It's a NullPointerException causing all your woes. In the Connect method
of DBConnection you are assigning to a local variable of type Connection
instead of the instance variable. The instance variable is always null,
which causes issues in the QueryDataBase and TotalRows methods.
The code as it stands is rather flaky, I'm afraid.
Look into connection pooling (docs on the tomcat site and many posts
related to it on this list) and defensive programming (checking for null
values etc, etc). Also, Wolfgang's advice is good: always close
ResultSets and Statements after you're done with them (and connections
for that matter).
HTH,
Jon
Maxime wrote:
Hello Everybody;
I'am asking for help because I have a problem that it's making me crazy.
To do some query to the Database, I am using a Class named DBConnection.
It's like around 1 week, I didn't do anything on the code (perhaps I did
because it doesn't working now).
Well... , in order to find the problem I did some test function, but I still
can't find it.
Here we go, it's not very long, it's just some basic code and 2 logs
This the JSP where my test start.
Test.jsp
HTML
HEAD
TITLEDataBase Test!/TITLE
/HEAD
DataBase Test Button
FORM ACTION=http://localhost:8080/Training/TEST2;
INPUT TYPE=SUBMIT VALUE = test
/FORM
DataBase Test Button2
FORM ACTION=http://localhost/Training/TEST3;
INPUT TYPE=SUBMIT VALUE = test
/FORM
/BODY
/HTML
We have 2 button to access on servlet Test2 and Test3
Here they go :
TEST3.java :
package Training;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;
import java.sql.DriverManager;
public class TEST3 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType(text/html);
PrintWriter out = response.getWriter();
// New Instance : DBConnection
DBConnection db = new DBConnection();
String req =Select * FROM User_Table;
try{
db.Connect();
out.println(br DRIVERS JDBC : OK!);
out.println(br Connexion TO DB : OK!);
ResultSet Result = db.QueryDataBase(req);
// This part was added to see if we can catch the total row
int col = db.TotalRows(Result);
if (col == 0)
{
out.println(brQuery to DB is not ok!br);
}
else{
out.println(col);
}
}
catch (ClassNotFoundException e)
{
out.println(PB with Drivers);
}
catch (Exception x)
{
out.println(x);
}
}
}
DBConnection.java
package Training;
import java.sql.*;
import java.sql.DriverManager;
public class DBConnection{
Connection connection;
Statement stmt;
ResultSet result;
public DBConnection(){
}
public void Connect() throws Exception, SQLException{
String url = jdbc:mysql://localhost:3306/HeroDB;
String user = Login;
String password = Password;
try {
// Load JDBC Drivers
Class.forName(com.mysql.jdbc.Driver);
// make the connection with the database
The problem's right here:
Connection connection = DriverManager.getConnection(url,user,password);
}
catch(SQLException sqle){
System.out.println(sqle.getMessage());
}
catch(Exception e){
System.out.println(The Connection Failed !+ e.getMessage());
}
}
public ResultSet QueryDataBase(String SQLFunc)throws SQLException, Exception{
try{
stmt = connection.createStatement();
result = stmt.executeQuery(SQLFunc);
}
catch(SQLException sqle){
System.out.println(Problem with getting Result1!+ sqle.getMessage());
System.out.println(Problem with getting Result2!+ sqle.getSQLState());
System.out.println(Problem with getting Result3!+ sqle.getErrorCode());
}
catch(Exception e){
System.out.println(Problem with getting Result4!+ e.getMessage());
}
return result;
}
public int TotalRows (ResultSet rs) throws SQLException, Exception
{
int numRows = 0;
try{
rs.last();
numRows = rs.getRow();
rs.first();
}
catch(SQLException sqle)
{
System.out.println(Problem with getting Row1+ sqle.getMessage());
System.out.println(Problem with getting Row2+ sqle.getSQLState());
System.out.println(Problem with getting Row3+ sqle.getErrorCode());
}
catch(Exception e){
System.out.println(Problem with getting getting Row4!+ e.getMessage());
}
return numRows;
}
}
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