Java regex to find a sequence of characters in a string

I would like to find out if my string has = & & sequence in it. If yes then I would like to encode second &. How using java regex can I find it?

开发者_StackOverflow社区My string is something like this:

a=cat&b=dog&cat&c=monkey

Thanks Chaitanya

Like Mosty and Ted suggested, perhaps the best way to go at this is by detecting and escaping the '&'.

However, if you want a single regex to do the work for you, here it is:

String s = "a=cat&b=dog&cat&c=monkey";

s = s.replaceAll("&(?=[^=]*&)", "&");

System.out.println(s);

Why don't you just split it?

First split it by "&", then take the second element

You can use this format:

if (string.contains("=&&"))
{
 // do something
}
else
{
 // do something else
}

I don't know what you mean by "encode the &" though. Could you clarify?

It would be easier to escape the & in the values before forming the concatenated name-value pair string. But given an already-encoded string, I think a variant of Mosty's suggestion might work best:

String escapeAmpersands(String nvp) {
    StringBuilder sb = new StringBuilder();
    String[] pairs = nvp.split("&");
    if (pairs[0].indexOf('=') < 0) {
        // Maybe do something smarter with "a&b=cat&c=dog"?
        throw new Exception("Can't handle names with '&'");
    }
    sb.append(pairs[0]);
    for (int i = 1; i < pairs.length; ++i) {
        String pair = pairs[i];
        sb.append(pair.indexOf('=') < 0 ? "&amp;" : "&");
        sb.append(pair);
    }
    return sb.toString();
}

This is likely to be faster than regular trying to do this with regular expressions.