Java：MySQL对象在关闭连接时引发错误

Question

I'm relativly new to java and i've written an object (with help from http://www.tutorialspoint.com/jdbc/ ) to handle a MySQL db connection like this:

package rekening.db;
import java.sql.*;

public class dbConnection1 {
private final String dbUrl;
private final String dbUser;
private final String dbPass;
private Connection conn = null;
private Statement stmt = null;
private ResultSet rs = null;

/**
 * @param args the command line arguments
 */
//Constructor
public dbConnection1(String dbUrl, String dbUser, String dbPass) {
    this.dbUrl = dbUrl;
    this.dbUser = dbUser;
    this.dbPass = dbPass;

}

public boolean initiateConnection() throws SQLException {
try{
   //STEP 2: Register JDBC driver
   Class.forName("com.mysql.jdbc.Driver");

   //STEP 3: Open a connection
   System.out.println("Connecting to database...");
   conn = DriverManager.getConnection(dbUrl,dbUser,dbPass);
   return true;
}catch(SQLException se){
   //Handle errors for JDBC
   se.printStackTrace(); 
}catch(Exception e){
   //Handle errors for Class.forName
   e.printStackTrace();
}
return false;
}

public ResultSet executeQuery(String dbStatement) throws SQLException {
try{
   //STEP 4: Execute a query
   System.out.println("Creating statement...");
   stmt = conn.createStatement();
   String sql;
   sql = dbStatement;
   ResultSet rs = stmt.executeQuery(sql);

   //STEP 5: Extract data from result set
   while(rs.next()){
      //Retrieve by column name
      String DESC_ORIGINAL = rs.getString("DESC_ORIGINAL");
      String DESC_TRIMMED = rs.getString("DESC_TRIMMED");
      String DESC_EDITED = rs.getString("DESC_EDITED");
      String DESC_CATEGORY_EDITED = rs.getString("DESC_CATEGORY_EDITED");
      String DESC_SUBCATEGORY = rs.getString("DESC_SUBCATEGORY");


      //Display values
      System.out.print("Orignal: " + DESC_ORIGINAL);
      System.out.print(", Trimmed: " + DESC_TRIMMED);
      System.out.print(", Edited: " + DESC_EDITED);
      System.out.println(", Category: " + DESC_CATEGORY_EDITED);
      System.out.println(", Subcategory: " + DESC_SUBCATEGORY);
   }
   return rs;
   }catch(SQLException se){
   //Handle errors for JDBC
   se.printStackTrace(); 
   }

return rs;
}

public void closeConnection() throws SQLException {
   //STEP 6: Clean-up environment
try{
   rs.close();
   stmt.close();
   conn.close();
}
catch (SQLException se){
   //Handle errors for JDBC
   se.printStackTrace(); 
} 
finally{
   //finally block used to close resources
   try{
      if(stmt!=null)
         stmt.close();
   }catch(SQLException se2){
   }// nothing we can do
   if(conn!=null)
       conn.close();
}//end try        
}
}

from the main i call the dbConnection1 object:

try {
    dbConnection1 dbConn = new dbConnection1("jdbc:mysql://192.168.1.550/Finance","test","");
    dbConn.initiateConnection();
    dbConn.executeQuery("SELECT DESC_ORIGINAL, DESC_TRIMMED, DESC_EDITED, DESC_CATEGORY_EDITED, DESC_SUBCATEGORY FROM `TOOL.DESCRIPTION`");
    dbConn.closeConnection(); 
} catch (SQLException ex) {
    Logger.getLogger(Rekening.class.getName()).log(Level.SEVERE, null, ex);
}

The output returns the errors below. But the strange thing is that it returns the rows from the db. The errors are in between the resultset. And in the end it says the build is succesfull. Can anybody help my please? Thanks!!

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at rekening.db.dbConnection1.closeConnection(dbConnection1.java:105)
at rekening.ui.Rekening$1.run(Rekening.java:85)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:312)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:694)
at java.awt.EventQueue$3.run(EventQueue.java:692)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:703)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
BUILD SUCCESSFUL (total time: 1 second)

Answer 1

First thing to notice is, that you close your stmt and connection twice in any case. First in the try block and then again in the finally block... Hard to say more, since your code does not have a line 105 ;-)