Add empty constructor

[dbgod]

Add empty constructor so gamification can successfully process messages from social-multipliation.

Without the empty constuctor the following error is thrown whenever gamification attempted to handle an incoming message: Could not read JSON: Can not construct instance of microservices.book.gamification.event.MultiplicationSolvedEvent: no suitable constructor found, can not deserialize from Object value (missing default constructor or creator, or perhaps need to add/enable type information?)

[mechero]

Hi @dbgod, thanks for the detailed description. JPA is not used for the event, so the empty constructor is not required. JSON serialization uses the required-arguments constructor built by Lombok in this case to create the object. It must be something else what is causing that problem:

• Did you modify any other source file?
• Did you change any configuration?
• JDK version?

[dbgod]

Thanks for responding! I'm reallying enjoying working through your book!

I didn't consider that JDK version, versions of the dependencies, and configuration would have contributed to my troubles. I have Java 1.8.0_171 installed, There are two deltas in my pom: later versions of Spring Boot (1.5.10.RELEASE) and Project Lombok (1.16.20). Lastly, in my application.properties the path to my H2 database file is "C:/Users/Chris/gamification" -- "~/gamficiation" wouldn't work for me, presumably because I'm running in Windows and not Linux.

[mechero]

OK, I got it, it's Lombok. Even though it's a minor version update, this new dependency brings some updates to make everything works with Java 9, which break the previous behavior of Lombok. It's nicely explained by several users in this issue: what happens is that Lombok is no longer using the parameter names and therefore Jackson can't find a proper constructor.

Your solution is valid. Another possibility to avoid creating boilerplate code is, as that issue suggests, creating a file called lombok.config in the root of the gamification project and adding the line

lombok.anyConstructor.addConstructorProperties=true

I just tried this and it works. If you're using your IDE to run the apps, remember to rebuild the source code after adding the config file.

I won't merge the pull-request since some readers might be confused by the code mismatch but I'll definitely add a section to the README files.

Good catch! I'm glad you're enjoying the book 😄

[dbgod]

Yes, I see: with lombok.config, Lombok adds the annotation "@java.beans.ConstructorProperties({"multiplicationResultAttemptId", "userId", "correct"})" to the cosntructor for MultiplicationSolvedEvent. Thanks again... onto Chapter 5!

[rahiakela]

After doing the above solution, I am getting this error:

Please suggest any solution because I am struggling for hours.

[mechero]

@rahiakela, could you provide more details? Are you also using a new version of Lombok? Did you try creating the empty constructor or using the Lombok configuration file?