How to Troubleshoot 'Communications link failure' Exceptions in Java MySQL JDBC Connections?

Troubleshooting "Communications link failure" Exception in Java MySQL JDBC Connection

This error ("com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure") arises when attempts to establish a connection to a MySQL database encounter an unexpected termination. The communication breakdown can stem from various causes.

To pinpoint the root cause, examine the entire stack trace, where you're likely to find a "SQLException: Connection refused" or "SQLException: Connection timed out" exception.

Potential Causes:

• Incorrect IP address or hostname in the JDBC URL
• DNS server unrecognized hostname in the JDBC URL
• Missing or incorrect port number in the JDBC URL
• Deactivated database server
• Disabled TCP/IP connections on the database server
• Interception of connections (e.g., firewall, proxy)

Troubleshooting Steps:

• Verify and test with a "ping" command
• Refresh DNS and consider using IP address in JDBC URL
• Confirm port number in MySQL configuration file
• Restart the database server
• Ensure "mysqld" does not include the "--skip-networking" option
• Disable or configure firewall/proxy to allow port access

Optimization Note:

Avoid loading the JDBC driver on every connection call. Instead, load it once during program initialization.

The above is the detailed content of How to Troubleshoot 'Communications link failure' Exceptions in Java MySQL JDBC Connections?. For more information, please follow other related articles on the PHP Chinese website!