Java DOM transforming and parsing arbitrary strings with invalid XML characters?

Question

First of all I want to mention that this is not a duplicate of How to parse invalid (bad / not well-formed) XML? because I don\'t have a given invalid (or not well-formed) X

Answer 1

I think the simplest solution is using XML 1.1 (supported by org.w3c.dom) by using this preprocessor:

version=1.1 encoding=UTF-8 standalone=yes?>

According to Wikipedia the only invalid characters in XML 1.1 are U+0000, surrogates, U+FFFE and U+FFFF

This code snippet ensures you always get a correct XML 1.1 string, omitting illegal chars (might not be what you looks for though if you need the exact same string back):

public static String escape(String orig) {
    StringBuilder builder = new StringBuilder();

    for (char c : orig.toCharArray()) {
        if (c == 0x0 || c == 0xfffe || c == 0xffff || (c >= 0xd800 && c <= 0xdfff)) {
            continue;
        } else if (c == '\'') {
            builder.append("'");
        } else if (c == '"') {
            builder.append(""");
        } else if (c == '&') {
            builder.append("&");
        } else if (c == '<') {
            builder.append("<");
        } else if (c == '>') {
            builder.append(">");
        } else if (c <= 0x1f) {
            builder.append("&#" + ((int) c) + ";");
        } else {
            builder.append(c);
        }
    }

    return builder.toString();
}