What causes "Class type not mapped to primitive default value." in java-native-access/jna?

Change the callback method's parameter types to ones the proxy supports (matching the real event signature)

java-native-access/jna · error · java.lang.IllegalArgumentException

Class type <paramTypes[i].getName()> not mapped to primitive

Error message

Class type <paramTypes[i].getName()> not mapped to primitive default value.

What it means

CallbackProxy builds a parameters array of default primitive values for the reflected event method; the chain of equals(...) checks only covers known primitives (boolean, int, long, float, double, etc.). If a parameter type is not in the map it throws this IllegalArgumentException. It indicates the callback method signature uses a type the proxy's default-value table does not handle.

Source

Thrown at contrib/platform/src/com/sun/jna/platform/win32/COM/util/CallbackProxy.java:230

        // exception occurs while doing the call into the target method
        for (int i = 0; i < params.length; i++) {
            if (params[i] == null && paramTypes[i].isPrimitive()) {
                if (paramTypes[i].equals(boolean.class)) {
                    params[i] = DEFAULT_BOOLEAN;
                } else if (paramTypes[i].equals(byte.class)) {
                    params[i] = DEFAULT_BYTE;
                } else if (paramTypes[i].equals(short.class)) {
                    params[i] = DEFAULT_SHORT;
                } else if (paramTypes[i].equals(int.class)) {
                    params[i] = DEFAULT_INT;
                } else if (paramTypes[i].equals(long.class)) {
                    params[i] = DEFAULT_LONG;
                } else if (paramTypes[i].equals(float.class)) {
                    params[i] = DEFAULT_FLOAT;
                } else if (paramTypes[i].equals(double.class)) {
                    params[i] = DEFAULT_DOUBLE;
                } else {
                    throw new IllegalArgumentException("Class type " + paramTypes[i].getName() + " not mapped to primitive default value.");
                }
            }
        }

        try {
            eventMethod.invoke(comEventCallbackListener, params);
        } catch (Exception e) {
            List<String> decodedClassNames = new ArrayList<>(params.length);
            for (Object o : params) {
                if (o == null) {
                    decodedClassNames.add("NULL");
                } else {
                    decodedClassNames.add(o.getClass().getName());
                }
            }
            CallbackProxy.this.comEventCallbackListener.errorReceivingCallbackEvent(
                    "Exception invoking method " + eventMethod + " supplied: " + decodedClassNames.toString(), e);
        }

View on GitHub (pinned to d036ad9781)

Solutions

Change the callback method's parameter types to ones the proxy supports (matching the real event signature)
Check CallbackProxy.invokeOnThread for the exact list of supported primitive types in your JNA version
If you need the real values rather than defaults, ensure the dispId-to-Method mapping matches so actual VARIANT args are converted instead of defaults being filled
Upgrade/patch JNA if your primitive type should be supported by a newer version

Example fix

// before
void onProgress(char stage);
// after
void onProgress(int stage);

Defensive patterns

Strategy: try-catch

Validate before calling

for (Class<?> p : callbackMethod.getParameterTypes()) {
    if (!p.isPrimitive() && p != String.class && !DISPATCHED_TYPES.contains(p))
        throw new IllegalArgumentException("unsupported callback param: " + p);
}

Try / catch

try { listenerMethod.invoke(target, args); } catch (IllegalArgumentException e) { if (e.getMessage().contains("not mapped to primitive default value")) { log.error("fix callback signature: " + e.getMessage()); } }

Prevention

Match callback method signatures exactly to the COM event signature
Use plain primitives (int, long, double, boolean, float) in event callbacks
Keep callbacks in sync with the type library

When it happens

Trigger: Defining an IComEventCallbackListener method whose parameters include an unmapped type (e.g. char, byte, or an object type) so CallbackProxy.invokeOnThread cannot synthesize default values for a discarded event call.

Common situations: Writing an event callback signature that does not match the actual COM dispinterface signature; using wrapper types (Integer, String[]) or custom objects where the proxy expects primitives; JNA version changes adding/removing supported primitive mappings.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of java-native-access/jna@d036ad9781 (2026-09-12). Data as JSON: /api/errors/1462b0c62299fc37. Report an issue: GitHub.