/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.collections4;
import java.util.Collection;
import java.util.Map;
import org.apache.commons.collections4.functors.ChainedTransformer;
import org.apache.commons.collections4.functors.CloneTransformer;
import org.apache.commons.collections4.functors.ClosureTransformer;
import org.apache.commons.collections4.functors.ConstantTransformer;
import org.apache.commons.collections4.functors.EqualPredicate;
import org.apache.commons.collections4.functors.ExceptionTransformer;
import org.apache.commons.collections4.functors.FactoryTransformer;
import org.apache.commons.collections4.functors.IfTransformer;
import org.apache.commons.collections4.functors.InstantiateTransformer;
import org.apache.commons.collections4.functors.InvokerTransformer;
import org.apache.commons.collections4.functors.MapTransformer;
import org.apache.commons.collections4.functors.NOPTransformer;
import org.apache.commons.collections4.functors.PredicateTransformer;
import org.apache.commons.collections4.functors.StringValueTransformer;
import org.apache.commons.collections4.functors.SwitchTransformer;
/**
* <code>TransformerUtils</code> provides reference implementations and
* utilities for the Transformer functor interface. The supplied transformers are:
* <ul>
* <li>Invoker - returns the result of a method call on the input object
* <li>Clone - returns a clone of the input object
* <li>Constant - always returns the same object
* <li>Closure - performs a Closure and returns the input object
* <li>Predicate - returns the result of the predicate as a Boolean
* <li>Factory - returns a new object from a factory
* <li>Chained - chains two or more transformers together
* <li>If - calls one transformer or another based on a predicate
* <li>Switch - calls one transformer based on one or more predicates
* <li>SwitchMap - calls one transformer looked up from a Map
* <li>Instantiate - the Class input object is instantiated
* <li>Map - returns an object from a supplied Map
* <li>Null - always returns null
* <li>NOP - returns the input object, which should be immutable
* <li>Exception - always throws an exception
* <li>StringValue - returns a <code>java.lang.String</code> representation of the input object
* </ul>
* <p>
* Since v4.1 only transformers which are considered to be safe are
* Serializable. Transformers considered to be unsafe for serialization are:
* <ul>
* <li>Invoker
* <li>Clone
* <li>Instantiate
* </ul>
*
* @since 3.0
* @version $Id$
*/
public class TransformerUtils {
/**
* This class is not normally instantiated.
*/
private TransformerUtils() {}
/**
* Gets a transformer that always throws an exception.
* This could be useful during testing as a placeholder.
*
* @param <I> the input type
* @param <O> the output type
* @return the transformer
* @see ExceptionTransformer
*/
public static <I, O> Transformer<I, O> exceptionTransformer() {
return ExceptionTransformer.exceptionTransformer();
}
/**
* Gets a transformer that always returns null.
*
* @param <I> the input type
* @param <O> the output type
* @return the transformer
* @see ConstantTransformer
*/
public static <I, O> Transformer<I, O> nullTransformer() {
return ConstantTransformer.nullTransformer();
}
/**
* 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).
*
* @param <T> the input/output type
* @return the transformer
* @see NOPTransformer
*/
public static <T> Transformer<T, T> nopTransformer() {
return NOPTransformer.nopTransformer();
}
/**
* Gets a transformer that returns a clone of the input object.
* The input object will be cloned using one of these techniques (in order):
* <ul>
* <li>public clone method
* <li>public copy constructor
* <li>serialization clone
* <ul>
*
* @param <T> the input/output type
* @return the transformer
* @see CloneTransformer
*/
public static <T> Transformer<T, T> cloneTransformer() {
return CloneTransformer.cloneTransformer();
}
/**
* Creates a Transformer that will return the same object each time the
* transformer is used.
*
* @param <I> the input type
* @param <O> the output type
* @param constantToReturn the constant object to return each time in the transformer
* @return the transformer.
* @see ConstantTransformer
*/
public static <I, O> Transformer<I, O> constantTransformer(final O constantToReturn) {
return ConstantTransformer.constantTransformer(constantToReturn);
}
/**
* Creates a Transformer that calls a Closure each time the transformer is used.
* The transformer returns the input object.
