java - Hibernate:在 Servlet 中运行时找不到合适的驱动程序

Question

所以，现在我正在制作我的第一个网络应用程序。这在网络方面是相对粗糙的事情。一些 servlet 和 JSP 页面，以及 Hibernate 和数据库访问。没有框架，MVC，任何这些(是的，这一切都非常重要，但这只是在我开始处理更大的事情之前对我对 Servlet 的理解程度的快速测试)。

无论如何，我在使用 Hibernate 时遇到了问题。奇怪的是，它与 Hibernate 与 servlet/服务器的交互有关。

让我解释一下:我有一个测试类(实际上是一个名为 Test 的类)，我只是用它来测试我的 ORM 映射注释。它工作完美。就像110%一样完美。建立连接、操作数据库等。这是它的代码，同样只是一个简单的测试(ClassesServiceImpl 是一个内部带有 Hibernate SessionFactory 的服务):

public static void main(String[] args) {
    ClassesServiceImpl service = (ClassesServiceImpl) ClassesServiceImpl.getInstance();

    Student student = service.createStudent("Bob", "Saget", LocalDate.of(1988,10,26), 11);
    Course math = new Course("Math", "Anderson", 5);
    student.addCourse(math);
    service.saveStudent(student);

    service.close();
}

我刚刚粘贴的代码有效。没问题，运行这个后我可以直接进入MySQL，变化就在那里。

问题是，当我尝试在 Servlet 中执行完全相同的操作时，出现异常。这是代码:

private ClassesService service;

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    List<Student> studentList = service.getAllStudents();
    req.setAttribute("studentList", studentList);
    req.getRequestDispatcher("/studentlist.jsp").forward(req, resp);
}

@Override
public void init(ServletConfig config) throws ServletException {
    service = ClassesServiceImpl.getInstance();
}

当我运行该 Servlet 时，出现 Hibernate ServiceException:无法创建请求的服务 [org.hibernate.engine.jdbc.env.spi.JdbcEnvironment]。堆栈跟踪有一系列原因，涉及调用 DriverManager#getConnection 的错误，并最终以 SQLException 结束:找不到 jdbc:mysql://localhost:3306/classes 的合适驱动程序。

我在下面粘贴了完整的堆栈跟踪。我只是不明白为什么会发生这种情况。当我不在服务器上使用它时它工作得很好，但是当我在服务器上使用它时就会发生这种情况。

如果有帮助，我们将不胜感激。谢谢。

org.hibernate.service.spi.ServiceException: Unable to create requested service [org.hibernate.engine.jdbc.env.spi.JdbcEnvironment]
org.hibernate.service.internal.AbstractServiceRegistryImpl.createService(AbstractServiceRegistryImpl.java:244)
org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:208)
org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:189)
org.hibernate.engine.jdbc.internal.JdbcServicesImpl.configure(JdbcServicesImpl.java:51)
org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.configureService(StandardServiceRegistryImpl.java:94)
org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:217)
org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:189)
org.hibernate.boot.model.process.spi.MetadataBuildingProcess.handleTypes(MetadataBuildingProcess.java:352)
org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:111)
org.hibernate.boot.model.process.spi.MetadataBuildingProcess.build(MetadataBuildingProcess.java:83)
org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:418)
org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:87)
org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:692)
org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:724)
io.craigmiller160.classes.servlet.StudentListServlet.doGet(StudentListServlet.java:29)
javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
root cause

