languagetool-org/languagetool · error · RuntimeException

Could not create filter class using constructor ${constructo

Error message

Could not create filter class using constructor ${constructor}

What it means

Instantiation failure inside RegexRuleFilterCreator.getFilter: the no-argument constructor of the filter class was found, but Constructor.newInstance() threw (for example the constructor itself failed or the class is abstract). The original exception is chained; the input at fault is the filter class referenced by the XML rule.

Source

Thrown at languagetool-core/src/main/java/org/languagetool/rules/patterns/RegexRuleFilterCreator.java:54

      Class<?> aClass = JLanguageTool.getClassBroker().forName(className);
      Constructor<?>[] constructors = aClass.getConstructors();
      if (constructors.length != 1) {
        throw new RuntimeException("Constructor of filter class '"
                + className + "' must have exactly one constructor, but it has " + constructors.length);
      }
      Constructor<?> constructor = constructors[0];
      try {
        if (constructor.getParameterTypes().length != 0) {
          throw new RuntimeException("Constructor of filter class '" + className + "' must not have arguments: " + constructor);
        }
        Object filter = constructor.newInstance();
        if (filter instanceof RegexRuleFilter) {
          return (RegexRuleFilter) filter;
        } else {
          throw new RuntimeException("Filter class '" + className + "' must implement interface " + RegexRuleFilter.class.getSimpleName());
        }
      } catch (Exception e) {
        throw new RuntimeException("Could not create filter class using constructor " + constructor, e);
      }
    } catch (ClassNotFoundException e) {
      throw new RuntimeException("Could not find filter class: '"
              + className + "' - make sure to use a fully qualified class name like 'org.languagetool.rules.MyFilter'");
    }
  }
 
}

View on GitHub (pinned to 2e990059ce)

Solutions

1. Check the chained cause to see why the constructor threw
2. Ensure the filter class is concrete (not abstract) and its constructor performs no failing initialization

When it happens

Trigger: Thrown at languagetool-core/src/main/java/org/languagetool/rules/patterns/RegexRuleFilterCreator.java:54 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of languagetool-org/languagetool@2e990059ce (2026-09-06). Data as JSON: /api/errors/c764f7d29300a9ed. Report an issue: GitHub.