11/01/2013

[Date Formatting] Java Default Engine AND Joda framework

A formatting string describes how date/time values should be read and written from(to) string representation

Now we compare the two kinds of formatting engines.
Engine
Formatter
Thread-safe?
Description
Example
Java
SimpleDateFormat

NO
Standard Java date implementation. Provides lenient, error-prone and full-featured parsing and writing. It has moderate speed and is generally a good choice unless you need to work with large quantities of date/time fields. For advanced study please refer to Java SimpleDateFormat documentation.
yyyy-MM-dd HH:mm:ss
Joda
DateTimeFormat
DateTimeFormatter

YES
An improved third-party date library. Joda is stricter on input data accuracy when parsing and does not work well with time zones. It does, however, provide a 20-30% speed increase compared to standard Java. For further reading please visit the project site at http://joda-time.sourceforge.net).
Joda may be convenient for AS/400 machines.
On the other hand, Joda is unable to read time zone expressed with any number of z letters and/or at least three Z letters in a pattern.
yyyy-MM-dd HH:mm:ss


****************************
Java Default:
****************************

1.1 Date Format Pattern Syntax (Java)
Letter
Date or Time Component
Presentation
Examples
G
Era designator
Text
AD
Y
Year
Year
1996; 96
M
Month in year
Month
July; Jul; VII; 07; 7
w
Week in year
Number
27
W
Week in month
Number
2
D
Day in year
Number
189
d
Day in month
Number
10
F
Day of week in month
Number
2
E
Day in week
Text
Tuesday; Tue
a
Am/pm marker
Text
PM
H
Hour in day (0-23)
Number
0
k
Hour in day (1-24)
Number
24
K
Hour in am/pm (0-11)
Number
0
h
Hour in am/pm (1-12)
Number
12
m
Minute in hour
Number
30
s
Second in minute
Number
55
S
Millisecond
Number
970
z
Time zone
General time zone
Pacific Standard Time; PST; GMT-08:00
Z
Time zone
RFC 822 time zone
-0800
'
Escape for text/id
Delimiter
(none)
''
Single quote
Literal
'

The number of symbol letters you specify also determines the format. For example, if the "zz" pattern results in "PDT", then the "zzzz" pattern generates "Pacific Daylight Time". The following table summarizes these rules:

1.2 Rules for Date Format Usage (Java)
Presentation
Processing
Number of Pattern Letters
Form
Text
Formatting
1 - 3
short or abbreviated form, if one exists
Text
Formatting
>= 4
full form
Text
Parsing
>= 1
both forms
Year
Formatting
2
truncated to 2 digits
Year
Formatting
1 or >= 3
interpreted as Number.
Year
Parsing
1
intepreted literally
Year
Parsing
2
interpreted relative to the century within 80 years before or 20 years after the time when theSimpleDateFormat instance is created
Year
Parsing
>= 3
intepreted literally
Month
Both
1-2
interpreted as a Number
Month
Parsing
>= 3
interpreted as Text (using Roman numbers, abbreviated month name - if exists, or full month name)
Month
Formatting
3
interpreted as Text (using Roman numbers, or abbreviated month name - if exists)
Month
Formatting
>= 4
interpreted as Text (full month name)
Number
Formatting
minimum number of required digits
shorter numbers are padded with zeros
Number
Parsing
number of pattern letters is ignored (unless needed to separate two adjacent fields)
any form
General time zone
Both
1-3
short or abbreviated form, if has a name. Otherwise, GMT offset value (GMT[sign][[0]0-23]:[00-59])
General time zone
Both
>= 4
full form, , if has a name. Otherwise, GMT offset value (GMT[sign][[0]0-23]:[00-59])
General time zone
Parsing
>= 1
RFC 822 time zone form is allowed
RFC 822 time zone
Both
>= 1
RFC 822 4-digit time zone format is used ([sign][0-23][00-59])
RFC 822 time zone
Parsing
>= 1
General time zone form is allowed

Examples:

