How to convert Calendar to java.sql.Date in Java?

java

date-conversion

calendar

sql-date

byAnton Shumikhin·Sep 13, 2024

Convert Calendar to java.sql.Date as follows:

java.sql.Date sqlDate = new java.sql.Date(Calendar.getInstance().getTimeInMillis());

Briefly, getTimeInMillis() extracts the time in milliseconds from the Calendar object, and the java.sql.Date constructor uses it to establish the SQL date.

Handling timezones

Addressing time zones is crucial when transforming a Calendar object to java.sql.Date. Below is how to work around timezone discrepancies:

Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
java.sql.Date date = new java.sql.Date(calendar.getTimeInMillis());

Essentially, this ensures a mutable Calendar object, susceptible to time zone variations, reliably converts into an immutable java.sql.Date object.

Managing exceptions

Incorporating comprehensive error handling is vital to ensure a smooth conversion process. Behavior during exceptions like database insert failure can be handled:

try {
    // Pretend you're cupid shooting an arrow(index), but instead of love you're inserting a date.
    PreparedStatement stmt = connection.prepareStatement("INSERT INTO events (date_field) VALUES (?)");
    stmt.setDate(1, new java.sql.Date(Calendar.getInstance().getTimeInMillis()));
    stmt.executeUpdate();
} catch (SQLException e) {
    e.printStackTrace(); // Spilled some coffee? Let's find where it happened.
}

It's all a game of catch and SQLException. Dodge those crashing exceptions!

Paying attention to the map

Keep an eye on field mapping when setting a date in a database:

The target field in the database must be date compatible, such as DATE, DATETIME, or similar data types.
The stmt.setDate(index, date) method dictates the position of the place you insert the date in your SQL statement. Make sure it points to the correct layer in your SQL lasagna.
Indices in SQL are like humans, they start from 1.

Conversion roulette

Occasionally, you'll need to convert a java.util.Date to a java.sql.Date; proceed as follows:

Date utilDate = new java.util.Date();
java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());

Herein, we're converting java.util.Date, which you can fetch right away from a Calendar instance using getTime(), into java.sql.Date.

Date field gotchas

While inserting your shiny new java.sql.Date into a database, validate all details of the date field:

Format check: Does the date need a Y2K-friendly YYYY-MM-DD format?
Constraints: NOT NULL and CHECK constraints can be a nasty surprise!
Default value: Any default value sneaking up to spoil your insert?

Back to the future (planning)

Before conversion, set the Calendar to the desired future date and time:

Calendar cal = Calendar.getInstance();
cal.set(Calendar.YEAR, 2100); // Who wants to party like it's 2100?
cal.set(Calendar.MONTH, Calendar.APRIL);
cal.set(Calendar.DAY_OF_MONTH, 1);
java.sql.Date sqlDate = new java.sql.Date(cal.getTimeInMillis());