provectus/kafka-ui · error · ValidationException

Error parsing ksql query:

Error message

Error parsing ksql query: 

What it means

KsqlGrammar.parseStatements catches any exception raised while driving the ANTLR parser over the ksql text (beyond listener-reported syntax errors) and rethrows it as ValidationException('Error parsing ksql query: ' + message). It is the fallback path for parser failures.

Solutions

1. Read the wrapped cause message after 'Error parsing ksql query: ' to identify the parser failure
2. Simplify the query into smaller statements and parse them individually
3. Validate the query with the ksqlDB CLI/parser to isolate the failing construct
4. Report/upgrade if the bundled grammar lags behind your ksqlDB server version

Example fix

// before
KsqlGrammar.parseStatements(complexQuery); // single opaque failure
// after
for (String stmt : complexQuery.split(";")) {
  KsqlGrammar.parseStatements(stmt + ";"); // isolates failing statement
}

// Pre-check: reject obviously malformed multi-statement input
if (query == null || query.isBlank()) throw new IllegalArgumentException("ksql query is empty");

try {
  var parser = KsqlGrammar.parsed(query);
} catch (ValidationException e) {
  if (e.getMessage().startsWith("Error parsing ksql query:")) {
    log.error("ksql parse failed: {}", e.getMessage());
  } else { throw e; }
}

When it happens

Trigger: parseStatements (exposed via KsqlGrammar.parsed) throwing a non-ANTLR exception during parsing — e.g. internal parser errors, PredictionMode.LL failures, stream/IO problems in the case-insensitive CharStream wrapper.

Common situations: Extremely large or exotic queries stressing the parser; grammar edge cases not handled by the copied Confluent implementation; corrupted input encoding.

Understand the failure class

Background: JSON parse error: "Unexpected token" / "not valid JSON" / "failed to parse" — what JSON parsers are really complaining about — this error's family across 45 libraries.

Related errors

• Invalid syntax:
• Invalid format for webclient.maxInMemoryBufferSize
• seekTo should be set if seekType is
• Wrong seekTo argument format. See API docs for details
• Unexpected script result

AI-assisted analysis of provectus/kafka-ui@83b5a60cc0 (2026-09-08). Data as JSON: /api/errors/eb0aaf9f619138e3. Report an issue: GitHub.

Appendix: source

Thrown at kafka-ui-api/src/main/java/com/provectus/kafka/ui/service/ksql/KsqlGrammar.java:61

  private static ksql.KsqlGrammarParser.StatementsContext parseStatements(final String sql) {
    var lexer = new KsqlGrammarLexer(CaseInsensitiveStream.from(CharStreams.fromString(sql)));
    var tokenStream = new CommonTokenStream(lexer);
    var grammarParser = new ksql.KsqlGrammarParser(tokenStream);

    lexer.addErrorListener(new BaseErrorListener() {
      @Override
      public void syntaxError(Recognizer<?, ?> recognizer, Object offendingSymbol,
                              int line, int charPositionInLine,
                              String msg, RecognitionException e) {
        throw new ValidationException("Invalid syntax: " + msg);
      }
    });
    grammarParser.getInterpreter().setPredictionMode(PredictionMode.LL);
    try {
      return grammarParser.statements();
    } catch (Exception e) {
      throw new ValidationException("Error parsing ksql query: " + e.getMessage());
    }
  }

  // impl copied from https://github.com/confluentinc/ksql/blob/master/ksqldb-parser/src/main/java/io/confluent/ksql/parser/CaseInsensitiveStream.java
  @RequiredArgsConstructor
  private static class CaseInsensitiveStream implements CharStream {
    @Delegate
    final CharStream stream;

    public static CaseInsensitiveStream from(CharStream stream) {
      // we only need to override LA method
      return new CaseInsensitiveStream(stream) {
        @Override
        public int LA(final int i) {
          final int result = stream.LA(i);
          switch (result) {
            case 0:
            case IntStream.EOF:

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