ssssssss-team/spider-flow · error · RuntimeException

Couldn't get value of field '" + javaField.getName() + "'…

Error message

Couldn't get value of field '" + javaField.getName() + "' from object of type '" + obj.getClass().getSimpleName() + "'

What it means

JavaReflection.getFieldValue retrieves a reflective Field's value from an object via Field.get(obj). If the reflective access throws for any reason (illegal access, mismatched object, initializer failure), it wraps it in a RuntimeException naming the field and the object's simple class name.

Solutions

1. Ensure the object passed is an instance of the field's declaring class
2. Make the field public or call setAccessible(true) on the Field before access
3. Add JVM args --add-opens for the relevant package when running on Java 9+
4. Catch the RuntimeException at the evaluation call site and log field name plus cause

Example fix

// before
Object v = reflection.getFieldValue(obj, field);
// after
Field f = (Field) field;
f.setAccessible(true);
if (!f.getDeclaringClass().isInstance(obj)) {
    throw new IllegalArgumentException(obj + " is not a " + f.getDeclaringClass());
}
Object v = reflection.getFieldValue(obj, field);

if (obj == null || !((Field) field).getDeclaringClass().isInstance(obj)) {
    throw new IllegalArgumentException("Object not compatible with field " + field);
}

boolean canRead(Object obj, Field f) {
    return obj != null && f.getDeclaringClass().isInstance(obj);
}

try {
    Object v = reflection.getFieldValue(obj, field);
} catch (RuntimeException e) {
    logger.error("Field access failed: {}", e.getMessage(), e.getCause());
    throw new ExpressionEvaluationException("Cannot read field", e);
}

When it happens

Trigger: Calling getFieldValue(obj, field) where the Field is inaccessible (non-public without setAccessible), obj is not an instance of the declaring class, or the field's class fails to initialize.

Common situations: Expression evaluation accessing object properties on beans with private fields; passing an object of the wrong type; JDK module system blocking reflective access (Java 9+).

Related errors

• Couldn't call method '" + javaMethod.getName() + "' with…
• file is null
• {message}

AI-assisted analysis of ssssssss-team/spider-flow@c799cca99c (2026-09-08). Data as JSON: /api/errors/c426df80a67cc359. Report an issue: GitHub.

Appendix: source

Thrown at spider-flow-core/src/main/java/org/spiderflow/core/expression/interpreter/JavaReflection.java:63

						fields.put(name, field);
					} catch (NoSuchFieldException e) {
						// fall through
					}
					parentClass = parentClass.getSuperclass();
				}
			}
		}

		return field;
	}

	@Override
	public Object getFieldValue (Object obj, Object field) {
		Field javaField = (Field)field;
		try {
			return javaField.get(obj);
		} catch (Throwable e) {
			throw new RuntimeException("Couldn't get value of field '" + javaField.getName() + "' from object of type '" + obj.getClass().getSimpleName() + "'");
		}
	}
	
	@Override
	public void registerExtensionClass(Class<?> target,Class<?> clazz){
		Method[] methods = clazz.getDeclaredMethods();
		if(methods != null){
			Map<String, List<Method>> cachedMethodMap = extensionmethodCache.get(target);
			if(cachedMethodMap == null){
				cachedMethodMap = new HashMap<>();
				extensionmethodCache.put(target,cachedMethodMap);
			}
			for (Method method : methods) {
				if(Modifier.isStatic(method.getModifiers()) && method.getParameterCount() > 0){
					List<Method> cachedList = cachedMethodMap.get(method.getName());
					if(cachedList == null){
						cachedList = new ArrayList<>();
						cachedMethodMap.put(method.getName(), cachedList);

View on GitHub (pinned to c799cca99c)