apache/dubbo · error · IllegalArgumentException

Can not create wrapper for primitive type: {}

Error message

Can not create wrapper for primitive type: {}

What it means

Thrown by makeWrapper when the class passed in is a Java primitive type (boolean.class, int.class, etc.). Wrapper generates bytecode to access properties and invoke methods, which is meaningless for primitives, so it rejects them up front.

Source

Thrown at dubbo-common/src/main/java/org/apache/dubbo/common/bytecode/Wrapper.java:130

     * @return Wrapper instance(not null).
     */
    public static Wrapper getWrapper(Class<?> c) {
        return ConcurrentHashMapUtils.computeIfAbsent(WRAPPER_MAP, c, (clazz) -> {
            while (ClassGenerator.isDynamicClass(clazz)) // can not wrapper on dynamic class.
            {
                clazz = clazz.getSuperclass();
            }

            if (clazz == Object.class) {
                return OBJECT_WRAPPER;
            }
            return makeWrapper(clazz);
        });
    }

    private static Wrapper makeWrapper(Class<?> c) {
        if (c.isPrimitive()) {
            throw new IllegalArgumentException("Can not create wrapper for primitive type: " + c);
        }

        String name = c.getName();
        ClassLoader cl = ClassUtils.getClassLoader(c);

        StringBuilder c1 = new StringBuilder("public void setPropertyValue(Object o, String n, Object v){ ");
        StringBuilder c2 = new StringBuilder("public Object getPropertyValue(Object o, String n){ ");
        StringBuilder c3 =
                new StringBuilder("public Object invokeMethod(Object o, String n, Class[] p, Object[] v) throws "
                        + InvocationTargetException.class.getName() + "{ ");

        c1.append(name)
                .append(" w; try{ w = ((")
                .append(name)
                .append(")$1); }catch(Throwable e){ throw new IllegalArgumentException(e); }");
        c2.append(name)
                .append(" w; try{ w = ((")
                .append(name)

View on GitHub (pinned to 3a3043227f)

Solutions

1. Box the primitive before wrapping: use the corresponding wrapper class (Integer.class for int.class) via ClassUtils or manually.
2. Check c.isPrimitive() before calling getWrapper and route primitives through a different path.
3. Inspect the calling code that resolves the Class to ensure it uses getReturnType()/getField().getType() correctly rather than a primitive literal.

Example fix

// before
Wrapper w = Wrapper.getWrapper(int.class);  // throws
// after
Class<?> c = int.class;
if (c.isPrimitive()) c = getBoxedType(c);
Wrapper w = Wrapper.getWrapper(c);

Class<?> c = someClass;
if (c.isPrimitive()) {
    // route primitive types away from Wrapper
    c = boxPrimitive(c); // or skip wrapping
}
Wrapper w = Wrapper.getWrapper(c);

static boolean isWrapperSafe(Class<?> c) {
    return !c.isPrimitive();
}

try {
    Wrapper w = Wrapper.getWrapper(c);
} catch (IllegalArgumentException e) {
    // c was primitive; use boxed type or alternate path
}

When it happens

Trigger: Calling Wrapper.getWrapper(int.class), Wrapper.getWrapper(boolean.class), or any c.isPrimitive() class directly, or a code path that resolves a field/return type to a primitive .class object and forwards it to getWrapper.

Common situations: A reflection utility or serialization layer obtains the raw primitive Class object (e.g. from a field of primitive type) and passes it to getWrapper instead of its wrapper type. Also happens when method return types are inspected incorrectly.

Related errors

• Unknown primitive type: {}
• Property [{}] not found.
• Invoke method [{}] argument number error.
• Method [{}] not found.
• pns.length != pvs.length

AI-assisted analysis of apache/dubbo@3a3043227f (2026-08-14). Data as JSON: /api/errors/919a8a6b79552e21. Report an issue: GitHub.