Question

In a java application what would a good compromise in terms of extracing and inputting date information with a MySQL database using a mix of datetimes and timestamps?

Answer 1

In Java side, the date is usually represented by the (poorly designed, but that aside) java.util.Date. It is basically backed by the Epoch time in flavor of a long, also known as a timestamp. It contains information about both the date and time parts. In Java, the precision is in milliseconds.

In SQL side, there are several standard date and time types, DATE, TIME and TIMESTAMP (at some DB’s also called DATETIME), which are represented in JDBC as java.sql.Date, java.sql.Time and java.sql.Timestamp, all subclasses of java.util.Date. The precision is DB dependent, often in milliseconds like Java, but it can also be in seconds.

In contrary to java.util.Date, the java.sql.Date contains only information about the date part (year, month, day). The Time contains only information about the time part (hours, minutes, seconds) and the Timestamp contains information about the both parts, like as java.util.Date does.

The normal practice to store a timestamp in the DB (thus, java.util.Date in Java side and java.sql.Timestamp in JDBC side) is to use PreparedStatement#setTimestamp().

java.util.Date date = getItSomehow();
Timestamp timestamp = new Timestamp(date.getTime());
preparedStatement = connection.prepareStatement("SELECT * FROM tbl WHERE ts > ?");
preparedStatement.setTimestamp(1, timestamp);

The normal practice to obtain a timestamp from the DB is to use ResultSet#getTimestamp().

Timestamp timestamp = resultSet.getTimestamp("ts");
java.util.Date date = timestamp; // You can just upcast.