JDBC mysql driver

[Eleeist]

Hi,

I am trying to connect to MySQL database using JDBC but no luck so far. I get errors "not suitable driver found". What should be the driver for MySQL called? Do I have to install something or it comes with Java?

[JosAH]

Just put the .jar file that contains your MySQL driver on your classpath; the (old) way of installing your driver is to use the Class.forName("nameOfYourDriverClass") method to make your driver install itself. The DriverManager class will know about the driver then and you can obtain a Connection from it given a suitable URL (specifying the database name etc.)

kind regards,

Jos

[Eleeist]

1. In folder "testapplication" I have folder "lib" (with mysql-connector) and Test.jar.
2. In Test.jar I have Database.class with the following code:

import java.sql.*;

public class Database {
    
    public static void main(String[] args) throws Exception {
     
            Class.forName("com.mysql.jdbc.Driver");
            Connection con = DriverManager.getConnection("jdbc:mysql:mydatabasename", "myusername", "mypassword");
            Statement stmt = con.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT * FROM test_table");
       
    }
    
}

3. When I try to run the code on server with "java Test" I get these error messages:

Exception in thread "main" java.lang.NoClassDefFoundError: Test
Caused by: java.lang.ClassNotFoundException: Test
    at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
    at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:334)
Could not find the main class: Test. Program will exit.

[DeNiS_M]

try java -jar Test

[arielb]

are using any ide?

[Eleeist]

@DeNiS_M
I get "Unable to access jarfile Test" message

@arielb
Yes, NetBeans, but I export the jar and upload it to the server.

[arielb]

I understand that the error is in development, if so you have to add the jar to the classpath of the IDE to recognize it.
Here I have a guide that I made earlier.

Add jar netbeans

[Tolls]

@DeNiS_M
I get "Unable to access jarfile Test" message

The run it against the jar file?
You can't expect it to work unless you are running that command in the directory that contains the jar file!

[Eleeist]

Do I even have to use jars? Maybe I could just put the lib folder with mysql-connector in the same directory as my Test.class and run "java Test"?

[Eleeist]

I experimented and got it to work... almost. I get these errors when compile:

Exception in thread "main" java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
    at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
    at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:334)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:186)
    at Database.main(Database.java:7)

(I changed the class name to Database.)

[JosAH]

See my first reply in this thread; the .jar file that contains the com.mysql.jdbc.Driver class is not on your classpath.

kind regards,

Jos

[Eleeist]

Ok, but I've got this line in my code:

Class.forName("com.mysql.jdbc.Driver");

Am I doing something wrong?

[JosAH]

Ok, but I've got this line in my code:

Class.forName("com.mysql.jdbc.Driver");

Am I doing something wrong?

Yup, that method calls a ClassLoader and that object doesn't know where it can find the mentioned driver class. It's the classpath variable the tells a ClassLoader object where it should look.

kind regards,

Jos

[Eleeist]

Ok, I understand now. In Netbeans in my project I went to Libraries -> Add Library... -> and added MySQL JDBC Driver. Its Library classpath is somewhere in my NetBeans installation folder on my computer. Should it match the directory structure on my server (where I'm running the program?). If so, then I can't see a way to change it inside NetBeans (there is no option for changing the classpath).

PS: thank you for your patience, as this is obviously quite easy and I just can't grasp it ;).

[JosAH]

There's another trick: the Java Runtime checks a special directory: JRE/lib/ext (JRE is where your Java Runtime is stored). .jar files in that directory don't have to be mentioned on the classpath environment variable; but be careful with it: it makes your jar (with all classes in it) available to each an every Java program you write and run (it can be a benefit though).

kind regards,

Jos

[Eleeist]

I put the driver in the directory you mentioned. I decided this time to not pack it into .jar and just upload and run Database.class. I get these error:

Exception in thread "main" java.sql.SQLException: No suitable driver found for jdbc:mysql:mud
    at java.sql.DriverManager.getConnection(DriverManager.java:640)
    at java.sql.DriverManager.getConnection(DriverManager.java:200)
    at Database.main(Database.java:8)

"mud" is the name of my MySQL database.

[Eleeist]

I've done some research and found that I should specify the URL. Because I am using localhost and default port for MySQL installation, I have changed it to:

"jdbc:mysql://mud"

Now I get these errors:

Exception in thread "main" com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Can this be regarded as some kind of a progress? :)

[JosAH]

Yep, that's (a bit of) progress; your driver can't find a server of some sort. Check your mySQL manuals how to start up that server. (it would surprise me if that documentation doesn't give a simple example).

kind regards,

Jos

[Eleeist]

YES! Got it to work without any errors... But the application exits from command line almsot immediately after launch. Any suggestions what is happening?

Here is the code after modifications:

import java.sql.*;

public class Database {
    
    public static void main(String[] args) throws Exception {

            Class.forName("com.mysql.jdbc.Driver");
      
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost/mud", "myusername", "mypassword");

    }
    
}

[JosAH]

So the driver class was found (and loaded) and it found the database; next your program stopped ...

kind regards,

Jos