apache/cassandra · error · RuntimeException

Unsupported injectable field type: in class . Only INodePro

Error message

Unsupported injectable field type:  in class . Only INodeProbeFactory and Output are supported.

What it means

NodeTool uses a small dependency-injection mechanism to populate @Inject annotated fields on command classes. Only two injectable types are supported: INodeProbeFactory and Output. Any command declaring an @Inject field of another type triggers this RuntimeException during bean creation.

Source

Thrown at src/java/org/apache/cassandra/tools/NodeTool.java:345

                {
                    Field[] fields = beanClass.getDeclaredFields();
                    for (Field field : fields)
                    {
                        if (!field.isAnnotationPresent(Inject.class))
                            continue;
                        if (field.getType().equals(INodeProbeFactory.class))
                        {
                            field.setAccessible(true);
                            field.set(bean, nodeProbeFactory);
                        }
                        else if (field.getType().equals(Output.class))
                        {
                            field.setAccessible(true);
                            field.set(bean, output);
                        }
                        else
                        {
                            throw new RuntimeException("Unsupported injectable field type: " + field.getType() +
                                    " in class " + beanClass.getName() + ". " +
                                    "Only INodeProbeFactory and Output are supported.");
                        }
                    }
                }
                while ((beanClass = beanClass.getSuperclass()) != null);
                return bean;
            }
            catch (Exception e)
            {
                throw new CommandLine.InitializationException("Failed to create instance of " + cls, e);
            }
        }
    }
}

View on GitHub (pinned to 88fd0f6a0e)

Solutions

Change the field type to INodeProbeFactory (and call create() on it to get a NodeProbe) or Output
Remove the @Inject annotation and obtain the dependency inside the command body instead
If you need a NodeProbe, inject INodeProbeFactory and have the factory construct it

Example fix

// before
@Inject
private NodeProbe probe;
// after
@Inject
private INodeProbeFactory nodeProbeFactory;
...
try (NodeProbe probe = nodeProbeFactory.create()) { /* use probe */ }

Defensive patterns

Strategy: validation

Validate before calling

for (Field f : commandClass.getDeclaredFields())
    if (f.isAnnotationPresent(Inject.class)
        && !INodeProbeFactory.class.isAssignableFrom(f.getType())
        && !Output.class.isAssignableFrom(f.getType()))
        throw new IllegalStateException("Unsupported @Inject type: " + f.getType());

Type guard

static boolean isInjectable(Class<?> t) {
    return INodeProbeFactory.class.isAssignableFrom(t) || Output.class.isAssignableFrom(t);
}

Try / catch

try { toolFactory.create(Cmd.class); }
catch (RuntimeException e) { LOG.error("command wiring failed", e); }

Prevention

Only inject INodeProbeFactory or Output in nodetool commands
Obtain other dependencies inside execute(), not via injection
Re-check inherited fields when moving @Inject fields to superclasses

When it happens

Trigger: Declaring an @Inject (NodeTool's injection annotation) field whose declared type is neither INodeProbeFactory nor Output in a NodeTool command (or a superclass of one), then invoking that command — create() iterates fields up the class hierarchy and throws on the first unsupported type.

Common situations: Developers writing custom nodetool commands try to inject a probe implementation class, a configuration object, or a service instead of using INodeProbeFactory/Output; refactoring moves an injected field into a parent class so it now gets scanned.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/35903c67965617ca. Report an issue: GitHub.