Object Mentor Blog: Always `close()` in a `finally` block

Always <tt>close()</tt> in a <tt>finally</tt> block

Dean Wampler — Thu, 31 Jul 2008 00:12:00 -0500

Here’s one for my fellow Java programmers, but it’s really generally applicable.

When you call close() on I/O streams, readers, writers, network sockets, database connections, etc., it’s easy to forgot the most appropriate idiom. I just spent a few hours fixing some examples of misuse in otherwise very good Java code.

What’s wrong the following code?

    
public void writeContentToFile(String content, String fileName) throws Exception {
    File output = new File(fileName);
    OutputStreamWriter writer = new OutputStreamWriter(new FileOutputStream(output), "UTF-8");
    writer.write(content);
    writer.close();
}

It doesn’t look all that bad. It tells it’s story. It’s easy to understand.

However, it’s quite likely that you won’t get to the last line, which closes the writer, from time to time. File and network I/O errors are common. For example, what if you can’t actually write to the location specified by fileName? So, we have to be more defensive. We want to be sure we always clean up.

The correct idiom is to use a try … finally … block.

    
public void writeContentToFile(String content, String fileName) throws Exception {
    File output = new File(getFileSystemPath() + contentFilename);
    OutputStreamWriter writer = null;
    try {
        writer = new OutputStreamWriter(new FileOutputStream(output), "UTF-8");
        writer.write(content);
    } finally {
        if (writer != null)
            writer.close();
    }
}

Now, no matter what happens, the writer will be closed, if it’s not null, even if writing the output was unsuccessful.

Note that we don’t necessarily need a catch block, because in this case we’re willing to let any Exceptions propagate up the stack (notice the throws clause). A lot of developers don’t realize that there are times when you need a try block, but not necessarily a catch block. This is one of those times.

So, anytime you need to clean up or otherwise release resources, use a finally block to ensure that the clean up happens, no matter what.

"Always `close()` in a `finally` block" by serial

Wed, 08 Feb 2012 10:17:52 -0600

Siècle Série classique américain de los angeles marque Ralph Lauren hommes d’hiver communiqué de 2012, los angeles principale saison des longues de design guy cuir, créateurs intelligents ajouté fermeture éclair dans los angeles couche moyenne de cuir, veste durante cuir cuando longtemps devient instantanément courtroom. Los angeles cou))))hey hee!

"Always `close()` in a `finally` block" by ralph lauren

Thu, 02 Feb 2012 02:49:08 -0600

"Always `close()` in a `finally` block" by tv show

Sat, 26 Nov 2011 10:09:02 -0600

good stuff. thanks for posting it!

"Always `close()` in a `finally` block" by koko

Fri, 25 Nov 2011 18:38:35 -0600

oakley mens antix sunglassesoakley batwolf sunglassesdiscount oakley batwolf sunglassesoakley batwolf sunglasses saleoakley mens batwolf sunglassesoakley dispatch sunglassesdiscount oakley dispatch sunglassesoakley dispatch sunglasses saleoakley mens dispatch sunglassesoakley fives squared sunglassesdiscount oakley fives squared sunglassesoakley fives squared sunglasses saleoakley mens fives squared sunglassesoakley fuel cell sunglassesdiscount oakley fuel cell sunglassesoakley fuel cell sunglasses saleoakley mens fuel cell sunglassesoakley gascan sunglassesdiscount oakley gascan sunglassesoakley gascan sunglasses saleoakley mens gascan sunglassesoakley half wire sunglassesdiscount oakley half wire sunglassesoakley half wire sunglasses saleoakley mens half wire sunglassesoakley hijinx sunglassesdiscount oakley hijinx sunglassesoakley hijinx sunglasses sale

"Always `close()` in a `finally` block" by christian louboutin

Thu, 03 Nov 2011 08:59:45 -0500

The professional design make you foot more comfortable. Even more tantalizing,this pattern make your legs look as long as you can,it will make you looked more attractive.Moveover,it has reasonable price.If you are a popular woman,do not miss it.

Technical details of Christian Louboutin Velours Scrunch Suede Boots Coffee:

Color: Coffee
Material: Suede
4(100mm) heel
Signature red sole x

Fashion, delicate, luxurious Christian louboutins shoes on sale, one of its series is Christian Louboutin Tall Boots, is urbanism collocation. This Christian louboutins shoes design makes people new and refreshing. Red soles shoes is personality, your charm will be wonderful performance.

"Always `close()` in a `finally` block" by Tips For Bowling

Thu, 20 Oct 2011 15:38:28 -0500

And, moreover, it is art in its most general and comprehensive form that is here discussed, for the dialogue embraces everything connected with it, from its greatest object, the state, to its least, the embellishment of sensuous existence.

"Always `close()` in a `finally` block" by ysbearing

Wed, 19 Oct 2011 03:34:27 -0500

Slewing ring is also called slewing bearing, some people called: rotary support, swing support. English Name: slewing bearing or slewing ring bearing or turn table bearing, slewing ring in the real industrial applications is very wide.

