apache/dubbo · error · IllegalArgumentException

non-public interfaces class from different packages

Error message

non-public interfaces class from different packages

What it means

Thrown by Mixin.mixin when two or more DELEGATE classes (the dcs array) are non-public AND come from different Java packages. Dubbo generates a single mixin class in one package; non-public types from other packages cannot be referenced there, so the JVM would reject the bytecode. The guard fails fast with IllegalArgumentException.

Source

Thrown at dubbo-common/src/main/java/org/apache/dubbo/common/bytecode/Mixin.java:98

    public static Mixin mixin(Class<?>[] ics, Class<?>[] dcs, ClassLoader cl) {
        assertInterfaceArray(ics);

        long id = MIXIN_CLASS_COUNTER.getAndIncrement();
        String pkg = null;
        ClassGenerator ccp = null, ccm = null;
        try {
            ccp = ClassGenerator.newInstance(cl);

            // impl constructor
            StringBuilder code = new StringBuilder();
            for (int i = 0; i < dcs.length; i++) {
                if (!Modifier.isPublic(dcs[i].getModifiers())) {
                    String npkg = dcs[i].getPackage().getName();
                    if (pkg == null) {
                        pkg = npkg;
                    } else {
                        if (!pkg.equals(npkg)) {
                            throw new IllegalArgumentException("non-public interfaces class from different packages");
                        }
                    }
                }

                ccp.addField("private " + dcs[i].getName() + " d" + i + ";");

                code.append('d')
                        .append(i)
                        .append(" = (")
                        .append(dcs[i].getName())
                        .append(")$1[")
                        .append(i)
                        .append("];\n");
                if (MixinAware.class.isAssignableFrom(dcs[i])) {
                    code.append('d').append(i).append(".setMixinInstance(this);\n");
                }
            }
            ccp.addConstructor(Modifier.PUBLIC, new Class<?>[] {Object[].class}, code.toString());

View on GitHub (pinned to 3a3043227f)

Solutions

Make the delegate classes public so the generated mixin can reference them from any package.
Restrict all non-public delegates to the same single package.
Wrap the non-public delegates behind a public facade before passing them to Mixin.

Example fix

// before
package a.b;
class DelegateA {} // package-private
package c.d;
class DelegateB {} // package-private
Mixin.mixin(ics, new Class[]{ DelegateA.class, DelegateB.class });

// after
package a.b;
public class DelegateA {} // make public (or keep all delegates in one package)

Defensive patterns

Strategy: validation

Validate before calling

for (Class<?> dc : dcs) {
    if (!Modifier.isPublic(dc.getModifiers())) {
        // ensure all non-public delegates share one package
    }
}

Prevention

Prefer public delegate classes when using Mixin.
If delegates must be package-private, keep them all in the same package.
Validate delegate visibility before calling Mixin.mixin.

When it happens

Trigger: Mixin.mixin(ics, dcs) where dcs contains package-private delegate classes whose packages differ from each other (or from the first non-public delegate).

Common situations: Passing internal/package-private implementation classes from multiple modules as delegates; mixing delegates from library A (package a.b) and library B (package c.d), both non-public.

Related errors

AI-assisted analysis of apache/dubbo@3a3043227f (2026-08-14). Data as JSON: /api/errors/dc9ee7285a6b0838. Report an issue: GitHub.