Conditional get in Spring framework - spring

Question

I am trying to learn Scala using Spring framework. I have to implement conditional get logic in my code. I understand it could be done using etag or Last-Modified option.
Here is my piece of code:
var lastModifiedTime: Long = _;
#RequestMapping(value= Array("/users/{id}"),method=Array(RequestMethod.GET),headers = Array("Content-Type=application/json"))
#ResponseBody
def getmeth(request: User_details, web: WebRequest): User_details = {
if (web.checkNotModified(lastModifiedTime)) {
return null
} else {
lastModifiedTime = System.currentTimeMillis()
}
Could you please help me to fix this code?

Answer 1

Disclaimer: I don't know Spring Web.
But according to the documentation fist of all you should take action if request is modified so you should remove bang (!) from condition. Also lastModifiedTime should be computed from the outside of the getmeth method.
Notice that unlike in Java if statement is an expression and it returns value so you shouldn't use return statement.
As it was said in comment conditional code can be easy and safely done using Scala's Option. In Scala you should always avoid null, as it is hard to distinguish it from incorrect behavior of your code, and it is very easy to forget or don't know that it is required to write logic dealing with it - you must always read the javadoc (assuming it exists and it is up to date). When you use Option type compiler will force you to deal with "nullability".
def getmeth(request: User_details, web: WebRequest): Option[User_details] =
if (web.checkNotModified(lastModifiedTime)) {
None
} else {
val userDetails = yourLogic()
Some(userDetails)
}
Then you can perform an action when option is a Some instance. To do that you can use map method.
getmeth(req, web) map { userDetails =>
userDetails.getName
}
EDIT: #optimus Now when you gave wider scope I see that your method signature is forced by framework and yon can't wrap your value with Option. I think that your problem may be that you update lastModifiedTime on every request so it seems reasonable to me that checkNotModified is always false. I think that you should use that feature only on requests that not always update checkNotModified to current time. It becomes pointless otherwise.
Update lastModifiedTime once your resource has become outdated.

Answer 2

#ResponseStatus(HttpStatus.OK)
#RequestMapping(value = Array("/users/{user_id}"),method = Array(RequestMethod.GET))
def getUser(#PathVariable("user_id") user_id: String,
#Context req : Request ): Any = {
val u = hm.get(user_id).asInstanceOf[User]
val tag = u.hashCode().asInstanceOf[EntityTag]
if (req.getMethod().equals("GET")) {
val rb : Response.ResponseBuilder = req.evaluatePreconditions(tag);
if (rb != null)
{
rb
}
else
{
// val u = hm.get(user_id).asInstanceOf[User]
u
}
}