Why is Files.lines (and similar Streams) not automatically closed?

Question

The javadoc for Stream states:

Streams have a BaseStream.close() method and implement AutoCloseable, but nearly all stream instances do not actually n

Answer 1

If you're lazy like me and don't mind the "if an exception is raised, it will leave the file handle open" you could wrap the stream in an autoclosing stream, something like this (there may be other ways):

  static Stream allLinesCloseAtEnd(String filename) throws IOException {
    Stream lines = Files.lines(Paths.get(filename));
    Iterator linesIter = lines.iterator();

    Iterator it = new Iterator() {
      @Override
      public boolean hasNext() {
        if (!linesIter.hasNext()) {
          lines.close(); // auto-close when reach end
          return false;
        }
        return true;
      }

      @Override
      public Object next() {
        return linesIter.next();
      }
    };
    return StreamSupport.stream(Spliterators.spliteratorUnknownSize(it, Spliterator.DISTINCT), false);
  }