I am facing a java.lang.ClassNotFoundException error with the message com.mysql.cj.jdbc.Driver when attempting to run my Java code for data insertion into a MySQL database. Surprisingly, the code compiles and runs without any errors, but the data is not being inserted into the database. Here’s an overview of the issue:
- I’m using Java and JDBC to connect to a MySQL database and insert data into a table.
- I have made sure to include the MySQL JDBC driver JAR file in my project’s classpath.
- When I run the code, I encounter the mentioned ClassNotFoundException error for the
com.mysql.cj.jdbc.Driverclass. - However, if I only compile the code without running it, there are no errors.
- Despite the successful compilation, the data is not getting inserted into the database.
Here’s a snippet of the code where I connect the JDBC:
import java.sql.*;
public class Conn {
/*
* JDBC Connection has 4 Stages
* (1)-Register the Driver Class
* (2)-Creating Connection String
* (3)-Creating Statement
* (4)-Executing MySQL Queries
* (5)-Closing the Connection
*/
Connection c; //reference variable
Statement s; //
Conn(){
try{
// (1)-Register the Driver Class
Class.forName("com.mysql.cj.jdbc.Driver");
//Class.forName("com.mysql.cj.jdbc.Driver").newInstance();
System.out.println("Driver Loaded");
// (2)-Creating Connection String
/*
* Connection String provides the information in which database you have connect
*/
c= DriverManager.getConnection("jdbc:mysql://localhost:3306/universitymanagementsystem","root", "123456789");
System.out.println("Connection Established");
// (3)
s= c.createStatement();
}catch(Exception e){
e.printStackTrace();
}
}
/*public static java.beans.Statement createStatement() {
return null;
}*/
}
Here is the snippet of the code of AddStudent.java file
import javax.swing.*;
import java.awt.*;
import java.util.*;
import java.awt.event.*;
import java.sql.*;
//import com.toedter.calendar.JDateChooser;
public class AddStudent extends JFrame implements ActionListener {
JTextField tfname, tffname, tffaddress, tfphone, tfemail, tfX, tfXII, tfAdhar, tfdob;
JLabel labelrollno;
JComboBox<String> cbCourse, cbBranch;
JButton btnSubmit, btnCancel;
// JDateChooser dobChooser;
/*
* create a object for random class
* which create some random number for roll number
*/
Random ran = new Random();
long first4 = Math.abs((ran.nextLong() % 9000L) + 1000L);
AddStudent() {
// for layout
setSize(900, 700);
setLocation(350, 50);
setLayout(null); // cause we want our own layout
// for heading
JLabel heading = new JLabel("New student Details");
heading.setBounds(310, 30, 500, 50);
heading.setFont(new Font("serif", Font.BOLD, 30));
add(heading);
// name label
JLabel labelName = new JLabel("Name");
labelName.setBounds(50, 150, 100, 30);
labelName.setFont(new Font("serif", Font.BOLD, 20));
add(labelName);
// name input box
tfname = new JTextField();
tfname.setBounds(200, 150, 150, 30);
add(tfname);
// father name label
JLabel labelFName = new JLabel("Fathers Name");
labelFName.setBounds(400, 150, 200, 30);
labelFName.setFont(new Font("serif", Font.BOLD, 20));
add(labelFName);
// father name input box
tffname = new JTextField();
tffname.setBounds(600, 150, 150, 30);
add(tffname);
// roll name label
JLabel lblRollNo = new JLabel("Roll Number");
lblRollNo.setBounds(50, 200, 200, 30);
lblRollNo.setFont(new Font("serif", Font.BOLD, 20));
add(lblRollNo);
setVisible(true);
// roll nameinput box
labelrollno = new JLabel("1533" + first4);
labelrollno.setBounds(200, 200, 200, 30);
labelrollno.setFont(new Font("serif", Font.BOLD, 20));
add(labelrollno);
setVisible(true);
// date of birth
JLabel lblDob = new JLabel("Date of Birth");
lblDob.setBounds(400, 200, 200, 30);
lblDob.setFont(new Font("serif", Font.BOLD, 20));
add(lblDob);
// date of birth input box
tfdob = new JTextField();
tfdob.setBounds(600, 200, 150, 30);
add(tfdob);
// date of birth input box
/*
* dobChooser = new JDateChooser();
* dobChooser.setBounds(600, 200, 150, 30);
* add(dobChooser);
*/
// address label
JLabel labeladdress = new JLabel("Address Name");
labeladdress.setBounds(50, 250, 200, 30);
labeladdress.setFont(new Font("serif", Font.BOLD, 20));
add(labeladdress);
// address name input box
tffaddress = new JTextField();
tffaddress.setBounds(200, 250, 150, 30);
add(tffaddress);
// phone number label
JLabel labelPhone = new JLabel("Phone Number");
labelPhone.setBounds(400, 250, 200, 30);
labelPhone.setFont(new Font("serif", Font.BOLD, 20));
add(labelPhone);
// phone number input box
tfphone = new JTextField();
tfphone.setBounds(600, 250, 150, 30);
add(tfphone);
// Email Id
JLabel labelemail = new JLabel("Email Id");
labelemail.setBounds(50, 300, 200, 30);
labelemail.setFont(new Font("serif", Font.BOLD, 20));
