Com. Mysql. Jdbc. Exceptions. Jdbc4. Communicationsexception: Communications Link Failure

In my case, I needed to do a replacement of Localhost to the actual database server IP address

Instead of

 Connection con = DriverManager.getConnection(
 "jdbc:mysql://localhost:3306/DBname", "root", "root");

I needed

 Connection con = DriverManager.getConnection(
 "jdbc:mysql://192.100.0.000:3306/DBname", "root", "root");

I catch this exception when Java out of heap. If I try to put in RAM many data items - first I catch "Communications link failure" and next "OutOfMemoryError".

I logged it and I decrease memory consumption (delete 1/2 data) and all ok.

This com.mysql.jdbc.exceptions.jdbc4.CommunicationsException exception occurs if your database connection is idle for long time.

This idle connection returns true on connection.isClosed(); but if we try to execute statement then it will fire this exception so I will suggest to go with database pooling.

In my case, the solution was to add the expected TLS protocol to the connection string like this:

jdbc:mysql://localhost:3306/database_name?enabledTLSProtocols=TLSv1.2

In my case, turn out to be that the version of mysql-connector-java was too old.

In my demo, I somehow use mysql-connector-java like this:

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.9</version>
</dependency>

But in the develop environment, I use this:

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.31</version>
</dependency>

And my MySQL version was 5.1.48(yes, it is old, just for mimic the product version). So I met the same error.

Since the reason is found, the solution is found, too. Match the version!

I've been having the same problem for hours. I'm using MAMP Server

Instead of using localhost:[Apache Port], use your MySQL port.

Below is the default MySQL Port for MAMP server.

String url = "jdbc:mysql://localhost:8889/db_name";

Connection conn = DriverManager.getConnection(url, dbUsername, dbPassword);

This error may also happen if Java tries to connect to MySQL over SSL, but something goes wrong. (In my case, I was configuring Payara Server 5.193.1 connection pools to MySQL.)

Some people suggested setting useSSL=false. However, since Connector/J version 8.0.13, that setting is deprecated. Here's an excerpt from MySQL Connector/J 8.0 Configuration Properties:

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sslMode

By default, network connections are SSL encrypted; this property permits secure connections to be turned off, or a different levels of security to be chosen. The following values are allowed: DISABLED - Establish unencrypted connections; PREFERRED - (default) Establish encrypted connections if the server enabled them, otherwise fall back to unencrypted connections; REQUIRED - Establish secure connections if the server enabled them, fail otherwise; VERIFY_CA - Like REQUIRED but additionally verify the server TLS certificate against the configured Certificate Authority (CA) certificates; VERIFY_IDENTITY - Like VERIFY_CA, but additionally verify that the server certificate matches the host to which the connection is attempted.

This property replaced the deprecated legacy properties useSSL, requireSSL, and verifyServerCertificate, which are still accepted but translated into a value for sslMode if sslMode is not explicitly set: useSSL=false is translated to sslMode=DISABLED; {"useSSL=true", "requireSSL=false", "verifyServerCertificate=false"} is translated to sslMode=PREFERRED; {"useSSL=true", "requireSSL=true", "verifyServerCertificate=false"} is translated to sslMode=REQUIRED; {"useSSL=true" AND "verifyServerCertificate=true"} is translated to sslMode=VERIFY_CA. There is no equivalent legacy settings for sslMode=VERIFY_IDENTITY. Note that, for ALL server versions, the default setting of sslMode is PREFERRED, and it is equivalent to the legacy settings of useSSL=true, requireSSL=false, and verifyServerCertificate=false, which are different from their default settings for Connector/J 8.0.12 and earlier in some situations. Applications that continue to use the legacy properties and rely on their old default settings should be reviewed.

The legacy properties are ignored if sslMode is set explicitly. If none of sslMode or useSSL is set explicitly, the default setting of sslMode=PREFERRED applies.

Default: PREFERRED

Since version: 8.0.13

So, in my case, setting sslMode=DISABLED was all I needed to resolve the issue. This was on a test machine. But for production, the secure solution would be properly configuring the Java client and MySQL server to use SSL.

Notice that by disabling SSL, you might also have to set allowPublicKeyRetrieval=true. (Again, not a wise decision from security standpoint). Further information is provided in MySQL ConnectionString Options: