removing invalid XML characters from a string in java

Question

Hi i would like to remove all invalid XML characters from a string. i would like to use a regular expression with the string.replace method.

like

line.replace(regExp,"");

what is the right regExp to use ?

invalid XML character is everything that is not this :

[#x1-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]

thanks.

Answer 1

Java's regex supports supplementary characters, so you can specify those high ranges with two UTF-16 encoded chars.

Here is the pattern for removing characters that are illegal in XML 1.0:

// XML 1.0
// #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]
String xml10pattern = "[^"
                    + "u0009
"
                    + "u0020-uD7FF"
                    + "uE000-uFFFD"
                    + "ud800udc00-udbffudfff"
                    + "]";

Most people will want the XML 1.0 version.

Here is the pattern for removing characters that are illegal in XML 1.1:

// XML 1.1
// [#x1-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]
String xml11pattern = "[^"
                    + "u0001-uD7FF"
                    + "uE000-uFFFD"
                    + "ud800udc00-udbffudfff"
                    + "]+";

You will need to use String.replaceAll(...) and not String.replace(...).

String illegal = "Hello, World!";
String legal = illegal.replaceAll(pattern, "");