xml

public class IndentFormatter {
    private static final Pattern ELEMENT = Pattern.compile("<[^<^>]+>|[^<^>]+");

    private static final Pattern ELEMENT_START = Pattern.compile("<[^/][^<^>]+[^/]>");

    private static final Pattern ELEMENT_END = Pattern.compile("</[^<^>]+>");

    private static final Pattern ELEMENT_EMPTY = Pattern.compile("<[^<^>]+/>");

    private static final Pattern ELEMENT_TEXT = Pattern.compile("[^<^>]+");

    private static Map<Integer, String> indentPool = new HashMap<Integer, String>();

    private static final String INDENT = "  ";

    public static String format(String xml) {
        StringBuffer buffer = new StringBuffer();
        try {

            Matcher matcher = ELEMENT.matcher(xml);

            int level = 0;
            String prev = null;
            while (matcher.find()) {
                String g = matcher.group();
                if (isStartElement(g)) {
                    if (isStartElement(prev)) {
                        level++;
                    }
                    if (prev != null) {
                        buffer.append("\n");
                    }
                    buffer.append(indent(level) + g);
                } else if (isText(g)) {
                    buffer.append(g);
                } else if (isEmptyElement(g)) {
                    if (isStartElement(prev)) {
                        level++;
                    }
                    buffer.append("\n" + indent(level) + g);
                } else if (isEndElement(g)) {
                    if (isEndElement(prev) || isEmptyElement(prev)) {
                        level--;
                        buffer.append("\n" + indent(level));
                    }
                    buffer.append(g);
                }
                prev = g;
            }
        } catch (Throwable e) {
            return xml;
        }
        return buffer.toString();
    }

    private static boolean isStartElement(String node) {
        if (node == null) {
            return false;
        }
        return ELEMENT_START.matcher(node).matches();
    }

    private static boolean isEndElement(String node) {
        if (node == null) {
            return false;
        }
        return ELEMENT_END.matcher(node).matches();
    }

    private static boolean isEmptyElement(String node) {
        if (node == null) {
            return false;
        }
        return ELEMENT_EMPTY.matcher(node).matches();
    }

    private static boolean isText(String node) {
        if (node == null) {
            return false;
        }
        return ELEMENT_TEXT.matcher(node).matches();
    }

    private static String indent(int level) {
        if (level < 1) {
            return "";
        }
        String indent = indentPool.get(level);
        if (indent == null) {
            StringBuffer buffer = new StringBuffer();
            for (int i = 0; i < level; i++) {
                buffer.append(INDENT);
            }
            indent = buffer.toString();
            indentPool.put(level, indent);
        }
        return indent;
    }

}