterator() method on the entryset collection of the map.

Parameters
predicatesAndTransformers a map of predicates to transformers
Returns
  • the transformer
Throws
IllegalArgumentException if the map is null
IllegalArgumentException if the map is empty
IllegalArgumentException if any transformer in the map is null
ClassCastException if the map elements are of the wrong type
See Also