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Commons Collections example source code file (InvokerTransformer.java)

This example Commons Collections source code file (InvokerTransformer.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Collections tags/keywords

class, class, functorexception, illegalaccessexception, illegalargumentexception, invokertransformer, invokertransformer, io, object, object, reflection, serializable, string, the, the, transformer

The Commons Collections InvokerTransformer.java source code

/*
 *  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.collections.functors;

import java.io.Serializable;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import org.apache.commons.collections.FunctorException;
import org.apache.commons.collections.Transformer;

/**
 * Transformer implementation that creates a new object instance by reflection.
 * 
 * @since Commons Collections 3.0
 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 *
 * @author Stephen Colebourne
 */
public class InvokerTransformer implements Transformer, Serializable {

    /** The serial version */
    private static final long serialVersionUID = -8653385846894047688L;
    
    /** The method name to call */
    private final String iMethodName;
    /** The array of reflection parameter types */
    private final Class[] iParamTypes;
    /** The array of reflection arguments */
    private final Object[] iArgs;

    /**
     * Gets an instance of this transformer calling a specific method with no arguments.
     * 
     * @param methodName  the method name to call
     * @return an invoker transformer
     * @since Commons Collections 3.1
     */
    public static Transformer getInstance(String methodName) {
        if (methodName == null) {
            throw new IllegalArgumentException("The method to invoke must not be null");
        }
        return new InvokerTransformer(methodName);
    }

    /**
     * Gets an instance of this transformer calling a specific method with specific values.
     * 
     * @param methodName  the method name to call
     * @param paramTypes  the parameter types of the method
     * @param args  the arguments to pass to the method
     * @return an invoker transformer
     */
    public static Transformer getInstance(String methodName, Class[] paramTypes, Object[] args) {
        if (methodName == null) {
            throw new IllegalArgumentException("The method to invoke must not be null");
        }
        if (((paramTypes == null) && (args != null))
            || ((paramTypes != null) && (args == null))
            || ((paramTypes != null) && (args != null) && (paramTypes.length != args.length))) {
            throw new IllegalArgumentException("The parameter types must match the arguments");
        }
        if (paramTypes == null || paramTypes.length == 0) {
            return new InvokerTransformer(methodName);
        } else {
            paramTypes = (Class[]) paramTypes.clone();
            args = (Object[]) args.clone();
            return new InvokerTransformer(methodName, paramTypes, args);
        }
    }

    /**
     * Constructor for no arg instance.
     * 
     * @param methodName  the method to call
     */
    private InvokerTransformer(String methodName) {
        super();
        iMethodName = methodName;
        iParamTypes = null;
        iArgs = null;
    }

    /**
     * Constructor that performs no validation.
     * Use <code>getInstance if you want that.
     * 
     * @param methodName  the method to call
     * @param paramTypes  the constructor parameter types, not cloned
     * @param args  the constructor arguments, not cloned
     */
    public InvokerTransformer(String methodName, Class[] paramTypes, Object[] args) {
        super();
        iMethodName = methodName;
        iParamTypes = paramTypes;
        iArgs = args;
    }

    /**
     * Transforms the input to result by invoking a method on the input.
     * 
     * @param input  the input object to transform
     * @return the transformed result, null if null input
     */
    public Object transform(Object input) {
        if (input == null) {
            return null;
        }
        try {
            Class cls = input.getClass();
            Method method = cls.getMethod(iMethodName, iParamTypes);
            return method.invoke(input, iArgs);
                
        } catch (NoSuchMethodException ex) {
            throw new FunctorException("InvokerTransformer: The method '" + iMethodName + "' on '" + input.getClass() + "' does not exist");
        } catch (IllegalAccessException ex) {
            throw new FunctorException("InvokerTransformer: The method '" + iMethodName + "' on '" + input.getClass() + "' cannot be accessed");
        } catch (InvocationTargetException ex) {
            throw new FunctorException("InvokerTransformer: The method '" + iMethodName + "' on '" + input.getClass() + "' threw an exception", ex);
        }
    }

}

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