Strange behavior using java list in scala class

Question

I have scala+java project where some POJO classes written on Java, and controllers written on Scala. So i have an entity:

@Entity @Table
public class SomeEntity extends GenericEntity { 
  //... some fields
  @OneToMany(...)
  private List<SomeOtherEntity> someOtherEntities;
  // getters, setters
}

and the following scala code:

val otherEntity = // construct object of type SomeOtherEntity 
val entity = //got entity from database
entity.getSomeOtherEntities.add(otherEntity)

Last line produces java.lang.UnsupportedOperationException at java.util.AbstractList.add . I used some debugger magic and discovered that entity.getSomeOtherEntities has type Wrappers$SeqWrapper . Is there simple scala way to add an item to java list in scala? Ofc I can construct new java.util.List and add all items to it and then use field setter in entity class, but is there a simple way?

Answer 1

Finally I solved this. The problem was that I used scala.collection.JavaConverters and did .asJava on Scala List somewhere. My application doesn't need to be particularly speedy, so I managed to solve it by replacing setter for SomeEntity.someOtherEntities field with this one:

public void setSomeOtherEntities(List<SomeOtherEntity> someOtherEntities) {
    this.someOtherEntities = new ArrayList<>();
    this.someOtherEntities.addAll(someOtherEntities);
}