Preferences...Setting Database Default Directory

Question

i have a JAR file that accesses a database outside of it, but im having a problem of how to put the db in the place that i want it to go. right now its directory is set to C:\Documents and Settings\Alex\.javaphonebook, using this code, from 1 of the classes inside the JAR: String userHomeDirectory = System.getProperty("user.home", ".");
        String systemDirectory = userHomeDirectory + "/.javaphonebook";
        System.setProperty("derby.system.home", systemDirectory);
        File databaseDirectory = new File(systemDirectory);
        databaseDirectory.mkdir(); but what i want is to have the db in the same directory as the JAR (at this point its in D:\Program Files\Java Phonebook) without having to hardcode it, so that my program can be used on different systems in any directory. this what the derectory looks like now: http://www.MyOnlineImages.com/Uploads/Images/3726778475000javaphonebook.bmp and this is what i want it to look like: http://www.MyOnlineImages.com/Uploads/Images/3726867537501javaphonebook2.bmp any help would be appreciated, thnx

Answer 1

ah k. im not too sure how this program works. i read
the commenting but i still have no clue. maybe u
could help me out? :)The VM uses a ClassLoader to load classes from various places (file system, inside JAR files, network, etc).
You can get the ClassLoader object by calling
ClassLoader classLoader = SomeClass.class.getClassLoader();which may be 'null' in which case you use:
classLoader = ClassLoader.getSystemClassLoader();Once you have the ClassLoader, you can ask it for the location of a particular class file:
String className = SomeClass.class.getName();
String classFileName = className + ".class";
URL someClassURL = classLoader.getResource(classFileName);
String urlString = someClassURL.toExternalForm();This gives you a String showing where the class file is located. For a class in a JAR file the String looks something like this:
jar:file:/C:/Junk/jartest.jar!/JarTest.classFor a class file not in a JAR file it might look like this:
file:/C:/Junk/JarTest.classSo, for classes in a JAR file the String starts with "jar:file:/"
You strip off that part using
String filename = urlString.substring(10);which leaves:
C:/Junk/jartest.jar!/JarTest.classDo some more String manipulation to strip off the "!/JarTest.class" leaving:
C:/Junk/jartest.jarOne more bit of String manipulation gets you:
C:/Junkwhich is the directory in which the JAR file is located.
So using only the Class object for a class that you know is in a particular JAR file, you can determine where in the file system that JAR is located, which is also where your database is located.