quarkusio/quarkus · error · IllegalArgumentException

Class '%s' which is used as %s in class '%s' must have a no-

Error message

Class '%s' which is used as %s in class '%s' must have a no-args constructor

What it means

List-of-object YAML config binding instantiates each element via its no-arg constructor. If the element class lacks a no-args constructor, Quarkus cannot create instances and deployment fails with IllegalArgumentException.

Source

Thrown at extensions/spring-boot-properties/deployment/src/main/java/io/quarkus/spring/boot/properties/deployment/YamlListObjectHandler.java:206

                            b.invokeVirtual(
                                    MethodDesc.of(HashMap.class, "put", Object.class, Object.class, Object.class),
                                    resultHandle, Const.of(entry.getKey()), Const.of(entry.getValue()));
                        }
                        b.return_(resultHandle);
                    });
                });
            }
        });
    }

    private void validateClass(ClassInfo classInfo, Member member) {
        if (Modifier.isInterface(classInfo.flags())) {
            throw new IllegalArgumentException(
                    "The use of interfaces as the generic type of Lists fields / methods is not allowed. Offending field is '"
                            + member.name() + "' of class '" + member.declaringClass().name().toString() + "'");
        }
        if (!classInfo.hasNoArgsConstructor()) {
            throw new IllegalArgumentException(
                    String.format("Class '%s' which is used as %s in class '%s' must have a no-args constructor", classInfo,
                            member.phraseUsage(), member.declaringClass().name().toString()));
        }
        if (!Modifier.isPublic(classInfo.flags())) {
            throw new IllegalArgumentException(
                    String.format("Class '%s' which is used as %s in class '%s' must be a public class", classInfo,
                            member.phraseUsage(), member.declaringClass().name().toString()));
        }
    }

    private ClassInfo validateType(Type type) {
        if (type.kind() != Type.Kind.PARAMETERIZED_TYPE) {
            throw new IllegalArgumentException(ILLEGAL_ARGUMENT_MESSAGE);
        }
        ParameterizedType parameterizedType = (ParameterizedType) type;
        if (!DotNames.LIST.equals(parameterizedType.name())) {
            throw new IllegalArgumentException(ILLEGAL_ARGUMENT_MESSAGE);
        }

View on GitHub (pinned to e1c734241f)

Solutions

Add a public no-args constructor to the element class
Use Lombok @NoArgsConstructor alongside the other constructors
Switch to standard Quarkus @ConfigMapping interface binding, which does not require a no-args constructor

Example fix

// before
public class ServerConfig { private final String host; public ServerConfig(String host){...} }
// after
public class ServerConfig { public ServerConfig(){} public ServerConfig(String host){...} }

Defensive patterns

Strategy: validation

Validate before calling

static void requireNoArgsConstructor(Class<?> c) {
    try { c.getDeclaredConstructor(); }
    catch (NoSuchMethodException e) { throw new IllegalStateException(c + " needs a public no-args constructor for YAML config binding"); }
}

Type guard

boolean isInstantiableForConfig(Class<?> c) {
    try { c.getDeclaredConstructor(); return java.lang.reflect.Modifier.isPublic(c.getModifiers()); }
    catch (NoSuchMethodException e) { return false; }
}

Try / catch

catch (IllegalArgumentException e) { if (e.getMessage().contains("no-args constructor")) { /* add no-args ctor */ } throw e; }

Prevention

Always give config POJOs a public no-args constructor
Pair Lombok @AllArgsConstructor with @NoArgsConstructor
Prefer @ConfigMapping interfaces which avoid instantiation requirements

When it happens

Trigger: A List<SomeClass> config member whose SomeClass has only constructors with parameters (e.g. required-args or builder-only style) processed by YamlListObjectHandler.

Common situations: Immutable config objects with constructor initialization, records-like patterns, or classes generated by Lombok @AllArgsConstructor without @NoArgsConstructor.

Related errors

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/7994c235ddc5dd9a. Report an issue: GitHub.