Are you having difficulties with the problem “com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure“? Don’t worry, we are here to help you. Let’s follow our article, we will give you some solutions to fix this error.

How Does The Problem “com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure” Happen?

When you run your program, you easily get the following error message:

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

This error happens due to many reasons, such as:

• The JDBC URL’s port number is incorrect or missing.
• The DB server is offline.
• The DB server does not accept TCP/IP connections.
• The DB server is out of the connection.
• The hostname or IP address is incorrect in JDBC URL.
• The local DNS server does not recognize the hostname in JDBC URL.
• A firewall or proxy, for example, or something restricts connections between Java and the database.

How To Solve The Error “com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure”?

Method 1: Follow these steps

Follow these steps to fix the error “com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure”:

Step 1: First, you need to use ping to test and confirm them.

Step 2: Next, you must use the IP address in the JDBC URL instead or refresh a DNS server.

Step 3: Use the MySQL database’s my.cnf to confirm it.

Step 4: Launch the DB.

Step 5: Confirm whether MySQL is launched without the —skip-networking option or not.

Step 6: Relaunch the DB and modify your code so that it finally terminates connections.

Step 7: Finally, the firewall should be disabled or configured to allow/forward the port.

Method 2: Upgrade the IP address

Another method to solve the error “com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure” is upgrading the IP address. Let’s follow two steps below to do that:

Step 1: Opening the /etc/mysql/my.cnf file.

Step 2: Changing the bind-address like bind-address = 0.0.0.0.

Method 3: Restart the MySQL database

The Java program tries to establish a connection with a stopped MySQL server. Perhaps the MySQL database server was shutdown or not launched. Now you have to log in to the MySQL server to check if the database is active or to shut it down. The error “com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure” can be resolved by restarting the MySQL database. Let’s use this command to do that:

start or restart mysql database

Method 4: Verify the MySQL database’s port and specify the correct port number

On a port, the MySQL database is runned. The default port is 3306. The MySQL database should be configured to run on some different ports. Verify the MySQL database’s port and specify the correct port number in the jdbc url configuration. The jdbc url might miss the port number.

spring.datasource.url=jdbc:mysql://localhost:3306/test

Conclusion

We hope you will enjoy our article about the error. With this knowledge, we believe that you can fix your error: “com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure” quickly by following these steps! If you still have any other questions about fixing this syntax error, please leave a comment below. Thank you for reading!

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