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Explanation of "Class.forName" and "Connecton con = DriveManager.getConnecton"

Posted on 2004-04-21
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Last Modified: 2011-10-03
Could someone explain to me the relavancy/pupose of the following two line of code, in the excerpt of code below?

Class.forName ("sun.jdbc.odbc.JdbcOdbcDriver");
Connection con = DriverManager.getConnection (url);



import java.sql.*;
public class P5 {
      public static void main (String args[]) {

            String url = "jdbc:odbc:P4";

            Class.forName ("sun.jdbc.odbc.JdbcOdbcDriver");
Connection con = DriverManager.getConnection (url);
Statement stmt = con.createStatement ();
String query = "SELECT ENO FROM Employee";
ResultSet rs = stmt.executeQuery (query);
while (rs.next())
{
        String eno = rs.getString("ENO");    
        System.out.println(eno);
}
      }
}
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Question by:aquemini001
6 Comments
 
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sciuriware earned 20 total points
ID: 10885964
Class.forName is a way to decide at runtime which class to load.
JAVA has the feature to let you refer a class, method, field ...  when your program
is already running, so you can't write the code anymore.
So, JAVA compiles a bit for you when running.

;JOOP!
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Expert Comment

by:sciuriware
ID: 10885973
Your second question: that's the same: choosing a database connection in the nick of time.
;JOOP!
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by:Daij-Djan
ID: 10886216
ClassForName loads the java class with the specified name (so kinda... string TO class)
DriverManager uses that class to build a connectio to the db - the url is vendor-specific though...AFAIK

You might as well use the oracleDataSource directly, no need for a driverManager :P
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Expert Comment

by:Mayank S
ID: 10887539
You might want to go through the JDBC tutorial to get a complete picture of what's happening:

http://java.sun.com/docs/books/tutorial/jdbc/
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Expert Comment

by:seanrowen
ID: 10892389
Daij-Djan is right -- Class.forName() simply causes the class to be loaded into the classloader. There is no compilation or anything, and in general this is not a mechanism for "selecting" a class.

As it happens, when JDBC driver classes load, they register themselves with JDBC's DriverManager. That way, DriverManager knows about the existence of your driver for your database and will use it when you later get a Connection.

This is the "old way" of obtaining a Connection. You ought to be using a DataSource. In a J2EE app,  you should configure the DataSource for your container and look it up using JNDI. Here is some more information, from the Tomcat documentation:
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/jndi-datasource-examples-howto.html
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Author Comment

by:aquemini001
ID: 10973081
thanks
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