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* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* 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.
*
* @since Commons Collections 3.0
* @version $Revision: 1.10 $ $Date: 2004/01/14 21:43:03 $
*
* @author Stephen Colebourne
* @author James Carman
*/
public class TransformerUtils {
/**
* This class is not normally instantiated.
*/
public TransformerUtils() {
super();
}
/**
* Gets a transformer that always throws an exception.
* This could be useful during testing as a placeholder.
*
* @return the transformer
*/
public static Transformer exceptionTransformer() {
return ExceptionTransformer.INSTANCE;
}
/**
* Gets a transformer that always returns null.
*
* @return the transformer
*/
public static Transformer nullTransformer() {
return ConstantTransformer.NULL_INSTANCE;
}
/**
* 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).
*
* @return the transformer
*/
public static Transformer nopTransformer() {
return NOPTransformer.INSTANCE;
}
/**
* 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
*
*
* @return the transformer
*/
public static Transformer cloneTransformer() {
return CloneTransformer.INSTANCE;
}
/**
* Creates a Transformer that will return the same object each time the
* transformer is used.
*
* @param constantToReturn the constant object to return each time in the transformer
* @return the transformer.
*/
public static Transformer constantTransformer(Object constantToReturn) {
return ConstantTransformer.getInstance(constantToReturn);
}
/**
* Creates a Transformer that calls a Closure each time the transformer is used.
* The transformer returns the input object.
*
* @param closure the closure to run each time in the transformer, not null
* @return the transformer
* @throws IllegalArgumentException if the closure is null
*/
public static Transformer asTransformer(Closure closure) {
return ClosureTransformer.getInstance(closure);
}
/**
* Creates a Transformer that calls a Predicate each time the transformer is used.
* The transformer will return either Boolean.TRUE or Boolean.FALSE.
*
* @param predicate the predicate to run each time in the transformer, not null
* @return the transformer
* @throws IllegalArgumentException if the predicate is null
*/
public static Transformer asTransformer(Predicate predicate) {
return PredicateTransformer.getInstance(predicate);
}
/**
* Creates a Transformer that calls a Factory each time the transformer is used.
* The transformer will return the value returned by the factory.
*
* @param factory the factory to run each time in the transformer, not null
* @return the transformer
* @throws IllegalArgumentException if the factory is null
*/
public static Transformer asTransformer(Factory factory) {
return FactoryTransformer.getInstance(factory);
}
/**
* Create a new Transformer that calls two transformers, passing the result of
* the first into the second.
*
* @param transformer1 the first transformer
* @param transformer2 the second transformer
* @return the transformer
* @throws IllegalArgumentException if either transformer is null
*/
public static Transformer chainedTransformer(Transformer transformer1, Transformer transformer2) {
return ChainedTransformer.getInstance(transformer1, transformer2);
}
/**
* Create a new Transformer that calls each transformer in turn, passing the
* result into the next transformer.
*
* @param transformers an array of transformers to chain
* @return the transformer
* @throws IllegalArgumentException if the transformers array is null
* @throws IllegalArgumentException if any transformer in the array is null
*/
public static Transformer chainedTransformer(Transformer[] transformers) {
return ChainedTransformer.getInstance(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.
*
* @param transformers a collection of transformers to chain
* @return the transformer
* @throws IllegalArgumentException if the transformers collection is null
* @throws IllegalArgumentException if any transformer in the collection is null
*/
public static Transformer chainedTransformer(Collection transformers) {
return ChainedTransformer.getInstance(transformers);
}
/**
* Create a new Transformer that calls one of two transformers depending
* on the specified predicate.
*
* @param predicate the predicate to switch on
* @param trueTransformer the transformer called if the predicate is true
* @param falseTransformer the transformer called if the predicate is false
* @return the transformer
* @throws IllegalArgumentException if the predicate is null
* @throws IllegalArgumentException if either transformer is null
*/
public static Transformer switchTransformer(Predicate predicate, Transformer trueTransformer, Transformer falseTransformer) {
return SwitchTransformer.getInstance(new Predicate[] { predicate }, new Transformer[] { trueTransformer }, falseTransformer);
}
/**
* 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.
