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/*
 * 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;

/**
 * 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 * @version $Id: TransformerUtils.java 1714362 2015-11-14 20:38:02Z tn $ */ 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 the input type * @param the output type * @return the transformer * @see ExceptionTransformer */ public static Transformer exceptionTransformer() { return ExceptionTransformer.exceptionTransformer(); } /** * Gets a transformer that always returns null. * * @param the input type * @param the output type * @return the transformer * @see ConstantTransformer */ public static Transformer 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 the input/output type * @return the transformer * @see NOPTransformer */ public static Transformer 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): *
    *
  • public clone method *
  • public copy constructor *
  • serialization clone *
      * * @param the input/output type * @return the transformer * @see CloneTransformer */ public static Transformer cloneTransformer() { return CloneTransformer.cloneTransformer(); } /** * Creates a Transformer that will return the same object each time the * transformer is used. * * @param the input type * @param the output type * @param constantToReturn the constant object to return each time in the transformer * @return the transformer. * @see ConstantTransformer */ public static Transformer 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 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 Transformer asTransformer(final Closure 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 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 Transformer asTransformer(final Predicate 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 the input type * @param 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 Transformer asTransformer(final Factory factory) { return FactoryTransformer.factoryTransformer(factory); } /** * Create a new Transformer that calls each transformer in turn, passing the * result into the next transformer. * * @param 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 Transformer chainedTransformer( final Transformer... 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 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 Transformer chainedTransformer( final Collection> 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 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 Transformer ifTransformer(final Predicate predicate, final Transformer trueTransformer) { return IfTransformer.ifTransformer(predicate, trueTransformer); } /** * Create a new Transformer that calls one of two transformers depending * on the specified predicate. * * @param the input type * @param 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 Transformer ifTransformer(final Predicate predicate, final Transformer trueTransformer, final Transformer falseTransformer) { return IfTransformer.ifTransformer(predicate, trueTransformer, falseTransformer); } /** * Create a new Transformer that calls one of two transformers depending * on the specified predicate. * * @param the input type * @param 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 Transformer switchTransformer(final Predicate predicate, final Transformer trueTransformer, final Transformer 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 the input type * @param 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 Transformer switchTransformer(final Predicate[] predicates, final Transformer[] 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 the input type * @param 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 Transformer switchTransformer(final Predicate[] predicates, final Transformer[] transformers, final Transformer defaultTransformer) { return SwitchTransformer.switchTransformer(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 the input type * @param 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 Transformer switchTransformer( final Map, Transformer> predicatesAndTransformers) { return SwitchTransformer.switchTransformer(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 the input type * @param 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 Transformer switchMapTransformer( final Map> objectsAndTransformers) { if (objectsAndTransformers == null) { throw new NullPointerException("The object and transformer map must not be null"); } final Transformer def = objectsAndTransformers.remove(null); final int size = objectsAndTransformers.size(); final Transformer[] trs = new Transformer[size]; final Predicate[] preds = new Predicate[size]; int i = 0; for (final Map.Entry> entry : objectsAndTransformers.entrySet()) { preds[i] = EqualPredicate.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 the output type * @return the transformer * @see InstantiateTransformer */ public static Transformer, 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 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 Transformer, 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 the input type * @param 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 Transformer mapTransformer(final Map 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. *

      * For example, TransformerUtils.invokerTransformer("getName"); * will call the getName/code> method on the input object to * determine the transformer result. * * @param the input type * @param 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 Transformer 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 the input type * @param 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 Transformer invokerTransformer(final String methodName, final Class[] paramTypes, final Object[] args) { return InvokerTransformer.invokerTransformer(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'. * * @param the input type * @return the transformer * @see StringValueTransformer */ public static Transformer stringValueTransformer() { return StringValueTransformer.stringValueTransformer(); } }