*
* @param <T> the input/output type
* @param closure the closure to run each time in the transformer, not null
* @return the transformer
* @throws NullPointerException if the closure is null
* @see ClosureTransformer
*/
public static <T> Transformer<T, T> asTransformer(final Closure<? super T> closure) {
return ClosureTransformer.closureTransformer(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 <T> the input type
* @param predicate the predicate to run each time in the transformer, not null
* @return the transformer
* @throws NullPointerException if the predicate is null
* @see PredicateTransformer
*/
public static <T> Transformer<T, Boolean> asTransformer(final Predicate<? super T> predicate) {
return PredicateTransformer.predicateTransformer(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 <I> the input type
* @param <O> the output type
* @param factory the factory to run each time in the transformer, not null
* @return the transformer
* @throws NullPointerException if the factory is null
* @see FactoryTransformer
*/
public static <I, O> Transformer<I, O> asTransformer(final Factory<? extends O> factory) {
return FactoryTransformer.factoryTransformer(factory);
}
/**
* Create a new Transformer that calls each transformer in turn, passing the
* result into the next transformer.
*
* @param <T> the input/output type
* @param transformers an array of transformers to chain
* @return the transformer
* @throws NullPointerException if the transformers array or any of the transformers is null
* @see ChainedTransformer
*/
public static <T> Transformer<T, T> chainedTransformer(
final Transformer<? super T, ? extends T>... transformers) {
return ChainedTransformer.chainedTransformer(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 <T> the input/output type
* @param transformers a collection of transformers to chain
* @return the transformer
* @throws NullPointerException if the transformers collection or any of the transformers is null
* @see ChainedTransformer
*/
public static <T> Transformer<T, T> chainedTransformer(
final Collection<? extends Transformer<? super T, ? extends T>> transformers) {
return ChainedTransformer.chainedTransformer(transformers);
}
/**
* Create a new Transformer that calls the transformer if the predicate is true,
* otherwise the input object is returned unchanged.
*
* @param <T> the input / output type
* @param predicate the predicate to switch on
* @param trueTransformer the transformer called if the predicate is true
* @return the transformer
* @throws NullPointerException if either the predicate or transformer is null
* @see IfTransformer
* @since 4.1
*/
public static <T> Transformer<T, T> ifTransformer(final Predicate<? super T> predicate,
final Transformer<? super T, ? extends T> trueTransformer) {
return IfTransformer.ifTransformer(predicate, trueTransformer);
}
/**
* Create a new Transformer that calls one of two transformers depending
* on the specified predicate.
*
* @param <I> the input type
* @param <O> the output type
* @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 NullPointerException if either the predicate or transformer is null
* @see IfTransformer
* @since 4.1
*/
public static <I, O> Transformer<I, O> ifTransformer(final Predicate<? super I> predicate,
final Transformer<? super I, ? extends O> trueTransformer,
final Transformer<? super I, ? extends O> falseTransformer) {
return IfTransformer.ifTransformer(predicate, trueTransformer, falseTransformer);
}
/**
* Create a new Transformer that calls one of two transformers depending
* on the specified predicate.
*
* @param <I> the input type
* @param <O> the output type
* @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 NullPointerException if either the predicate or transformer is null
* @see SwitchTransformer
* @deprecated as of 4.1, use {@link #ifTransformer(Predicate, Transformer, Transformer))
*/
@SuppressWarnings("unchecked")
@Deprecated
public static <I, O> Transformer<I, O> switchTransformer(final Predicate<? super I> predicate,
final Transformer<? super I, ? extends O> trueTransformer,
final Transformer<? super I, ? extends O> falseTransformer) {
return SwitchTransformer.switchTransformer(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 <I> the input type
* @param <O> the output type
* @param predicates an array of predicates to check
* @param transformers an array of transformers to call
* @return the transformer
* @throws NullPointerException if the either array is null
* @throws NullPointerException if any element in the arrays is null
* @throws IllegalArgumentException if the arrays have different sizes
* @see SwitchTransformer
*/
public static <I, O> Transformer<I, O> switchTransformer(final Predicate<? super I>[] predicates,
final Transformer<? super I, ? extends O>[] transformers) {
return SwitchTransformer.switchTransformer(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 <I> the input type
* @param <O> the output type
* @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 NullPointerException if the either array is null
* @throws NullPointerException if any element in the arrays is null
* @throws IllegalArgumentException if the arrays have different sizes
* @see SwitchTransformer
*/
public static <I, O> Transformer<I, O> switchTransformer(final Predicate<? super I>[] predicates,
final Transformer<? super I, ? extends O>[] transformers,
final Transformer<? super I, ? extends O> defaultTransformer) {
return SwitchTransformer.switchTransformer(predicates, transformers, defaultTransformer);
}
/**
* Create a new Transformer that calls one of the transformers depending
* on the predicates.
