What's the Difference Between `java.util.Date` and `java.sql.Date` in Java?

Differentiating java.util.Date and java.sql.Date

Understanding the Distinction

Java offers two Date classes with very similar names: java.util.Date and java.sql.Date. This can lead to confusion, especially when working with database connectivity via JDBC.

Key Differences

The primary difference lies in the representation of date and time data:

• java.sql.Date: Represents SQL DATE values, storing only year, month, and day. It disregards time components and is timezone-agnostic.
• java.util.Date: Stores date and time together as milliseconds since midnight, January 1, 1970, UTC.

Implications for Database Connectivity

When working with databases, it's crucial to match the JDBC Date class with the appropriate SQL data type.

• For SQL DATE (e.g., DATE or YYYY-MM-DD columns), use java.sql.Date.
• For SQL TIME (e.g., TIME or HH:MM:SS columns), use java.sql.Time.
• For SQL TIMESTAMP (e.g., TIMESTAMP or YYYY-MM-DD HH:MM:SS columns), use java.sql.Timestamp.

Handling Date Consistency

One common pitfall is that using java.util.Date with PreparedStatements can lead to inconsistencies if the driver assumes it represents a different SQL type. To avoid this, use the appropriate setters, such as setDate() for java.sql.Date.

Avoid Date Classes for Portability

The author strongly advocates against using any of the Java Date classes when working with database date and time values. Instead, it suggests storing milliseconds/nanoseconds as plain longs and managing date and time conversions manually with external libraries like Joda-Time or Java 8 Time API. This ensures portability and avoids potential issues with timezone handling and SQL type conversions.

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