Netflix/Hystrix · warning · UnsupportedOperationException

It's prohibited to create instances of the class.

Error message

It's prohibited to create instances of the class.

What it means

AopUtils is a static-only utility class in Javanica, and its private constructor throws UnsupportedOperationException to prevent instantiation (even via reflection-based constructor access within the class itself or by test tooling). This is a deliberate guard, not a runtime failure of library logic — you only see it if something tries to `new AopUtils()`.

Source

Thrown at hystrix-contrib/hystrix-javanica/src/main/java/com/netflix/hystrix/contrib/javanica/utils/AopUtils.java:36

import com.google.common.base.Optional;
import com.google.common.base.Throwables;
import org.apache.commons.lang3.Validate;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.reflect.MethodSignature;

import java.io.IOException;
import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.Type;

/**
 * Provides common methods to retrieve information from JoinPoint and not only.
 */
public final class AopUtils {

    private AopUtils() {
        throw new UnsupportedOperationException("It's prohibited to create instances of the class.");
    }

    /**
     * Gets a {@link Method} object from target object (not proxy class).
     *
     * @param joinPoint the {@link JoinPoint}
     * @return a {@link Method} object or null if method doesn't exist or if the signature at a join point
     *         isn't sub-type of {@link MethodSignature}
     */
    public static Method getMethodFromTarget(JoinPoint joinPoint) {
        Method method = null;
        if (joinPoint.getSignature() instanceof MethodSignature) {
            MethodSignature signature = (MethodSignature) joinPoint.getSignature();
            method = getDeclaredMethod(joinPoint.getTarget().getClass(), signature.getName(),
                    getParameterTypes(joinPoint));
        }
        return method;
    }

View on GitHub (pinned to 5ce3bc58c3)

Solutions

1. Remove the instantiation — call the static helpers (getMethodFromTarget, etc.) directly
2. If a framework is constructing it, exclude the class from scanning/serialization (e.g. @ComponentScan filter, Kryo serializer config)
3. If you copied the class into your own package, delete the copy and depend on the artifact instead

Example fix

// before
AopUtils utils = new AopUtils();
Method m = utils.getMethodFromTarget(joinPoint);

// after
Method m = AopUtils.getMethodFromTarget(joinPoint);

if (AopUtils.class.equals(clazz)) { throw new IllegalStateException("AopUtils is static-only; do not instantiate"); }

catch (UnsupportedOperationException e) { /* remove the instantiation; call static methods directly */ }

When it happens

Trigger: Explicitly calling new AopUtils(); a reflection framework (XStream, Kryo, certain mocking libs, JSON deserializers) instantiating the class because it appears on a classpath scan; a copy-paste of the class into your source and constructing it.

Common situations: Component scanning (e.g. Spring picking it up after copying the package into your source tree); serializers that require no-arg constructors; accidental instantiation in unit tests.

Related errors

• method cannot be annotated with HystrixCommand and HystrixCo
• Collapser method must have one argument: {}
• batch method is absent: {}
• required batch method for collapser is absent, wrong generic
• Return type of batch method must be java.util.List parametri

AI-assisted analysis of Netflix/Hystrix@5ce3bc58c3 (2026-08-14). Data as JSON: /api/errors/01c0b1c07c34f2ad. Report an issue: GitHub.