add(labelemail);
// Email Id input box
tfemail = new JTextField();
tfemail.setBounds(200, 300, 150, 30);
add(tfemail);
// Class X label
JLabel labelX = new JLabel("Class X(%)");
labelX.setBounds(400, 300, 200, 30);
labelX.setFont(new Font("serif", Font.BOLD, 20));
add(labelX);
// Class X input box
tfX = new JTextField();
tfX.setBounds(600, 300, 150, 30);
add(tfX);
// Class XII label
JLabel labelXII = new JLabel("Class XII(%)");
labelXII.setBounds(50, 350, 200, 30);
labelXII.setFont(new Font("serif", Font.BOLD, 20));
add(labelXII);
// Class XII input box
tfXII = new JTextField();
tfXII.setBounds(200, 350, 150, 30);
add(tfXII);
// Adhar Number label
JLabel labelAdhar = new JLabel("Adhar Number");
labelAdhar.setBounds(400, 350, 200, 30);
labelAdhar.setFont(new Font("serif", Font.BOLD, 20));
add(labelAdhar);
// Adhar Number input box
tfAdhar = new JTextField();
tfAdhar.setBounds(600, 350, 150, 30);
add(tfAdhar);
// dropdown for course
/*
* JLabel labelCourse = new JLabel("Course");
* labelCourse.setBounds(50, 400, 200, 30);
* labelCourse.setFont(new Font("serif", Font.BOLD, 20));
* add(labelCourse);
* String course[] = { "B.Tech", "M.Tech", "BBA", "MBA", "BCA", "MCA" };
* cbCourse = new JComboBox(course);
* cbCourse.setBounds(200, 400, 150, 30);
* cbCourse.setBackground(Color.WHITE);
* add(cbCourse);
*/
// dropdown for course
JLabel labelCourse = new JLabel("Course");
labelCourse.setBounds(50, 400, 200, 30);
labelCourse.setFont(new Font("serif", Font.BOLD, 20));
add(labelCourse);
String course[] = { "B.Tech", "M.Tech", "BBA", "MBA", "BCA", "MCA" };
cbCourse = new JComboBox<>(course);
cbCourse.setBounds(200, 400, 150, 30);
cbCourse.setBackground(Color.WHITE);
add(cbCourse);
// dropdown for branch
JLabel labelBranch = new JLabel("Branch");
labelBranch.setBounds(400, 400, 200, 30);
labelBranch.setFont(new Font("serif", Font.BOLD, 20));
add(labelBranch);
String[] branch = { "CSE", "ECE", "EEE", "ME", "CE", "IT", "Not Applicable" };
cbBranch = new JComboBox<>(branch);
cbBranch.setBounds(600, 400, 150, 30);
cbBranch.setBackground(Color.WHITE);
add(cbBranch);
// submit button
btnSubmit = new JButton("Submit");
btnSubmit.setBounds(200, 450, 150, 30);
btnSubmit.setBackground(Color.BLACK);
btnSubmit.setForeground(Color.WHITE);
btnSubmit.addActionListener(this);
add(btnSubmit);
// cancel button
btnCancel = new JButton("Cancel");
btnCancel.setBounds(400, 450, 150, 30);
btnCancel.setBackground(Color.BLACK);
btnCancel.setForeground(Color.WHITE);
btnCancel.addActionListener(this);
add(btnCancel);
setVisible(true);
}
public void actionPerformed(ActionEvent ae) {
if (ae.getSource() == btnSubmit) {
// taking all the values
String fname = tfname.getText();
String ffname = tffname.getText();
String rollno = labelrollno.getText();
String dob = tfdob.getText();
String address = tffaddress.getText();
String phone = tfphone.getText();
String email = tfemail.getText();
String class_x = tfX.getText();
String class_xii = tfXII.getText();
String adhar = tfAdhar.getText();
String course = (String) cbCourse.getSelectedItem();
String branch = (String) cbBranch.getSelectedItem();
// inserting into database
try {
String query = "insert into student values('"+fname+"', '"+ffname+"', '"+rollno+"', '"+dob+"', '"+address+"', '"+phone+"', '"+email+"', '"+class_x+"', '"+class_xii+"', '"+adhar+"', '"+course+"', '"+branch+"')";
Conn con = new Conn();
con.s.executeUpdate(query);
JOptionPane.showMessageDialog(null, "Student Details Inserted Successfully");
setVisible(false);
} catch (Exception e) {
e.printStackTrace();
}
} else {
setVisible(false);
}
}
public static void main(String[] args) {
new AddStudent();
}
}
Here is the proof that I already include the mysql-Connector jar file
Error and excception while I run the code
java.lang.ClassNotFoundException: com.mysql.cj.jdbc.Driver
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
at java.base/java.lang.Class.forName0(Native Method)
at java.base/java.lang.Class.forName(Class.java:375)
at Conn.<init>(Conn.java:19)
at AddStudent.actionPerformed(AddStudent.java:225)
at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1972)
at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2313)
at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405)
at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262)
at java.desktop/javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:279)
at java.desktop/java.awt.Component.processMouseEvent(Component.java:6626)
at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3389)
at java.desktop/java.awt.Component.processEvent(Component.java:6391)
at java.desktop/java.awt.Container.processEvent(Container.java:2266)
