Most Java libraries that would cause issues due to blocking or side effects are covered by the big Scala frameworks like Play/Akka or the large healthy ecosyste

Most Java libraries that would cause issues due to blocking or side effects are covered by the big Scala frameworks like Play/Akka or the large healthy ecosystem of alternatives such as those from Typelevel, 47Degs and many others. If I do need to pull in a Java library it's usually used for something minor and without side effects. On occasion I've had to write small wrappers around blocking or mutable Java API's but it's no big deal. wrt to junior devs they generally write code based on established patterns and we review everything in detail.