Class TransformerUtils
- java.lang.Object
-
- org.apache.commons.collections4.TransformerUtils
-
public class TransformerUtils extends java.lang.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 safe are Serializable. Transformers considered to be unsafe for serialization are:
- Invoker
- Clone
- Instantiate
- Since:
- 3.0
-
-
Method Summary
All Methods Static Methods Concrete Methods Deprecated Methods Modifier and Type Method Description static <T> Transformer<T,T>
asTransformer(Closure<? super T> closure)
Creates a Transformer that calls a Closure each time the transformer is used.static <I,O>
Transformer<I,O>asTransformer(Factory<? extends O> factory)
Creates a Transformer that calls a Factory each time the transformer is used.static <T> Transformer<T,java.lang.Boolean>
asTransformer(Predicate<? super T> predicate)
Creates a Transformer that calls a Predicate each time the transformer is used.static <T> Transformer<T,T>
chainedTransformer(java.util.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.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.static <T> Transformer<T,T>
cloneTransformer()
Gets a transformer that returns a clone of the input object.static <I,O>
Transformer<I,O>constantTransformer(O constantToReturn)
Creates a Transformer that will return the same object each time the transformer is used.static <I,O>
Transformer<I,O>exceptionTransformer()
Gets a transformer that always throws an exception.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.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.static <T> Transformer<java.lang.Class<? extends T>,T>
instantiateTransformer()
Gets a Transformer that expects an input Class object that it will instantiate.static <T> Transformer<java.lang.Class<? extends T>,T>
instantiateTransformer(java.lang.Class<?>[] paramTypes, java.lang.Object[] args)
Creates a Transformer that expects an input Class object that it will instantiate.static <I,O>
Transformer<I,O>invokerTransformer(java.lang.String methodName)
Gets a Transformer that invokes a method on the input object.static <I,O>
Transformer<I,O>invokerTransformer(java.lang.String methodName, java.lang.Class<?>[] paramTypes, java.lang.Object[] args)
Gets a Transformer that invokes a method on the input object.static <I,O>
Transformer<I,O>mapTransformer(java.util.Map<? super I,? extends O> map)
Creates a Transformer that uses the passed in Map to transform the input object (as a simple lookup).static <T> Transformer<T,T>
nopTransformer()
Gets a transformer that returns the input object.static <I,O>
Transformer<I,O>nullTransformer()
Gets a transformer that always returns null.static <T> Transformer<T,java.lang.String>
stringValueTransformer()
Gets a transformer that returns ajava.lang.String
representation of the input object.static <I,O>
Transformer<I,O>switchMapTransformer(java.util.Map<I,Transformer<I,O>> objectsAndTransformers)
Create a new Transformer that uses the input object as a key to find the transformer to call.static <I,O>
Transformer<I,O>switchTransformer(java.util.Map<Predicate<I>,Transformer<I,O>> predicatesAndTransformers)
Create a new Transformer that calls one of the transformers depending on the predicates.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.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.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, useifTransformer(Predicate, Transformer, Transformer)
-
-
-
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 typeO
- 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 typeO
- 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 typeO
- 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:
java.lang.NullPointerException
- if the closure is null- See Also:
ClosureTransformer
-
asTransformer
public static <T> Transformer<T,java.lang.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:
java.lang.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 typeO
- the output type- Parameters:
factory
- the factory to run each time in the transformer, not null- Returns:
- the transformer
- Throws:
java.lang.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:
java.lang.NullPointerException
- if the transformers array or any of the transformers is null- See Also:
ChainedTransformer
-
chainedTransformer
public static <T> Transformer<T,T> chainedTransformer(java.util.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:
java.lang.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 ontrueTransformer
- the transformer called if the predicate is true- Returns:
- the transformer
- Throws:
java.lang.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 typeO
- the output type- Parameters:
predicate
- the predicate to switch ontrueTransformer
- the transformer called if the predicate is truefalseTransformer
- the transformer called if the predicate is false- Returns:
