How to solve the issue of a jar file not connecting to the database.

If your IDEA packaged JAR file is unable to connect to the database, please check the following points:

1. Database configuration: Verify if the configuration file in the JAR package (such as application.properties or application.yml) has the correct database connection information set, including the database URL, username, and password. Make sure these configurations match your database server settings.
2. Database driver: Make sure the correct version of the database driver is included in the JAR file. You can manually add the database driver’s JAR file to the JAR package, or use a build tool (such as Maven or Gradle) to import dependencies.
3. Internet connection: Make sure your computer can establish a network connection with the database server. You can try using other database client tools such as MySQL Workbench to connect to the database and confirm if the database server is accessible.
4. Firewall configuration: If a firewall is enabled on your computer, please check to see if it allows the JAR file to access the network ports of the database server. You may need to add specific rules in the firewall settings to allow communication between the JAR file and the database server.

If the problem still cannot be solved after trying the above steps, you can attempt the following additional troubleshooting methods:

1. Log output: Add logging statements in the code to view error messages when connecting to the database. You can use a logging framework (such as log4j or slf4j) to record and output log information.
2. Debugging mode: set breakpoints in the code and use a debugger to track the execution process of the program. This can help you identify the issues, such as whether exceptions are thrown or if the code for connecting to the database is executed correctly.
3. Unit Testing: Create a simple unit test that includes code related to database connection. This will help you eliminate other factors and focus on debugging database connection issues.

If you are still unable to resolve the issue, we suggest providing more detailed information such as error logs and code examples so we can better assist you in solving the problem.