`JacksonBlackbirdAccess` Class access exception with Groovy Script Serialization using `BlackbirdModule`

[apoorvam]

I'm encountering an issue when attempting to use the BlackbirdModule in a Spring Boot 3.2 application with Groovy scripting. The goal is to serialize a Groovy object into JSON using the Jackson ObjectMapper with the BlackbirdModule. However, the test case below fails with an exception during the serialization of a Groovy object.

 @Test
    void testGroovySerializationWithBlackbird() throws Exception {
        // Define a Groovy script as a String
        String script = """
                    import com.fasterxml.jackson.databind.ObjectMapper
                    import com.fasterxml.jackson.module.blackbird.BlackbirdModule

                    class Person {
                        String name
                        int age
                    }

                    def mapper = new ObjectMapper()
                    mapper.registerModule(new BlackbirdModule())

                    def person = new Person(name: "Groovy User", age: 35)
                    def json = mapper.writeValueAsString(person)

                    return json // Returning the JSON string
                """;

        // Execute the Groovy script
        GroovyShell shell = new GroovyShell();
        Object result = shell.evaluate(script);

        assertNotNull(result);
    }

Exception:

java.lang.ClassFormatError: Illegal class name "/$$JacksonBlackbirdAccess" in class file /$$JacksonBlackbirdAccess
	at java.base/java.lang.ClassLoader.defineClass0(Native Method)
	at java.base/java.lang.System$2.defineClass(System.java:2394)
	at java.base/java.lang.invoke.MethodHandles$Lookup$ClassDefiner.defineClass(MethodHandles.java:2505)
	at java.base/java.lang.invoke.MethodHandles$Lookup$ClassDefiner.defineClass(MethodHandles.java:2480)
	at java.base/java.lang.invoke.MethodHandles$Lookup.defineClass(MethodHandles.java:1865)
	at com.fasterxml.jackson.module.blackbird.CrossLoaderAccess.accessClassIn(CrossLoaderAccess.java:131)
	at com.fasterxml.jackson.module.blackbird.CrossLoaderAccess.grantAccess(CrossLoaderAccess.java:94)
	at com.fasterxml.jackson.module.blackbird.CrossLoaderAccess.apply(CrossLoaderAccess.java:83)
	at com.fasterxml.jackson.module.blackbird.CrossLoaderAccess.apply(CrossLoaderAccess.java:11)
	at com.fasterxml.jackson.module.blackbird.ser.BBSerializerModifier.createProperty(BBSerializerModifier.java:109)
	at com.fasterxml.jackson.module.blackbird.ser.BBSerializerModifier.lambda$findProperties$0(BBSerializerModifier.java:67)
	at com.fasterxml.jackson.module.blackbird.util.Unchecked.lambda$runnable$0(Unchecked.java:31)
	at com.fasterxml.jackson.module.blackbird.ser.BBSerializerModifier.findProperties(BBSerializerModifier.java:68)
	at com.fasterxml.jackson.module.blackbird.ser.BBSerializerModifier.changeProperties(BBSerializerModifier.java:52)
	at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.constructBeanOrAddOnSerializer(BeanSerializerFactory.java:415)
	at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.findBeanOrAddOnSerializer(BeanSerializerFactory.java:295)
	at com.fasterxml.jackson.databind.ser.BeanSerializerFactory._createSerializer2(BeanSerializerFactory.java:240)
	at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.createSerializer(BeanSerializerFactory.java:174)
	at com.fasterxml.jackson.databind.SerializerProvider._createUntypedSerializer(SerializerProvider.java:1503)
	at com.fasterxml.jackson.databind.SerializerProvider._createAndCacheUntypedSerializer(SerializerProvider.java:1451)
	at com.fasterxml.jackson.databind.SerializerProvider.findValueSerializer(SerializerProvider.java:556)
	at com.fasterxml.jackson.databind.SerializerProvider.findTypedValueSerializer(SerializerProvider.java:834)
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:307)
	at com.fasterxml.jackson.databind.ObjectMapper._writeValueAndClose(ObjectMapper.java:4719)
	at com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(ObjectMapper.java:3964)
	at org.codehaus.groovy.vmplugin.v8.IndyInterface.fromCache(IndyInterface.java:321)
	at Script1.run(Script1.groovy:13)
	at groovy.lang.GroovyShell.evaluate(GroovyShell.java:460)
	at groovy.lang.GroovyShell.evaluate(GroovyShell.java:495)
	at groovy.lang.GroovyShell.evaluate(GroovyShell.java:469)
	at JacksonBlackbirdTest.testGroovySerializationWithBlackbird(JacksonBlackbirdTest.java:100)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)