org.hibernate.exception.JDBCConnectionException: Error calling DriverManager#getConnection
org.hibernate.exception.internal.SQLStateConversionDelegate.convert(SQLStateConversionDelegate.java:115)
org.hibernate.engine.jdbc.connections.internal.BasicConnectionCreator$1$1.convert(BasicConnectionCreator.java:101)
org.hibernate.engine.jdbc.connections.internal.BasicConnectionCreator.convertSqlException(BasicConnectionCreator.java:123)
org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionCreator.makeConnection(DriverManagerConnectionCreator.java:37)
org.hibernate.engine.jdbc.connections.internal.BasicConnectionCreator.createConnection(BasicConnectionCreator.java:58)
org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl.configure(DriverManagerConnectionProviderImpl.java:89)
org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.configureService(StandardServiceRegistryImpl.java:94)
org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:217)
org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:189)
org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator.buildJdbcConnectionAccess(JdbcEnvironmentInitiator.java:145)
org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator.initiateService(JdbcEnvironmentInitiator.java:66)
org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator.initiateService(JdbcEnvironmentInitiator.java:35)
org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.initiateService(StandardServiceRegistryImpl.java:88)
org.hibernate.service.internal.AbstractServiceRegistryImpl.createService(AbstractServiceRegistryImpl.java:234)
org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:208)
org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:189)
org.hibernate.engine.jdbc.internal.JdbcServicesImpl.configure(JdbcServicesImpl.java:51)
org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.configureService(StandardServiceRegistryImpl.java:94)
org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:217)
org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:189)
org.hibernate.boot.model.process.spi.MetadataBuildingProcess.handleTypes(MetadataBuildingProcess.java:352)
org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:111)
org.hibernate.boot.model.process.spi.MetadataBuildingProcess.build(MetadataBuildingProcess.java:83)
org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:418)
org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:87)
org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:692)
org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:724)
io.craigmiller160.classes.servlet.StudentListServlet.doGet(StudentListServlet.java:29)
javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
root cause

java.sql.SQLException: No suitable driver found for jdbc:mysql://localhost:3306/classes
java.sql.DriverManager.getConnection(DriverManager.java:689)
java.sql.DriverManager.getConnection(DriverManager.java:208)
org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionCreator.makeConnection(DriverManagerConnectionCreator.java:34)
org.hibernate.engine.jdbc.connections.internal.BasicConnectionCreator.createConnection(BasicConnectionCreator.java:58)
org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl.configure(DriverManagerConnectionProviderImpl.java:89)
org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.configureService(StandardServiceRegistryImpl.java:94)
org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:217)
org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:189)
org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator.buildJdbcConnectionAccess(JdbcEnvironmentInitiator.java:145)
org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator.initiateService(JdbcEnvironmentInitiator.java:66)
org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator.initiateService(JdbcEnvironmentInitiator.java:35)
org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.initiateService(StandardServiceRegistryImpl.java:88)
org.hibernate.service.internal.AbstractServiceRegistryImpl.createService(AbstractServiceRegistryImpl.java:234)
org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:208)
org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:189)
org.hibernate.engine.jdbc.internal.JdbcServicesImpl.configure(JdbcServicesImpl.java:51)
org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.configureService(StandardServiceRegistryImpl.java:94)
org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:217)
org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:189)
org.hibernate.boot.model.process.spi.MetadataBuildingProcess.handleTypes(MetadataBuildingProcess.java:352)
org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:111)
org.hibernate.boot.model.process.spi.MetadataBuildingProcess.build(MetadataBuildingProcess.java:83)
org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:418)
org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:87)
org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:692)
org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:724)
io.craigmiller160.classes.servlet.StudentListServlet.doGet(StudentListServlet.java:29)
javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)

编辑:

有些人提到驱动程序需要位于我的类路径中。嗯，确实如此。记住我说过的话:当我不在 servlet 中运行它时它会起作用。我上面粘贴的测试代码工作正常。只有当我在 servlet 中运行它时才会出现问题。

<!-- MySQL ConnectorJ -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.36</version>
</dependency>

Answer 1

No sutiable driver found for jdbc:mysql://localhost:3306/classes

此错误只是表明当您在 Web 应用程序中执行时，MySQL-JDBC 驱动程序不在您的类路径中。

• 确保 WEB-INF/lib 目录中存在 jar 文件并添加到 类路径 - Follow this

您在简单 Java 程序中没有遇到任何问题，因为该 Jar 文件已添加到您的 Windows/Linux 操作系统类路径中 - Check this