How I Integrated Antlr into Seata’s SQL Parser to Fix Transaction Parsing Issues

Background

Seata is an open‑source distributed‑transaction framework. Its SqlParser module originally relied on Alibaba Druid, which limited consistent SQL parsing across micro‑services.

Why Antlr

Antlr offers flexible grammar definitions and is used by projects such as Hive, Spark, and NetBeans. It enables generation of a dedicated lexer and parser for the MySQL dialect, providing better extensibility and maintainability than Druid.

Implementation Details

Created MySQL lexer and parser grammars ( MySqlLexer.g4, MySqlParser.g4) compatible with Antlr v4.0.

Implemented a visitor that traverses the Antlr parse tree and builds Seata’s internal AST (e.g., InsertSpecificationSql).

Replaced the previous look‑ahead (LA) traversal with Antlr’s CommonTokenStream to avoid case‑conversion errors.

Adapted the existing SqlParser API so that method signatures remain unchanged while delegating to the Antlr‑generated parser.

Addressed loss of whitespace when rendering the parsed SQL back to text. Overrode visitTerminal and added a shouldAddSpace helper to insert spaces only when syntactically required.

Space‑Preserving Rendering

@Override
public StringBuilder visitTerminal(TerminalNode node) {
    String text = node.getText();
    if (text != null && !"".equals(text.trim())) {
        if (shouldAddSpace(text.trim())) {
            sb.append(" ");
        }
        sb.append(text);
    }
    return sb;
}

private boolean shouldAddSpace(String text) {
    if (sb.length() == 0) return false;
    char lastChar = sb.charAt(sb.length() - 1);
    switch (lastChar) {
        case '.': case ',': case '(':
            return false;
        default:
            break;
    }
    switch (text.charAt(0)) {
        case '.': case ',': case ')':
            return false;
        default:
            break;
    }
    return true;
}

Supported SQL Statements

The Antlr‑based parser successfully handles MySQL INSERT, SELECT, UPDATE, DELETE statements and batch operations. The design allows straightforward extension for additional MySQL syntax.

Integration Outcome

The new parser was merged into the Seata GitHub repository, improving the framework’s SQL parsing flexibility, reducing dependency on Druid, and simplifying future grammar extensions.

Illustration of the Whitespace Issue