[java] What is the use of the @Temporal annotation in Hibernate?

The Hibernate Documentation has the information below for the @Temporal annotation:

In plain Java APIs, the temporal precision of time is not defined. When dealing with temporal data you might want to describe the expected precision in database. Temporal data can have DATE, TIME, or TIMESTAMP precision (ie the actual date, only the time, or both). Use the @Temporal annotation to fine tune that.

What does temporal precision of time is not defined mean? What is temporal data and its precision? How does it fine tune?

If you're looking for short answer:

In the case of using java.util.Date, Java doesn't really know how to directly relate to SQL types. This is when @Temporal comes into play. It's used to specify the desired SQL type.

Source: Baeldung

Temporal types are the set of time-based types that can be used in persistent state mappings.

The list of supported temporal types includes the three java.sql types java.sql.Date, java.sql.Time, and java.sql.Timestamp, and it includes the two java.util types java.util.Date and java.util.Calendar.

The java.sql types are completely hassle-free. They act just like any other simple mapping type and do not need any special consideration.

The two java.util types need additional metadata, however, to indicate which of the JDBC java.sql types to use when communicating with the JDBC driver. This is done by annotating them with the @Temporal annotation and specifying the JDBC type as a value of the TemporalType enumerated type.

There are three enumerated values of DATE, TIME, and TIMESTAMP to represent each of the java.sql types.

use this

@Temporal(TemporalType.TIMESTAMP)
@Column(name="create_date")
private Calendar createDate;

public Calendar getCreateDate() {
    return createDate;
}

public void setCreateDate(Calendar createDate) {
    this.createDate = createDate;
}

We use @Temporal annotation to insert date, time or both in database table.Using TemporalType we can insert data, time or both int table.

@Temporal(TemporalType.DATE) // insert date
@Temporal(TemporalType.TIME) // insert time
@Temporal(TemporalType.TIMESTAMP) // insert  both time and date.

I use Hibernate 5.2 and @Temporal is not required anymore.
java.util.date, sql.date, time.LocalDate are stored into DB with appropriate datatype as Date/timestamp.

@Temporal is a JPA annotation which can be used to store in the database table on of the following column items:

1. DATE (java.sql.Date)
2. TIME (java.sql.Time)
3. TIMESTAMP (java.sql.Timestamp)

Generally when we declare a Date field in the class and try to store it.
It will store as TIMESTAMP in the database.

@Temporal
private Date joinedDate;

Above code will store value looks like 08-07-17 04:33:35.870000000 PM

If we want to store only the DATE in the database,
We can use/define TemporalType.

@Temporal(TemporalType.DATE)
private Date joinedDate;

This time, it would store 08-07-17 in database

There are some other attributes as well as @Temporal which can be used based on the requirement.