[java] What is the best way to find the users home directory in Java?

The difficulty is that it should be cross platform. Windows 2000, XP, Vista, OSX, Linux, other unix variants. I am looking for a snippet of code that can accomplish this for all platforms, and a way to detect the platform.

Now, you should be aware of bug 4787931 that user.home does not work correctly, so please do not provide me of textbook answers, I can find these myself in the manuals.

Alternative would be to use Apache CommonsIO FileUtils.getUserDirectory() instead of System.getProperty("user.home"). It will get you the same result and there is no chance to introduce a typo when specifying system property.

There is a big chance you already have Apache CommonsIO library in your project. Don't introduce it if you plan to use it only for getting user home directory.

Actually with Java 8 the right way is to use:

System.getProperty("user.home");

The bug JDK-6519127 has been fixed and the "Incompatibilities between JDK 8 and JDK 7" section of the release notes states:

Area: Core Libs / java.lang

Synopsis

The steps used to determine the user's home directory on Windows have changed to follow the Microsoft recommended approach. This change might be observable on older editions of Windows or where registry settings or environment variables are set to other directories. Nature of Incompatibility

behavioral RFE

6519127

Despite the question being old I leave this for future reference.

As I was searching for Scala version, all I could find was McDowell's JNA code above. I include my Scala port here, as there currently isn't anywhere more appropriate.

import com.sun.jna.platform.win32._
object jna {
    def getHome: java.io.File = {
        if (!com.sun.jna.Platform.isWindows()) {
            new java.io.File(System.getProperty("user.home"))
        }
        else {
            val pszPath: Array[Char] = new Array[Char](WinDef.MAX_PATH)
            new java.io.File(Shell32.INSTANCE.SHGetSpecialFolderPath(null, pszPath, ShlObj.CSIDL_MYDOCUMENTS, false) match {
                case true => new String(pszPath.takeWhile(c => c != '\0'))
                case _    => System.getProperty("user.home")
            })
        }
    }
}

As with the Java version, you will need to add Java Native Access, including both jar files, to your referenced libraries.

It's nice to see that JNA now makes this much easier than when the original code was posted.

I would use the algorithm detailed in the bug report using System.getenv(String), and fallback to using the user.dir property if none of the environment variables indicated a valid existing directory. This should work cross-platform.

I think, under Windows, what you are really after is the user's notional "documents" directory.

System.getProperty("user.home");

See the JavaDoc.

The concept of a HOME directory seems to be a bit vague when it comes to Windows. If the environment variables (HOMEDRIVE/HOMEPATH/USERPROFILE) aren't enough, you may have to resort to using native functions via JNI or JNA. SHGetFolderPath allows you to retrieve special folders, like My Documents (CSIDL_PERSONAL) or Local Settings\Application Data (CSIDL_LOCAL_APPDATA).

Sample JNA code:

public class PrintAppDataDir {

    public static void main(String[] args) {
        if (com.sun.jna.Platform.isWindows()) {
            HWND hwndOwner = null;
            int nFolder = Shell32.CSIDL_LOCAL_APPDATA;
            HANDLE hToken = null;
            int dwFlags = Shell32.SHGFP_TYPE_CURRENT;
            char[] pszPath = new char[Shell32.MAX_PATH];
            int hResult = Shell32.INSTANCE.SHGetFolderPath(hwndOwner, nFolder,
                    hToken, dwFlags, pszPath);
            if (Shell32.S_OK == hResult) {
                String path = new String(pszPath);
                int len = path.indexOf('\0');
                path = path.substring(0, len);
                System.out.println(path);
            } else {
                System.err.println("Error: " + hResult);
            }
        }
    }

    private static Map<String, Object> OPTIONS = new HashMap<String, Object>();
    static {
        OPTIONS.put(Library.OPTION_TYPE_MAPPER, W32APITypeMapper.UNICODE);
        OPTIONS.put(Library.OPTION_FUNCTION_MAPPER,
                W32APIFunctionMapper.UNICODE);
    }

    static class HANDLE extends PointerType implements NativeMapped {
    }

    static class HWND extends HANDLE {
    }

    static interface Shell32 extends Library {

        public static final int MAX_PATH = 260;
        public static final int CSIDL_LOCAL_APPDATA = 0x001c;
        public static final int SHGFP_TYPE_CURRENT = 0;
        public static final int SHGFP_TYPE_DEFAULT = 1;
        public static final int S_OK = 0;

        static Shell32 INSTANCE = (Shell32) Native.loadLibrary("shell32",
                Shell32.class, OPTIONS);

        /**
         * see http://msdn.microsoft.com/en-us/library/bb762181(VS.85).aspx
         * 
         * HRESULT SHGetFolderPath( HWND hwndOwner, int nFolder, HANDLE hToken,
         * DWORD dwFlags, LPTSTR pszPath);
         */
        public int SHGetFolderPath(HWND hwndOwner, int nFolder, HANDLE hToken,
                int dwFlags, char[] pszPath);

    }

}

Others have answered the question before me but a useful program to print out all available properties is:

for (Map.Entry<?,?> e : System.getProperties().entrySet()) {
    System.out.println(String.format("%s = %s", e.getKey(), e.getValue())); 
}

If you want something that works well on windows there is a package called WinFoldersJava which wraps the native call to get the 'special' directories on Windows. We use it frequently and it works well.