How to escape certain characters in java

Question

I need to escape characters like ^, ., [, ], + and \ (tabs and newlines won't be an issue), while leaving others like * and ?.

EDIT = More specifically, I have a string with these characters, and I need to escape them so that they are not matched by regular expressions. I need to prepend \ to each of these characters, but doing so individually would take 7 or 8 scans and I'd like to do it within just one pass (IE: anything that matches is prepended with \)

How do I do this?

Thanks.

Answer 1

Would this work?

StringBuilder sb = new StringBuilder();
for (char c : myString.toCharArray())
{
    switch(c)
    {
        case '[':
        case ']':
        case '.':
        case '^':
        case '+':
        case '\\':
            sb.append('\\');
            // intended fall-through
        default:
            sb.append(c);
    }
}
String escaped = sb.toString();

Answer 2

There's an app for that: Pattern.quote()

It escapes anything that would be recognized as regex pattern language.

Answer 3

To escape a String to be used as a literal in a regular expression you can use Pattern.quote()

or just surround the string with \\Q and \\E.

Answer 4

The \Q and \E and java.util.Pattern.quote() are the same approach.

However, this approach only works for a subset of regex flavors.

Check out the following link and you'll see that 4 of 15 flavors support it. So you're better off using Grodriguez's approach if you need to execute your regex in anything other than Java, such as javascript (which uses ECMA).

http://www.regular-expressions.info/refflavors.html

Here is a one-liner that might work.

"text to escape".replaceAll("([\\\\\\[\\]\\.\\^\\+])","\\\\$1");

Answer 5

You do this by prepending \ to the character you want to escape.