"Always `close()` in a `finally` block" by Fake Oakley Polarized Sunglasses

Tue, 11 Oct 2011 03:40:01 -0500

It’s wonderful, thank you. Oakley Ten Sunglasses wholesale replica Oakley Ten Sunglasses cheap Oakley Zero Sunglasses Oakley Zero Sunglasses Oakley Zero Sunglasses wholesale replica Oakley Zero Sunglasses Replica Oakley Ten Replica Oakley Zero Replica Oakley Minute Sunglasses Replica Oakley Monster Dog Sunglasses Replica Oakley Pit Boss Sunglasses Fake Oakley Half X sunglasses Fake Oakley Hijinx sunglasses Fake Oakley M Frame sunglasses Oakley Antix Sunglasses Oakley Batwolf Sunglasses Oakley Dispatch Sunglasses Oakley Fives Squared Sunglasses

"Always `close()` in a `finally` block" by Fake Oakley Radar

Tue, 11 Oct 2011 00:56:15 -0500

It really a good article.Fake Oakley Juliet Fake Oakley Jury Fake Oakley Monster Dog Fake Oakley Oil Rig replica oakley dispatch sunglasses cheap Oakley Encounter Sunglasses Oakley Encounter Sunglasses Oakley Encounter Sunglasses wholesale replica Oakley Encounter Sunglasses cheap Oakley Enduring Pace Sunglasses Oakley Enduring Pace Sunglasses wholesale Replica Oakley Polarized Sunglasses Replica Oakley Radar Sunglasses Replica Oakley M Frame Sunglasses Replica Oakley Flak Jacket Sunglasses Fake Oakley Jupiter sunglasses Fake Oakley Holbrook sunglasses Fake Oakley Half Wire sunglasses Fake Oakley Jawbone sunglasses Oakley Half Jacket Sunglasses Oakley Flak Jacket Sunglasses Oakley Bottlecap Sunglasses Oakley Commit SQ Sunglasses

"Always `close()` in a `finally` block" by Fake Oakley Gascan sunglasses

Mon, 10 Oct 2011 20:21:25 -0500

I love this article, it’s very well.Fake Oakley Forsake sunglasses Fake Oakley Frogskins sunglasses Fake Oakley Fuel Cell sunglasses Fake Oakley Gascan sunglasses Replica Oakley Half Wire Sunglasses Replica Oakley Half X Sunglasses

"Always `close()` in a `finally` block" by discount oakley fives sunglasses

Mon, 10 Oct 2011 20:18:04 -0500

I like it. This is a very good works, come on oakley active sunglasses discount oakley active sunglasses oakley active sunglasses sale oakley mens active sunglasses oakley bottlecap sunglasses discount oakley bottlecap sunglasses

"Always `close()` in a `finally` block" by ferragamo shoes

Fri, 16 Sep 2011 03:11:50 -0500

Ferragmo belt from ferragamo outlet has top quality with best craftsmanship. Now Salvatore ferragamo sale belts online with reasonable price and free shipping.

"Always `close()` in a `finally` block" by canada goose coat

Thu, 15 Sep 2011 21:10:39 -0500

When it comes to feather dress, what appears in your mind? Which kind brand of down jacket do you like prefer? Though there are many down jackets for you to choose from, on the word, which one you really enjoy? I want to say that canada goose coats is really your best choice. I believe you can’t agree with me any more. When you take the quality into consideration, you will find that it is superior to any other kind of coat. Besides, discount canada goose jackets is a world well-known brand, which has gained high reputation in the world, which has accepted by our customers and some organization. Because of its high quality, some of our loyal customers have promoted it to the people around them. In their opinion, it is good to informing others to know it. Recently, Canada Goose Trillium Parka is on hot sale. What I have to inform you is that all the products there are made by hand, so they are elaborative and elegant enough. It is really beautiful once you dress in. So, if you are a lovely girl or woman, go to the store to buy one for you. You will appreciate it that you have such a coat.In addition, they also have any other products like canada goose Gloves and canada goose jacket supplier.Hope your will like its!

"Always `close()` in a `finally` block" by Diablo3

Wed, 14 Sep 2011 12:23:01 -0500

it needs a bokmark so i can come back to it later ,nice stuff

"Always `close()` in a `finally` block" by beats by dr dre

Mon, 29 Aug 2011 20:52:35 -0500

’m looking for but anyway this is interresting and could be useful some day,thanks for tabeats by dr dre beats by dre saleking time to write such cool stuff

"Always `close()` in a `finally` block" by Bowtrol

Mon, 08 Aug 2011 16:51:24 -0500

hmm ,i’m not sure if this is what i’m looking for but anyway this is interresting and could be useful some day,thanks for taking time to write such cool stuff

"Always `close()` in a `finally` block" by christian louboutin shoes on sale

Fri, 03 Jun 2011 02:34:31 -0500

Have the christian louboutin patent leather pumps is a happy thing. Here have the most complete kinds of christian louboutin leather platform pumps.