* <p>
* 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 <I> the input type
* @param <O> the output type
* @param predicatesAndTransformers a map of predicates to transformers
* @return the transformer
* @throws NullPointerException if the map is null
* @throws NullPointerException if any transformer in the map is null
* @throws ClassCastException if the map elements are of the wrong type
* @see SwitchTransformer
*/
public static <I, O> Transformer<I, O> switchTransformer(
final Map<Predicate<I>, Transformer<I, O>> predicatesAndTransformers) {
return SwitchTransformer.switchTransformer(predicatesAndTransformers);
}
/**
* Create a new Transformer that uses the input object as a key to find the
* transformer to call.
* <p>
* 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 <I> the input type
* @param <O> the output type
* @param objectsAndTransformers a map of objects to transformers
* @return the transformer
* @throws NullPointerException if the map is null
* @throws NullPointerException if any transformer in the map is null
* @see SwitchTransformer
*/
@SuppressWarnings("unchecked")
public static <I, O> Transformer<I, O> switchMapTransformer(
final Map<I, Transformer<I, O>> objectsAndTransformers) {
if (objectsAndTransformers == null) {
throw new NullPointerException("The object and transformer map must not be null");
}
final Transformer<? super I, ? extends O> def = objectsAndTransformers.remove(null);
final int size = objectsAndTransformers.size();
final Transformer<? super I, ? extends O>[] trs = new Transformer[size];
final Predicate<I>[] preds = new Predicate[size];
int i = 0;
for (final Map.Entry<I, Transformer<I, O>> entry : objectsAndTransformers.entrySet()) {
preds[i] = EqualPredicate.<I>equalPredicate(entry.getKey());
trs[i++] = entry.getValue();
}
return TransformerUtils.switchTransformer(preds, trs, def);
}
/**
* Gets a Transformer that expects an input Class object that it will instantiate.
*
* @param <T> the output type
* @return the transformer
* @see InstantiateTransformer
*/
public static <T> Transformer<Class<? extends T>, T> instantiateTransformer() {
return InstantiateTransformer.instantiateTransformer();
}
/**
* 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 <T> the output type
* @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
* @see InstantiateTransformer
*/
public static <T> Transformer<Class<? extends T>, T> instantiateTransformer(
final Class<?>[] paramTypes, final Object[] args) {
return InstantiateTransformer.instantiateTransformer(paramTypes, args);
}
/**
* Creates a Transformer that uses the passed in Map to transform the input
* object (as a simple lookup).
*
* @param <I> the input type
* @param <O> the output type
* @param map the map to use to transform the objects
* @return the transformer, or {@link ConstantTransformer#nullTransformer()} if the
* {@code map} is {@code null}
* @see MapTransformer
*/
public static <I, O> Transformer<I, O> mapTransformer(final Map<? super I, ? extends O> map) {
return MapTransformer.mapTransformer(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.
* <p>
* For example, <code>TransformerUtils.invokerTransformer("getName");</code>
* will call the <code>getName/code> method on the input object to
* determine the transformer result.
*
* @param <I> the input type
* @param <O> the output type
* @param methodName the method name to call on the input object, may not be null
* @return the transformer
* @throws NullPointerException if the methodName is null.
* @see InvokerTransformer
*/
public static <I, O> Transformer<I, O> invokerTransformer(final String methodName) {
return InvokerTransformer.invokerTransformer(methodName, null, null);
}
/**
* Gets a Transformer that invokes a method on the input object.
* The method parameters are specified. If the input object is {@code null},
* {@code null} is returned.
*
* @param <I> the input type
* @param <O> the output type
* @param methodName the name of the method
* @param paramTypes the parameter types
* @param args the arguments
* @return the transformer
* @throws NullPointerException if the method name is null
* @throws IllegalArgumentException if the paramTypes and args don't match
* @see InvokerTransformer
*/
public static <I, O> Transformer<I, O> invokerTransformer(final String methodName, final Class<?>[] paramTypes,
final Object[] args) {
return InvokerTransformer.invokerTransformer(methodName, paramTypes, args);
}
/**
* Gets a transformer that returns a <code>java.lang.String</code>
* representation of the input object. This is achieved via the
* <code>toString</code> method, <code>null</code> returns 'null'.
*
* @param <T> the input type
* @return the transformer
* @see StringValueTransformer
*/
public static <T> Transformer<T, String> stringValueTransformer() {
return StringValueTransformer.stringValueTransformer();
}
}