ZoneInfoFile reads Zone information files in the
<java.home>/lib/zi directory and provides time zone
information in the form of a
ZoneInfo object. Also, it
reads the ZoneInfoMappings file to obtain time zone IDs information
that is used by the
ZoneInfo class. The directory layout
and data file formats are as follows.
Directory layout
All zone data files and ZoneInfoMappings are put under the
<java.home>/lib/zi directory. A path name for a given time
zone ID is a concatenation of <java.home>/lib/zi/ and the
time zone ID. (The file separator is replaced with the platform
dependent value. e.g., '\' for Win32.) An example layout will look
like as follows.
<java.home>/lib/zi/Africa/Addis_Ababa
/Africa/Dakar
/America/Los_Angeles
/Asia/Singapore
/EET
/Europe/Oslo
/GMT
/Pacific/Galapagos
...
/ZoneInfoMappings
A zone data file has specific information of each zone.
ZoneInfoMappings has global information of zone IDs so
that the information can be obtained without instantiating all time
zones.
File format
Two binary-file formats based on a simple Tag-Length-Value format are used
to describe TimeZone information. The generic format of a data file is:
DataFile {
u1 magic[7];
u1 version;
data_item data[];
}
where magic is a magic number identifying a file
format, version is the format version number, and
data is one or more data_items. The
data_item structure is:
data_item {
u1 tag;
u2 length;
u1 value[length];
}
where tag indicates the data type of the item,
length is a byte count of the following
value that is the content of item data.
All data is stored in the big-endian order. There is no boundary
alignment between date items.
1. ZoneInfo data file
Each ZoneInfo data file consists of the following members.
ZoneInfoDataFile {
u1 magic[7];
u1 version;
SET OF1 {
transition transitions2;
offset_table offsets2;
simpletimezone stzparams2;
raw_offset rawoffset;
dstsaving dst;
checksum crc32;
gmtoffsetwillchange gmtflag2;
}
}
1: an unordered collection of zero or one occurrences of each item
2: optional item
magic is a byte-string constant identifying the
ZoneInfo data file. This field must be "javazi\0"
defined as
ZoneInfoFile.JAVAZI_LABEL .
version is the version number of the file format. This
will be used for compatibility check. This field must be
0x01 in this version.
transition, offset_table and
simpletimezone have information of time transition
from the past to the future. Therefore, these structures don't
exist if the zone didn't change zone names and haven't applied DST in
the past, and haven't planned to apply it. (e.g. Asia/Tokyo zone)
raw_offset, dstsaving and checksum
exist in every zoneinfo file. They are used by TimeZone.class indirectly.
1.1 transition structure
transition {
u1 tag; // 0x04 : constant
u2 length; // byte length of whole values
s8 value[length/8]; // transitions in `long'
}
See
ZoneInfo.transitions ZoneInfo.transitions about the value.
1.2 offset_table structure
offset_table {
u1 tag; // 0x05 : constant
u2 length; // byte length of whole values
s4 value[length/4]; // offset values in `int'
}
1.3 simpletimezone structure
See
ZoneInfo.simpleTimeZoneParams ZoneInfo.simpleTimeZoneParams about the value.
simpletimezone {
u1 tag; // 0x06 : constant
u2 length; // byte length of whole values
s4 value[length/4]; // SimpleTimeZone parameters
}
See
ZoneInfo.offsets ZoneInfo.offsets about the value.
1.4 raw_offset structure
raw_offset {
u1 tag; // 0x01 : constant
u2 length; // must be 4.
s4 value; // raw GMT offset [millisecond]
}
See
ZoneInfo.rawOffset ZoneInfo.rawOffset about the value.
1.5 dstsaving structure
Value has dstSaving in seconds.
dstsaving {
u1 tag; // 0x02 : constant
u2 length; // must be 2.
s2 value; // DST save value [second]
}
See
ZoneInfo.dstSavings ZoneInfo.dstSavings about value.
1.6 checksum structure
checksum {
u1 tag; // 0x03 : constant
u2 length; // must be 4.
s4 value; // CRC32 value of transitions
}
See
ZoneInfo.checksum ZoneInfo.checksum .
1.7 gmtoffsetwillchange structure
This record has a flag value for
ZoneInfo.rawOffsetWillChange .
If this record is not present in a zoneinfo file, 0 is assumed for
the value.
gmtoffsetwillchange {
u1 tag; // 0x07 : constant
u2 length; // must be 1.
u1 value; // 1: if the GMT raw offset will change
// in the future, 0, otherwise.
}
2. ZoneInfoMappings file
The ZoneInfoMappings file consists of the following members.
ZoneInfoMappings {
u1 magic[7];
u1 version;
SET OF {
versionName version;
zone_id_table zoneIDs;
raw_offset_table rawoffsets;
raw_offset_index_table rawoffsetindices;
alias_table aliases;
}
}
magic is a byte-string constant which has the file type.
This field must be "javazm\0" defined as
ZoneInfoFile.JAVAZM_LABEL .
version is the version number of this file
format. This will be used for compatibility check. This field must
be 0x01 in this version.
versionName shows which version of Olson's data has been used
to generate this ZoneInfoMappings. (e.g. tzdata2000g)
This field is for trouble-shooting and isn't usually used in runtime.
zone_id_tableraw_offset_index_table and
alias_table are general information of supported
zones.
2.1 zone_id_table structure
zone_id_table {
u1 tag; // 0x40 : constant
u2 length; // byte length of whole values
u2 zone_id_count;
zone_id value[zone_id_count];
}
zone_id {
u1 byte_length; // byte length of id
u1 id[byte_length]; // zone name string
}
2.2 raw_offset_table structure
raw_offset_table {
u1 tag; // 0x41 : constant
u2 length; // byte length of whole values
s4 value[length/4]; // raw GMT offset in milliseconds
}
2.3 raw_offset_index_table structure
raw_offset_index_table {
u1 tag; // 0x42 : constant
u2 length; // byte length of whole values
u1 value[length];
}
2.4 alias_table structure
alias_table {
u1 tag; // 0x43 : constant
u2 length; // byte length of whole values
u2 nentries; // number of id-pairs
id_pair value[nentries];
}
id_pair {
zone_id aliasname;
zone_id ID;
}
2.5 versionName structure
versionName {
u1 tag; // 0x44 : constant
u2 length; // byte length of whole values
u1 value[length];
}
since:
1.4 | 