Quickest way to use common OpenOption combinations

Question

Is there a concise, idiomatic way (maybe using Apache Commons) to specify common combinations of OpenOption like StandardOpenOption.WRITE, StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING

Te

Common combinations are specified as defaults anyway. – Parasitic

@franzebner Are they? – Te

As listed beyond, yes they are :) The OpenOptions in Files.new* are optional, and defaults are predefined. – Parasitic

Answer 1

These are the easy possibilities you have.

Static Imports, to increase readability:

import static java.nio.file.StandardOpenOption.CREATE_NEW;
import static java.nio.file.StandardOpenOption.WRITE;

OpenOption[] options = new OpenOption[] { WRITE, CREATE_NEW };

Use defaults:

     //no Options anyway
     Files.newBufferedReader(path, cs)

     //default: CREATE, TRUNCATE_EXISTING, and WRITE not allowed: READ
     Files.newBufferedWriter(path, cs, options)

     //default: READ not allowed: WRITE
     Files.newInputStream(path, options)

     //default: CREATE, TRUNCATE_EXISTING, and WRITE not allowed: READ
     Files.newOutputStream(path, options)

     //default: READ do whatever you want
     Files.newByteChannel(path, options)

Finally it's possible to specify optionsets like this:

     Files.newByteChannel(path, EnumSet.of(CREATE_NEW, WRITE));

Parasitic

Those are good suggestions, thanks! Btw, do you know if it's possible to get these methods to create necessary directories? – Te

As a hint: Files.createDirectories(dir, attrs) and Files.createDirectory(dir, attrs)! Note the diff. – Parasitic

I mean that FileUtils.writeByteArrayToFile will create non-existent directories in the path, while Files.write fails. – Te

Implementation specific.. Apache Commons != JDK 7 SE! – Parasitic

What's implementation specific? I know Commons isn't JDK. I'm asking if there is a way to get the same behavior. – Te

let us continue this discussion in chat – Parasitic

Answer 2

The best suggestion I can offer would be to cheat on the equivalence of T... and T[], which one of the other stackoverflow discussions says should work

Can I pass an array as arguments to a method with variable arguments in Java?

So...

OpenOption myOptions[] = {StandardOpenOption.WRITE, StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING};
OutputStream foo=OutputStream.newOutputStream(myPath,myOptions);

Caveat: Untested.

Ligate

This will definitely work. I was kind of hoping that Apache Commons or Guava have already done this. But it seems few people use NIO.2 in Java 7 – Te

You could vote up the answer, since it will work and nothing better's on tap. But since the bounty isn't awarded unless it gets at least two up votes, I'm not sure that would make a difference. – Ligate

Answer 3

java.nio.file.Files has 5 flavours of methods with OpenOption varargs parameters:

Files
    .newBufferedWriter(...)
    .write(...)
    .newOutputStream(...)
    .newInputStream(...) 
    .newByteChannel(...)

They directly don't restrict any OpenOption combination, but all of them under the hood call to some of these 3 methods at java.nio.file.spi.FileSystemProvider:

FileSystemProvider
    .newInputStream(Path, OpenOption...)
    .newOutputStream(Path, OpenOption...)
    .newByteChannel(Path, Set<? extends OpenOption>, FileAttribute<?>...)

FileSystemProvider.newInputStream(...) is called by: Files.newInputStream(...)

FileSystemProvider.newOutputStream(...) is called by:

Files
    .newBufferedWriter(...)
    .newOutputStream(...)
    .write(...)

abstract FileSystemProvider.newByteChannel(...) is called by:

• Files.newByteChannel(...)
• FileSystemProvider.newInputStream(...)
• FileSystemProvider.newOutputStream(...)

OptenOption combination restrictions:

• FileSystemProvider.newInputStream(...)
  • UnsupportedOperationException: WRITE || APPEND
• FileSystemProvider.newOutputStream(...)
  • Implicitly: WRITE
  • IllegalArgumentException: READ
  • default (if non options): CREATE && TRUNCATE_EXISTING

The abstract FileSystemProvider.newByteChannel(...) method has a platform dependent implementation, which may extend the OpenOption combination restrictions (as in sun.nio.fs.WindowsFileSystemProvider).

All Files method which uses OpenOption vargars under the hood ends in the abstract FileSystemProvider.newByteChannel(...), which implementation is platform dependent. So, the OpenOption combinations restriction in Files methods are platform dependent.

Intellectualism