java try-with-resource not working with scala

Question

In Scala application, am trying to read lines from a file using java nio try-with-resource construct.

Scala version 2.11.8
Java version 1.8

try(Stream<String> stream = Files.lines(Paths.get("somefile.txt"))){
    stream.forEach(System.out::println); // will do business process here
}catch (IOException e) {
    e.printStackTrace(); // will handle failure case here
}  

But the compiler throws error like
◾not found: value stream
◾A try without a catch or finally is equivalent to putting its body in a block; no exceptions are handled.

Not sure what is the problem. Am new to using Java NIO, so any help is much appreciated.

Answer 1

Alternatively, you can use Choppy's (Disclaimer: I am the author) TryClose monad do this in a for-comprehension in a composeable manner similar to Scala's Try.

val ds = new JdbcDataSource()
val output = for {
  conn  <- TryClose(ds.getConnection())
  ps    <- TryClose(conn.prepareStatement("select * from MyTable"))
  rs    <- TryClose.wrap(ps.executeQuery())
} yield wrap(extractResult(rs))

Here's how you would do it with your stream:

val output = for {
  stream  <- TryClose(Files.lines(Paths.get("somefile.txt")))
} yield wrap(stream.findAny())

More info here: https://github.com/choppythelumberjack/tryclose

Answer 2

You have the already mentioned in one of the answers approach:

  def autoClose[A <: AutoCloseable, B](resource: A)(code: A ? B): B = {
    try
      code(resource)
    finally
      resource.close()
  }

But I think the following is much more elegant:

  def autoClose[A <: AutoCloseable, B](resource: A)(code: A ? B): Try[B] = {
    val tryResult = Try {code(resource)}
    resource.close()
    tryResult
  }

With the last one IMHO it's easier to handle the control flow.