How can i match particular format in input using java.util.regex in java?

Question

INPUT

Input can be in any of the form shown below with following mandatory content TXT{Any comma separated strings in any format}

String loginURL = "http://ip:port/path?username=abcd&location={LOCATION}&TXT{UE-IP,UE-Username,UE-Password}&password={PASS}";
String loginURL1 = "http://ip:port/path?username=abcd&location={LOCATION}&password={PASS}&TXT{UE-IP,UE-Username,UE-Password}";
String loginURL2 = "http://ip:port/path?TXT{UE-IP,UE-Username,UE-Password}&username=abcd&location={LOCATION}&password={PASS}";
String loginURL3 = "http://ip:port/path?TXT{UE-IP,UE-Username,UE-Password}";
String loginURL4 = "http://ip:port/path?username=abcd&password={PASS}";

Required Output

1. OutputURL corresponding to loginURL.

String outputURL = "http://ip:port/path?username=abcd&location={LOCATION}&password={PASS}";
String outputURL1 = "http://ip:port/path?username=abcd&location={LOCATION}&password={PASS}";
String outputURL2 = "http://ip:port/path?username=abcd&location={LOCATION}&password={PASS}";
String outputURL3 = "http://ip:port/path?";
String outputURL4 = "http://ip:port/path?username=abcd&password={PASS}";

2. Deleted pattern(if any)

String deletedPatteren = TXT{UE-IP,UE-Username,UE-Password}

My Attempts

String loginURLPattern = TXT+"\\{([\\w-,]*)\\}&*";

System.out.println("1. ");
getListOfTemplates(loginURL, loginURLPattern);
System.out.println();

System.out.println("2. ");
getListOfTemplates(loginURL1, loginURLPattern);
System.out.println();

private static void getListOfTemplates(String inputSequence,String pattern){
    System.out.println("Input URL : " + inputSequence);
    Matcher templateMatcher =  Pattern.compile(pattern).matcher(inputSequence);
    if (templateMatcher.find() && templateMatcher.group(1).length() > 0) {
        System.out.println(templateMatcher.group(1));
        System.out.println("OutputURL : " + templateMatcher.replaceAll(""));
    }
}

OUTPUT obtained

1. 
Input URL : http://ip:port/path?username=abcd&location={LOCATION}&TXT{UE-IP,UE-Username,UE-Password}&password={PASS}
UE-IP,UE-Username,UE-Password}&password={PASS
OutputURL : http://ip:port/path?username=abcd&location={LOCATION}&

2. 
Input URL : http://ip:port/path?username=abcd&location={LOCATION}&password={PASS}&TXT{UE-IP,UE-Username,UE-Password}
UE-IP,UE-Username,UE-Password
OutputURL : http://ip:port/path?username=abcd&location={LOCATION}&password={PASS}&

DRAWBACK OF ABOVE PATTERN

If i add any String containing character like #,%,@ in between TXT{} then my code breaks.

How can i achieve it using java.util.regex library so that user can input any comma separated String between TXT{Any Comma Separated Strings}.

You are misinterpreting it with word JSON, i have changed it to TXT.please see update — Prateek, Mar 21 '14 at 08:46
Do you really want to keep the `&` at the end of `outputURL1`? — Keppil, Mar 21 '14 at 08:52

score 4 · Accepted Answer · edited May 23 '17 at 12:28

I would recommend using Matcher.appendReplacement:

public static void main(final String[] args) throws Exception {
    final String[] loginURLs = {
        "http://ip:port/path?username=abcd&location={LOCATION}&TXT{UE-IP,UE-Username,UE-Password}&password={PASS}",
        "http://ip:port/path?username=abcd&location={LOCATION}&password={PASS}&TXT{UE-IP,UE-Username,UE-Password}",
        "http://ip:port/path?TXT{UE-IP,UE-Username,UE-Password}&username=abcd&location={LOCATION}&password={PASS}",
        "http://ip:port/path?TXT{UE-IP,UE-Username,UE-Password}",
        "http://ip:port/path?username=abcd&password={PASS}"};
    final Pattern patt = Pattern.compile("(\\?)?&?(TXT\\{[^}]++})(&)?");
    for (final String loginURL : loginURLs) {
        System.out.printf("%1$-10s %2$s%n", "Processing", loginURL);
        final StringBuffer sb = new StringBuffer();
        final Matcher matcher = patt.matcher(loginURL);
        while (matcher.find()) {
            final String found = matcher.group(2);
            System.out.printf("%1$-10s %2$s%n", "Found", found);
            if (matcher.group(1) != null && matcher.group(3) != null) {
                matcher.appendReplacement(sb, "$1");                
            } else {
                matcher.appendReplacement(sb, "$3");
            }
        }
        matcher.appendTail(sb);
        System.out.printf("%1$-10s %2$s%n%n", "Processed", sb.toString());
    }
}

