Question

I have an input string in the following format

String input = "00IG356001110002005064007000000";

Characters 3-7 is the code.

Characters 8-12 is the amount.

Based on the code in the input string (IG356 in the sample input string), i need to capture the amount(00111 in the sample).
The value in the amount (characters 8-12) should be picked up only for specific codes and the logic is detailed below.

1. The code should not be SG356. If it is SG356, not a match and exit.

2. a. If the code is not SG356, check if the codes are IG902 or SG350, in this case capture the amount(00111)

   else

   b. Check for the 3 numbers in the code (characters 5-7, 356 in this sample). If they are 200,201,356,370. go ahead and capture the amount

I am using the regular expression shown below:
Using positive lookahead and if then else construct.

String regex= ".{2}(?!SG356)((?=IG902|SG350).{5}(.{5}).+|.{2}(?=200|201|356|370).{3}(.{5}).+)";

The regular expression works fine if the code in the input string is IG902 or SG350 (when the ‘if’ part of the regex is getting matched). but if the ‘else’ is getting matched, i am unable to capture the amount.

This regular expression is working fine while just checking for a match.

.{2}(?!SG356)((?=IG902|SG350).+|.{2}(?=200|201|356|370).+) 

The problem is only while capturing the group.
I am running this in Java. Any help would be greatly appreciated.

The java code i am using is :

public String getTsqlSum(String input, String regex){
     String value = null;
     Matcher m = Pattern.compile(regex).matcher(input);
     System.out.println("Group Count: " + m.groupCount());
     if (m.matches()) {
    for (int i=0;i<m.groupCount();i++){
        System.out.println("For i: " + i +" Value: " + m.group(i));
         }
     }
     return value;
}

public void forumTest(){
    //String input = "00IG902001110002005064007000000";
         String input = "00IG356001110002005064007000000";
    String regex= ".{2}(?!SG356)(?:(?=IG902|SG350).{5}|.{2}(?=200|201|356|370).{3})(.{5}).+";
    System.out.println(match(input, regex));
    String match = getTsqlSum(input, regex);
    System.out.println("Match: " + match);
}

Answer 1

The regular expression works fine if the code in the input string is IG902 or SG350 (when the ‘if’ part of the regex is getting matched). but if the ‘else’ is getting matched, i am unable to capture the amount.

You are not unable to capture the amount, the expression is working fine. But if you are in the second part of the alternation (This is not a regex if-then-else) then your result is in a different capturing group. You will find it in the capturing group 3 and not in the second one like when you are matching in the first part of the alternation.

String regex= ".{2}(?!SG356)((?=IG902|SG350).{5}(.{5}).+|.{2}(?=200|201|356|370).{3}(.{5}).+)";
        Group number        1                   2                                   3

In a regular expression the capturing groups are numbered by their opening brackets and this continues also in an alternation. In Perl there would be a construct that gives the capturing groups of an alternation the same number, but I think thats the only flavour that is able to do this.

In Java you need to check after the expression in which group you have the result.

See my answer here, similar topic

You can change your regex and make the alternation before the capturing group

try this

.{2}(?!SG356)(?:(?=IG902|SG350).{5}|.{2}(?=200|201|356|370).{3})(.{5}).+

You will find your result in both cases in the group 1. (I made the first one a non capturing group using the ?:)

Update after the source was added

Your loop is wrong, that means the groups are starting at 1, if you want the content of group one, you have to use m.group(1).

In group m.group(0) you will find the whole matched string.

Try this

for (int i=1;i<=m.groupCount();i++){
    System.out.println("For i: " + i +" Value: " + m.group(i));
}