With Java regex find functions with any number of nesting

Question

Hello fellow programmers

i have a small problem and can't seem to find the right answere.

So my idea is i get a String with a predefined function from me. It will look something like this:

 String expression = "map(%set@IDENTIFIER%, get(%key@Longitude:Number%), get(%key@Latitude:Number%), map(%set@IDENTIFIER%, get(%key@Longitude:Number%), get(%key@Latitude:Number%)))";

It can be much more complicated or even simpler when i only use get for example.

What i want to do is to split every function in to its parameter this can also be functions or a normal String or Number.

What i thought is i can use regex to do this but i can't seem to find the right thing.

My regex so far:

String regex = "((?<method>map|get)\\((?<parameter>\\%(?<dynamic>set\\@[a-zA-Z_]+|\\$[0-9]+|key\\@[a-zA-Z_]+|set\\@[a-zA-Z_]+)(?<type>:[a-zA-Z]+)*\\%,*)+\\))";

What i do is

Pattern pa = Pattern.compile(regex);
Matcher m = pa.matcher(expression);
while (m.find()) {
   System.out.println("Method " + m.group("method"));
   System.out.println("Parameter " + m.group("parameter"));
   System.out.println("Type" + m.group("type"));
}

My Output is than this:
Method get
Parameter %key@Longitude:Number%
Type:Number
Method get
Parameter %key@Latitude:Number%
Type:Number
Method get
Parameter %key@Longitude:Number%
Type:Number
Method get
Parameter %key@Latitude:Number%
Type:Number

But what i miss is the function map with all its parameter.

Hope it is kind of understandable what i mean.

You miss it because all the methods are nested inside the maps. See demo. Java regex does not support recursion. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jan 29, 2016 at 16:23
This sounds more like a job for a recursive descent parser. Check out ANTLR for example if you do not want to write it yourself. — Sorcen
– Sorcen, Commented Jan 29, 2016 at 17:05

user4910279 · Accepted Answer · 2016-01-29 17:50:36Z

3

Try this ANTRL syntax.

grammar Method;

method      : ('map' | 'get') '(' element (',' element )* ')';
element     : method | parameter;
parameter   : '%' dynamic type* '%';
dynamic     : 'set' '@' ID | 'key' '@' ID | '$' NUMBER;
type        : ':' ID;

ID          : [a-zA-Z]+;
NUMBER      : [0-9]+;
Skip        : [ \t\n\r]+ -> skip;

Result is

answered Jan 29, 2016 at 17:50

user4910279

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kazagistar · Accepted Answer · 2016-01-29 17:50:26Z

0

Java regular expressions do not support recursion, which is required for arbitrary nested parenthesis matching in a regex. Even if it did, the best solution would be to actually parse the expression.

If you don't want to use a proper parser, then you should tokenize it. Split it into a stream of function starts, parameters, and function ends, and then add logic to process that stream.

answered Jan 29, 2016 at 17:50

kazagistar

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