为什么杰克逊无法序列化jnativehook NativeKeyEvent？

Question

I am trying to serialize the keyevent captured by jnativehook using java json library, jackson .

I followed this instructions Can't get a basic Jackson Mixin to work to serialize 3rd party class.

However it fails with following exception:

The class of event object is : org.jnativehook.keyboard.NativeKeyEvent
com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class org.jnativehook.GlobalScreen and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: org.jnativehook.keyboard.NativeKeyEvent["source"])
    at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.failForEmpty(UnknownSerializer.java:59)
    at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.serialize(UnknownSerializer.java:26)
    at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:569)
    at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:597)
    at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:142)
    at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:118)
    at com.fasterxml.jackson.databind.ObjectWriter._configAndWriteValue(ObjectWriter.java:681)
    at com.fasterxml.jackson.databind.ObjectWriter.writeValueAsString(ObjectWriter.java:567)
    at GlobalKeyListenerExample.nativeKeyReleased(GlobalKeyListenerExample.java:45)
    at org.jnativehook.GlobalScreen.processKeyEvent(Unknown Source)
    at org.jnativehook.GlobalScreen$1.run(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:662)

The source and links of jar files are available in this gist .

I tried to see what are the elements jackson is serializing in the debugger. I see "source" attribute which I don't see in the jnativehook library. This is the element where jackson fails to serialize. I think this element is added at runtime, but not sure why and when.

Is there any way in jackson so that I can instruct it to not serialize this field OR only serialize few select attributes?

Answer 1

In exception description you have tip how to solve this bug:

mapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);

Could you try with this?

You can also implement custom serializer for this field, if you want to serialize only some properties.