org.apache.commons.collections4

Class TransformerUtils


  • public class TransformerUtils
extends Object
    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
    • If - calls one transformer or another based on a predicate
    • 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

    Since v4.1 only transformers which are considered to be unsafe are Serializable. Transformers considered to be unsafe for serialization are:

    • Invoker
    • Clone
    • Instantiate
    Since:
    3.0

    • Method Detail

      • exceptionTransformer

        public static <I,O> Transformer<I,O> exceptionTransformer()
        Gets a transformer that always throws an exception. This could be useful during testing as a placeholder.
        Type Parameters:
        I - the input type
        O - the output type
        Returns:
        the transformer
        See Also:
        ExceptionTransformer

      • nullTransformer

        public static <I,O> Transformer<I,O> nullTransformer()
        Gets a transformer that always returns null.
        Type Parameters:
        I - the input type
        O - the output type
        Returns:
        the transformer
        See Also:
        ConstantTransformer

      • nopTransformer

        public static <T> Transformer<T,T> 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).
        Type Parameters:
        T - the input/output type
        Returns:
        the transformer
        See Also:
        NOPTransformer

      • cloneTransformer

        public static <T> Transformer<T,T> 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
          Type Parameters:
          T - the input/output type
          Returns:
          the transformer
          See Also:
          CloneTransformer

        • constantTransformer

          public static <I,O> Transformer<I,O> constantTransformer(O constantToReturn)
          Creates a Transformer that will return the same object each time the transformer is used.
          Type Parameters:
          I - the input type
          O - the output type
          Parameters:
          constantToReturn - the constant object to return each time in the transformer
          Returns:
          the transformer.
          See Also:
          ConstantTransformer

        • asTransformer

          public static <T> Transformer<T,T> asTransformer(Closure<? super T> closure)
          Creates a Transformer that calls a Closure each time the transformer is used. The transformer returns the input object.
          Type Parameters:
          T - the input/output type
          Parameters:
          closure - the closure to run each time in the transformer, not null
          Returns:
          the transformer
          Throws:
          NullPointerException - if the closure is null
          See Also:
          ClosureTransformer

        • asTransformer

          public static <T> Transformer<T,Boolean> asTransformer(Predicate<? super T> predicate)
          Creates a Transformer that calls a Predicate each time the transformer is used. The transformer will return either Boolean.TRUE or Boolean.FALSE.
          Type Parameters:
          T - the input type
          Parameters:
          predicate - the predicate to run each time in the transformer, not null
          Returns:
          the transformer
          Throws:
          NullPointerException - if the predicate is null
          See Also:
          PredicateTransformer

        • asTransformer

          public static <I,O> Transformer<I,O> asTransformer(Factory<? extends O> factory)
          Creates a Transformer that calls a Factory each time the transformer is used. The transformer will return the value returned by the factory.
          Type Parameters:
          I - the input type
          O - the output type
          Parameters:
          factory - the factory to run each time in the transformer, not null
          Returns:
          the transformer
          Throws:
          NullPointerException - if the factory is null
          See Also:
          FactoryTransformer

        • chainedTransformer

          public static <T> Transformer<T,T> chainedTransformer(Transformer<? super T,? extends T>... transformers)
          Create a new Transformer that calls each transformer in turn, passing the result into the next transformer.
          Type Parameters:
          T - the input/output type
          Parameters:
          transformers - an array of transformers to chain
          Returns:
          the transformer
          Throws:
          NullPointerException - if the transformers array or any of the transformers is null
          See Also:
          ChainedTransformer

        • chainedTransformer

          public static <T> Transformer<T,T> chainedTransformer(Collection<? extends Transformer<? super T,? extends T>> 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.
          Type Parameters:
          T - the input/output type
          Parameters:
          transformers - a collection of transformers to chain
          Returns:
          the transformer
          Throws:
          NullPointerException - if the transformers collection or any of the transformers is null
          See Also:
          ChainedTransformer

        • ifTransformer

          public static <T> Transformer<T,T> ifTransformer(Predicate<? super T> predicate,
                                                 Transformer<? super T,? extends T> trueTransformer)
          Create a new Transformer that calls the transformer if the predicate is true, otherwise the input object is returned unchanged.
          Type Parameters:
          T - the input / output type
          Parameters:
          predicate - the predicate to switch on
          trueTransformer - the transformer called if the predicate is true
          Returns:
          the transformer
          Throws:
          NullPointerException - if either the predicate or transformer is null
          Since:
          4.1
          See Also:
          IfTransformer

