scala training example - monad

biz-logic-in.java

//in post controller

User user = null;

try {
  user = userService.findById(userId)
} catch (UserNotFoundException e) {
  throw //handling exception
}

List<Post> posts;

if(user != null) {
  try {
      posts = postService.findByUser(user)
  } catch (PostNotFoundException e) {
      //handling exception
  } catch (PostDeletedException e) {
      //handling exception
  }
}

//render result page with posts

biz-logic-in.scala

// Try[T] is monad 

case class Try[T]
case class Success[T] extends Try[T]
case class Failure[T] extends Try[T]


// in post controller

//String => Try[User]
val user: Try[User] = userService.findById(userId) 

// User => Try[List[Post]]
val posts: Try[List[Post] = postService.findByUser(user)

posts match {
    case Success(p) => render(p)
    case Failure(e) => error(e)
}

//String => Try[List[Post]
val posts: Try[List[Post]] = userService.findById(userId).map{ user => postService.findByUser(user)}

posts match {
    case Success(p) => render(p)
    case Failure(e) => error(e)
}

//note: go out of monad is dangerous!!!