Need Help

[MInu]

I am new to XML.i am getting "java.lang.NullPointerException" when i run the program.pls give me advice.My java code is

import java.sql.*;
import javax.xml.parsers.*;
import org.w3c.dom.*;
import org.xml.sax.*;
import java.io.IOException;
import java.util.StringTokenizer;

public class JAXP5
{
static Connection db=null;
static Statement statement=null;
static String thisusername=null;
static String thispassword=null;
static String thisurl=null;
static String thisdriver=null;
static Document d ;
static Element thisconn;


public static void main(String[] args)
{

String connectFile=args[0];

try
{
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder parser = factory.newDocumentBuilder();
//JAXP5 counter = new JAXP5();
try
{
d = parser.parse(connectFile);
}
catch(Exception e)
{
System.err.println(e);
}
try
{
Class.forName(thisdriver);
System.out.println("Connected");
db = DriverManager.getConnection(thisurl,thisusername,thispassword);
statement = db.createStatement();
System.out.println("DBConnected");
}
catch(Exception e)
{
System.err.println(e);
}
try
{
Element connectRoot = d.getDocumentElement();
NodeList dbconn = connectRoot.getElementsByTagName("dbconnection");

for (int i = 0; i < dbconn.getLength(); i++)
{
Element thisconn = (Element)dbconn.item(i);
}
}
catch(Exception e)
{
System.err.println(e);
}

thisusername = thisconn.getElementsByTagName("username")
.item(0)
.getFirstChild().getNodeValue();
System.out.println("Username: " + thisusername);

thispassword = thisconn.getElementsByTagName("password")
.item(0)
.getFirstChild().getNodeValue();
System.out.println("Password: " + thispassword);

thisurl = thisconn.getElementsByTagName("url")
.item(0)
.getFirstChild().getNodeValue();
System.out.println("Url: " + thisurl);

thisdriver = thisconn.getElementsByTagName("driver")
.item(0)
.getFirstChild().getNodeValue();
System.out.println("Driver: " + thisdriver);

}

catch(Exception e)
{
System.err.println(e);
}


}
}

and my XML code is

<dbconnection>
<username>jim</username>
<password>jim123</password>
<url>jdbc:mysql://192.168.1.49/jibin</url>
<driver>com.mysql.jdbc.Driver</driver>
</dbconnection>

hope i could get a reply soon.

minu

[Lasse Koskela]

It would help if you'd
1) surround your Java code with the UBB CODE tags, and
2) tell us from which line the NullPointerException is thrown.

[MInu]

Thanks for the advice.is my logic correct in the program ?. The reason i am asking because the values(username,passsword,url,driver) are not getting printed.hope you would debug the program.

i think the problem resides in this part of the code :

Element connectRoot = d.getDocumentElement();
NodeList dbconn = connectRoot.getElementsByTagName("dbconnection");
}
catch(Exception e)
{
System.out.println("Error creating class: "+e.getMessage());
}

for (int i = 0; i < dbconn.getLength(); i++)
{
Element thisconn = (Element)dbconn.item(i);
}


hope i could get a reply soon.

[Lasse Koskela]

I would strongly recommend using "e.printStackTrace()" instead of "System.err.println(e)" because the former gives you essential information about where the exception originates from.

Anyway, your current problem is this line:
Class.forName(thisdriver);

You're getting a NullPointerException because 'thisdriver' is null when this statement is executed.

[MInu]

Hi,
Thanks for the reply....

Yes....you are right.....

Can u plz suggest me a good solution...here in the code below, i am not getting 'username' printed.do you find any problem in my code and logic.

------------------------------------------------------------------------
thisusername = thisconn.getElementsByTagName("username").item(0)
.getFirstChild().getNodeValue();

System.out.println("Username: " + thisusername);


-------------------------------------------------------------------------

i am totally confused...

[Lasse Koskela]

I'd suggest that you split your code from the huge main() method into multiple, smaller methods like:

public class JAXP5 {
 
    public static void main(String[] args) {
        Document doc = parse(args[0]);
        Element dbconnectionElement = findDbconnectionElement(doc);
        MyDescriptor descriptor = parseDbconnectionElement(dbconnectionElement);
    }
 
    private static Document parse(String filename) {
        // parse the XML file into a Document
    }
 
    private static Element findDbconnectionElement(Document doc) {
        // locate the <dbconnection> element from the given Document
    }
 
    private static MyDescriptor parseDbconnectionElement(Element element) {
        MyDescriptor descriptor = new MyDescriptor();
        descriptor.setDriver(parseConnectionDriverClass(element));
        descriptor.setURL(parseConnectionUrl(element));
        descriptor.setUsername(parseConnectionUsername(element));
        descriptor.setPassword(parseConnectionPassword(element));
        return descriptor;
    }
 
    ...
}

This way, you'll have a lot easier time fixing things one small piece at a time.