1.3 Date and Time Format Patterns and Results (Java)
Date and Time Pattern
Result
"yyyy.MM.dd G 'at' HH:mm:ss z"
2001.07.04 AD at 12:08:56 PDT
"EEE, MMM d, ''yy"
Wed, Jul 4, '01
"h:mm a"
12:08 PM
"hh 'o''clock' a, zzzz"
12 o'clock PM, Pacific Daylight Time
"K:mm a, z"
0:08 PM, PDT
"yyyyy.MMMMM.dd GGG hh:mm aaa"
02001.July.04 AD 12:08 PM
"EEE, d MMM yyyy HH:mm:ss Z"
Wed, 4 Jul 2001 12:08:56 -0700
"yyMMddHHmmssZ"
010704120856-0700
"yyyy-MM-dd'T'HH:mm:ss.SSSZ"
2001-07-04T12:08:56.235-0700

****************************
JODA:
****************************
2.1 Date Format Pattern Syntax (Joda)
Symbol
Meaning
Presentation
Examples
G
Era designator
Text
AD
C
Century of era (>=0)
Number
20
Y
Year of era (>=0)
Year
1996
y
Year
Year
1996
x
Week of weekyear
Year
1996
M
Month of year
Month
July; Jul; 07
w
Week of year
Number
27
D
Day of year
Number
189
d
Day of month
Number
10
e
Day of week
Number
2
E
Day of week
Text
Tuesday; Tue
a
Halfday of day
Text
PM
H
Hour of day (0-23)
Number
0
k
Clockhour of day (1-24)
Number
24
K
Hour of halfday (0-11)
Number
0
h
Clockhour of halfday (1-12)
Number
12
m
Minute of hour
Number
30
s
Second of minute
Number
55
S
Fraction of second
Number
970
z
Time zone
Text
Pacific Standard Time; PST
Z
Time zone offset/id
Zone
-0800; -08:00; America/Los_Angeles
'
Escape for text/id
Delimiter
(none)
''
Single quote
Literal
'

We can see from above table, although actual format strings for Java and Joda are almost 100% compatible with each other, still there are differences. The 'F' in default java is not supported in Joda.

Basically, 'F' means 'Day of week in month', for example, '2013-11-8' is the second friday in Nov of 2013, so 'F' will get 2 as result. While 'E' means 'Day of week' only, with the same example, '2013-11-8', 'E' will get 5 as result, because it's Friday, the fifth day in the week.

The number of symbol letters you specify also determines the format. The following table summarizes these rules:

2.2 Rules for Date Format Usage (Joda)
Presentation
Processing
Number of Pattern Letters
Form
Text
Formatting
1 - 3
short or abbreviated form, if one exists
Text
Formatting
>= 4
full form
Text
Parsing
>= 1
both forms
Year
Formatting
2
truncated to 2 digits
Year
Formatting
1 or >= 3
interpreted as Number.
Year
Parsing
>= 1
intepreted literally
Month
Both
1-2
interpreted as a Number
Month
Parsing
>= 3
interpreted as Text (using Roman numbers, abbreviated month name - if exists, or full month name)
Month
Formatting
3
interpreted as Text (using Roman numbers, or abbreviated month name - if exists)
Month
Formatting
>= 4
interpreted as Text (full month name)
Number
Formatting
minimum number of required digits
shorter numbers are padded with zeros
Number
Parsing
>= 1
any form
Zone name
Formatting
1-3
short or abbreviated form
Zone name
Formatting
>= 4
full form
Time zone offset/id
Formatting
1
Offset without a colon between hours and minutes
Time zone offset/id
Formatting
2
Offset with a colon between hours and minutes
Time zone offset/id
Formatting
>= 3
Full textual form like this: "Continent/City"
Time zone offset/id
Parsing
1
Offset without a colon between hours and minutes
Time zone offset/id
Parsing
2
Offset with a colon between hours and minutes


For more details, the official docs are the best place to go.

Reference:
Micosoft: StandardDate and Time Format Strings


No comments:

Post a Comment