Unable to connect to mysql through JDBC connector through Tomcat or externally

Question

I've installed a stock mysql 5.5 installation, and while I can connect to the mysql service via the mysql command, and the service seems to be running, I cannot connect to it through spring+tomcat or from an external jdbc connector.

I'm using the following URL:

jdbc:mysql://myserver.com:myport/mydb

with proper username/password, but I receive the following message:

server.com: 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.

and tomcat throws:

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.
    sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)

Which seems to be the same issue as if I try to connect externally.

Answer 1

This can happen for a variety of reasons. I just saw it myself a few weeks ago but I can't remember what the fix was for me.

1) Verify the address mysql is bound to, it's probably 127.0.0.1 (only) which I believe is the default (at least on standard Ubuntu server). You'll have to comment out the bind-address parameter in my.cnf to bind to all available addresses (you can't choose multiple, it's one or all).

2) If it is bound to 127.0.0.1 and you can't connect using "localhost", make sure it's not resolving to the IPv6 localhost address instead of IPv4. (or just use the IP address)

3) Double and triple-check the port that mysql is listening on.

4) Make sure you're using the right JDBC connector for your JDK.

5) Make sure you're not doing something really silly like starting mysql with --skip-networking.

I think my first suggestion has the most promise...in fact I think that's where I saw it recently...I was trying to connect to mysql remotely (also on Ubuntu 8.04).

Answer 2

If you are running a Linux installation, you probably have lokkit blocking incoming communications except via SSH.

Log in as root, and run the command lokkit from the prompt, disable firewall and SElinux and see if you have the same problem.

Also check your permissions have been set correctly, so everything can write to the correct locations.

Answer 3

There is also this huge bug in version 5.1.9 of mysql-jdbc driver :

http://bugs.mysql.com/bug.php?id=47494

Answer 4

i had a very similar problem for almost a day, and it drove me crazy! but i managed to found the solution, and it was very, very simple, you just need to /etc/init.d/tomcat6 to change TOMCAT6_SECURITY=yes to TOMCAT6_SECURITY=no. it's not my solution, i found it here, as you can see, i am running ubuntu, hope this works.

Answer 5

I had the same problem. Changed the "bind-address" property in /etc/mysql/my.cnf file to 0.0.0.0, and it works. Corresponding line in my.cnf looks like this:

bind-address = 0.0.0.0

Before it was set to the outside ip address of the server, so it looked something like:

bind-address = 196.152.4.145

I think when it's set to the outside ip address and not the localhost loop, mysql server is just connected to the network card and does not listen to the connections from the local loop.

Answer 6

This can also be caused by wrong proxy settings. I had this problem trying to connect via jdbc to a MySQL instance running in a Parallels virtual appliance on my Mac. The jdbc connection uses the system-level network settings and since I was behind a SOCKS proxy I had to set the MySql host as a non-proxy host (e.g., on a Mac you can configure that in Settings->Network->Advanced->Proxies, and finally add the hostname or IP address in the "Bypass proxy settings for these Hosts and Domains").

Answer 7

try your local address to bind address in my.cnf file

Connection con = null;

    try {
        Class.forName("com.mysql.jdbc.Driver");
        con = DriverManager.getConnection("jdbc:mysql://x62.xx8.x4x.x5:3306/mydb", "root", "root");
        try {
            System.out.println(con.getMetaData());
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    } catch (ClassNotFoundException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }