org.apache.commons.collections

Class TransformerUtils


public class TransformerUtils
extends java.lang.Object

TransformerUtils provides reference implementations and utilities for the Transformer functor interface. The supplied transformers are: All the supplied transformers are Serializable.
Version:
$Revision: 1.13 $ $Date: 2004/05/26 21:50:52 $
Authors:
Stephen Colebourne
James Carman
Since:
Commons Collections 3.0

Constructor Summary

TransformerUtils()
This class is not normally instantiated.

Method Summary

static Transformer
asTransformer(Closure closure)
Creates a Transformer that calls a Closure 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(Predicate predicate)
Creates a Transformer that calls a Predicate 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(Map predicatesAndTransformers)
Create a new Transformer that calls one of the transformers depending on the predicates.
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.

Constructor Details

TransformerUtils

public TransformerUtils()
This class is not normally instantiated.

Method Details

asTransformer

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

asTransformer

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

asTransformer

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

chainedTransformer

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

chainedTransformer

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

chainedTransformer

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

cloneTransformer

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

    constantTransformer

    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.

    exceptionTransformer

    public static Transformer exceptionTransformer()
    Gets a transformer that always throws an exception. This could be useful during testing as a placeholder.
    Returns:
    the transformer

    instantiateTransformer

    public static Transformer instantiateTransformer()
    Gets a Transformer that expects an input Class object that it will instantiate.
    Returns:
    the transformer

    instantiateTransformer

    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

    invokerTransformer

    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

    invokerTransformer

    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

    mapTransformer

    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

    nopTransformer

    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

    nullTransformer

    public static Transformer nullTransformer()
    Gets a transformer that always returns null.
    Returns:
    the transformer

    stringValueTransformer

    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

    switchMapTransformer

    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

    switchTransformer

    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

    switchTransformer

    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

    switchTransformer

    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

    switchTransformer

    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

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