reading/writing to files so it works in both a linux/windows environment

Question

If someone installs my java application on their computer (windows/linux/mac), how can I make sure my applications ability to read/write files works in all environments.

Is there a way for my application to figure out where in the file system it is installed, and then read/write safely?

Note: these files that are being read/written are all application files i.e. it is not trying to reference any operating system file/registry.

So all files can be within the applications root folder (wherever it is installed)

Answer 1

Java's file IO library is platform independent and should work on any OS that the jvm is installed on. With that said, some file systems behave differently (permissions, user/group, etc), which can cause your file operations to succeed on one platform, but fail on another. For this reason, it is always a good idea to test your code on all systems you wish your system to run on.

Answer 2

Using the java.io.File (or perhaps java.nio package). This will generally work cross-platform, but you will need to be aware of platform differences and code around these. For example, you need to use things like File.pathSeparator to ensure you use the correct path separator for the platform. Also, depending on what you are doing, there are differences between how locking works etc, and not all operations are guaranteed to work - some just fail silently.

Answer 3

Is there a way for my application to figure out where in the file system it is installed, and then read/write safely?

You can maybe read the user.dir system property to get the path that the application was started in. Note that user.dir is a read only property, i.e. you can't change the "current directory" by setting the user.dir property. You read system properties with the System.getProperty(String) method. This is not exactly the same thing as "installed in" but it may work. But it's kinda weak.

If really you want the location of the install directory, either force the user to set an environment variable (MYAPP_HOME) or scan the whole file system. Personally, I don't like these options.

Actually, and if the data are user specific, the best choice in my opinion would be to read/write data in the user home directory (use the system property user.home to get it), for example in something like ~/.yourapp (Windows users never go in their %USER_HOME% anyway) or, even better, in a directory following Freedesktop XDG Base Directory Specification (obviously, only Linux users would care of that).

Then, to read/write, just use the java.io.File which is cross-platform when used properly (e.g. use File.separator if you need to build a path, don't use an hard coded version of the name-separator).

Answer 4

You need to set a property, e.g., with "-Dapphome=abx" at the command line or in some configuration file. In the former you can retrieve it with System.getProperty("apphome"), in the latter you still need to have some way to find that configuration file unfortunately.

If it helps you can find the user's home directory with System.getProperty("user.home"). This can be very helpful since you can read per-user configuration files by using that as a starting point. Common files for multiple users will need to go into the system somewhere, e.g., /etc/appname/config.properties or C:\

BTW you should use System.getProperty("java.io.tmpdir") for your temporary files. Don't clutter up the directory where your app was launched (if you can -- you may not have the necessary permissions!) or the user's home directory. You need to be careful though - create a subdirectory for your app, and maybe a subdirectory for each user, to avoid the risk of one app stepping on the temporary files used by a second app.

Answer 5

The Java File class accepts "/" as path separators, so just use that. If you need the root drives do not code C: or anything but ask the JRE for the roots, and use them.