Handling errors in ANTLR4

Since I’ve had a little bit of a struggle with the two existing answers, I’d like to share the solution I ended up with.

First of all I created my own version of an ErrorListener like Sam Harwell suggested:

public class ThrowingErrorListener extends BaseErrorListener {

   public static final ThrowingErrorListener INSTANCE = new ThrowingErrorListener();

   @Override
   public void syntaxError(Recognizer<?, ?> recognizer, Object offendingSymbol, int line, int charPositionInLine, String msg, RecognitionException e)
      throws ParseCancellationException {
         throw new ParseCancellationException("line " + line + ":" + charPositionInLine + " " + msg);
      }
}

Note the use of a ParseCancellationException instead of a RecognitionException since the DefaultErrorStrategy would catch the latter and it would never reach your own code.

Creating a whole new ErrorStrategy like Brad Mace suggested is not necessary since the DefaultErrorStrategy produces pretty good error messages by default.

I then use the custom ErrorListener in my parsing function:

public static String parse(String text) throws ParseCancellationException {
   MyLexer lexer = new MyLexer(new ANTLRInputStream(text));
   lexer.removeErrorListeners();
   lexer.addErrorListener(ThrowingErrorListener.INSTANCE);

   CommonTokenStream tokens = new CommonTokenStream(lexer);

   MyParser parser = new MyParser(tokens);
   parser.removeErrorListeners();
   parser.addErrorListener(ThrowingErrorListener.INSTANCE);

   ParserRuleContext tree = parser.expr();
   MyParseRules extractor = new MyParseRules();

   return extractor.visit(tree);
}

(For more information on what MyParseRules does, see here.)

This will give you the same error messages as would be printed to the console by default, only in the form of proper exceptions.