at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:5001)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2324)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4833)
at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4948)
at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Container.java:4575)
at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Container.java:4516)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2310)
at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2780)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4833)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:773)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:722)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:716)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:97)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:746)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:744)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:743)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
java.lang.NullPointerException: Cannot invoke "java.sql.Statement.executeUpdate(String)" because "<local15>.s" is null
at AddStudent.actionPerformed(AddStudent.java:226)
at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1972)
at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2313)
at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405)
at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262)
at java.desktop/javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:279)
at java.desktop/java.awt.Component.processMouseEvent(Component.java:6626)
at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3389)
at java.desktop/java.awt.Component.processEvent(Component.java:6391)
at java.desktop/java.awt.Container.processEvent(Container.java:2266)
at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:5001)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2324)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4833)
at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4948)
at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Container.java:4575)
at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Container.java:4516)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2310)
at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2780)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4833)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:773)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:722)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:716)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:97)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:746)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:744)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:743)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
But when I hit Run Java that time no problem but the data is not inserted into database
Data is not insert image
I have been working on a Java code snippet to insert data into a MySQL database table, but I’m encountering unexpected behavior. Here’s a summary of what I’ve tried and the expected outcome:
I have established a JDBC connection to the MySQL database using the appropriate connection parameters (URL, username, and password).
After successfully establishing the connection, I attempted to insert data into the table using an SQL insert statement.
However, despite running the code without any errors, the data is not being stored in the database table as expected.
I was expecting the code to insert the provided data into the specified table, but it seems to complete without any errors, yet the data is not being stored. I have verified that the connection parameters and SQL query are correct.
Any guidance or suggestions regarding this issue would be greatly appreciated. Thank you in advance for your help!
2
Answers
There could be multiple reasons for ClassNotFoundException :
[1] Incorrect Jar Placement: Ensure that you have placed the MySQL jar file in the correct location within your project structure. Typically, you would add the jar file to the "lib" folder or include it as a dependency in your build tool configuration (e.g., Maven or Gradle).
[2] Jar file compatibility : Make sure your jar file compatible with your MySQL server version. For example if you are using MySQL latest version then you should use latest/newer version of MySQL connector jar file
[3] IDE Configuration : If you are using IntelliJ or Eclipse then correctly setting into your project settings or build path
make sure you have add the mysql Driver jar. Since you use reflection to load class Driver, it won’t prompt errors when compiling.Only when the code is running to the process of loading class Driver, errors merge.