I am using jackson-bom version 2.15.4 and Groovy 4.0.17 that's default with Spring Boot 3.2. Any suggestions? Removing Blackbird module in above test passes, works even with afterburner module. Just not with blackbird module.

[apoorvam]

Hi, would like to know if there are any workarounds for this. Any suggestions?

[cowtowncoder]

My main suggestion would be to try a more recent version -- ideally 2.18.2 -- of Jackson components.
There are occasionally fixes to Blackbird and this would rule out possibility later version works better.

Otherwise I suspect Groovy-generated class has name that somehow Blackbird has issues with. Perhaps it is in the "default package" (i.e. one without name) and BB does not handle that case well.

@stevenschlansker WDYT?

[apoorvam]

I tried with 2.18.2 and see the same error unfortunately.

java.lang.ClassFormatError: Illegal class name "/$$JacksonBlackbirdAccess" in class file /$$JacksonBlackbirdAccess
	at java.base/java.lang.ClassLoader.defineClass0(Native Method)
	at java.base/java.lang.System$2.defineClass(System.java:2394)
	at java.base/java.lang.invoke.MethodHandles$Lookup$ClassDefiner.defineClass(MethodHandles.java:2505)
	at java.base/java.lang.invoke.MethodHandles$Lookup$ClassDefiner.defineClass(MethodHandles.java:2480)
	at java.base/java.lang.invoke.MethodHandles$Lookup.defineClass(MethodHandles.java:1865)
	at com.fasterxml.jackson.module.blackbird.CrossLoaderAccess.accessClassIn(CrossLoaderAccess.java:131)
	at com.fasterxml.jackson.module.blackbird.CrossLoaderAccess.grantAccess(CrossLoaderAccess.java:94)
	at com.fasterxml.jackson.module.blackbird.CrossLoaderAccess.apply(CrossLoaderAccess.java:83)
	at com.fasterxml.jackson.module.blackbird.CrossLoaderAccess.apply(CrossLoaderAccess.java:11)
	at com.fasterxml.jackson.module.blackbird.ser.BBSerializerModifier.createProperty(BBSerializerModifier.java:111)
	at com.fasterxml.jackson.module.blackbird.ser.BBSerializerModifier.lambda$findProperties$0(BBSerializerModifier.java:69)
	at com.fasterxml.jackson.module.blackbird.util.Unchecked.lambda$runnable$0(Unchecked.java:31)
	at com.fasterxml.jackson.module.blackbird.ser.BBSerializerModifier.findProperties(BBSerializerModifier.java:70)
	at com.fasterxml.jackson.module.blackbird.ser.BBSerializerModifier.changeProperties(BBSerializerModifier.java:54)
	at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.constructBeanOrAddOnSerializer(BeanSerializerFactory.java:415)
	at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.findBeanOrAddOnSerializer(BeanSerializerFactory.java:295)
	at com.fasterxml.jackson.databind.ser.BeanSerializerFactory._createSerializer2(BeanSerializerFactory.java:240)
	at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.createSerializer(BeanSerializerFactory.java:174)
	at com.fasterxml.jackson.databind.SerializerProvider._createUntypedSerializer(SerializerProvider.java:1523)
	at com.fasterxml.jackson.databind.SerializerProvider._createAndCacheUntypedSerializer(SerializerProvider.java:1471)
	at com.fasterxml.jackson.databind.SerializerProvider.findValueSerializer(SerializerProvider.java:578)
	at com.fasterxml.jackson.databind.SerializerProvider.findTypedValueSerializer(SerializerProvider.java:856)
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:330)
	at com.fasterxml.jackson.databind.ObjectMapper._writeValueAndClose(ObjectMapper.java:4811)
	at com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(ObjectMapper.java:4052)
	at org.codehaus.groovy.vmplugin.v8.IndyInterface.fromCache(IndyInterface.java:321)
	at Script1.run(Script1.groovy:13)
	at groovy.lang.GroovyShell.evaluate(GroovyShell.java:460)
	at groovy.lang.GroovyShell.evaluate(GroovyShell.java:495)
	at groovy.lang.GroovyShell.evaluate(GroovyShell.java:469)

