This Maven project shows how to use the connection pool included with the MariaDB JDBC driver and showcases the importance of using pooling when interacting with databases.

Run the app as is. See the error in the output (SQLException: too many connections). Change Service constructor to use a MariaDbPoolDataSource and run the app again. Now it works.

• Java 21 or later. Previous versions should work (update the version in the pom.xml file).
• Apache Maven.
• MariaDB server.
• An SQL client tool like mariadb, DBeaver, or an SQL integration for your IDE.

See the instructions here.

Insert some data:

INSERT INTO demo.programming_language(name, rating)
VALUES
    ('Java', 10),
    ('C++', 9);

Run the following from the command line:

git clone git@github.com:mariadb-developers/java-quickstart.git
cd java-quickstart/jdbc/mariadb-pool/
mvn package
java -jar target/mariadb-pool-1.0-SNAPSHOT.jar

The application simulates concurrent requests to the Service class, which reads data from the MariaDB database (you can configure the connection details in the constructor of this class). Currently, the application DOES NOT use a connection pool, but creates a new connection every time the service method is requested.

You'll see that some of the requests to the service work (printint data from the database), but eventually, you'll find some of them fail. For example, you probably see exceptions like:

java.sql.SQLException: Too many connections

This happens because the datbase can only have a limited number of opened connections. A database connection pool maintains a set of connections that threads can "borrow". The MariaDB JDBC driver (Connector/J) includes a connection pool ready to use.

To use a connection pool, just change the type of DataSource instanciated in the Service constructor from MariaDbDataSource to MariaDbPoolDataSource. Compile and run the app again and see how it can now handle all the requests without errors.