PrintWriter behaviour

Question

I want to use single piece code which writes to a file if parameter is not null and otherwise uses standard output.

I have following snippet

  val fileName: String = null

  var writer: java.io.PrintWriter = null

  if (fileName==null)
    writer = new java.io.PrintWriter(System.out)
  else
    writer = new java.io.PrintWriter(new java.io.File(fileName))

  writer.println("111")
  writer.flush()
  //writer.close()
  System.out.println("222")

Everything works as expected but I was assuming in general case I need to close writer after using it . Please correct me if I'm wrong.

If however I uncomment writer.close() then "222" is not pronted so looks like closing PrintWriter disables standard output.

Another question is how to rewrite code without var .

UPDATE

Code without var s can be like below (I intentionally did not use import )

  def getWriter(filename: String): java.io.PrintWriter = {
    if (fileName==null)
      new java.io.PrintWriter(System.out)
    else
      new java.io.PrintWriter(new java.io.File(fileName))
  }

  val writer = getWriter(fileName)

Answer 1

Yup. Don't close standard out.

You can wrap System.out to make the close call do nothing. In java, it'd look something like:

PrintStream closeIgnoringOut = new PrintStream(System.out) {
    @Override public void close() {}
};

Answer 2

Even if filename is a proper String , it might not be a writable file.

def getWriter(filename: String): java.io.PrintWriter =
  util.Try(new java.io.PrintWriter(new java.io.File(filename)))
      .getOrElse(new java.io.PrintWriter(System.out){
        override def close() = ()
      })

This will default to System.out if filename fails for any reason.