        • ifTransformer

          public static <I,O> Transformer<I,O> ifTransformer(Predicate<? super I> predicate,
                                                   Transformer<? super I,? extends O> trueTransformer,
                                                   Transformer<? super I,? extends O> falseTransformer)
          Create a new Transformer that calls one of two transformers depending on the specified predicate.
          Type Parameters:
          I - the input type
          O - the output type
          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:
          NullPointerException - if either the predicate or transformer is null
          Since:
          4.1
          See Also:
          IfTransformer

        • switchTransformer

          @Deprecated
public static <I,O> Transformer<I,O> switchTransformer(Predicate<? super I> predicate,
                                                                   Transformer<? super I,? extends O> trueTransformer,
                                                                   Transformer<? super I,? extends O> falseTransformer)
          Deprecated.  as of 4.1, use {@link #ifTransformer(Predicate, Transformer, Transformer))
          Create a new Transformer that calls one of two transformers depending on the specified predicate.
          Type Parameters:
          I - the input type
          O - the output type
          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:
          NullPointerException - if either the predicate or transformer is null
          See Also:
          SwitchTransformer

        • switchTransformer

          public static <I,O> Transformer<I,O> switchTransformer(Predicate<? super I>[] predicates,
                                                       Transformer<? super I,? extends O>[] 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.
          Type Parameters:
          I - the input type
          O - the output type
          Parameters:
          predicates - an array of predicates to check
          transformers - an array of transformers to call
          Returns:
          the transformer
          Throws:
          NullPointerException - if the either array is null
          NullPointerException - if any element in the arrays is null
          IllegalArgumentException - if the arrays have different sizes
          See Also:
          SwitchTransformer

        • switchTransformer

          public static <I,O> Transformer<I,O> switchTransformer(Predicate<? super I>[] predicates,
                                                       Transformer<? super I,? extends O>[] transformers,
                                                       Transformer<? super I,? extends O> 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.
          Type Parameters:
          I - the input type
          O - the output type
          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:
          NullPointerException - if the either array is null
          NullPointerException - if any element in the arrays is null
          IllegalArgumentException - if the arrays have different sizes
          See Also:
          SwitchTransformer

        • switchTransformer

          public static <I,O> Transformer<I,O> switchTransformer(Map<Predicate<I>,Transformer<I,O>> 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.

          Type Parameters:
          I - the input type
          O - the output type
          Parameters:
          predicatesAndTransformers - a map of predicates to transformers
          Returns:
          the transformer
          Throws:
          NullPointerException - if the map is null
          NullPointerException - if any transformer in the map is null
          ClassCastException - if the map elements are of the wrong type
          See Also:
          SwitchTransformer

        • switchMapTransformer

          public static <I,O> Transformer<I,O> switchMapTransformer(Map<I,Transformer<I,O>> 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.

          Type Parameters:
          I - the input type
          O - the output type
          Parameters:
          objectsAndTransformers - a map of objects to transformers
          Returns:
          the transformer
          Throws:
          NullPointerException - if the map is null
          NullPointerException - if any transformer in the map is null
          See Also:
          SwitchTransformer

        • instantiateTransformer

          public static <T> Transformer<Class<? extends T>,T> instantiateTransformer()
          Gets a Transformer that expects an input Class object that it will instantiate.
          Type Parameters:
          T - the output type
          Returns:
          the transformer
          See Also:
          InstantiateTransformer

        • instantiateTransformer

          public static <T> Transformer<Class<? extends T>,T> 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.
          Type Parameters:
          T - the output type
          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:
          InstantiateTransformer

        • mapTransformer

          public static <I,O> Transformer<I,O> mapTransformer(Map<? super I,? extends O> map)
          Creates a Transformer that uses the passed in Map to transform the input object (as a simple lookup).
          Type Parameters:
          I - the input type
          O - the output type
          Parameters:
          map - the map to use to transform the objects
          Returns:
          the transformer, or ConstantTransformer.nullTransformer() if the map is null
          See Also:
          MapTransformer

        • invokerTransformer

          public static <I,O> Transformer<I,O> 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.

          Type Parameters:
          I - the input type
          O - the output type
          Parameters:
          methodName - the method name to call on the input object, may not be null
          Returns:
          the transformer
          Throws:
          NullPointerException - if the methodName is null.
          See Also:
          InvokerTransformer

        • invokerTransformer

          public static <I,O> Transformer<I,O> 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.
          Type Parameters:
          I - the input type
          O - the output type
          Parameters:
          methodName - the name of the method
          paramTypes - the parameter types
          args - the arguments
          Returns:
          the transformer
          Throws:
          NullPointerException - if the method name is null
          IllegalArgumentException - if the paramTypes and args don't match
          See Also:
          InvokerTransformer

        • stringValueTransformer

          public static <T> Transformer<T,String> 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'.
          Type Parameters:
          T - the input type
          Returns:
          the transformer
          See Also:
          StringValueTransformer