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.
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.
closure
- the closure to run each time in the transformer, not null
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.
factory
- the factory to run each time in the transformer, not null
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.
predicate
- the predicate to run each time in the transformer, not null
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.
transformers
- a collection of transformers to chain
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.
transformer1
- the first transformertransformer2
- the second 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.
transformers
- an array of transformers to chain
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
constantTransformer
public static Transformer constantTransformer(Object constantToReturn)
Creates a Transformer that will return the same object each time the
transformer is used.
constantToReturn
- the constant object to return each time in the transformer
exceptionTransformer
public static Transformer exceptionTransformer()
Gets a transformer that always throws an exception.
This could be useful during testing as a placeholder.
instantiateTransformer
public static Transformer instantiateTransformer()
Gets a Transformer that expects an input Class object that it will instantiate.
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.
paramTypes
- parameter types for the constructor, can be nullargs
- the arguments to pass to the constructor, can be null
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.
methodName
- the method name to call on the input object, may not be null
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.
methodName
- the name of the methodparamTypes
- the parameter typesargs
- the arguments
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).
map
- the map to use to transform the objects
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).
nullTransformer
public static Transformer nullTransformer()
Gets a transformer that always returns null.
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'.
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.
objectsAndTransformers
- a map of objects to transformers
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.
predicatesAndTransformers
- a map of predicates to transformers
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.
predicate
- the predicate to switch ontrueTransformer
- the transformer called if the predicate is truefalseTransformer
- the transformer called if the predicate is false
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.
predicates
- an array of predicates to checktransformers
- an array of transformers to call
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.
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