common/src/main/java/com/streamsets/pipeline/lib/parser/shaded/org/aicer/grok/dictionary/GrokDictionary.java
public Grok compileExpression(final String expression) {

    throwErrorIfDictionaryIsNotReady();

    final String digestedExpression = digestExpressionAux(expression);

    logger.debug("Digested [" + expression + "] into [" + digestedExpression + "] before compilation");
    return new Grok(Pattern.compile(digestedExpression));
  }
public Grok compileExpression(final String expression) {

    throwErrorIfDictionaryIsNotReady();

    final String digestedExpression = digestExpressionAux(expression);

    logger.debug("Digested [" + expression + "] into [" + digestedExpression + "] before compilation");
    return new Grok(Pattern.compile(digestedExpression));
  }
Compiles the expression into a pattern

This uses the internal dictionary of named regular expressions

@param expression
@return The compiled expression