Java's equivalent of Ruby's __FILE__ ?

Question

In Ruby I frequently use File.dirname(__FILE__) to open configuration files and such. For those that don't know Ruby, this will give the location on the file system of the file it's called from. This allows me to package libraries with data and config files and open those files with relative paths.

What's the Java equivalent of this? If there is a data file I want to package with a jar how would I open the data file from Java code that is also in the jar?

Answer 1

Please see Java Applications and the "Current Directory":

In Java, you use File objects to construct a relative view of the file system. Two of the constructors for the File object take a 'parent' argument that specifies a parent path that is prefixed to the path of the file itself to create the full abstract path to the file. What you do is, create a File object with the path that represents your current directory and then create all your file objects using that File object as the parent. Voila, a current directory.

Also I would recommend Reading and Writing a Properties File:

// Read properties file.
Properties properties = new Properties();
try {
    properties.load(new FileInputStream("filename.properties"));
} catch (IOException e) {
}

// Write properties file.
try {
    properties.store(new FileOutputStream("filename.properties"), null);
} catch (IOException e) {
}

Answer 2

The equivalent API in Java is getResourceAsStream. This will open a stream to a file stored in the JAR relative to the class on which it is invoked.

There are variants, such as getResource, which returns a URL, or methods on ClassLoader that use an absolute path inside the JAR file.

Answer 3

I voted for @andrew, but I'd like to point out that in Java, the directory the file itself is pretty meaningless except for a few highly reflective (and most likely wrong) purposes.

It will be in a directory based on a package structure, and could be located in a jar or pretty much anywhere.

Java's a little less ad-hock, allowing for less shortcuts, but usually improving consistency and reliability at deployment time.

Answer 4

if you just specify the file name, the JVM will look for that file in the same directory your application was started (not necessarily the same directory your application is located).