}
        catch (SecurityException se) {}
        // return empty string if property value is empty string.
        if (userDir.length() == 0) 
            return new URI("file", "", "", null, null);
        
        // compute the new escaped value if the new property value doesn't
        // match the previous one
        if (gUserDirURI != null && userDir.equals(gUserDir)) {
            return gUserDirURI;
        }
        // record the new value as the global property value
        gUserDir = userDir;
        char separator = java.io.File.separatorChar;
        userDir = userDir.replace(separator, '/');
        int len = userDir.length(), ch;
        StringBuffer buffer = new StringBuffer(len*3);
        // change C:/blah to /C:/blah
        if (len >= 2 && userDir.charAt(1) == ':') {
            ch = Character.toUpperCase(userDir.charAt(0));
            if (ch >= 'A' && ch <= 'Z') {
                buffer.append('/');
            }
        }
        // for each character in the path
        int i = 0;
        for (; i < len; i++) {
            ch = userDir.charAt(i);
            // if it's not an ASCII character, break here, and use UTF-8 encoding
            if (ch >= 128)
                break;
            if (gNeedEscaping[ch]) {
                buffer.append('%');
                buffer.append(gAfterEscaping1[ch]);
                buffer.append(gAfterEscaping2[ch]);
                // record the fact that it's escaped
            }
            else {
                buffer.append((char)ch);
            }
        }
        // we saw some non-ascii character
        if (i < len) {
            // get UTF-8 bytes for the remaining sub-string
            byte[] bytes = null;
            byte b;
            try {
                bytes = userDir.substring(i).getBytes("UTF-8");
            } catch (java.io.UnsupportedEncodingException e) {
                // should never happen
                return new URI("file", "", userDir, null, null);
            }
            len = bytes.length;
            // for each byte
            for (i = 0; i < len; i++) {
                b = bytes[i];
                // for non-ascii character: make it positive, then escape
                if (b < 0) {
                    ch = b + 256;
                    buffer.append('%');
                    buffer.append(gHexChs[ch >> 4]);
                    buffer.append(gHexChs[ch & 0xf]);
                }
                else if (gNeedEscaping[b]) {
                    buffer.append('%');
                    buffer.append(gAfterEscaping1[b]);
                    buffer.append(gAfterEscaping2[b]);
                }
                else {
                    buffer.append((char)b);
                }
            }
        }
        // change blah/blah to blah/blah/
        if (!userDir.endsWith("/"))
            buffer.append('/');
        
        gUserDirURI = new URI("file", "", buffer.toString(), null, null);
        return gUserDirURI;
    }