/**
     * Gets the platform defined TimeZone ID.
     **/
    private static native String getSystemTimeZoneID(String javaHome);

    private static synchronized TimeZone setDefaultZone() {
        TimeZone tz;
        // get the time zone ID from the system properties
        String zoneID = AccessController.doPrivileged(
                new GetPropertyAction("user.timezone"));

        // if the time zone ID is not set (yet), perform the
        // platform to Java time zone ID mapping.
        if (zoneID == null || zoneID.isEmpty()) {
            String javaHome = AccessController.doPrivileged(
                    new GetPropertyAction("java.home"));
            try {
                zoneID = getSystemTimeZoneID(javaHome);
                if (zoneID == null) {
                    zoneID = GMT_ID;
                }
            } catch (NullPointerException e) {
                zoneID = GMT_ID;
            }
        }

        // Get the time zone for zoneID. But not fall back to
        // "GMT" here.
        tz = getTimeZone(zoneID, false);

        if (tz == null) {
            // If the given zone ID is unknown in Java, try to
            // get the GMT-offset-based time zone ID,
            // a.k.a. custom time zone ID (e.g., "GMT-08:00").
            String gmtOffsetID = getSystemGMTOffsetID();
            if (gmtOffsetID != null) {
                zoneID = gmtOffsetID;
            }
            tz = getTimeZone(zoneID, true);
        }
        assert tz != null;

        final String id = zoneID;
        AccessController.doPrivileged(new PrivilegedAction<Void>() {
            @Override
                public Void run() {
                    System.setProperty("user.timezone", id);
                    return null;
                }
            });

        defaultTimeZone = tz;
        return tz;
    }

Java_java_util_TimeZone_getSystemTimeZoneID(JNIEnv *env, jclass ign,
                                            jstring java_home, jstring country)
{
    const char *cname;
    const char *java_home_dir;
    char *javaTZ;

    if (java_home == NULL)
        return NULL;

    java_home_dir = JNU_GetStringPlatformChars(env, java_home, 0);
    if (java_home_dir == NULL)
        return NULL;

    if (country != NULL) {
        cname = JNU_GetStringPlatformChars(env, country, 0);
        /* ignore error cases for cname */
    } else {
        cname = NULL;
    }

    /*
     * Invoke platform dependent mapping function
     */
    javaTZ = findJavaTZ_md(java_home_dir, cname);

    free((void *)java_home_dir);
    if (cname != NULL) {
        free((void *)cname);
    }

    if (javaTZ != NULL) {
        jstring jstrJavaTZ = JNU_NewStringPlatform(env, javaTZ);
        free((void *)javaTZ);
        return jstrJavaTZ;
    }
    return NULL;
}

/*
 * findJavaTZ_md() maps platform time zone ID to Java time zone ID
 * using <java_home>/lib/tzmappings. If the TZ value is not found, it
 * trys some libc implementation dependent mappings. If it still
 * can't map to a Java time zone ID, it falls back to the GMT+/-hh:mm
 * form. `country', which can be null, is not used for UNIX platforms.
 */
/*ARGSUSED1*/
char *
findJavaTZ_md(const char *java_home_dir, const char *country)
{
    char *tz;
    char *javatz = NULL;
    char *freetz = NULL;

    tz = getenv("TZ");

#ifdef __linux__
    if (tz == NULL) {
#else
#ifdef __solaris__
    if (tz == NULL || *tz == '\0') {
#endif
#endif
        tz = getPlatformTimeZoneID();
        freetz = tz;
    }

    if (tz != NULL) {
        if (*tz == ':') {
            tz++;
        }
#ifdef __linux__
        /*
         * Ignore "posix/" prefix.
         */
        if (strncmp(tz, "posix/", 6) == 0) {
            tz += 6;
        }
#endif
        javatz = strdup(tz);
        if (freetz != NULL) {
            free((void *) freetz);
        }
    }
    return javatz;
}


/*
 * Performs libc implementation specific mapping and returns a zone ID
 * if found. Otherwise, NULL is returned.
 */
static char *
getPlatformTimeZoneID()
{
    struct stat statbuf;
    char *tz = NULL;
    FILE *fp;
    int fd;
    char *buf;
    size_t size;

    /*
     * Try reading the /etc/timezone file for Debian distros. There's
     * no spec of the file format available. This parsing assumes that
     * there's one line of an Olson tzid followed by a '\n', no
     * leading or trailing spaces, no comments.
     */
    if ((fp = fopen(ETC_TIMEZONE_FILE, "r")) != NULL) {
        char line[256];

        if (fgets(line, sizeof(line), fp) != NULL) {
            char *p = strchr(line, '\n');
            if (p != NULL) {
                *p = '\0';
            }
            if (strlen(line) > 0) {
                tz = strdup(line);
            }
        }
        (void) fclose(fp);
        if (tz != NULL) {
            return tz;
        }
    }

    /*
     * Next, try /etc/localtime to find the zone ID.
     */
    if (lstat(DEFAULT_ZONEINFO_FILE, &statbuf) == -1) {
        return NULL;
    }

    /*
     * If it's a symlink, get the link name and its zone ID part. (The
     * older versions of timeconfig created a symlink as described in
     * the Red Hat man page. It was changed in 1999 to create a copy
     * of a zoneinfo file. It's no longer possible to get the zone ID
     * from /etc/localtime.)
     */
    if (S_ISLNK(statbuf.st_mode)) {
        char linkbuf[PATH_MAX+1];
        int len;

        if ((len = readlink(DEFAULT_ZONEINFO_FILE, linkbuf, sizeof(linkbuf)-1)) == -1) {
            jio_fprintf(stderr, (const char *) "can't get a symlink of %s\n",
                        DEFAULT_ZONEINFO_FILE);
            return NULL;
        }
        linkbuf[len] = '\0';
        tz = getZoneName(linkbuf);
        if (tz != NULL) {
            tz = strdup(tz);
        }
        return tz;
    }

    /*
     * If it's a regular file, we need to find out the same zoneinfo file
     * that has been copied as /etc/localtime.
     */
    size = (size_t) statbuf.st_size;
    buf = (char *) malloc(size);
    if (buf == NULL) {
        return NULL;
    }
    if ((fd = open(DEFAULT_ZONEINFO_FILE, O_RDONLY)) == -1) {
        free((void *) buf);
        return NULL;
    }

    if (read(fd, buf, size) != (ssize_t) size) {
        (void) close(fd);
        free((void *) buf);
        return NULL;
    }
    (void) close(fd);

    tz = findZoneinfoFile(buf, size, ZONEINFO_DIR);
    free((void *) buf);
    return tz;
}