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$Id: bestpractices.xml,v 1.1 2004/01/16 17:05:03 jeremias Exp $
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<section name="Overview">
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This document presents a number of "best practices" in the IO area.
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<section name="java.io.File">
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Often, you have to deal with files and filenames. There are many
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things that can go wrong:
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<li>A class works in Unix but doesn't on Windows (or vice versa)</li>
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<li>Invalid filenames due to double or missing path separators</li>
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<li>UNC filenames (on Windows) don't work with my home-grown filename utility function</li>
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These are good reasons not to work with filenames as Strings. Use
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java.io.File instead which handles many of the above cases nicely. Too
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many people are still always using Strings for filenames and risk
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platform dependencies, for example.
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Let's look at an example. BTW, it's one of the functions that made us
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skip the class FilenameUtils for the initial release of Commons IO.
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public static String getExtension(String filename) {
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int index = filename.lastIndexOf('.');
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return filename.substring(index + 1);
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Easy enough? Right, but what happens if someone passes in a full path
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instead of only a filename? Consider the following, perfectly legal path:
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"C:\Temp\documentation.new\README"
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Please use java.io.File for filenames instead of Strings. The functionality
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that the class provides is well tested. In FileUtils you will find other
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useful utility functions around java.io.File.
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String tmpdir = "/var/tmp";
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String tmpfile = tmpdir + System.getProperty("file.separator") + "test.tmp";
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InputStream in = new java.io.FileInputStream(tmpfile);</source>
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File tmpdir = new File("/var/tmp");
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File tmpfile = new File(tmpdir, "test.tmp");
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InputStream in = new java.io.FileInputStream(tmpfile);</source>
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<section name="Buffering streams">
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IO performance depends a lot from the buffering strategy. Usually, it's
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quite fast to read packets with the size of 512 or 1024 bytes because
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these sizes match well with the packet sizes used on harddisks in
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file systems or file system caches. But as soon as you have to read only
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a few bytes and that many times performance drops significantly.
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Make sure you're properly buffering streams when reading or writing
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streams, especially when working with files. Just decorate your
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FileInputStream with a BufferedInputStream:
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InputStream in = new java.io.FileInputStream(myfile);
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in = new java.io.BufferedInputStream(in);
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IOUtils.closeQuietly(in);
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Pay attention that you're not buffering an already buffered stream. Some
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components like XML parsers may do their own buffering so decorating
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the InputStream you pass to the XML parser does nothing but slowing down
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your code. If you use our CopyUtils or IOUtils you don't need to
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additionally buffer the streams you use as the code in there already
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buffers the copy process. Always check the Javadocs for information.
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Another case where buffering is unnecessary is when you write to a
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ByteArrayOutputStream since you're writing to memory only.
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