java class

[sensory21]

Hi all,

can you see something wrong with my class as when I tried to compile it, I got the message error:
package javax.servlet does not exist?
Thanks for your time.

package Mypackage;
import java.util.*;
import java.sql.*;
import javax.servlet.UnavailableException;

public class ConnectionManager {

public ConnectionManager(){

}
static Connection getConnection(){

try{
Class.forName("com.mysql.jdbc.Driver").newInstance();
String url = "dbUrl";
String pwd = "dbPwd";
String user = "dbUser";
Connection conn = DriverManager.getConnection(url,pwd,user);
}
catch (Exception e){
throw new UnavailableException(e.getMessage());
}
}

}

 

[sedj]

You have not included the javax.servlet package in your CLASSPATH.

Theis package is contained within a file named servlet.jar or servlet-api.jar and can be downloaded from

http://www.java.sun.com

as part of the servlet API or comes with Tomcat / Resin etc.

To be honest though, I would not throw this exception from that code - bacause it is not really a servlet API exception - I would code it like such :

public class ConnectionManager {

    public ConnectionManager(){
            
        }
        static Connection getConnection() throws SQLException {
            
                Class.forName("com.mysql.jdbc.Driver").newInstance();
                String url = "dbUrl";
                String pwd = "dbPwd";
                String user = "dbUser";
                Connection conn = DriverManager.getConnection(url,pwd,user);
    
    
}

 

[sensory21]

Thanks very much Sedj for your help

I have so much to learn to write java classes!

 

[sensory21]

That's the amended class: but now I've got 3 errors
- missing return statement

-ConnectionManager.java:13: unreported exception java.lang.ClassNotFoundException
; must be caught or declared to be thrown
Class.forName("com.mysql.jdbc.Driver").newInstance();

-ConnectionManager.java:13: unreported exception java.lang.ClassNotFoundException
; must be caught or declared to be thrown
Class.forName("com.mysql.jdbc.Driver").newInstance();

package Mypackage;
import java.lang.*;
import java.sql.*;
import java.io.*;

public class ConnectionManager {

public ConnectionManager(){
//default constructor
}
static Connection getConnection() throws SQLException
{
Class.forName("com.mysql.jdbc.Driver").newInstance();
String url = "dbUrl";
String pwd = "dbPwd";
String user = "dbUser";
Connection conn = DriverManager.getConnection(url,pwd,user);
}
}

 

[sedj]

Try :

import java.sql.*;
public class ConnectionManager {

    public ConnectionManager(){}
        static Connection getConnection() throws SQLException {
            	try {
            	    Class.forName("com.mysql.jdbc.Driver");
            	    String url = "dbUrl";
            	    String pwd = "dbPwd";
            	    String user = "dbUser";
            	    return DriverManager.getConnection(url,pwd,user);
            	} catch (Exception e) {
            	    e.printStackTrace(System.err);
            	    throw new SQLException(e.toString());
            	}


	}
}

 

[sensory21]

Dear Sedj, you are great, the class compile and Im learning good java too; but another question: now that Im using that class in my jsp file I get this Apache errors:

-cannot resolve symbol symbol : method prepareStatement (java.lang.String)
location: class Mypackage.ConnectionManager
PreparedStatement prep = C.prepareStatement("SELECT * FROM staff");

-cannot resolve symbol symbol : method close ()
location: class Mypackage.ConnectionManager
C.close();
^


That's what in my jsp file:

1-ConnectionManager C = new ConnectionManager();
2-PreparedStatement prep = C.prepareStatement("SELECT * FROM staff");
3-ResultSet RS = prep.executeQuery();

I thought that I could use the class as I have done in the line 1? or do I have to have the PreparedStatement in the class?
I would like to be able to use the connection class just to connect to mysql?

Many thanks

 

[sedj]

Try :

Connection c = ConnectionManager.getConnection();
PreparedStatement prep = c.prepareStatement("SELECT * FROM staff");
ResultSet rs = prep.executeQuery();

You do not have to instantiate a new ConnectionManager class because the getConnection() method is static.

 

[sensory21]

Sedj, I do understand about
Connection c =
instead of
ConnectionManager c =

then I got this error:

getConnection() is not public in Mypackage.ConnectionManager; cannot be accessed from outside package
Connection C = ConnectionManager.getConnection();

So I wrote:
public static Connection getConnection() throws SQLException

but then I got this error:
javax.servlet.ServletException: java.sql.SQLException: No suitable driver

??
Cheers
Vero

 

[sensory21]

do I need a
public static void main ?

