java.lang.ClassNotFoundException Every time I change something in my code (Neo4j OGM + Play!)

Question

Im using Neo4J OGM + Play Framework since 2 weeks succesfully, but today it doesn't work anymore. Every time I change something in my code, no matter if in a NodeEntity Class or in any other Class, it causes a java.lang.ClassNotFoundException when I try to get something from the database using the find method from org.neo4j.ogm.session.Session. Only if I clear the database and refill it I'm able to insert and get my NodesEntities.

Java version: 1.8
Scala version: 2.11.7
Sbt version: 2.6.3

build.sbt:

libraryDependencies += "org.neo4j" % "neo4j-ogm-core" % "3.0.0-RC1"
libraryDependencies += "org.neo4j" % "neo4j-ogm-bolt-driver" % "3.0.0-RC1"

Neo4JSessionFactory.java

public class Neo4jSessionFactory {

    private Config config;

    @Inject
    private Neo4jSessionFactory(Config config) {
        this.config = config;
    }


    public Session getNeo4jSession() {
        String uri = config.getString("ogm.db.uri");
        String username = config.getString("ogm.db.username");
        String password = config.getString("ogm.db.password");
        List<String> modelList = config.getStringList("ogm.db.models");

        String[] models = modelList.toArray(new String[modelList.size()]);

        Configuration configuration = new Configuration.Builder()
                .uri(uri)
                .credentials(username, password)
                .build();
        return new SessionFactory(configuration, models).openSession();
    }
}

application.conf

ogm{
   db{
     uri = "bolt://XXX.de:7687"
     username = "XXX"
     password = "XXX"
     models = ["neo4j.nodes", "neo4j.relationships", "neo4j.entities"]
   }
}

UserNode.java

@NodeEntity(label = "UserNode")
public class UserNode extends AbstractNode {

    @JsonProperty("username")
    private String username;

    @JsonProperty("firstname")
    private String firstname;

    @JsonProperty("lastname")
    private String lastname;

    @JsonProperty("email")
    private String email;

    @JsonProperty("password")
    private String password;

    @JsonProperty("picture")
    private String picture;

    @Relationship(type = Friendship.TYPE)
    @JsonProperty("friendships")
    private Set<Friendship> friendships = new HashSet<>();

    @Relationship(type = Posted.TYPE)
    @JsonProperty("postings")
    private Set<Posted> postings = new HashSet<>();

    @Relationship(type = Pinned.TYPE, direction = Relationship.INCOMING)
    @JsonProperty("pinnings")
    private Set<Pinned> pinnings = new HashSet<>();


    public UserNode() {
    }
}

UserService.java

public class UserService extends AbstractService<UserNode> {

    @Inject
    public UserService(Neo4jSessionFactory neo4jSessionFactory) {
        super(neo4jSessionFactory);
    }

    @Override
    public Class<UserNode> getEntityType() {
        return UserNode.class;
    }
}

AbstractService.java

public abstract class AbstractService<T extends AbstractNode> {

    private static final int DEPTH_LIST = 1;
    private static final int DEPTH_ENTITY = 1;

    protected Session session;

    @Inject
    public AbstractService(Neo4jSessionFactory neo4jSessionFactory) {
        this.session = neo4jSessionFactory.getNeo4jSession();
    }


    public Collection<T> findAll() {
        return session.loadAll(getEntityType(), DEPTH_LIST);    <-- (AbstractService:27)
    }

    public Optional<T> find(Long id) {
        return Optional.ofNullable(session.load(getEntityType(), id, DEPTH_ENTITY));
    }

    public void delete(Long id) {
        session.delete(session.load(getEntityType(), id));
    }

    public Optional<T> createOrUpdate(T entity){
        T updated = find(entity.getId())
                .map(existing -> {
                    entity.setCreated(existing.getCreated());
                    return entity;
                 }).orElse(entity);

        session.save(updated, DEPTH_ENTITY);
        return find(updated.getId());
    }
}

AbstactController.java

public Result all(){
    return toJsonResult(service.findAll());  <-- (AbstractCRUDController.java:19)
}

