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Posts Tagged Regex

Java Regex Search and Replace

Aug 12

Posted by Christopher J. Stehno in Programming | No Comments

For many years, I felt that there was nothing “regular” about Regular Expressions, but lately I have been warming up to them a bit. The QuickRex Eclipse plug-in has really helped make them easier to manage, but that’s not what this post is about.

I recently needed to do a regex-based search and replace operation to convert all the html entities in a string to their actual character equivalents, basically unescape all the entities in an html string (don’t ask why). With a little regex and a little searching documentation browsing I found that it is very easy to do.

Start out with the pattern, which should be a static class member (it is thread-safe once created):

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private static final Pattern entityPattern = Pattern.compile("(&[a-z]*;)");

The pattern will match any html entity, which have the form &name;. Next we need the search and replace code:

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private String unescapeEntities(final String html){
    final StringBuffer buffer = new StringBuffer();
    final Matcher matcher = entityPattern.matcher(html);
    while (matcher.find()) {
        matcher.appendReplacement(buffer, StringEscapeUtils.unescapeHtml(matcher.group()));
    }
    matcher.appendTail(buffer);

    return buffer.toString();
}

Your StringBuffer will end up with the replaced content of your string. The StringEscapeUtils class is from the Jakarta Commons – Lang API.

Sorry, this isn’t much of a tutorial… it’s more of a code snippet for future use.

Popularity: 7% [?]

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Finding Matching Ints Using Regex

Jun 4

Posted by Christopher J. Stehno in Programming | No Comments

If you are following along you may have noticed that I have been compiling a long list of solutions to my Finding Matching Ints problem. I was talking to one of my co-workers, who is not a developer but used to do some Perl hacking, and he suggested that it could be done with regular expressions. Lo and behold, with the help of another of my more regular-expression-ized co-workers we found this to be true:

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public int findDuplicate(final int[] array){
    final Pattern p = Pattern.compile(".*?(\\d+. ).*?\\1.*");
    final Matcher m = p.matcher(join(array));
    if(m.find()){
        return Integer.valueOf(m.group(1).trim());
    }
    throw new IllegalArgumentException("No match found!");
}

private String join(final int[] array){
    final StringBuilder str = new StringBuilder();
    for(final int i : array){
        str.append(i).append(" ");
    }
    return str.toString();
}

Granted, it’s not quite as straight-forward as the other solutions, but it is a very novel approach to solving the problem… leave it to a Perl guy. :-) I wonder what the runtime of this would be?

Popularity: 1% [?]

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