How do I get the original text that an antlr4 rule matched?

java antlr antlr4
monty0 picture monty0 · May 2, 2013 · Viewed 8.9k times · Source

Using the Java 7 grammar https://github.com/antlr/grammars-v4/blob/master/java7/Java7.g4 I want to find methods with a specific name and then just print out that method. I see that I can use the methodDeclaration rule when I match. So I subclass Java7BaseListener and override this listener method:

@Override public void enterMethodDeclaration(Java7Parser.MethodDeclarationContext ctx) { }

How do I get the original text out? ctx.getText() gives me a string with all the whitespace stripped out. I want the comments and original formatting.

Answer

monty0 picture monty0 · May 2, 2013

ANTLR's CharStream class has a method getText(Interval interval) which will return the original source in the give range. The Context object has methods to get the beginning and end. Assuming you have a field in your listener called input which has the CharStream being parsed, you can do this:

    int a = ctx.start.getStartIndex();
    int b = ctx.stop.getStopIndex();
    Interval interval = new Interval(a,b);
    input.getText(interval);

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