Java Hibernate-无法连接到H2

Question

我需要帮助。我不知道这个项目出了什么问题。我无法连接到h2数据库。即使我没有持久化任何对象，只是关闭连接，我也会得到错误。

对不起，我知道，这已经被问过几次了，但没有一个答案符合我的情况。

我得到的错误：

pom.xml：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>brudnopis.com</groupId>
    <artifactId>brudnopis2</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>

        <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>5.2.12.Final</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/com.h2database/h2 -->
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <version>1.4.196</version>
            <scope>test</scope>
        </dependency>

    </dependencies>

</project>

Hibernate Utils类：

public class HibernateUtils {

    private static final SessionFactory sessionFactory;

    static {
        try {
            sessionFactory = new Configuration().configure("hibernate.cfg.xml").buildSessionFactory();
        } catch (Throwable ex) {
            ex.printStackTrace();
            System.err.println("########### Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError("Connection to database error!");
        }
    }

    public static Session openSession() throws Exception {
        Session session;
        try {
            session = sessionFactory.openSession();
        } catch (Exception e) {
            e.printStackTrace();
            throw new Exception("Connection to database error!");
        }
        return session;
    }

    public static void closeSession(){
        sessionFactory.close();
    }
}

储存库

public class EmployeeRepository {

    // Create

    public static void addNewEmployee(EmployeeEntity employee){

        Session session = null;
        try {
            session = HibernateUtils.openSession();
            session.getTransaction().begin();
            session.saveOrUpdate(employee);
            session.getTransaction().commit();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            if (session != null && session.isOpen()) {
                session.close();
            }
        }
    }

    // Read

    public static List<EmployeeEntity> listAllEmployees(){

        List<EmployeeEntity> listEmployees = new ArrayList<EmployeeEntity>();

        Session session = null;
        try {
            session = HibernateUtils.openSession();
            listEmployees = session.createQuery("SELECT e FROM EmployeeEntity e").getResultList();
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            if (session != null && session.isOpen()) {
                session.close();
            }
        }
        return listEmployees;
    }

    // Update

    public static void editExistingEmployee(EmployeeEntity employee){

        Session session = null;
        try {
            session = HibernateUtils.openSession();
            session.getTransaction().begin();
            session.merge(employee);
            session.getTransaction().commit();
        }catch (Exception e){
            e.printStackTrace();
        }finally{
            if (session != null && session.isOpen()) {
                session.close();
            }
        }
    }

    //Delete

    public static void deleteEmployee(int idToDelete){

        Session session = null;
        try {
            session = HibernateUtils.openSession();
            EmployeeEntity employeeToDelete = session.find(EmployeeEntity.class, idToDelete);
            session.getTransaction().begin();
            session.remove(employeeToDelete);
            session.getTransaction().commit();
        }catch (Exception e){
            e.printStackTrace();
        }finally{
            if (session != null && session.isOpen()) {
                session.close();
            }
        }
    }
}

@Entity
@Table(name = "employees")
public class EmployeeEntity {

    @Id
    @Column(name = "id")
    private int id;
    @Column(name = "employee_id")
    private int employeeId;
    @Column(name = "first_name")
    private String firstName;
    @Column(name = "last_name")
    private String lastName;

    public EmployeeEntity(int id, int employeeId, String firstName, String lastName) {
        this.id = id;
        this.employeeId = employeeId;
        this.firstName = firstName;
        this.lastName = lastName;
    }

    public EmployeeEntity(){}

    @Override
    public String toString() {
        return "EmployeeEntity{" +
                "id=" + id +
                ", employeeId=" + employeeId +
                ", firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                '}';
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public int getEmployeeId() {
        return employeeId;
    }

    public void setEmployeeId(int employeeId) {
        this.employeeId = employeeId;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
}

public class EmployeesApp {
    public static void main(String[] args) throws Exception {

        Scanner sc = new Scanner(System.in);

        System.out.println("Menu");
        System.out.println("====");
        System.out.println("1. Write data to database");
        System.out.println("2. Read data from database");
        System.out.println("3. Exit");

        int userChoice = sc.nextInt();

        switch(userChoice){
            case 1:
                EmployeeEntity employee1 = new EmployeeEntity(1,10001,"Jon", "Doe");
                EmployeeRepository.addNewEmployee(employee1);
                System.out.println(EmployeeRepository.listAllEmployees());
            case 3:
                break;
        }
        HibernateUtils.closeSession();
    }
}

项目结构：

Answer 1

您的应用程序无法在运行时找到数据库驱动程序，因此由:java.lang.ClassNotFoundException引起的错误：无法加载请求的类:org.h2.driver。

按以下方式更改您的H2依赖项：

    <dependency>
        <groupId>com.h2database</groupId>
        <artifactId>h2</artifactId>
        <version>1.4.196</version>
        <scope>runtime</scope> <!-- Here you are saying this dependency is needed at runtime, not just at testing -->
    </dependency>

再见！