Output:

Processing http://ip:port/path?username=abcd&location={LOCATION}&TXT{UE-IP,UE-Username,UE-Password}&password={PASS}
Found      TXT{UE-IP,UE-Username,UE-Password}
Processed  http://ip:port/path?username=abcd&location={LOCATION}&password={PASS}

Processing http://ip:port/path?username=abcd&location={LOCATION}&password={PASS}&TXT{UE-IP,UE-Username,UE-Password}
Found      TXT{UE-IP,UE-Username,UE-Password}
Processed  http://ip:port/path?username=abcd&location={LOCATION}&password={PASS}

Processing http://ip:port/path?TXT{UE-IP,UE-Username,UE-Password}&username=abcd&location={LOCATION}&password={PASS}
Found      TXT{UE-IP,UE-Username,UE-Password}
Processed  http://ip:port/path?username=abcd&location={LOCATION}&password={PASS}

Processing http://ip:port/path?TXT{UE-IP,UE-Username,UE-Password}
Found      TXT{UE-IP,UE-Username,UE-Password}
Processed  http://ip:port/path

Processing http://ip:port/path?username=abcd&password={PASS}
Processed  http://ip:port/path?username=abcd&password={PASS}

As you rightly point out, there are 3 possible cases:

"?{TEXT}&" -> "?"
"&{TEXT}&" -> "&"
"?{TEXT}" -> ""

So what we need to do is test for those cases in the regex. Here is the pattern:

(\\?)?&?(TXT\\{[^}]++})(&)?

Explanation:

(\\?)? optionally matches and captures a ?
&? optionally captures an &
(TXT\\{[^}]++}) matches and captures TXT, followed by {, followed by one or most not } (possessively), followed by } (closing brackets don't need to be escaped
(&)? optionally matches and captures a &

We have 3 groups:

potentially a ?
the required text
potentially an &

Now when we find a match we need to replace with the appropriate capture of case 1..3

if (matcher.group(1) != null && matcher.group(3) != null) {
    matcher.appendReplacement(sb, "$1");                
} else {
    matcher.appendReplacement(sb, "$3");
}

If groups 1 and 3 are both present:

We must be in case 1; we must replace with "?" which is in group 1 so $1.

Otherwise we are in case 2 or 3:

In case 2 we need to replace with "&" and in 3 with "".
In case 2 group 3 will hold "&" and in case 3 it will hold "" so we can replace with $3 in both these cases.

Here I only capture the TXT{...} part using a match group. This means that although the leading ? or & is replaced it is not in the String found. I you only want the bit between {} then just move the parenthesis.

Note that I reuse the Pattern - you can also reuse the Matcher if performance is a concern. You should always reuse the Pattern as it is (very) expensive to create. Store it in a static final if you can - it's threadsafe, matchers are not. The usual way to do it is to store the Pattern in a static final and then reuse the Matcher in the context of a method.

Also, the use of Matcher.appendReplacement is much more efficient than your current approach as it only needs to process the input once. Your approach parses the string twice.

It has not solved my problem, For third input, actual is *http://ip:port/path&username=abcd&location={LOCATION}&password={PASS}* and desired is *http://ip:port/path?username=abcd&location={LOCATION}&password={PASS}* — Prateek, Mar 21 '14 at 09:51
@Prateek [this](http://stackoverflow.com/questions/22557708/regex-possesive-quantifier/22558236#22558236) might be of interest - that's why it took quite so long to find the answer. — Boris the Spider, Mar 21 '14 at 12:48

How can i match particular format in input using java.util.regex in java?

INPUT

Required Output

My Attempts

DRAWBACK OF ABOVE PATTERN

1 Answers1

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