*
* @param predicates an array of predicates to check
* @param transformers an array of transformers to call
* @return the transformer
* @throws IllegalArgumentException if the either array is null
* @throws IllegalArgumentException if the either array has 0 elements
* @throws IllegalArgumentException if any element in the arrays is null
* @throws IllegalArgumentException if the arrays are different sizes
*/
public static Transformer switchTransformer(Predicate[] predicates, Transformer[] transformers) {
return SwitchTransformer.getInstance(predicates, transformers, null);
}
/**
* 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.
*
* @param predicates an array of predicates to check
* @param transformers an array of transformers to call
* @param defaultTransformer the default to call if no predicate matches, null means return null
* @return the transformer
* @throws IllegalArgumentException if the either array is null
* @throws IllegalArgumentException if the either array has 0 elements
* @throws IllegalArgumentException if any element in the arrays is null
* @throws IllegalArgumentException if the arrays are different sizes
*/
public static Transformer switchTransformer(Predicate[] predicates, Transformer[] transformers, Transformer defaultTransformer) {
return SwitchTransformer.getInstance(predicates, transformers, defaultTransformer);
}
/**
* 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.
*
* @param predicatesAndTransformers a map of predicates to transformers
* @return the transformer
* @throws IllegalArgumentException if the map is null
* @throws IllegalArgumentException if the map is empty
* @throws IllegalArgumentException if any transformer in the map is null
* @throws ClassCastException if the map elements are of the wrong type
*/
public static Transformer switchTransformer(Map predicatesAndTransformers) {
return SwitchTransformer.getInstance(predicatesAndTransformers);
}
/**
* 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.
*
* @param objectsAndTransformers a map of objects to transformers
* @return the transformer
* @throws IllegalArgumentException if the map is null
* @throws IllegalArgumentException if the map is empty
* @throws IllegalArgumentException if any transformer in the map is null
*/
public static Transformer switchMapTransformer(Map objectsAndTransformers) {
Transformer[] trs = null;
Predicate[] preds = null;
if (objectsAndTransformers == null) {
throw new IllegalArgumentException("The object and transformer map must not be null");
}
Transformer def = (Transformer) objectsAndTransformers.remove(null);
int size = objectsAndTransformers.size();
trs = new Transformer[size];
preds = new Predicate[size];
int i = 0;
for (Iterator it = objectsAndTransformers.entrySet().iterator(); it.hasNext();) {
Map.Entry entry = (Map.Entry) it.next();
preds[i] = PredicateUtils.equalPredicate(entry.getKey());
trs[i] = (Transformer) entry.getValue();
i++;
}
return switchTransformer(preds, trs, def);
}
/**
* Gets a Transformer that expects an input Class object that it will instantiate.
*
* @return the transformer
*/
public static Transformer instantiateTransformer() {
return InstantiateTransformer.NO_ARG_INSTANCE;
}
/**
* 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.
*
* @param paramTypes parameter types for the constructor, can be null
* @param args the arguments to pass to the constructor, can be null
* @return the transformer
* @throws IllegalArgumentException if the paramTypes and args don't match
*/
public static Transformer instantiateTransformer(Class[] paramTypes, Object[] args) {
return InstantiateTransformer.getInstance(paramTypes, args);
}
/**
* Creates a Transformer that uses the passed in Map to transform the input
* object (as a simple lookup).
*
* @param map the map to use to transform the objects
* @return the transformer
* @throws IllegalArgumentException if the map is null
*/
public static Transformer mapTransformer(Map map) {
return MapTransformer.getInstance(map);
}
/**
* 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.
*
* @param methodName the method name to call on the input object, may not be null
* @return the transformer
* @throws IllegalArgumentException if the methodName is null.
*/
public static Transformer invokerTransformer(String methodName){
return InvokerTransformer.getInstance(methodName, null, null);
}
/**
* 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.
*
* @param methodName the name of the method
* @param paramTypes the parameter types
* @param args the arguments
* @return the transformer
* @throws IllegalArgumentException if the method name is null
* @throws IllegalArgumentException if the paramTypes and args don't match
*/
public static Transformer invokerTransformer(String methodName, Class[] paramTypes, Object[] args){
return InvokerTransformer.getInstance(methodName, paramTypes, args);
}
/**
* Gets a transformer that returns a java.lang.String
* representation of the input object. This is achieved via the
* toString method, null returns 'null'.
*
* @return the transformer
*/
public static Transformer stringValueTransformer() {
return StringValueTransformer.INSTANCE;
}
}