Re: Closing Files that Weren't Successfully Opened

From:

Michal Kleczek <kleku75@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Wed, 16 Mar 2011 10:30:06 +0100

Message-ID:

<ilpvuv$pr$1@news.onet.pl>

Michal Kleczek wrote:

On Tue, 15 Mar 2011 10:56:46 -0700, Lew wrote:

Michal Kleczek wrote:

Lew wrote:

Michal Kleczek wrote:

Robert Klemme wrote:

If you want BufferedReader you can do

final BufferedReader reader =
new BufferedReader(new InputStreamReader(new
FileInputStream("foo.txt")));
try {
for (String line; (line = reader.readLine()) != null;) {
System.out.println("Found line: " + line);
}
}
finally {
reader.close();
}

That only works because both InputStreamReader and BufferedReader
constructors don't throw.
But it is not safe to do the same for: final ObjectInputStream ois =
new ObjectInputStream(new FileInputStream("foo.txt"));

[snip]

The whole freaking *point* of my post was to show one way to guarantee
release of resources!

Look, make all the legitimate points you want, but don't lie.

You're right - I've read your post again and I admit your way of handling
this does not have problems I wanted to raise.

I've re-read your post again and I think my point holds. This code (copied
from your post):

  public void useResource( String src, String dst )
  {
    final BufferedReader reader;
    try
    {
      reader = new BufferedReader( new FileReader( src ));
    }
    catch ( IOException exc )
    {
      final String msg = "cannot open \"+ src +"\". "
           + exc.getLocalizedMessage();
      logger.error( msg, exc );
      throw new IllegalStateException( msg, exc );
    }
    assert reader != null;

is not exception safe - if BufferedReader constructor throws you've got a
resource leak.

[snip]

Sometimes it would be good to have destructors...

.>
Nonsense. Destructors are to release memory.
What Java needs are 'finally' blocks. Hey, good news! It's
got them! Yay! Problem solved!

As you can see above the problem is not solved. Above code would be
perfectly valid (in terms of exception safety) if we had destructors (and -
of course - if FileReader destructor was implemented to release resources
propely).

--
Michal