1. Error reporting issues
Caused by: java.lang.ClassNotFoundException: Could not load requested class : com.mysql.jdbc.Driver
2. Problem background
Create a new Java project, add Hibernate framework support, start the test (run the main() method in the default Main class), and an error occurs.
Main.java
import org.hibernate.HibernateException;
import org.hibernate.Metamodel;
import org.hibernate.query.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import javax.persistence.metamodel.EntityType;
import java.util.Map;
public class Main {
private static final SessionFactory ourSessionFactory;
static {
try {
Configuration configuration = new Configuration();
configuration.configure();
ourSessionFactory = configuration.buildSessionFactory();
} catch (Throwable ex) {
throw new ExceptionInInitializerError(ex);
}
}
public static Session getSession() throws HibernateException {
return ourSessionFactory.openSession();
}
public static void main(final String[] args) throws Exception {
final Session session = getSession();
try {
System.out.println("querying all the managed entities...");
final Metamodel metamodel = session.getSessionFactory().getMetamodel();
for (EntityType<?> entityType : metamodel.getEntities()) {
final String entityName = entityType.getName();
final Query query = session.createQuery("from " + entityName);
System.out.println("executing: " + query.getQueryString());
for (Object o : query.list()) {
System.out.println(" " + o);
}
}
} finally {
session.close();
}
}
}
The project structure is shown below:
3. Cause analysis
The driver package for the corresponding version of mysql is missing.
4. Solution
Step 1: Go to the official website to download the corresponding version of the driver, and then unzip it to get the jar package (this article takes downloading version 5.1.47 as an example)
Official website to download the corresponding version of the driver (jar package) address: https://downloads.mysql.com/archives/cj/
Downloaded file: mysql-connector-java-5.1.47.zip
Unzip the file and get the jar package: mysql-connector-java-5.1.47.jar
Step 2: Import the jar package into the project
Select mysql-connector-java-5.1.47.jar, as shown in the figure below.
After adding mysql-connector-java-5.1.47.jar, it is as shown in the figure below. Then click the "OK" button.
