* The result of this method is given to the method * TimeZone.getDefaultTimeZone(String) which tries to map the time * zone id to a known TimeZone. See that method on how the returned * String is mapped to a real TimeZone object. *
* The reference implementation which is made for GNU/Posix like
* systems calls System.getenv("TZ"),
* readTimeZoneFile("/etc/timezone"),
* readtzFile("/etc/localtime") and finally
* getSystemTimeZoneId() till a supported TimeZone is
* found through TimeZone.getDefaultTimeZone(String).
* If every method fails null is returned (which means
* the TimeZone code will fall back on GMT as default time zone).
*
* Note that this method is called inside a
* AccessController.doPrivileged() block and runs with
* the priviliges of the java.util system classes. It will only be
* called when the default time zone is not yet set, the system
* property user.timezone isn't set and it is requested for the
* first time.
*/
static TimeZone getDefaultTimeZoneId()
{
TimeZone zone = null;
// See if TZ environment variable is set and accessible.
String tzid = System.getenv("TZ");
if (tzid != null && !tzid.equals(""))
zone = TimeZone.getDefaultTimeZone(tzid);
// Try to parse /etc/timezone.
if (zone == null)
{
tzid = readTimeZoneFile("/etc/timezone");
if (tzid != null && !tzid.equals(""))
zone = TimeZone.getDefaultTimeZone(tzid);
}
// Try to parse /etc/localtime
if (zone == null)
{
tzid = readtzFile("/etc/localtime");
if (tzid != null && !tzid.equals(""))
zone = TimeZone.getDefaultTimeZone(tzid);
}
// Try some system specific way
if (zone == null)
{
tzid = getSystemTimeZoneId();
if (tzid != null && !tzid.equals(""))
zone = TimeZone.getDefaultTimeZone(tzid);
}
return zone;
}
/**
* Tries to read the time zone name from a file. Only the first
* consecutive letters, digits, slashes, dashes and underscores are
* read from the file. If the file cannot be read or an IOException
* occurs null is returned.
*
* The /etc/timezone file is not standard, but a lot of systems have
* it. If it exist the first line always contains a string
* describing the timezone of the host of domain. Some systems
* contain a /etc/TIMEZONE file which is used to set the TZ
* environment variable (which is checked before /etc/timezone is
* read).
*/
private static String readTimeZoneFile(String file)
{
File f = new File(file);
if (!f.exists())
return null;
InputStreamReader isr = null;
try
{
FileInputStream fis = new FileInputStream(f);
BufferedInputStream bis = new BufferedInputStream(fis);
isr = new InputStreamReader(bis);
StringBuffer sb = new StringBuffer();
int i = isr.read();
while (i != -1)
{
char c = (char) i;
if (Character.isLetter(c) || Character.isDigit(c)
|| c == '/' || c == '-' || c == '_')
{
sb.append(c);
i = isr.read();
}
else
break;
}
return sb.toString();
}
catch (IOException ioe)
{
// Parse error, not a proper tzfile.
return null;
}
finally
{
try
{
if (isr != null)
isr.close();
}
catch (IOException ioe)
{
// Error while close, nothing we can do.
}
}
}
/**
* Tries to read a file as a "standard" tzfile and return a time
* zone id string as expected by getDefaultTimeZone(String).
* If the file doesn't exist, an IOException occurs or it isn't a tzfile
* that can be parsed null is returned.
*
* The tzfile structure (as also used by glibc) is described in the Olson
* tz database archive as can be found at
* ftp://elsie.nci.nih.gov/pub/.
*
* At least the following platforms support the tzdata file format * and /etc/localtime (GNU/Linux, Darwin, Solaris and FreeBSD at * least). Some systems (like Darwin) don't start the file with the * required magic bytes 'TZif', this implementation can handle * that). */ private static String readtzFile(String file) { File f = new File(file); if (!f.exists()) return null; DataInputStream dis = null; try { FileInputStream fis = new FileInputStream(f); BufferedInputStream bis = new BufferedInputStream(fis); dis = new DataInputStream(bis); // Make sure we are reading a tzfile. byte[] tzif = new byte[4]; dis.readFully(tzif); if (tzif[0] == 'T' && tzif[1] == 'Z' && tzif[2] == 'i' && tzif[3] == 'f') // Reserved bytes, ttisgmtcnt, ttisstdcnt and leapcnt skipFully(dis, 16 + 3 * 4); else // Darwin has tzdata files that don't start with the TZif marker skipFully(dis, 16 + 3 * 4 - 4); int timecnt = dis.readInt(); int typecnt = dis.readInt(); if (typecnt > 0) { int charcnt = dis.readInt(); // Transition times plus indexed transition times. skipFully(dis, timecnt * (4 + 1)); // Get last gmt_offset and dst/non-dst time zone names. int abbrind = -1; int dst_abbrind = -1; int gmt_offset = 0; while (typecnt-- > 0) { // gmtoff int offset = dis.readInt(); int dst = dis.readByte(); if (dst == 0) { abbrind = dis.readByte(); gmt_offset = offset; } else dst_abbrind = dis.readByte(); } // gmt_offset is the offset you must add to UTC/GMT to // get the local time, we need the offset to add to // the local time to get UTC/GMT. gmt_offset *= -1; // Turn into hours if possible. if (gmt_offset % 3600 == 0) gmt_offset /= 3600; if (abbrind >= 0) { byte[] names = new byte[charcnt]; dis.readFully(names); int j = abbrind; while (j < charcnt && names[j] != 0) j++; String zonename = new String(names, abbrind, j - abbrind, "ASCII"); String dst_zonename; if (dst_abbrind >= 0) { j = dst_abbrind; while (j < charcnt && names[j] != 0) j++; dst_zonename = new String(names, dst_abbrind, j - dst_abbrind, "ASCII"); } else dst_zonename = ""; // Only use gmt offset when necessary. // Also special case GMT+/- timezones. String offset_string; if ("".equals(dst_zonename) && (gmt_offset == 0 || zonename.startsWith("GMT+") || zonename.startsWith("GMT-"))) offset_string = ""; else offset_string = Integer.toString(gmt_offset); String id = zonename + offset_string + dst_zonename; return id; } } // Something didn't match while reading the file. return null; } catch (IOException ioe) { // Parse error, not a proper tzfile. return null; } finally { try { if (dis != null) dis.close(); } catch(IOException ioe) { // Error while close, nothing we can do. } } } /** * Skips the requested number of bytes in the given InputStream. * Throws EOFException if not enough bytes could be skipped. * Negative numbers of bytes to skip are ignored. */ private static void skipFully(InputStream is, long l) throws IOException { while (l > 0) { long k = is.skip(l); if (k <= 0) throw new EOFException(); l -= k; } } /** * Tries to get the system time zone id through native code. */ private static native String getSystemTimeZoneId(); }