Is there a nice, safe, quick way to write an InputStream to a File in Scala?

Question

Specifically, I'm saving a file upload to local file in a Lift web app.

Answer 1

I don't know about any Scala specific API, but since Scala is fully compatible to Java you can use any other library like Apache Commons IO and Apache Commons FileUpload.

Here is some example code (untested):

//using Commons IO:
val is = ... //input stream you want to write to a file
val os = new FileOutputStream("out.txt")
org.apache.commons.io.IOUtils.copy(is, os)
os.close()

//using Commons FileUpload
import javax.servlet.http.HttpServletRequest
import org.apache.commons.fileupload.{FileItemFactory, FileItem}
import apache.commons.fileupload.disk.DiskFileItemFactory
import org.apache.commons.fileupload.servlet.ServletFileUpload
val request: HttpServletRequest = ... //your HTTP request
val factory: FileItemFactory = new DiskFileItemFactory()
val upload = new ServletFileUpload(factory)
val items = upload.parseRequest(request).asInstanceOf[java.util.List[FileItem]]
for (item <- items) item.write(new File(item.getName))

Answer 2

If it's a text file, and you want to limit yourself to Scala and Java, then using scala.io.Source to do the reading is probably the fastest--it's not built in, but easy to write:

def inputToFile(is: java.io.InputStream, f: java.io.File) {
  val in = scala.io.Source.fromInputStream(is)
  val out = new java.io.PrintWriter(f)
  try { in.getLines().foreach(out.print(_)) }
  finally { out.close }
}

But if you need other libraries anyway, you can make your life even easier by using them (as Michel illustrates).

(P.S.--in Scala 2.7, getLines should not have a () after it.)