mysql-connector 8.0中是否仍需用Class.forName()注册驱动？

Great question—this is a super common gotcha when upgrading to MySQL Connector/J 8.x, especially in Tomcat environments. Let’s break down exactly why this happens:

1. The Driver Class Name Changed in MySQL 8.x #

Starting with MySQL Connector/J 8.0, the official JDBC driver class was renamed from com.mysql.jdbc.Driver to com.mysql.cj.jdbc.Driver. The old com.mysql.jdbc.Driver still exists in 8.x as a legacy compatibility class, but here’s the key detail:

• JDBC 4.0’s automatic driver discovery relies on the META-INF/services/java.sql.Driver file inside the driver JAR. For Connector/J 8.x, this file lists only the new com.mysql.cj.jdbc.Driver, not the legacy class.

2. Tomcat’s Class Loader Behavior Can Block Auto-Discovery #

Tomcat uses a hierarchical class loader system where each web app has its own isolated class loader. While JDBC 4.0 should auto-discover drivers in your app’s WEB-INF/lib, two scenarios often break this with Connector/J 8.x:

• ServiceLoader fails to scan the web app’s JAR: In some Tomcat configurations, the ServiceLoader (the mechanism behind auto-discovery) doesn’t properly scan META-INF/services files in web app-specific JARs. This means the new com.mysql.cj.jdbc.Driver never gets registered with DriverManager. When you explicitly call Class.forName("com.mysql.jdbc.Driver"), you force the legacy driver class to load—and it has a static initializer that registers itself with DriverManager, which fixes the error.
• Missing required URL parameters (a related gotcha): MySQL 8.x requires extra parameters in the JDBC URL (like serverTimezone) to connect properly. If your URL doesn’t include these, even if the driver loads, it might reject the URL and throw the same "No suitable driver" error. Since your issue was fixed by adding Class.forName, this isn’t the root cause here, but it’s worth checking for future use.

3. The Proper Fixes #

Instead of relying on the legacy driver class, here’s how to get auto-discovery working again (or use the explicit loading correctly):

• Update your JDBC URL: Add required 8.x parameters, e.g., jdbc:mysql://localhost:3306/mysql?serverTimezone=UTC&useSSL=false (adjust timezone and SSL settings to match your environment).
• Use the new driver class explicitly: If auto-discovery still fails, replace Class.forName("com.mysql.jdbc.Driver") with Class.forName("com.mysql.cj.jdbc.Driver") to use the official 8.x driver.
• Verify driver placement: Ensure mysql-connector-java-8.0.11.jar is in your web app’s WEB-INF/lib directory (not Tomcat’s global lib folder). Global placement can cause class loader conflicts that block auto-discovery.

To sum it up: The auto-discovery wasn’t working because the new 8.x driver class wasn’t being registered automatically (thanks to Tomcat’s class loader quirks), and the legacy class you loaded manually filled that gap. Switching to the new driver class and fixing your URL will let you drop the Class.forName call again if you want.

内容的提问来源于stack exchange，提问作者Shafin Mahmud