accessing properties files outside the .jar?

Question

I have a .jar file I'm putting together. I want to create a really really simple .properties file with configurable things like the user's name & other stuff, so that they can hand-edit rather than my having to include a GUI editor.

What I'd like to do is to be able to search, in this order:

1. a specified properties file (args[0])
2. MyApp.properties in the current directory (the directory from which Java was called)
3. MyApp.properties in the user's directory (the user.home system property?)
4. MyApp.properties in the directory where the application .jar is stored

I know how to access #1 and #3 (I think), but how can I determine at runtime #2 and #4?

Answer 1

For the current working directory:

new File(".");

For a file named MyApp.properties in the current directory:

new File(new File("."), "MyApp.properties");

Answer 2

For 4, you could try this. Get the classpath:

String classpath = System.getProperty("java.class.path");

Then search it for the name of your application jar:

int jarPos = classpath.indexOf("application.jar");

Parse out the path leading up to it:

int jarPathPos = classpath.lastIndexOf(File.pathSeparatorChar, jarPos) + 1;
String path = classpath.substring(jarPathPos, jarPos);

Then append MyApp.properties. Make sure to check for jarPos == -1, meaning the jar isn't found if the classpath (perhaps when running in your dev environment).

Answer 3

#2 is the "user.dir" system property. #3 is the "user.home" property.

#4 is a bit of a kludge no matter how you approach it. Here's an alternate technique that works if you have a class loaded from a JAR not on the system classpath.

CodeSource src = MyClass.class.getProtectionDomain().getCodeSource();
if (src != null) {
  URL url = new URL(src.getLocation(), "MyApp.properties");
  ...
} 
else {
  /* Fail... */
}

Answer 4

For such a long time to find the answer, erickson's works well, Thanks a lot