spring-projects/spring-framework · error · IllegalArgumentException

Invalid method signature: unable to resolve type [${paramete

Error message

Invalid method signature: unable to resolve type [${parameterTypeName}] for argument ${i}. Root cause: ${ex}

What it means

Thrown as IllegalArgumentException by resolveSignature when one of the parameter type names inside the argument list cannot be resolved to a Class via ClassUtils.forName using the target class's ClassLoader (BeanUtils.java:473-481). The offending type name, argument index, and root cause are included.

Source

Thrown at spring-beans/src/main/java/org/springframework/beans/BeanUtils.java:479

		else if (startParen == -1 && endParen > -1) {
			throw new IllegalArgumentException("Invalid method signature '" + signature +
					"': expected opening '(' for args list");
		}
		else if (startParen == -1) {
			return findMethodWithMinimalParameters(clazz, signature);
		}
		else {
			String methodName = signature.substring(0, startParen);
			String[] parameterTypeNames =
					StringUtils.commaDelimitedListToStringArray(signature.substring(startParen + 1, endParen));
			Class<?>[] parameterTypes = new Class<?>[parameterTypeNames.length];
			for (int i = 0; i < parameterTypeNames.length; i++) {
				String parameterTypeName = parameterTypeNames[i].trim();
				try {
					parameterTypes[i] = ClassUtils.forName(parameterTypeName, clazz.getClassLoader());
				}
				catch (Throwable ex) {
					throw new IllegalArgumentException("Invalid method signature: unable to resolve type [" +
							parameterTypeName + "] for argument " + i + ". Root cause: " + ex);
				}
			}
			return findMethod(clazz, methodName, parameterTypes);
		}
	}


	/**
	 * Retrieve the JavaBeans {@code PropertyDescriptor}s of a given class.
	 * @param clazz the Class to retrieve the PropertyDescriptors for
	 * @return an array of {@code PropertyDescriptors} for the given class
	 * @throws BeansException if PropertyDescriptor look fails
	 */
	public static PropertyDescriptor[] getPropertyDescriptors(Class<?> clazz) throws BeansException {
		return CachedIntrospectionResults.forClass(clazz).getPropertyDescriptors();
	}

View on GitHub (pinned to e8729d0438)

Solutions

1. Use the fully-qualified type name exactly matching a class resolvable by the target class's ClassLoader.
2. Add the missing type's dependency/artifact to the runtime classpath.
3. For nested types use 'com.example.Outer$Inner'; for arrays use the JVM notation 'java.lang.String[]' or the canonical form ClassUtils.forName accepts.
4. After a rename, update all method-signature strings in config and grep for the old name.

Example fix

// before
resolveSignature("process(com.example.OldName)", clazz); // OldName renamed

// after
resolveSignature("process(com.example.NewName)", clazz);

String[] parts = sig.substring(sig.indexOf('(')+1, sig.indexOf(')')).split(",");
ClassLoader cl = clazz.getClassLoader();
for (String t : parts) ClassUtils.forName(t.trim(), cl); // throws early if unresolvable

public static boolean signatureTypesResolvable(Class<?> c, String sig) {
  try { BeanUtils.resolveSignature(sig, c); return true; }
  catch (IllegalArgumentException e) { return false; }
}

try { BeanUtils.resolveSignature(sig, clazz); }
catch (IllegalArgumentException e) {
  // message names the unresolvable type; fix config or add the dependency
}

When it happens

Trigger: resolveSignature('foo(com.example.Missing, java.lang.String)', clazz) where 'com.example.Missing' is not on the classpath, is misspelled, or the classloader cannot load it. Also triggered by array/notational mistakes like 'String[]' spelled incorrectly or unimported nested classes.

Common situations: Refactoring/renaming a class referenced in config without updating the signature string; missing dependency providing the parameter type; using simple names where fully-qualified names are required; nested classes referenced without the enclosing$Inner syntax; multi-module classloader isolation.

Related errors

• Unresolvable class definition
• Invalid method signature '${signature}': expected closing ')
• Invalid method signature '${signature}': expected opening '(
• Specified class is an interface
• Is it an abstract class?

AI-assisted analysis of spring-projects/spring-framework@e8729d0438 (2026-08-04). Data as JSON: /data/errors/2384f843c15252e1.json. Report an issue: GitHub.