Exception

play.api.http.HttpErrorHandlerExceptions$$anon$1: Execution exception[[MappingException: Error mapping GraphModel to instance of neo4j.nodes.UserNode]]
at play.api.http.HttpErrorHandlerExceptions$.throwableToUsefulException(HttpErrorHandler.scala:255)
at play.api.http.DefaultHttpErrorHandler.onServerError(HttpErrorHandler.scala:180)
at play.core.server.AkkaHttpServer$$anonfun$13$$anonfun$apply$1.applyOrElse(AkkaHttpServer.scala:251)
at play.core.server.AkkaHttpServer$$anonfun$13$$anonfun$apply$1.applyOrElse(AkkaHttpServer.scala:250)
at scala.concurrent.Future$$anonfun$recoverWith$1.apply(Future.scala:344)
at scala.concurrent.Future$$anonfun$recoverWith$1.apply(Future.scala:343)
at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:32)
at play.api.libs.streams.Execution$trampoline$.execute(Execution.scala:70)
at scala.concurrent.impl.CallbackRunnable.executeWithValue(Promise.scala:40)
at scala.concurrent.impl.Promise$DefaultPromise.scala$concurrent$impl$Promise$DefaultPromise$$dispatchOrAddCallback(Promise.scala:280)
Caused by: org.neo4j.ogm.exception.MappingException: Error mapping GraphModel to instance of neo4j.nodes.UserNode
at org.neo4j.ogm.context.GraphEntityMapper.mapEntities(GraphEntityMapper.java:168)
at org.neo4j.ogm.context.GraphEntityMapper.map(GraphEntityMapper.java:124)
at org.neo4j.ogm.context.GraphEntityMapper.map(GraphEntityMapper.java:89)
at org.neo4j.ogm.session.delegates.LoadByTypeDelegate.loadAll(LoadByTypeDelegate.java:65)
at org.neo4j.ogm.session.delegates.LoadByTypeDelegate.loadAll(LoadByTypeDelegate.java:99)
at org.neo4j.ogm.session.Neo4jSession.loadAll(Neo4jSession.java:167)
at neo4j.services.AbstractService.findAll(AbstractService.java:27)
at controllers.AbstractCRUDController.all(AbstractCRUDController.java:19)
at router.Routes$$anonfun$routes$1$$anonfun$applyOrElse$2$$anonfun$apply$2.apply(Routes.scala:364)
at router.Routes$$anonfun$routes$1$$anonfun$applyOrElse$2$$anonfun$apply$2.apply(Routes.scala:364)
Caused by: org.neo4j.ogm.exception.MappingException: Unable to load class with FQN: neo4j.nodes.UserNode
at org.neo4j.ogm.metadata.reflect.EntityFactory.instantiateObjectFromTaxa(EntityFactory.java:109)
at org.neo4j.ogm.metadata.reflect.EntityFactory.newObject(EntityFactory.java:58)
at org.neo4j.ogm.context.GraphEntityMapper.mapNodes(GraphEntityMapper.java:179)
at org.neo4j.ogm.context.GraphEntityMapper.mapEntities(GraphEntityMapper.java:165)
at org.neo4j.ogm.context.GraphEntityMapper.map(GraphEntityMapper.java:124)
at org.neo4j.ogm.context.GraphEntityMapper.map(GraphEntityMapper.java:89)
at org.neo4j.ogm.session.delegates.LoadByTypeDelegate.loadAll(LoadByTypeDelegate.java:65)
at org.neo4j.ogm.session.delegates.LoadByTypeDelegate.loadAll(LoadByTypeDelegate.java:99)
at org.neo4j.ogm.session.Neo4jSession.loadAll(Neo4jSession.java:167)
at neo4j.services.AbstractService.findAll(AbstractService.java:27)
Caused by: java.lang.ClassNotFoundException: neo4j.nodes.UserNode
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at org.neo4j.ogm.metadata.reflect.EntityFactory.instantiateObjectFromTaxa(EntityFactory.java:106)
at org.neo4j.ogm.metadata.reflect.EntityFactory.newObject(EntityFactory.java:58)
at org.neo4j.ogm.context.GraphEntityMapper.mapNodes(GraphEntityMapper.java:179)
at org.neo4j.ogm.context.GraphEntityMapper.mapEntities(GraphEntityMapper.java:165)
at org.neo4j.ogm.context.GraphEntityMapper.map(GraphEntityMapper.java:124)

Can anyone tell me if I'm going to go crazy or if it's still to be saved?

Answer 1

I have tried your code and found that this error only occurs with a GET-request. I found this when I tried an insert with a POST-request. In this case, the "find"-method has found the appropriate class, but the subsequent GET-request does not. But I don't understand why it doesn't work with a GET-request. Maybe the header is different than a POST-request? It is also not a permanent solution to give up the get, to get the resource.