Java8 Stream of files, how to control the closing of files?

Question

Suppose I have a Java8 Stream and that I use that stream to map and such, how can I control the closing of the FileReader

Answer 1

Just for the sake of the argument ( though I agree with Louis above ) : You can pass around the original Reader/InputStream ( or any object, but the case you provided is actually flawed programming, because you can pass the FileReader instead of encapsulating it with BufferedReader) using common-lang3 Pair Class. Jool is also a valid library that provides Tuple* classes.

Example :

filenames.map(File::new)
    .filter(File::exists)
    .map(f->{
        BufferedReader br = null;
        FileReader fr = null;
        try {
            fr = new FileReader(f)
            br = new BufferedReader(fr);
            return Optional.of(Pair.of(br,fr)) ;
        } catch(Exception e) {}
            return Optional.ofNullable(br);
        })
    .filter(Optional::isPresent)
    .map(Optional::get)
    .flatMap( pair -> { 
        try {
            // do something with br               
        } finally {
             try {
                 pair.getRight().close();
             } catch (IOException x ){
                 throw new RuntimeException(x) ;
             }
        }
    })