CODEWITHSUNDEEP
javajpaentity
Carlos Goce
Carlos Goce

Reputation: 1665

Choosing between java.util.Date or java.sql.Date

Should I use java.util.Date or java.sql.Date?

I have a VisualFox database and I have retrieved the entities with the IntelliJ Idea wizard using an appropiate jdbc type 4 driver.

The ide (or the driver) has created the date fields as Timestamp. However, the date fields are not timestamps but Date fields, they store year, month and day only.

So I wonder if I should switch to java.util.Date or java.sql.Date. At first glance I thought that java.sql.Date should be the appropiate one, but it has many methods declared as deprecated.

Upvotes: 22

Views: 22622

Answers (4)

Basil Bourque
Basil Bourque

Reputation: 340118

tl;dr

Should I use java.util.Date or java.sql.Date?

Neither.

Both are obsolete as of JDBC 4.2 and later. Use java.time classes instead.

  • date-only value
    For a database type akin to SQL-standard DATE, use java.time.LocalDate.
    • LocalDate ld = myResultSet.getObject( … , LocalDate.class ) ;
    • myPreparedStatement.setObject( ld , … ) ;
  • date with time-of-day in UTC value
    For a database type akin to SQL-standard TIMESTAMP WITH TIME ZONE, use java.time.Instant.
    • Instant instant = myResultSet.getObject( … , Instant.class ) ;
    • myPreparedStatement.setObject( instant , … ) ;

Details

The question and other answers seem to be over-thinking the issue. A java.sql.Date is merely a java.util.Date with its time set to 00:00:00.

From the java.sql.Date doc (italicized text is mine)…

Class Date

java.lang.Object

    java.util.Date        ← Inherits from j.u.Date

        java.sql.Date

…

A thin wrapper around a millisecond value that allows JDBC to identify this as an SQL DATE value. A milliseconds value represents the number of milliseconds that have passed since January 1, 1970 00:00:00.000 GMT.  ← Time-of-day set to Zero, midnight GMT/UTC

To conform with the definition of SQL DATE, the millisecond values wrapped by a java.sql.Date instance must be 'normalized' by setting the hours, minutes, seconds, and milliseconds to zero in the particular time zone with which the instance is associated.

Date-Only versus Date-Time

The core problem is:

  • SQL
    In SQL, the DATE data type stores a date-only, without a time-of-day.
  • JAVA
    In the badly designed date-time library bundled with the early versions of Java, they failed to include a class to represent a date-only.

Instead of creating a date-only class, the Java team made a terrible hack. They took their date-time class (the misnamed java.util.Date class, containing both date and time) and extended it to have an instance set its time-of-day to midnight UTC, 00:00:00. That hack, that subclass of j.u.Date, is java.sql.Date.

All this hacking, poor design, and misnaming has made a confusing mess.

Which To Use

So when to use which? Simple, after cutting through the confusion.

  • When reading or writing to a database’s date-only column, use java.sql.Date as it clumsily tries to mask its time-of-day.
  • Everywhere else in Java, where you need a time-of-day along with your date, use java.util.Date.
  • When you have a java.sql.Date in hand but need a java.util.Date, simply pass the java.sql.Date. As a subclass, a java.sql.Date is a java.util.Date.

Even Better

In modern Java, you now have a choice of decent date-time libraries to supplant the old and notoriously troublesome java.util.Date, Calendar, SimpleTextFormat, and java.sql.Date classes bundled with Java. The main choices are:

Both offer a LocalDate class to represent a date only, with no time-of-day and no time zone.

A JDBC driver updated to JDBC 4.2 or later can be used to directly exchange java.time objects with the database. Then we can completely abandon the ugly mess that is the date-time classes in the java.util.* and java.sql.* packages.

setObject | getObject

This article published by Oracle explains that the JDBC in Java 8 has been updated transparently to map a SQL DATE value to the new java.time.LocalDate type if you call getObject and setObject methods.

In obtuse language, the bottom of the JDBC 4.2 update spec confirms that article, with new mappings added to the getObject and setObject methods. 

myPreparedStatement.setObject( … , myLocalDate ) ;

…and…

LocalDate myLocalDate = myResultSet.getObject( … , LocalDate.class ) ;

Convert

The spec also says new methods have been added to the java.sql.Date class to convert back and forth to java.time.LocalDate.

Time Zone

The old java.util.Date, java.sql.Date, and java.sql.Timestamp are always in UTC. The first two (at least) have a time zone buried deep in their source code but is used only under-the-surface such as the equals method, and has no getter/setter.

More confusingly, their toString methods apply the JVM’s current default time zone. So to the naïve programmer it seems like they have a time zone but they do not.

Both the buried time zone and the toString behavior are two of many reasons to avoid these troublesome old legacy classes.

Write your business logic using java.time (Java 8 and later). Where java.time lacks, use Joda-Time. Both java.time and Joda-Time have convenient methods for going back and forth with the old classes where need be.

Replacements:

The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds (up to nine (9) digits of a decimal fraction).

All three java.time.Local… classes are all lacking any concept of time zone or offset-from-UTC.

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.

Upvotes: 45

Sandeep Kumar
Sandeep Kumar

Reputation: 702

According to Java doc, it is suggested to use appropriate Date type as per underlying database. However, with Java 8, a rich set of classes under java.time package have been provided and it must be used if application is written with Java 8.

The class javaxjava.sql.Date extends java.util.Date with minor changes for miliseconds container so that it can support the Database DATE type effectively. This, we can save the @Temporal annotation typing from entity class.

However, java.util.Date could be used for better scalability in entire application so that it can be easily used to store time along with date.

Upvotes: 0

Petr Mensik
Petr Mensik

Reputation: 27536

Well, according to this article you can use javax.sql.Date without @Temporal annotation which can save some coding from you. However java.util.Date is easier to use across your whole application.

So I would use 

@Column(name = "date")
@Temporal(TemporalType.DATE)
private java.util.Date date;

Upvotes: 3

kostja
kostja

Reputation: 61578

In general, I find it advisable to use the java.util.Date, since you can use it anywhere in your program without either converting the type or polluting your application with SQL-specific code.

I am not aware of a scenario where 'java.sql.Date' would be a better fit.

Upvotes: 2

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