Transform.java

/*
 * ====================
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2008-2009 Sun Microsystems, Inc. All rights reserved.
 *
 * The contents of this file are subject to the terms of the Common Development
 * and Distribution License("CDDL") (the "License").  You may not use this file
 * except in compliance with the License.
 *
 * You can obtain a copy of the License at
 * http://opensource.org/licenses/cddl1.php
 * See the License for the specific language governing permissions and limitations
 * under the License.
 *
 * When distributing the Covered Code, include this CDDL Header Notice in each file
 * and include the License file at http://opensource.org/licenses/cddl1.php.
 * If applicable, add the following below this CDDL Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
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 * ====================
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package org.identityconnectors.patternparser;

import java.io.StringReader;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;

/**
 * Transforms may be applied to the result of a pattern match.
 * <p>
 * Transforms have completely arbitrary input and output; they can simply modify
 * an input string, or change it into a different object, such as an array, a
 * Date, or a List.
 * <p>
 * Transforms may be applied to the output of other Transforms, creating a chain
 * of transforms.
 * <p>
 * Predefined transforms each have their own XML representation. If additional
 * Transforms are needed, it is possible to create new subclasses of Transform.
 * If you do this, you must implement the methods:
 * <ul>
 * <li><b>transform</b> -- perform the transform.</li>
 * <li><b>getChildren</b> -- if your Transform has child Transforms, this must
 * produce an XML string representing the children.</li>
 * <li><b>getAttributes</b> -- if your Transform has attributes, this must
 * produce a string representing the attributes.</li>
 *
 * </ul>
 * Represented in XML by
 *
 * <pre>
 * <Transform class='<b>class</b>' ...attributes...>
 *   ...children...
 * </Transform>
 * </pre>
 *
 * where
 * <ul>
 * <li><b>class</b> -- the fully-qualified name of the Transform subclass
 * </ul>
 *
 * @param <T>
 *            Type of the transformed object.
 */

public abstract class Transform<T> {
    protected static final String CLASS = "class";

    protected static Element getFirstChildElement(Element element) {
        NodeList nodes = element.getChildNodes();
        for (int i = 0; i < nodes.getLength(); i++) {
            if (nodes.item(i) instanceof Element) {
                return (Element) nodes.item(i);
            }
        }
        return null;
    }

    protected static String attributeToString(String name, String value) {
        return " " + name + "='" + value.replaceAll("'", "'") + "'";
    }

    protected String getAttributes() {
        if (getClass().getPackage().equals(Transform.class.getPackage())) {
            return "";
        } else {
            return attributeToString(CLASS, getClass().getName());
        }
    }

    protected String getChildren(int indent) {
        return "";
    }

    public String toXml(int indent) {
        String children = getChildren(indent);
        StringBuffer pad = new StringBuffer();
        String className;
        if (getClass().getPackage().equals(Transform.class.getPackage())) {
            className = getClass().getSimpleName();
        } else {
            className = "Transform";
        }
        for (int i = 0; i < indent; i++) {
            pad.append(" ");
        }
        if (children.length() == 0) {
            return pad + "<" + className + getAttributes() + "/>\n";
        } else {
            return pad + "<" + className + getAttributes() + ">\n" + children + pad + "</"
                    + className + ">\n";
        }
    }

    /**
     * Transform an input object.
     *
     * @param input
     *            the object to be transformed
     * @return the transformed object
     * @throws Exception
     */
    public abstract T transform(Object input) throws Exception;

    /**
     * Factory method to create a Transform from an Element representing the
     * transform.
     *
     * @param element
     * @return
     * @throws IllegalArgumentException
     * @throws InstantiationException
     * @throws IllegalAccessException
     * @throws InvocationTargetException
     * @throws SecurityException
     * @throws NoSuchMethodException
     * @throws ClassNotFoundException
     */
    @SuppressWarnings("unchecked")
    public static Transform newTransform(Element element) throws InstantiationException,
            IllegalAccessException, InvocationTargetException, NoSuchMethodException,
            ClassNotFoundException {
        String className = element.getAttribute(CLASS);
        if (className.length() == 0) {
            className = Transform.class.getPackage().getName() + "." + element.getTagName();
        }
        Class<? extends Transform> clazz = (Class<? extends Transform>) Class.forName(className);
        Constructor<? extends Transform> constructor = clazz.getConstructor(Element.class);
        return constructor.newInstance(element);
    }

    public static Transform newTransform(String string) throws Exception {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setValidating(false);
        DocumentBuilder parser = factory.newDocumentBuilder();
        Document document = parser.parse(new InputSource(new StringReader(string)));
        NodeList elements = document.getChildNodes();
        for (int i = 0; i < elements.getLength(); i++) {
            if (elements.item(i) instanceof Element) {
                return Transform.newTransform((Element) elements.item(i));
            }
        }
        return null;
    }
};