MyMessage.java

/* Example of a custom class with automatically generated Coder */
@DefaultSchema(AutoValueSchema.class)
@AutoValue
abstract static class MyMessage {
    public static MyMessage of(byte[] payload, Map<String, String> attributes) {
        return new AutoValue_MyMessage(paylod, attributes);
    }
    public abstract byte[] getPayload();
    public abstract Map<String, String> getAttributes();
}