Connecting to database 1

[JTan]

Hi all,

I have tried to use the following codes to connect to my mySQL database and the results given is always "Cannot connect to server". May I know what is wrong? Or is there anything which I shld add before I compile n run the codes below?

I can confirm the password and username are correct.

TIA....


import java.sql.*;

public class Connect
{
public static void main (String []args)
{
Connection conn = null;
String url = "jdbc:mysql://localhost/vpg";
String userName = "root";
String password = "root";

try
{
Class.forName("com.mysql,jdbc.Driver").newInstance();
conn = DriverManager.getConnection(url, userName, password);
System.out.println("Connected");
}
catch (Exception e)
{
System.err.println ("Cannot connect to server.");
}
finally
{
if (conn!=null)
{
try {
conn.close();
System.out.println ("Disconnected.");
}
catch (Exception e) {}
}
}
}
}

 

[pzepernick]

Try changing your url to this:

String url = "jdbc:mysql://localhost:3306/vpg";

I have never tried connecting without specifying the port before. If your mysql server is not running on 3306, then you will have to change this to the correct port.

Paul

 

[timw]

Also, if you copy/pasted the code in, then I've spotted a typo in your driver loading line:

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

The comma should be a full stop.

(If this is the case it's always a good idea to put in a

e.printStackTrace();

in your catch block when trying these things out. Your current exception handling doesn't give you any info on what went wrong.)

Tim

 

[JTan]

Hi all,

thanks for your replies. I did some amendments to my codes and I think the problem lies in my driver.

I have some queries in regards to the installation of mySQL connector/J....I tried to set my classpath as stated in mySQL official site....

The official codes are:

C:\> set CLASSPATH=\path\to\mysql-connector-java-[version]-bin.jar;%CLASSPATH%

Just to ensure that the correct thing has been done, I tried to change the version to the version that I have now, as below:

C:\> set CLASSPATH=\path\to\mysql-connector-java-[3-0-16-ga]-bin.jar;%CLASSPATH%

But I kept getting errors when I tried to run the program now...

Exception in thread "main" java.lang.NoClassDefFoundError: Connect

Could someone kindly enlighten me what should be the correct commands that I should enter to install the connector, or at least how to set the classptah correctly?

TIA!

 

[timw]

I tend not to bother with the CLASSPATH environment variable. I prefer to specify an explicit classpath when I invoke the java command using the -cp <Classpath> form. This prevents any problems with the classpath needed for one app clashing with that for another.

That said, I would think that you definitely have a problem with your classpath. Maybe you are running the thing using the -cp with some other classpath? This would force the JVM to ignore the environment CLASSPATH.

Can you post the exact classpath. Might be able to spot something.

(There's a lot of 'classpath's in this reply )


Tim

 

[sedj]

The error : Exception in thread "main" java.lang.NoClassDefFoundError: Connect

- the poster's class is named "Connect" so you should add the directory where your Connect.class file is to your CLASSPATH.

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[timw]

Also, my MySQL jdbc connector jar doesn't even have a Connect class (it does have a Connection class). So it may not even be a problem with the MySQL connector on the classpath.


Tim

 

[timw]

..ah, I should have had a quick look again at the top post before I replied.. The main class is called Connect.. doh! Think I need another coffee.


Tim

 

[JTan]

Okie, the following is what I have done:

1) change the classpath back to where the COnnect file lies.
2) run the program using the -cp command (don't know if I state the command correctly...but it manages to get past compile error).

Results:

java.sql.SQLException: No suitable driver

Just a question, does it matter where I unzip the connector archive?

 

[timw]

Sorry if I'm stating the obvious here; you do need both the jdbc connector jar AND your Connect class on the classpath. It doesn't matter where the mysql-connector-java-version-stable-bin.jar is as long as its location is in the classpath.


Tim

 

[JTan]

the jar file is placed in the stated classpath now.

However, when I tried to execute the following codes, I got the ClassNotFoundException error:com.mysql.jdbc.Driver

import java.sql.*;



public class Connect
{
public static void main (String []args)
{
Connection conn = null;
//String url = "jdbc:mysql://localhost:3306/vpg";
//String userName = "root";
//String password = "root";

try
{
Class.forName("com.mysql.jdbc.Driver").newInstance();
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/vpg?user=root&password=root");
//conn = DriverManager.getConnection(url, userName, password);
System.out.println("Connected");
}
catch (Exception e)
{
e.printStackTrace();
System.err.println ("Cannot connect to server.");
}
finally
{
if (conn!=null)
{
try {
conn.close();
System.out.println ("Disconnected.");
}
catch (Exception e) {}
}
}
}
}

 

[timw]

The code is fine, it runs okay for me. Can you please post your exact classpath as you have it, warts-and-all?

 

[sedj]

Just do this :

set CLASSPATH=\path\to\mysql_driver.jar;\the\directory\where\Connect.class\is
java Connect

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--------------------------------------------------
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http://www.primrose.org.uk

 

[JTan]

Hi all,

thanks for your help.
I manage to resolve the problem.