Error when trying to use Retrofit

Plugins Plugin Development
1

Hey guys,
Sorry for this question, but I’m very new to sponge. I wanted to develop a plugin, sending requests to a RESTFUL Webservice (API).
After I read the docs, I was able to set up a working (very basic hello world) plugin. After that, I wanted to implement an API caller framework (because doing it in “plain” java isn’t what I want, haha)

Unfortunately, the current state of Sponge doesn’t provide a built-in solution. After some research, I decided to give Retrofit a try (should I use another tool, or is retrofit a good choice?).

When I start my sponge (vanilla) server, I get following error:

[17:22:24 ERROR] [Sponge]: Failed to load plugin: Plugin 1.0 (from mods\Plugin-1.0.jar)
java.lang.NoClassDefFoundError: retrofit2/Converter$Factory
    at java.lang.Class.forName0(Native Method) ~[?:1.8.0_192]
    at java.lang.Class.forName(Unknown Source) ~[?:1.8.0_192]
    at org.spongepowered.server.plugin.VanillaPluginManager.loadPlugin(VanillaPluginManager.java:161) ~[VanillaPluginManager.class:1.12.2-7.1.2]
    at java.util.ArrayList.forEach(Unknown Source) ~[?:1.8.0_192]
    at org.spongepowered.server.plugin.VanillaPluginManager.loadPlugins(VanillaPluginManager.java:89) ~[VanillaPluginManager.class:1.12.2-7.1.2]
    at org.spongepowered.server.SpongeVanilla.preInitialize(SpongeVanilla.java:120) ~[SpongeVanilla.class:1.12.2-7.1.2]
    at net.minecraft.server.dedicated.DedicatedServer.handler$onServerLoad$bba000(SourceFile:1234) ~[nz.class:?]
    at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(SourceFile:117) ~[nz.class:?]
    at net.minecraft.server.MinecraftServer.run(SourceFile:434) ~[MinecraftServer.class:?]
    at java.lang.Thread.run(Unknown Source) [?:1.8.0_192]
Caused by: java.lang.ClassNotFoundException: retrofit2.Converter$Factory
    at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191) ~[launchwrapper-1.12.jar:?]
    at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_192]
    at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_192]
    ... 10 more
Caused by: java.lang.NullPointerException

It’s funny that I get an error, because I really tried to stick to Retrofit’s doc’s example (this lets me believe, that there has to be something different causing problems).

Maybe I should also show you my gradle.build file:

plugins {
    id 'org.spongepowered.plugin' version '0.8.1'
}

group = pluginGroup
version = pluginVersion

dependencies {
    implementation 'org.spongepowered:spongeapi:7.1.0-SNAPSHOT'
    implementation 'com.squareup.retrofit2:retrofit:2.4.0'
    implementation 'com.squareup.retrofit2:converter-gson:2.1.0'
}

sponge.plugin.id = pluginId

That’s how my main plugin class looks like (removed @Plugin)

public class Core {

@Inject
private Logger logger;

@Listener
public void onServerStart(GameStartedServerEvent event) {

    Retrofit.Builder builder = new Retrofit.Builder()
            .baseUrl("http://localhost:3000/")
            .addConverterFactory(GsonConverterFactory.create());

    Retrofit retrofit = builder.build();

    APICaller apiCaller = retrofit.create(APICaller.class);

    Call<List<User>> call = apiCaller.users();

    call.enqueue(new Callback<List<User>>() {
        @Override
        public void onResponse(Call<List<User>> call, Response<List<User>> response) {
            logger.info("async request done");
        }

        @Override
        public void onFailure(Call<List<User>> call, Throwable t) {
            logger.info("async request failed");
        }
    });

}
}

User.java

public class User {

    private int id;
    private String name;

    public String getName() {
        return this.name;
    }
}

APICaller interface:

public interface APICaller {
    @GET("user/")
    Call<List<User>> users();
}

So what did I do wrong? I hope I didn’t miss anything. If I did, please tell me :slight_smile:
Thanks guys!

Edit

The error occurs, because gradle does not bundle dependencies (by default). I managed to get it working by using following gradle plugin: GitHub - johnrengelman/shadow: Gradle plugin to create fat/uber JARs, apply file transforms, and relocate packages for applications and libraries. Gradle version of Maven's Shade plugin.