Solving a “communications link failure” with JDBC

Question

This question already has an answer here:

• com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure 30 answers

I'm trying to connect to the local MySQL server but I keep getting an error.

Here is the code.

public class Connect {

    public static void main(String[] args) {
        Connection conn = null;

        try {
            String userName = "myUsername";
            String password = "myPassword";

            String url = "jdbc:mysql://localhost:3306/myDatabaseName";
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            conn = DriverManager.getConnection(url, userName, password);
            System.out.println("Database connection established");
        } catch (Exception e) {
            System.err.println("Cannot connect to database server");
            System.err.println(e.getMessage());
            e.printStackTrace();
        } finally {
            if (conn != null) {
                try {
                    conn.close();
                    System.out.println("Database Connection Terminated");
                } catch (Exception e) {}
            }
        }
    }
}

and the errors :

Cannot connect to database server
Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
        at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
        at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1116)
        at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:344)
        at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2333)
        at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2370)
        at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2154)
        at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:792)
        at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
        at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
        at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:381)
        at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:305)
        at java.sql.DriverManager.getConnection(DriverManager.java:582)
        at java.sql.DriverManager.getConnection(DriverManager.java:185)
        at Connect.main(Connect.java:16)
    Caused by: java.net.ConnectException: Connection refused
        at java.net.PlainSocketImpl.socketConnect(Native Method)
        at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351)
        at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:213)
        at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:200)
        at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
        at java.net.Socket.connect(Socket.java:529)
        at java.net.Socket.connect(Socket.java:478)
        at java.net.Socket.<init>(Socket.java:375)
        at java.net.Socket.<init>(Socket.java:218)
        at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:257)
        at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:294)
        ... 15 more

I've set the classpath, made sure my.cnf had the skip network option commented out.

java version is 1.2.0_26 (64 bit) mysql 5.5.14 mysql connector 5.1.17

I made sure that the user had access to my database.

Answer 1

If you are using hibernate, this error can be caused for keeping open a Session object more time than wait_timeout

I've documented a case in here for those who are interested.

Answer 2

I found the solution

since MySQL need the Localhost in-order to work.

go to /etc/network/interfaces file and make sure you have the localhost configuration set there:

auto lo
iface lo inet loopback

NOW RESTART the Networking subsystem and the MySQL Services:

sudo /etc/init.d/networking restart

sudo /etc/init.d/mysql restart

Try it now

Answer 3

In case you are having problem with a set of Docker containers, then make sure that you do not only EXPOSE the port 3306, but as well map the port from outside the container -p 3306:3306. For docker-compose.yml:

version: '2'

services:
    mdb:
        image: mariadb:10.1
        ports:
            - "3306:3306"
        …

Answer 4

In my case (I am a noob), I was testing Servlet that make database connection with MySQL and one of the Exception is the one mentioned above.

It made my head swing for some seconds but I came to realize that it was because I have not started my MySQL server in localhost.
After starting the server, the problem was fixed.

So, check whether MySQL server is running properly.

Answer 5

I've just faced the same problem. It happened because the MySQL Daemon was binded to the IP of the machine, which is required to make connection with an user that has permission to connect @your_machine. In this case, the user should have permission to connect USER_NAME@MACHINE_NAME_OR_IP

I wanted remote access to my machine so I changed in my.cnf from

bind-address = MY_IP_ADDRESS

To

bind-address = 0.0.0.0

Which will allow an user from localhost AND even outside (in my case) to connect to the instance. Both below permissions will work if you bind the MySQL to 0.0.0.0:

USER_NAME@MACHINE_NAME_OR_IP

USER_NAME@localhost

Answer 6

The resolution provided by Soheil was successful in my case.

To clarify, the only change I needed to make was with MySQL's server configuration;

bind-address = **INSERT-IP-HERE**

I am using an external MySQL server for my application. It is a basic Debian 7.5 installation with MySQL Server 5.5 - default configuration.

IMPORTANT:

Always backup the original of any configuration files you may modify. Always take care when elevated as super user.

File

/etc/mysql/my.cnf

Line

bind-address        = 192.168.0.103 #127.0.0.1

Restart your MySQL Server service:

/usr/sbin/service mysql restart

As you can see, I simply provided the network IP of the server and commented out the default entry. Please note that simply copy and paste my solution will not work for you, unless by some miracle our hosts share the same IP.

Thanks @ Soheil