HikariCP validates a connection before handing it to your application using a connection test query or JDBC-standard connection validation methods, depending on your configuration:
🔹 1. Connection test query (connectionTestQuery)
You can explicitly set a lightweight SQL statement (e.g., SELECT 1) that HikariCP will execute to check if the connection is still valid before giving it out.
Example:
spring.datasource.hikari.connection-test-query=SELECT 1
🔹 2. JDBC isValid() method (preferred)
By default, HikariCP uses the JDBC Connection.isValid(timeout) method to validate a connection if no connectionTestQuery is provided.
This is more efficient than a query for modern drivers because it avoids unnecessary SQL statements.
The validationTimeout setting controls how long HikariCP waits for a response during this check.
🔹 3. When validation happens
HikariCP doesn’t validate idle connections continuously by default — instead, it validates them just before handing them out to the application, minimizing overhead.
🔹 4. Configuration example for validationTimeout
spring.datasource.hikari.validation-timeout=5000 # 5 seconds
✅ Key point:
Using Connection.isValid() is usually faster and more efficient, but if your driver doesn’t support it properly, falling back to a simple connectionTestQuery is a reliable alternative.