apache/cassandra · error · ConfigurationException

Error instantiating %s class '%s'.

Error message

Error instantiating %s class '%s'.

What it means

FBUtilities.classForName/<T>construct instantiates a class by its configured class name via reflection. If instantiation throws any exception whose cause is not a ConfigurationException, it is rethrown as a ConfigurationException with this message. It means a class named in configuration exists and loaded but its constructor failed (or the class could not be instantiated).

Source

Thrown at src/java/org/apache/cassandra/utils/FBUtilities.java:915

    {
        try
        {
            return cls.newInstance();
        }
        catch (IllegalAccessException e)
        {
            throw new ConfigurationException(String.format("Default constructor for %s class '%s' is inaccessible.", readable, classname));
        }
        catch (InstantiationException e)
        {
            throw new ConfigurationException(String.format("Cannot use abstract class '%s' as %s.", classname, readable));
        }
        catch (Exception e)
        {
            // Catch-all because Class.newInstance() "propagates any exception thrown by the nullary constructor, including a checked exception".
            if (e.getCause() instanceof ConfigurationException)
                throw (ConfigurationException)e.getCause();
            throw new ConfigurationException(String.format("Error instantiating %s class '%s'.", readable, classname), e);
        }
    }

    public static <T> NavigableSet<T> singleton(T column, Comparator<? super T> comparator)
    {
        NavigableSet<T> s = new TreeSet<T>(comparator);
        s.add(column);
        return s;
    }

    public static <T> NavigableSet<T> emptySortedSet(Comparator<? super T> comparator)
    {
        return new TreeSet<T>(comparator);
    }

    /**
     * Make straing out of the given {@code Map}.
     *

View on GitHub (pinned to 88fd0f6a0e)

Solutions

1. Inspect the wrapped cause exception in the stack trace to find why the class constructor failed
2. Fix the class's no-arg constructor (throw ConfigurationException directly if the failure is a config problem)
3. Verify the class and all its dependencies are on the Cassandra classpath (lib/)
4. Correct the fully-qualified class name in cassandra.yaml if the wrong class is configured

Example fix

// before: public class MyAuthenticator implements IAuthenticator { public MyAuthenticator() { init(); } }
// after:  public class MyAuthenticator implements IAuthenticator { public MyAuthenticator() { try { init(); } catch (Exception e) { throw new ConfigurationException("init failed: " + e.getMessage()); } } }

try { Class.forName(className).getDeclaredConstructor().newInstance(); } catch (Throwable t) { /* class/ctor problem before config load */ }

try { T impl = FBUtilities.construct(className, "authenticator"); } catch (ConfigurationException e) { logger.error("Bad class config: {}", e.getCause(), e); throw e; }

When it happens

Trigger: Calling FBUtilities.classForName(...).newInstance() or construct() with a class whose no-arg constructor throws (e.g. IAuthenticator, IAuthorizer, SeedProvider, IEndpointSnitch configured in cassandra.yaml whose constructor throws RuntimeException/other checked exceptions).

Common situations: Custom authenticator/authorizer/seed provider classes that throw in their constructors, misconfigured dependencies missing at runtime (NoClassDefFoundError wrapped as cause), or wrong constructor signatures after upgrading a plugin.

Related errors

• No valid constructor found for class <class_name>
• Failed to instantiate %s
• No readable property '%s' on class: %s
• Unable to find getter for property '%s' on class %s
• Unable to instantiate parameterized class <class_name>

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/f1a2d8e301a29c22. Report an issue: GitHub.