CODEWITHSUNDEEP
java
Rikki Ahuja
Rikki Ahuja

Reputation: 11

Compare database time with current time

I need to compare current time with the time that i am getting from database. I am getting time from database in Java class in java.sql.Time format (16:12:00).

I just need to display a error message if current time matches with the time present in DB.

Upvotes: 0

Views: 1276

Answers (2)

Martin
Martin

Reputation: 1150

To compare your current time with the time from the database you could simply construct a sql.Time from System.currentTimeMillis() and compare the two toString()s like so:

java.sql.Time serverTime = getServerTime();
java.sql.Time currentTime = new java.sql.Time(System.currentTimeMillis());

if(serverTime.toString().compareTo(currentTime.toString()) == 0)
{
   //yay
}
else //nay

You could also compare the two sql.Time's directly using it's compareTo method, but this is trickier. This is because even though sql.Time's setDate/Year/Month is deprecated and will throw an exception if you use them( which makes sense because they're not a date, only a time) the sql.Time's compareTo uses its superclass implementation, which means it compares not only the time but also the date, which sucks 'cus your database sql.Time object will probably always have the date 1970.01.01 whereas any sql.Time you construct off of System.currentTimeMillis() will have the current date. You can get around this by using a Calendar object as shown.

Calendar tmp = new GregorianCalendar();
tmp.setTimeInMillis(System.currentTimeMillis());
tmp.set(Calendar.YEAR, 1970);
tmp.set(Calendar.MONTH, 0); // 0 == January
tmp.set(Calendar.DATE, 1);
tmp.set(Calendar.MILLISECOND, 0);

java.sql.Time currentTime = new java.sql.Time(c.toInstant().toEpochMilli());        
java.sql.Time serverTime = getServerTime();

if(currentTime.compareTo(serverTime) == 0)
{
   //yay
}
else //nay

Or you could compare the long times directly as in Simone Gianni's answer, which would probably be the more efficient solution.

Upvotes: 0

Simone Gianni
Simone Gianni

Reputation: 11672

When dealing with dates and times, you can use one of the many libraries like Joda Time, or you can simply consider a time as a given millisecond since 1/1/1970 (unix epoch), expressed as a normal long.

To convert a java.util.Date, or a java.sql.Time,Date etc.. that extends from java.util.Date, to a simple long, you can call getTime() : http://docs.oracle.com/javase/6/docs/api/java/util/Date.html#getTime()

Current time, expressed as milliseconds from unix epoch so comparable with results of getTime(), can be obtained with System.currentTimeMillis();

Once you have that, comparing it is very easy :

Time dbTime = // the time you obtained from the db
long dbLong = dbTime.getTime();
long now = System.currentTimeMillis();

if (dbLong < now) // data in the db is in the past
if (dbLong > now) // data in the db is in the future
if (dbLong == now) // data in the db is exactly now

Take care of the dbLong == now, cause it's precise to the millisecond, so it will rarely happen in practice, unless you use a range or reduce the precision, say, to the second or minute :

long dbLongSeconds = dbLong / 1000;
long dbLongMinutes = dbLong / (60*1000);
long nowSeconds = now / 1000;
long nowMinutes = now / (60*1000);

if (dbLongSeconds == nowSeconds) // data in the db is in this second
if (dbLongMinutes == nowMinutes) // data in the db is in this minute

If you need more sophisticated comparisons, like day or month, you should use either a library like Joda Time, or built in classes like Calendar, cause the math is way more complex given how western calendar divides the year.

Upvotes: 1

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