- the transformer
- Throws:
java.lang.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, useifTransformer(Predicate, Transformer, Transformer)
Create a new Transformer that calls one of two transformers depending on the specified predicate.- Type Parameters:
I
- the input typeO
- the output type- Parameters:
predicate
- the predicate to switch ontrueTransformer
- the transformer called if the predicate is truefalseTransformer
- the transformer called if the predicate is false- Returns:
- the transformer
- Throws:
java.lang.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 typeO
- the output type- Parameters:
predicates
- an array of predicates to checktransformers
- an array of transformers to call- Returns:
- the transformer
- Throws:
java.lang.NullPointerException
- if the either array is nulljava.lang.NullPointerException
- if any element in the arrays is nulljava.lang.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 typeO
- the output type- Parameters:
predicates
- an array of predicates to checktransformers
- an array of transformers to calldefaultTransformer
- the default to call if no predicate matches, null means return null- Returns:
- the transformer
- Throws:
java.lang.NullPointerException
- if the either array is nulljava.lang.NullPointerException
- if any element in the arrays is nulljava.lang.IllegalArgumentException
- if the arrays have different sizes- See Also:
SwitchTransformer
-
switchTransformer
public static <I,O> Transformer<I,O> switchTransformer(java.util.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 typeO
- the output type- Parameters:
predicatesAndTransformers
- a map of predicates to transformers- Returns:
- the transformer
- Throws:
java.lang.NullPointerException
- if the map is nulljava.lang.NullPointerException
- if any transformer in the map is nulljava.lang.ClassCastException
- if the map elements are of the wrong type- See Also:
SwitchTransformer
-
switchMapTransformer
public static <I,O> Transformer<I,O> switchMapTransformer(java.util.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 typeO
- the output type- Parameters:
objectsAndTransformers
- a map of objects to transformers- Returns:
- the transformer
- Throws:
java.lang.NullPointerException
- if the map is nulljava.lang.NullPointerException
- if any transformer in the map is null- See Also:
SwitchTransformer
-
instantiateTransformer
public static <T> Transformer<java.lang.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<java.lang.Class<? extends T>,T> instantiateTransformer(java.lang.Class<?>[] paramTypes, java.lang.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 nullargs
- the arguments to pass to the constructor, can be null- Returns:
- the transformer
- Throws:
java.lang.IllegalArgumentException
- if the paramTypes and args don't match- See Also:
InstantiateTransformer
-
mapTransformer
public static <I,O> Transformer<I,O> mapTransformer(java.util.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 typeO
- the output type- Parameters:
map
- the map to use to transform the objects- Returns:
- the transformer, or
ConstantTransformer.nullTransformer()
if themap
isnull
- See Also:
MapTransformer
-
invokerTransformer
public static <I,O> Transformer<I,O> invokerTransformer(java.lang.String methodName)
Gets a Transformer that invokes a method on the input object. The method must have no parameters. If the input object isnull
,null
is returned.For example,
TransformerUtils.invokerTransformer("getName");
will call thegetName
method on the input object to determine the transformer result.- Type Parameters:
I
- the input typeO
- the output type- Parameters:
methodName
- the method name to call on the input object, may not be null- Returns:
- the transformer
- Throws:
java.lang.NullPointerException
- if the methodName is null.- See Also:
InvokerTransformer
-
invokerTransformer
public static <I,O> Transformer<I,O> invokerTransformer(java.lang.String methodName, java.lang.Class<?>[] paramTypes, java.lang.Object[] args)
Gets a Transformer that invokes a method on the input object. The method parameters are specified. If the input object isnull
,null
is returned.- Type Parameters:
I
- the input typeO
- the output type- Parameters:
methodName
- the name of the methodparamTypes
- the parameter typesargs
- the arguments- Returns:
- the transformer
- Throws:
java.lang.NullPointerException
- if the method name is nulljava.lang.IllegalArgumentException
- if the paramTypes and args don't match- See Also:
InvokerTransformer
-
stringValueTransformer
public static <T> Transformer<T,java.lang.String> stringValueTransformer()
Gets a transformer that returns ajava.lang.String
representation of the input object. This is achieved via thetoString
method,null
returns 'null'.- Type Parameters:
T
- the input type- Returns:
- the transformer
- See Also:
StringValueTransformer
-
-