"Always `close()` in a `finally` block" by canada goose jackets

Wed, 18 May 2011 22:26:05 -0500

I loved this chapter. I can’t wait for the next one.

"Always `close()` in a `finally` block" by okey oyunu oyna

Wed, 27 Apr 2011 13:27:49 -0500

very good for your explanation.

internette görüntülü olarak okey oyunu oyna, gerçek kisilerle tanis, turnuva heyecanini yasa.

"Always `close()` in a `finally` block" by ralph lauren

Tue, 26 Apr 2011 02:28:55 -0500

Easily alter the brightness 80-fuschia pink vibe, the ghd striking styler arrives with three pink lip high shine ghd to complement every solitary mood, Dare, Dazzle and good for design and high shine in a fellow or young lady splendid package.

"Always `close()` in a `finally` block" by Ray Ban

Sat, 02 Apr 2011 08:19:52 -0500

Finally it has been explained, thank you

"Always `close()` in a `finally` block" by Criminal Records

Mon, 14 Feb 2011 15:57:50 -0600

A lot of developers don’t realize that there are times when you need a try block, but not necessarily a catch block. This is one of those times.

"Always `close()` in a `finally` block" by Low Carb Snacks

Sun, 30 Jan 2011 23:38:31 -0600

et any Exceptions propagate up the stack (notice the throws clause). A lot of developers don’t realize that there are times when you need a try block, but not necessarily a catch block. This is one of those times.

"Always `close()` in a `finally` block" by Criminal Check

Wed, 12 Jan 2011 12:48:57 -0600

@ Andrew Rea

Thanks for giving a hint.

"Always `close()` in a `finally` block" by http://www.blacktowhiteiphone4.com

Fri, 24 Dec 2010 02:56:16 -0600

Without switching lense on my 550D I couldn’t get any closer than this so the 100% crop below isn’t really accurate but it shows what kind of sharpness the white iPhone 4 is capable of. Impressive

Object Mentor Blog: Always close() in a finally block

Always <tt>close()</tt> in a <tt>finally</tt> block

"Always close() in a finally block" by serial

"Always close() in a finally block" by ralph lauren

"Always close() in a finally block" by tv show

"Always close() in a finally block" by koko

"Always close() in a finally block" by christian louboutin

"Always close() in a finally block" by Tips For Bowling

"Always close() in a finally block" by ysbearing

"Always close() in a finally block" by Fake Oakley Polarized Sunglasses

"Always close() in a finally block" by Fake Oakley Radar

"Always close() in a finally block" by Fake Oakley Gascan sunglasses

"Always close() in a finally block" by discount oakley fives sunglasses

"Always close() in a finally block" by ferragamo shoes

"Always close() in a finally block" by canada goose coat

"Always close() in a finally block" by Diablo3

"Always close() in a finally block" by beats by dr dre

"Always close() in a finally block" by Bowtrol

"Always close() in a finally block" by christian louboutin shoes on sale

"Always close() in a finally block" by canada goose jackets

"Always close() in a finally block" by okey oyunu oyna

"Always close() in a finally block" by ralph lauren

"Always close() in a finally block" by Ray Ban

"Always close() in a finally block" by Criminal Records

"Always close() in a finally block" by Low Carb Snacks

"Always close() in a finally block" by Criminal Check

"Always close() in a finally block" by http://www.blacktowhiteiphone4.com

Object Mentor Blog: Always `close()` in a `finally` block

"Always `close()` in a `finally` block" by serial

"Always `close()` in a `finally` block" by ralph lauren

"Always `close()` in a `finally` block" by tv show

"Always `close()` in a `finally` block" by koko

"Always `close()` in a `finally` block" by christian louboutin

"Always `close()` in a `finally` block" by Tips For Bowling

"Always `close()` in a `finally` block" by ysbearing

"Always `close()` in a `finally` block" by Fake Oakley Polarized Sunglasses

"Always `close()` in a `finally` block" by Fake Oakley Radar

"Always `close()` in a `finally` block" by Fake Oakley Gascan sunglasses

"Always `close()` in a `finally` block" by discount oakley fives sunglasses

"Always `close()` in a `finally` block" by ferragamo shoes

"Always `close()` in a `finally` block" by canada goose coat

"Always `close()` in a `finally` block" by Diablo3

"Always `close()` in a `finally` block" by beats by dr dre

"Always `close()` in a `finally` block" by Bowtrol

"Always `close()` in a `finally` block" by christian louboutin shoes on sale

"Always `close()` in a `finally` block" by canada goose jackets

"Always `close()` in a `finally` block" by okey oyunu oyna

"Always `close()` in a `finally` block" by ralph lauren

"Always `close()` in a `finally` block" by Ray Ban

"Always `close()` in a `finally` block" by Criminal Records

"Always `close()` in a `finally` block" by Low Carb Snacks

"Always `close()` in a `finally` block" by Criminal Check

"Always `close()` in a `finally` block" by http://www.blacktowhiteiphone4.com