XMLWriter.java

/*
 * Copyright 2011-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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 com.amazonaws.util;

import com.amazonaws.AmazonClientException;

import java.io.IOException;
import java.io.Writer;
import java.util.Date;
import java.util.Stack;

/**
 * Utility for creating easily creating XML documents, one element at a time.
 */
public class XMLWriter {

    /** Standard XML prolog to add to the beginning of each XML document. */
    private static final String PROLOG = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>";

    /**
     * The writer to which the XML document created by this writer will be
     * written.
     */
    private final Writer writer;

    /** Optional XML namespace attribute value to include in the root element. */
    private final String xmlns;

    private Stack<String> elementStack = new Stack<String>();
    private boolean rootElement = true;

    /**
     * Creates a new XMLWriter, ready to write an XML document to the specified
     * writer. The XML document will not specify an xmlns attribute.
     *
     * @param w The writer this XMLWriter will write to.
     */
    public XMLWriter(Writer w) {
        this(w, null);
    }

    /**
     * Creates a new XMLWriter, ready to write an XML document to the specified
     * writer. The root element in the XML document will specify an xmlns
     * attribute with the specified namespace parameter.
     *
     * @param w The writer this XMLWriter will write to.
     * @param xmlns The XML namespace to include in the xmlns attribute of the
     *            root element.
     */
    public XMLWriter(Writer w, String xmlns) {
        this.writer = w;
        this.xmlns = xmlns;
        append(PROLOG);
    }

    /**
     * Starts a new element with the specified name at the current position in
     * the in-progress XML document.
     *
     * @param element The name of the new element.
     * @return This XMLWriter so that additional method calls can be chained
     *         together.
     */
    public XMLWriter startElement(String element) {
        append("<" + element);
        if (rootElement && xmlns != null) {
            append(" xmlns=\"" + xmlns + "\"");
            rootElement = false;
        }
        append(">");
        elementStack.push(element);
        return this;
    }

    /**
     * Closes the last opened element at the current position in the in-progress
     * XML document.
     *
     * @return This XMLWriter so that additional method calls can be chained
     *         together.
     */
    public XMLWriter endElement() {
        String lastElement = elementStack.pop();
        append("</" + lastElement + ">");
        return this;
    }

    /**
     * Adds the specified value as text to the current position of the in
     * progress XML document.
     *
     * @param s The text to add to the XML document.
     * @return This XMLWriter so that additional method calls can be chained
     *         together.
     */
    public XMLWriter value(String s) {
        append(escapeXMLEntities(s));
        return this;
    }

    /**
     * Adds the specified date as text to the current position of the
     * in-progress XML document.
     *
     * @param date The date to add to the XML document.
     * @return This XMLWriter so that additional method calls can be chained
     *         together.
     */
    public XMLWriter value(Date date) {
        append(escapeXMLEntities(StringUtils.fromDate(date)));
        return this;
    }

    /**
     * Adds the string representation of the specified object to the current
     * position of the in progress XML document.
     *
     * @param obj The object to translate to a string and add to the XML
     *            document.
     * @return This XMLWriter so that additional method calls can be chained
     *         together.
     */
    public XMLWriter value(Object obj) {
        append(escapeXMLEntities(obj.toString()));
        return this;
    }

    private void append(String s) {
        try {
            writer.append(s);
        } catch (IOException e) {
            throw new AmazonClientException("Unable to write XML document", e);
        }
    }

    private String escapeXMLEntities(String s) {
        /**
         * Unescape any escaped characters.
         */
        if (s.contains("&")) {
            s = s.replace(""", "\"");
            s = s.replace("'", "'");
            s = s.replace("<", "<");
            s = s.replace(">", ">");
            // Ampersands should always be the last to unescape
            s = s.replace("&", "&");
        }
        // Ampersands should always be the first to escape
        s = s.replace("&", "&");
        s = s.replace("\"", """);
        s = s.replace("'", "'");
        s = s.replace("<", "<");
        s = s.replace(">", ">");
        return s;
    }

}