Why is the CLASSPATH failing for Python but working for RazorSQL?

Question

On Windows Server 2016, we are trying to connect over JDBC with a Jython script but it is giving following error:

java.lang.ClassNotFoundException: java.lang.ClassNotFoundException: com.microsoft.sqlserver.jdbc.SQLServerDriver

RazorSQL, on the same machine, connects without error using these settings:

Driver Class: com.microsoft.sqlserver.jdbc.SQLServerDriver 
Driver Location: \Program Files (x86)\RazorSQL\drivers\sqlserver\sqljdbc.jar

As a result, we set the CLASSPATH to same location with this command:

set CLASSPATH=C:\Program Files (x86)\RazorSQL\drivers\sqlserver\sqljdbc.jar

...but when running the code below - we still get the same ClassNotFound error.

This is our Python code:

jclassname = "com.microsoft.sqlserver.jdbc.SQLServerDriver" 
database = "our_database_name"
db_elem = ";databaseName={}".format(database) if database else ""
host = "###.##.###.###" # ip address
port = "1433"
    
user = "user_name"
    
password = "password"
  

url = (
    jdbc:sqlserver://{host}:{port}{db_elem}"
        ";user={user};password={password}".format(
host=host, port=port, db_elem=db_elem,
  er=user, password=password)
    )
    
print url
    
  
driver_args = [url]
   
jars = None
  
libs = None
 
db = jaydebeapi.connect(jclassname, driver_args, jars=jars,
libs=libs)

This is how we are running our Python script:

C:\jython2.7.0\bin\jython.exe C:\path_to_our_script.py

How is that RazorSQL is connecting fine - but somehow Python cannot? How do we remove this CLASSPATH error?

Answer 1

You have to load the JARs at runtime using the system Classloader.

Please refer to this answer.

The following code snippet has been taken from this Gist.

def loadJar(jarFile):
    '''load a jar at runtime using the system Classloader (needed for JDBC)

    adapted from http://forum.java.sun.com/thread.jspa?threadID=300557
    Author: Steve (SG) Langer Jan 2007 translated the above Java to Jython
    Reference: https://wiki.python.org/jython/JythonMonthly/Articles/January2007/3
    Author: seansummers@gmail.com simplified and updated for jython-2.5.3b3+

    >>> loadJar('jtds-1.3.1.jar')
    >>> from java import lang, sql
    >>> lang.Class.forName('net.sourceforge.jtds.jdbc.Driver')
    <type 'net.sourceforge.jtds.jdbc.Driver'>
    >>> sql.DriverManager.getDriver('jdbc:jtds://server')
    jTDS 1.3.1
    '''
    from java import io, net, lang
    u = io.File(jarFile).toURL() if type(jarFile) <> net.URL else jarFile
    m = net.URLClassLoader.getDeclaredMethod('addURL', [net.URL])
    m.accessible = 1
    m.invoke(lang.ClassLoader.getSystemClassLoader(), [u])

if __name__ == '__main__':
    import doctest
    doctest.testmod()

Also look at - https://wiki.python.org/jython/JythonMonthly/Articles/January2007/3