Why yoda time?

Original - https://mestachs.wordpress.com/tag/jodatime/

Don’t use java built-in classes, use jodatime and enforce this rule with sonar !

Don’t use java built-in classes

How many bugs in 5 lines of code ?

Date date = new Date(2007, 12, 13, 16, 40);
TimeZone zone = TimeZone.getInstance("Europe/Bruxelles");
Calendar cal = new GregorianCalendar(date, zone);
DateFormat fm = new SimpleDateFormat("HH:mm Z");
String str = fm.format(cal);

Just 6 bugs !

int year = 2007 - 1900;
int month = 12 - 1;
Date date = new Date(year, month, 13, 16, 40);
TimeZone zone = TimeZone.getInstance("Europe/Brussels");
Calendar cal = new GregorianCalendar(zone);
cal.setTime(date);
DateFormat fm = new SimpleDateFormat("HH:mm Z");
fm.setTimeZone(zone);
Date calDate = cal.getTime();
String str = fm.format(calDate);

If you want deeper explanations see this [presentation]

java.util.Date issues

• From JDK1.0
• Uses two digit years (from 1900)
• January is 0, December is 11
• Should have been immutable
• Most methods deprecated in JDK1.1
• Uses milliseconds from 1970 representation

java.util.Calendar issues

• From JDK1.1
• Uses subclasses for different calendar systems
• January is 0, December is 11
• Should have been immutable
• Uses dual representation internally
  • value for each field
  • milliseconds from 1970 representation
• Odd performance and bugs

java.util.DateFormat issues

• Pattern based date formatting
• “dd MMM yyyy”
• Requires Date object
• Not thread-safe : see rule findbugs : Multithreaded correctness – Call to static DateFormat
• Not especially fast
• Sun RFE to make thread-safe ignored

SQL – java.util.sql.Date, Time, Timestamp issues

Subclass java.util.Date

• Date extends Date (!)
• Time extends Date (!)
• Override superclass to block methods (throws Exception)
• Timestamp adds nanoseconds
• equals() broken
• All the problems of java.util.Date and more
• timezone problem new Time(long)

Avoid millis manipulation and let’s use Jodatime !

when playing with java.util.Date you end up doing calculation in millis

int days = 40;

Date now = new Date();

long nowMillis = now.getTime();

Timestamp nowTimestamp = new Timestamp(nowMillis);

long future = 3600 * 24 * days * 1000;

Timestamp expiryTimestamp = new Timestamp(nowMillis + future);

System.out.println("nowTimestamp " + nowTimestamp);

System.out.println("expiryTimestamp " + expiryTimestamp);

this last code sample contains a bug… int vs long for days !

see this explaination the expiryTimestamp is before the nowTimestamp for “large days count”

nowTimestamp  2011-02-04 12:45:40.381
expiryTimestamp 2011-01-25 19:42:53.085

now let’s write the same code with joda time

DateTime nowTimestamp2 = new DateTime();

System.out.println("nowTimestamp    " + nowTimestamp2);

System.out.println("expiryTimestamp " + nowTimestamp2.plusDays(days));

it’s more readable… and most important it return the correct value ;)

nowTimestamp  2011-02-04T12:45:40.443+01:00
expiryTimestamp 2011-03-16T12:45:40.443+01:00

Sonar to the rescue

sonar can detect these issues :

• Multithreaded correctness – Call to static Calendar
• Multithreaded correctness – Call to static DateFormat

to fix them with jodatime let’s use the DateTimeFormat.

fmt=DateTimeFormat.forPattern("MMMM, yyyy");
DateTime datetime = fmt.parseDateTime(duedate);

this one is threadsafe and can be static and final field. or use the toString

datetime.toString("dd:MM:yy");

but the step further is to banish jdk date from your code base !
To do so, let’s define sonar architectural constraint like

• Arch : avoid java.util.GregorianCalendar
• Arch : avoid java.util.Date
• Arch : avoid java.text.SimpleDateFormat
• Arch : avoid java.sql.Timestamp
• Arch : avoid java.sql.Date

to banish jdk dates from your model, you may implement hibernate usertype, jaxb adapter,…