net.snowflake.common.core.CalendarCache Maven / Gradle / Ivy
package net.snowflake.common.core;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.HashMap;
import java.util.TimeZone;
/**
* Created by mzukowski on 3/13/16.
*
* Implements a simple thread-local cache for GregorianCalendar objects.
* Note, by default it is not enabled, and will re-create the objects.
*
*/
public class CalendarCache
{
private static class CalendarCacheState
{
HashMap map;
boolean enabled;
/**
* If set, we will always produce clones of cached objects.
* This still makes it faster than completely new object, but makes
* objects safe for external operations that modify Calendar
* (e.g. SimpleDateFormat can change the timezone).
*/
boolean produceClones;
/** If set, we always use Gregorian calendar, even before 1582 */
boolean alwaysGregorian;
public CalendarCacheState()
{
map = new HashMap();
enabled = false;
produceClones = true;
alwaysGregorian = false;
}
};
/** Thread local state */
private static final ThreadLocal localState =
new ThreadLocal()
{
@Override protected CalendarCacheState initialValue()
{
return new CalendarCacheState();
}
};
/**
* Enable or disable the cache
* @param enabled true to enable cache or false
*/
public static void setEnabled(boolean enabled)
{
localState.get().enabled = enabled;
}
/**
* Configure the CalendarCache to produce clones of cached objects
* (default behavior) or not.
* It can be beneficial performance wise to not clone them, but it's
* possibly dangerous as _some_ operations using calendars
* (e.g. SimpleDateFormat) can modify the Calendar object.
*
* @param produceClones should it produce clones of cached objects.
*/
public static void setProduceClones(boolean produceClones)
{
localState.get().produceClones = produceClones;
}
/**
* Set if the the calendars produced should not observe Julian calendar
* before 1582.
*
* Calling this function also clears the cache.
*/
public static void setAlwaysGregorian(boolean alwaysGregorian)
{
localState.get().alwaysGregorian = alwaysGregorian;
// Clear the cache, in case old values had a different setting
localState.get().map.clear();
}
/**
* Helper function.
* Returns a GregorianCalendar object.
* @param timezone Timezone to create the calendar in.
* @param tzId The id of the timezone (e.g. "America/Los_Angeles")
* @param calId Explicit ID of the calendar. Can be used e.g.
* if more than one copy of the calendar for the same
* timezone is needed.
* Note, if specified, the caller is responsible for
* making sure it's always the same timezone.
* @return The GregorianCalendar object. Note, it can be reused by other
* consumers, so be careful changing any settings in it
*/
public static GregorianCalendar get(TimeZone timezone,
String tzId,
String calId)
{
CalendarCacheState state = localState.get();
GregorianCalendar res;
if (state.enabled)
{
res = state.map.get(calId);
if (res == null)
{ // Not found, create it
res = createCalendar(timezone, tzId);
// Save a fully-prepped entry in the cache
state.map.put(calId, res);
}
else
{ // Found in cache
// Verify it's the same timezone, just in case
if (timezone != null & !res.getTimeZone().hasSameRules(timezone))
{
throw new IllegalArgumentException(
"Cached timezone is not equivalent to the requested one:"
+ timezone + " VS " + res.getTimeZone());
}
// Verify it's the same gregorian offset, just in case
if (state.alwaysGregorian &&
res.getGregorianChange().getTime() != Long.MIN_VALUE)
{
throw new IllegalArgumentException(
"Cached calendar gregorian offset is not set as expected:"
+ res.getGregorianChange().getTime() + " VS " + Long.MIN_VALUE);
}
}
if (state.produceClones)
{
// Produce clones - for both newly created and previously cached calendars
res = (GregorianCalendar)res.clone();
}
else
{
// Returning a possibly previously used calendar, clear it
res.clear();
}
return res;
}
else
{
// Cache disabled, just create it
return createCalendar(timezone, tzId);
}
}
/** Create a properly initialized GregorianCalendar */
private static GregorianCalendar createCalendar(TimeZone timezone, String tzId)
{
if (timezone == null)
{
// If not specified, create a timezone from an id
timezone = TimeZone.getTimeZone(tzId);
}
// Create a new calendar
GregorianCalendar cal = new GregorianCalendar(timezone);
// Clear it, seems sometimes needed
cal.clear();
// Set always gregorian if needed
if (localState.get().alwaysGregorian)
{
cal.setGregorianChange(new Date(Long.MIN_VALUE));
}
return cal;
}
/**
* Return a GregorianCalendar object identified by id.
* If caching is enabled and an object with the same id existed, it will be returned,
* otherwise a new object will be created.
* @param timezone Timezone to create the calendar in
* @param calId Explicit ID of the calendar. Can be used e.g.
* if more than one copy of the calendar for the same
* timezone is needed.
* Note, if specified, the caller is responsible for
* making sure it's always the same timezone.
* @return The GregorianCalendar object. Note, it can be reused by other
* consumers, so be careful changing any settings in it
*/
public static GregorianCalendar get(TimeZone timezone, String calId)
{
return get(timezone, null, calId);
}
/**
* Return a cached GregorianCalendar object. If doesn't exist, will be created.
* @param timezone Timezone to create the calendar in
* @return The GregorianCalendar object. Note, it can be reused by other
* consumers, so do not change any non-basic settings in it
* (like date).
*/
public static GregorianCalendar get(TimeZone timezone)
{
// Use TimeZone id to lookup the Calendar
return get(timezone, null, timezone.getID());
}
/**
* Return a cached GregorianCalendar object. If doesn't exist, will be created.
* @param tzId The id of the timezone (e.g. "America/Los_Angeles")
* @return The GregorianCalendar object. Note, it can be reused by other
* consumers, so do not change any non-basic settings in it
* (like date).
*/
public static GregorianCalendar get(String tzId)
{
// Pass null as timezone - we'll create it when needed.
// We use tzId also as a calendar ID.
return get(null, tzId, tzId);
}
}
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