java file handling and exceptions

Question

The standard way of handling file reading and writing in java goes something like this:

try
{
    ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("file.dat"));
    oos.writeObject(h);
    oos.close();
}
catch (FileNotFoundException ex)
{
}
catch (IOException ex)
{
}

But I'm bothered by that code, because it could be possible here that the file is never closed if an exception is thrown. Sure we could add a finally clause and initialise the ObjectOutputStream outside the try block. However, when you do that you need to add another try/catch block INSIDE the finally block again...that's just ugly. Is there a better way of handling this problem?

Adding another try/catch block helps you isolate the problem when an exception occurs — Alpine
– Alpine, Commented Feb 25, 2011 at 21:32
@Alpine it doesn't help you any more than the information provided by the stack trace *shrug* — corsiKa
– corsiKa, Commented Feb 25, 2011 at 21:35
@Nathan Hughes: Bad formulation of my part, am aware of the dangers, but thanks for pointing that out. — Rene
– Rene, Commented Feb 25, 2011 at 21:53

darkpbj · Accepted Answer · 2014-11-29 00:25:17Z

8

use apache commons io

http://commons.apache.org/proper/commons-io/

look at their FileUtils class. Full of gold. Gold I say....

edited Nov 29, 2014 at 0:25

darkpbj

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answered Feb 25, 2011 at 21:31

hvgotcodes

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2 Comments

Dead Programmer Over a year ago

Apache commons is the best, no need to write nested try catch

PunDefeated Over a year ago

That link has expired!

JB Nizet · Accepted Answer · 2011-02-25 21:43:09Z

6

This is not the standard way at all. This is the bad way.

The way I use most of the time is this one :

ObjectOutputStream out = null;
try {
    out = new ObjectOutputStream(new FileOutputStream("file.dat"));
    // use out
}
finally {
    if (out != null) {
        try {
            out.close();
        }
        catch (IOException e) {
            // nothing to do here except log the exception
        }
    }
}

The code in the finally block can be put in a helper method, or you can use commons IO to close the stream quietly, as noted in other answers.

A stream must always be closed in a finally block.

Note that JDK7 will make it much easier with the new syntax, which will automatically close the stream at the end of the try block :

try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("file.dat"))) {
    // use out
}

edited Feb 25, 2011 at 21:43

answered Feb 25, 2011 at 21:35

JB Nizet

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2 Comments

Rene Over a year ago

Am aware that not closing it in the finally block is risky, hence my question. But naming it the standard way was indeed a bad formulation.However the JDK7 info is new to me, and looks interesting. Is this comparable to the using{} syntax that C# uses in case you or someone know both languages?

z0r Over a year ago

I don't know about C#, but it's like Python's with syntax. python.org/dev/peps/pep-0343

Aravind Yarram · Accepted Answer · 2011-02-25 21:32:49Z

3

This why I use commons-io's IOUtils.closeQuitely(...)

try
{
...
}
finally 
{
   IOUtils.closeQuietly(costream);
}

answered Feb 25, 2011 at 21:32

Aravind Yarram

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Comments

corsiKa · Accepted Answer · 2011-02-25 21:32:55Z

0

try
{
    ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("file.dat"));
    oos.writeObject(h);
    //oos.close(); // glow coder removed
}
catch (FileNotFoundException ex)
{
}
catch (IOException ex)
{
}
// glowcoder adds:
finally {
    try {
        oos.close();
    }
    catch(IOException ex) {
        // dammit we tried!
    }
}

answered Feb 25, 2011 at 21:32

corsiKa

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3 Comments

Rene Over a year ago

Works, but this is just what I wanted to avoid doing.

corsiKa Over a year ago

@Rene what exactly are you trying to avoid, and why are you trying to avoid it?

Rene Over a year ago

As I wrote in my question, I just think this way is ugly, creating a huge block of code, for handling exceptions on just 3 statements. So my question was purely about coding style, maybe I'm too fussy about it ;) Thanks for your response anyway :)

Mazyod · Accepted Answer · 2011-02-25 21:33:00Z

0

add this finally:

finally{
   if(oos != null)
      oos.close();
}

answered Feb 25, 2011 at 21:33

Mazyod

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1 Comment

Rene Over a year ago

you'll need to add another try...catch here and that's just what i wanted to avoid

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