Pattern: Static SimpleDateFormat field
Issue: -
SimpleDateFormat objects should not be used as static fields. SimpleDateFormats are inherently unsafe for multi-threaded use. Sharing a single instance across thread boundaries without proper synchronization will result in erratic behavior of the application.
Under 1.4 problems seem to surface less often than under Java 5 where you will probably see random ArrayIndexOutOfBoundsException or IndexOutOfBoundsException in sun.util.calendar.BaseCalendar.getCalendarDateFromFixedDate(). You may also experience serialization problems. Using an instance field or a ThreadLocal is recommended.
Examples:
// Violations
class SomeClass {
static SimpleDateFormat dateFormat1
static java.text.SimpleDateFormat dateFormat2
static final DATE1 = new SimpleDateFormat()
static final DATE2 = new SimpleDateFormat('MM/dd')
static final DATE3 = new SimpleDateFormat('MM/dd', DateFormatSymbols.instance)
static date4 = new SimpleDateFormat('MM/dd', Locale.FRANCE)
static date5 = new java.text.SimpleDateFormat('MM/dd')
}
// These usages are OK
class SomeCorrectClass {
private SimpleDateFormat calendar1
static ThreadLocal<SimpleDateFormat> calendar2
}