You can use this code to get the required results

protected Timestamp timestamp = new Timestamp(Calendar.getInstance().getTimeInMillis());


protected String today_Date=timestamp.toString().split(" ")[0];

Here you add/get date + time as key in the map. It will not work because you have to add the date without time if you want to be able to have the same key for same date but with different time.
Note that you should use LocalDateTime instead of Date that is a better designed API and that has the advantage to be immutable, which is advised for map keys.

With a few change you could do that :

LocalDate date = invoiceHeader.getInvoice_Date().toLocalDate();
if(map.containsKey(date)){
    map.get(date).add(invoiceId);        
}
else{    
    List<Integer> invoicesList = new ArrayList<>();
    invoicesList.add(invoiceId);
    map.put(date,invoicesList);
 }

With Map.computeIfAbsent() that provides a fluent API : you could simplify the whole logic such as :

LocalDate date = invoiceHeader.getInvoice_Date().toLocalDate();
map.computeIfAbsent(date, k-> new ArrayList<>()).add(invoiceId);

// timestamp to Date
long timestamp = 5607059900000; //Example -> in ms
Date d = new Date(timestamp );

// Date to timestamp
long timestamp = d.getTime();

//If you want the current timestamp :
Calendar c = Calendar.getInstance();
long timestamp = c.getTimeInMillis();

The accepted answer by Yatendra Goel is correct.

Joda-Time

For fun, here's the same kind of code using the Joda-Time 2.3 library.

Note that Joda-Time is now in maintenance mode. The team advises migration to java.time. See my other Answer for java.time code.

FYI… India is five and a half hours ahead of UTC/GMT. Hence the thirty minute difference in the outputs below.

String input = "2014-02-15 05:18:08";
input = input.replace( " ", "T" ); // Replace space in middle with a "T" to get ISO 8601 format.

// Parse input as DateTime in UTC/GMT.
DateTime dateTimeUtc = new DateTime( input, DateTimeZone.UTC );
// Adjust to India time.
DateTimeZone timeZone = DateTimeZone.forID( "Asia/Kolkata" );
DateTime dateTime = dateTimeUtc.withZone( timeZone );

// Using "en" for English here because (a) it is irrelevant in our case, and (b) I don't know any Indian language codes.
java.util.Locale localeIndiaEnglish = new Locale( "en", "IN" ); // ( language code, country code );
DateTimeFormatter formatter = DateTimeFormat.forStyle( "SS" ).withLocale( localeIndiaEnglish ).withZone( timeZone );
String output = formatter.print( dateTime );

DateTimeFormatter formatterDateOnly = DateTimeFormat.forPattern( "dd-MM-yyyy" ).withLocale( localeIndiaEnglish ).withZone( timeZone );
DateTimeFormatter formatterTimeOnly = DateTimeFormat.forPattern( "hh:mm:ss a" ).withLocale( localeIndiaEnglish ).withZone( timeZone );
String dateOnly = formatterDateOnly.print( dateTime );
String timeOnly = formatterTimeOnly.print( dateTime );

Dump to console…

System.out.println( "input: " + input );
System.out.println( "dateTimeUtc: " + dateTimeUtc );
System.out.println( "dateTime: " + dateTime );
System.out.println( "output: " + output );
System.out.println( "dateOnly: " + dateOnly );
System.out.println( "timeOnly: " + timeOnly );

When run…

input: 2014-02-15T05:18:08
dateTimeUtc: 2014-02-15T05:18:08.000Z
dateTime: 2014-02-15T10:48:08.000+05:30
output: 15/2/14 10:48 AM
dateOnly: 15-02-2014
timeOnly: 10:48:08 AM

Here is what I used to get today's date with time set to 00:00:00:

DateFormat formatter = new SimpleDateFormat("dd/MM/yyyy");

Date today = new Date();

Date todayWithZeroTime = formatter.parse(formatter.format(today));

If I have understood the question correctly 2014-09-01 10:00:00.000 is in a string and 10:00:00 has to be extracted from that. Given below is my solution.

• First split the string with space as the delimiter.
• Then from that take the second part of the string.
• After that split the string again using . as the delimiter and take the first sting from that.

The above things are done using the line.

str.split("\\s")[1].split("\\.")[0];

COMPLETE CODE

String str = new String("2014-09-01 10:00:00.000");
String time = str.split("\\s")[1].split("\\.")[0];
System.out.print(time);

OUTPUT

10:00:00

For more details check the links given below:

• String.split().
• Patterns

Use java.util.Date class instead of Timestamp.

String timeStamp = new SimpleDateFormat("yyyy.MM.dd.HH.mm.ss").format(new java.util.Date());

This will get you the current date in the format specified.

tl;dr

java.sql.Timestamp                  
.valueOf(                           // Class-method parses SQL-style formatted date-time strings.
    "2007-11-11 12:13:14"
)                                   // Returns a `Timestamp` object.
.toInstant()                        // Converts from terrible legacy classes to modern *java.time* class.

java.sql.Timestamp.valueOf parses SQL format

If you can use the full four digits for the year, your input string of 2007-11-11 12:13:14 would be in standard SQL format assuming this value is meant to be in UTC time zone.

The java.sql.Timestamp class has a valueOf method to directly parse such strings.

String input = "2007-11-11 12:13:14" ;
java.sql.Timestamp ts = java.sql.Timestamp.valueOf( input ) ;

java.time

In Java 8 and later, the java.time framework makes it easier to verify the results. The j.s.Timestamp class has a nasty habit of implicitly applying your JVM’s current default timestamp when generating a string representation via its toString method. In contrast, the java.time classes by default use the standard ISO 8601 formats.

System.out.println( "Output: " + ts.toInstant().toString() );

Try this -

SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss.S");
String valueFromDB = "2012-12-31 00:00:00.0";
Date d1 = sdf1.parse(valueFromDB);
SimpleDateFormat sdf = new SimpleDateFormat("dd-MM-yyyy");
String dateWithoutTime = sdf.format(d1);
System.out.println("sdf.format(d) " + dateWithoutTime);

java.time.Instant.ofEpochSecond

Java 8 introduced a new API for working with dates and times: the java.time package.

With java.time you can parse your count of whole seconds since the epoch reference of first moment of 1970 in UTC, 1970-01-01T00:00Z. The result is an Instant.

Instant instant = Instant.ofEpochSecond( timeStamp );

If you need a java.util.Date to interoperate with old code not yet updated for java.time, convert. Call new conversion methods added to the old classes.

Date date = Date.from( instant );