Скачать или смотреть Reading MySQL DATETIME into java.sql.Date with JDBI

Learn how to handle MySQL DATETIME data types in Java using JDBI. This guide provides clear solutions and best practices for mapping DATETIME values without errors.
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This video is based on the question https://stackoverflow.com/q/66356957/ asked by the user 'semej' ( https://stackoverflow.com/u/15277461/ ) and on the answer https://stackoverflow.com/a/66368598/ provided by the user 'Yurii Melnychuk' ( https://stackoverflow.com/u/6099243/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction: The Problem with MySQL DATETIME and JDBI

When working with Java applications that interact with a MySQL database, handling DATETIME fields can sometimes be tricky. Developers often face issues while reading these fields into Java types like java.sql.Date, java.util.Date, or java.sql.Timestamp when using JDBI (Java Database Interface).

In this guide, we'll explore a common scenario involving a user table with a DATETIME field for storing birth dates and discuss how to effectively retrieve these values without encountering exceptions like NoSuchMapperException or NullPointerException.

Understanding the MySQL DATETIME Field

MySQL Table Structure

Consider a user table with the following structure:

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In this case, the birth_date is a DATETIME field, and your objective is to retrieve this field without error through JDBI.

Common Mistakes When Fetching DATETIME

While attempting to fetch the birth_date, developers often try variations such as:

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or

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Unfortunately, these approaches can lead to common errors, namely:

NoSuchMapperException: This error indicates that JDBI lacks a mapper for the specified type.

NullPointerException: Occurs when the retrieved value is null, suggesting potential issues with database connectivity or data.

The Solution: Correctly Configuring JDBI

To properly handle MySQL DATETIME types, here are the steps you should follow:

Step 1: Create a Custom Mapper

To read DATETIME values, create a custom RowMapper that JDBI will use to map your birth_date column to a Java type.

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Step 2: Update your DAO Interface

Ensure your DAO interface correctly uses the mapper:

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Step 3: Check Database Data

If you're receiving NullPointerExceptions, double-check your database to verify that the birth_date field actually contains valid data. Empty or incorrect values could result in unexpected null references.

Step 4: Use the Correct JDBI Setup

When initializing JDBI, ensure you're registering the SQL Object plugin:

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This ensures that your annotations, including mappers, are recognized and correctly processed by JDBI.

Sample Code: Putting It All Together

Here's a complete example demonstrating how to set up your test for reading DATETIME values:

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Output

The expected output should show a correctly formatted date, proving that the fetch was successful:

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Dependencies

Ensure you have the following dependencies in your pom.xml:

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Conclusion

Working with MySQL's DATETIME type in Java through JDBI can be performed effortlessly if you follow the correct setup and ensure your data is in order. By implementing a custom RowMapper and carefully configuring your DAO interfaces, you can retrieve DATETIME values without encountering common pitfalls.

Stay tuned for more insightful posts on database management and Java programming!