JDBC or Springboot or hibernate throw this exception when you mentioned driver as org.hsqldb.jdbcDriver in your JDBC code or XML configuration or data source configuration properties file but required database driver jar or dependencies is not added in class path.

This exception occurs by below methods :

• The forName method in the class Class.

                 Class.forName(java.lang.String)

• The findSystemClass method in the class ClassLoader.

                ClassLoader.findSystemClass()

• The loadClass method in class ClassLoader.

                ClassLoader.loadClass(java.lang.String, boolean)

java.lang.ClassNotFoundException is Checked Exception which is subclass of  java.lang.ReflectiveOperationException. This  is thrown when application load a class by String name whose definition is not found.

Constructors

• ClassNotFoundException(): Constructs a ClassNotFoundException with no detail message.
• ClassNotFoundException(String s) : Constructs a ClassNotFoundException with the specified detail message.
• ClassNotFoundException(String s, Throwable ex) : Constructs a ClassNotFoundException with the specified detail message and optional exception that was raised while loading the class.

 Difference between Class.forName() and ClassLoader.loadClass()

Example 1: ClassNotFoundException

Below is example of connecting with database and retrieve data from sql table. This will throw ClassNotFoundException because sql driver jar is not in classpath. After this example also mentioned solution.

package example;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class ClassNotFoundException1 {

public static void main(String[] args) {
try {
Class.forName("<strong>org.hsqldb.jdbcDriver</strong>");

Connection con = DriverManager.getConnection("jdbc:hsqldb:hsql//localhost:3306/FacingIssuesOnITDB", "root", "");

Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("select name from employee");
String dbtime;
while (rs.next()) {
dbtime = rs.getString(1);
System.out.println(dbtime);
}

con.close();

} catch (ClassNotFoundException | SQLException e) {
System.out.println("Connection Failed! Check output console");
e.printStackTrace();
}

}

}

Output:

Connection Failed! Check output console
<pre><code>
<strong>java.lang.ClassNotFoundException: org.hsqldb.jdbcDriver</strong>
	at java.net.URLClassLoader.findClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at org.springframework.util.ClassUtils.forName(ClassUtils.java:251)
	at org.springframework.jdbc.datasource.embedded.HsqlEmbeddedDatabaseConfigurer.getInstance(HsqlEmbeddedDatabaseConfigurer.java:48)
	at org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseConfigurerFactory.getConfigurer(EmbeddedDatabaseConfigurerFactory.java:43)
	... 54 common frames omitted
</code></pre>

Solutions:

For solving ClassNotFoundException by Class.ForName() method  considering above example to load MySQL driver same way you can follow for other classes and different DB drivers.

• Download connector from here https://sourceforge.net/projects/hsqldb/files/
• Select JDBC driver for HSQLDB
• Click on Platform Independent (Architecture Independent), ZIP Archive
• Download the file and unzip it

Solution in Eclipse :Follow below steps :

• Right click your project folder and open up Properties.
• From the right panel, select Java Build Path then go to Libraries tab.
• Select Add External JARs to import the HSQLDB driver.
• From the right panel, select Deployment Assembly.
• Select Add…, then select Java Build Path Entries and click Next.
• You should see the SQL driver on the list. Select it and click first.

Tomcat :

If directly running from tomcat. Just copy the HSQL-Connector.jar into Tomcat’s lib folder/directory, and then remove the jar from the webApp’s lib folder, and then, run the project.

Maven Springboot application

Add below dependency in your pom.xml file

<dependency>
    <groupId>org.hsqldb</groupId>
    <artifactId>hsqldb</artifactId>
</dependency>

Summary :

• Define what is ClassNotFoundException.
• What are methods throws ClassNotFoundException?
• Example for ClassNotFoundException.
• How to fix ClassNotFoundException in Eclipse and Tomcat.
• How to fix Springboot maven applications.