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The Amazon Web Services SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).

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/*
 * Copyright 2010-2014 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.services.s3.internal;
import static com.amazonaws.util.StringUtils.UTF8;

import java.util.ArrayList;
import java.util.List;


/**
 * Basic XML Writer helper library. It does not do full XML Well-Formedness
 * checks, but provides basic element and attribute value escaping, and tracks
 * open tags to simplify use.
 * 
 * Sampe usage:
 * 
 * 
 * XmlWriter w = new XmlWriter();
 * w.start(DOC_TAG, "xmlns", DOC_NAMESPACE);
 * if (foo != null)
 *   w.start(FOO_TAG).value(foo).end();
 * w.end();
 * 
 * 
 */
public class XmlWriter {
    List tags = new ArrayList();
    StringBuilder sb = new StringBuilder();

    public XmlWriter start(String name) {
        sb.append("<").append(name).append(">");
        tags.add(name);
        return this;
    }

    public XmlWriter start(String name, String attr, String value) {
        sb.append("<").append(name);
        writeAttr(attr, value);
        sb.append(">");
        tags.add(name);
        return this;
    }

    public XmlWriter start(String name, String[] attrs, String[] values) {
        sb.append("<").append(name);
        for (int i = 0; i < Math.min(attrs.length, values.length); i++) {
            writeAttr(attrs[i], values[i]);
        }
        sb.append(">");
        tags.add(name);
        return this;
    }

    public XmlWriter end() {
        assert(tags.size() > 0);
        String name = tags.remove(tags.size() - 1);
        sb.append("");
        return this;
    }

    public byte[] getBytes() {
        assert(tags.size() == 0);
        return this.toString().getBytes(UTF8);
    }

    public String toString() {
        return sb.toString();
    }

    public XmlWriter value(String value) {
        appendEscapedString(value, sb);
        return this;
    }

    private void writeAttr(String name, String value) {
        sb.append(' ').append(name).append("=\"");
        appendEscapedString(value, sb);
        sb.append("\"");
    }

    /**
     * Appends the specified string (with any non-XML-compatible characters
     * replaced with the corresponding escape code) to the specified
     * StringBuilder.
     *
     * @param s
     *            The string to escape and append to the specified
     *            StringBuilder.
     * @param builder
     *            The StringBuilder to which the escaped string should be
     *            appened.
     */
    private void appendEscapedString(String s, StringBuilder builder) {
        if (s == null)
            s = "";
        int pos;
        int start = 0;
        int len = s.length();
        for (pos = 0; pos < len; pos++) {
            char ch = s.charAt(pos);
            String escape;
            switch (ch) {
            case '\t':
                escape = "	";
                break;
            case '\n':
                escape = "
";
                break;
            case '\r':
                escape = "";
                break;
            case '&':
                escape = "&";
                break;
            case '"':
                escape = """;
                break;
            case '<':
                escape = "<";
                break;
            case '>':
                escape = ">";
                break;
            default:
                escape = null;
                break;
            }

            // If we found an escape character, write all the characters up to that
            // character, then write the escaped char and get back to scanning
            if (escape != null) {
                if (start < pos)
                    builder.append(s, start, pos);
                sb.append(escape);
                start = pos + 1;
            }
        }

        // Write anything that's left
        if (start < pos) sb.append(s, start, pos);
    }

}