 

[sedj]

Have you added the mysql driver to TOMCAT_HOME/common/lib ?

 

[sensory21]

yes the connection was working fine when it was in the jsp file as:

/*Class.forName("com.mysql.jdbc.Driver").newInstance();
String url = application.getInitParameter("dbUrl");
String pwd = application.getInitParameter("dbPwd");
String user = application.getInitParameter("dbUser");
Connection C = DriverManager.getConnection(url,pwd,user);
*/

but then I want to improve my programming skills and create classes instead of having all these codes in my jsp files

 

[sedj]

The problem is that your dbUrl String should be something like :

"jdbc:mysql://localhost:3306/test"

not :

"dbUrl

 

[sensory21]

dbUrl refers to the value in the
WEB-INF>web.xml
<param-value>jdbc:mysql://localhost/intranet</param-value>

it's why I had this:
String url = application.getInitParameter("dbUrl");

but do I have to change it in the class as you said:
String url = jdbc:mysql://localhost/intranet;

or could I have this in the class?
String url = application.getInitParameter("dbUrl");

 

[sedj]

Of course you can have it as :

String url = application.getInitParameter("dbUrl");

- its only a String - but in your code that you originally posted it was down as :

String url = "dbUrl";

which is not going to work ...

 

[sensory21]

You are right but now it doesn't compile

ConnectionManager.java:15: cannot resolve symbol
symbol : variable application

 

[sensory21]

I've now tried
String url = "jdbc:mysql://localhost/intranet";

and still getting the error:

C:\Program Files\Apache Software Foundation\Tomcat 5.0\webapps\intranet\WEB-INFclasses\Mypackage>javac ConnectionManager.java

C:\Program Files\Apache Software Foundation\Tomcat 5.0\webapps\intranet\WEB-INFclasses\Mypackage>java ConnectionManager
Exception in thread "main" java.lang.NoClassDefFoundError: ConnectionManager (wr
ong name: Mypackage/ConnectionManager)
at java.lang.ClassLoader.defineClass0(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)

when you asked me earlier if I had added the mysql driver to TOMCAT_HOME/common/lib ?
is it a jar file?
Our administrator has changed from Tomcat 4.1 to Tomcat 5.0 and I guess he kept the same settings as we all work with mysql, can you give me some more info?

 

[sedj]

Yes the driver is in a jar file - mmsql-*.jar or something like that.

To fix your above error, type :

cd "C:\Program Files\Apache Software Foundation\Tomcat 5.\webapps\intranet\WEB-INF\classes"
java Mypackage.ConnectionManager

(you will need a main method - ie

    	public static void main(String args[]) throws Exception {
			System.err.println(ConnectionManager.getConnection());
		}

 

[sensory21]

Ive found this on java.sun:

String url = getServletConfig().getInitParameter("dbUrl");

and still error message:
cannot resolve symbol symbol : method getServletConfig()

that's the look of my class now:

package Mypackage;
import java.sql.*;
import java.io.*;
import java.text.*;
import javax.servlet.*;

public class ConnectionManager
{
public ConnectionManager()
{
//default constructor
}
public static Connection getConnection() throws SQLException
{
try
{
Class.forName("com.mysql.jdbc.Driver");
String url = getServletConfig().getInitParameter("dbUrl");
String pwd = getServletConfig().getInitParameter("dbPwd");
String user = getServletConfig().getInitParameter("dbUser");
return DriverManager.getConnection(url,pwd,user);
}
catch (Exception e)
{
e.printStackTrace(System.err);
throw new SQLException(e.toString());
}
}
}

it's so difficult, can you see the problem?

 

[sensory21]

to answer your previous reply;
this piece of code wouldn't work if I didn't have the mysql driver, would it?
/*Class.forName("com.mysql.jdbc.Driver").newInstance();
String url = application.getInitParameter("dbUrl");
String pwd = application.getInitParameter("dbPwd");
String user = application.getInitParameter("dbUser");
Connection C = DriverManager.getConnection(url,pwd,user);
*/
and this works fine! I just want to put it in a class and use this in the jsp file:
Connection C = ConnectionManager.getConnection();

but can't do it!

 

[sedj]

getServletConfig() is a method of HttpServlet - so you cannot use it it a standalone application ... only in a jsp/servlet