@cowtowncoder How can I inspect this Groovy generated class to root cause this?

[cowtowncoder]

To be honest, I don't know. Maybe debugging on com.fasterxml.jackson.module.blackbird.CrossLoaderAccess.accessClassIn would show name of dynamic class being generated?

[apoorvam]

@cowtowncoder Debugging accessClassIn method,

accessClassName = ".$$JacksonBlackbirdAccess"
fqcn = "/$$JacksonBlackbirdAccess"
and finally throws a ClassFormatError: java.lang.ClassFormatError: Illegal class name "/$$JacksonBlackbirdAccess" in class file /$$JacksonBlackbirdAccess at line:
return (Class<?>) DEFINE_CLASS.invokeExact(lookup, classBytes.toByteArray());

What made my test pass is adding a package name at beginning of script

    @Test
    void testGroovySerializationWithBlackbird() throws Exception {
        // Define a Groovy script as a String
        String script = """
                    package abc;
                    import com.fasterxml.jackson.databind.ObjectMapper
                    import com.fasterxml.jackson.module.blackbird.BlackbirdModule

                    class Person {
                        String name
                        int age
                    }

                    def mapper = new ObjectMapper()
                    mapper.registerModule(new BlackbirdModule())

                    def person = new Person(name: "Groovy User", age: 35)
                    def json = mapper.writeValueAsString(person)

                    return json // Returning the JSON string
                """;

        // Execute the Groovy script
        GroovyShell shell = new GroovyShell();
        Object result = shell.evaluate(script);

        assertNotNull(result);
    }

While i couldn't test this exactly, i think handling case where pkg.getName() is empty in accessClassIn method would fix this.

            String fqcn = pkg.getName()
                    .replace('.', '/')
                + "/" + CLASS_NAME;

to

String fqcn = (pkg.getName().isEmpty() ? "" : pkg.getName().replace('.', '/') + "/") + CLASS_NAME;

[cowtowncoder]

@apoorvam Thank you for sharing! This should help resolve the issue -- main challenge is probably just adding a test to verify (ideally not adding Groovy dependency even just for tests). Might work with just root-level test class -- or maybe using JDK script support.

That is: I think your fix would probably work, but we'd need a verification of some kind to prove it (and guard against regression).

[apoorvam]

    public static class Dummy {
    }

    @Test
    public void testAccessClassInDefaultPackage() throws Exception {
        MethodHandles.Lookup lookup = MethodHandles.lookup().in(Dummy.class);
        
        Class<?> accessClass = CrossLoaderAccess.accessClassIn(lookup);
        
        assertNotNull(accessClass);
        assertEquals("$$JacksonBlackbirdAccess", accessClass.getSimpleName());
    }

@cowtowncoder Something like this? I'll have to test it though. I couldn't test it because CrossLoaderAccess class isn't exposed externally

[cowtowncoder]

I was thinking more an actual end-to-end test of serializing/deserializing root-level value class. Sort of reproducing your actual use case wrt value class not being in any package.

[apoorvam]

Is there a CI pipeline that i can run my test on? #289 @cowtowncoder

[stevenschlansker]

Thanks for tracking this down, I did not consider the default package when writing this, I agree that is likely the problem.

[cowtowncoder]

@apoorvam I had to approve running of CI since you're new contributor.