Catching (and keeping) all comments with ANTLR

Question

I\'m writing a grammar in ANTLR that parses Java source files into ASTs for later analysis. Unlike other parsers (like JavaDoc) I\'m trying to keep all of the comments. This

Answer 1

first: direct all comments to a certain channel (only comments)

COMMENT
    : '/*' .*? '*/' -> channel(2)
    ;

LINE_COMMENT
    : '//' ~[\r\n]* -> channel(2)
    ;

second: print out all comments

      CommonTokenStream tokens = new CommonTokenStream(lexer);
      tokens.fill();
      for (int index = 0; index < tokens.size(); index++)
      {
         Token token = tokens.get(index);
         // substitute whatever parser you have
         if (token.getType() != Parser.WS) 
         {
            String out = "";
            // Comments will be printed as channel 2 (configured in .g4 grammar file)
            out += "Channel: " + token.getChannel();
            out += " Type: " + token.getType();
            out += " Hidden: ";
            List hiddenTokensToLeft = tokens.getHiddenTokensToLeft(index);
            for (int i = 0; hiddenTokensToLeft != null && i < hiddenTokensToLeft.size(); i++)
            {
               if (hiddenTokensToLeft.get(i).getType() != IDLParser.WS)
               {
                  out += "\n\t" + i + ":";
                  out += "\n\tChannel: " + hiddenTokensToLeft.get(i).getChannel() + "  Type: " + hiddenTokensToLeft.get(i).getType();
                  out += hiddenTokensToLeft.get(i).getText().replaceAll("\\s", "");
               }
            }
            out += token.getText().replaceAll("\\s", "");
            System.out.println(out);
         }
      }