无法加载类[org.postgresql.Driver]。

Question

与Hibernate 4.3.11和Tomcat 7一起使用的Hibernate hibernate.cfg.xml

以下是内容：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>

        <property name="hibernate.dialect">org.hibernate.dialect.PostgreSQLDialect</property>
        <property name="hibernate.connection.driver_class">org.postgresql.Driver</property>
        <property name="hibernate.connection.url">jdbc:postgresql://localhost:5432/firstapp</property>
        <property name="hibernate.connection.username">postgres</property>
        <property name="hibernate.connection.password">root</property>
        <property name="show_sql">false</property>

        </session-factory>
    </hibernate-configuration>

我收到了以下错误信息：

   SEVERE: Servlet.service() for servlet [com.pgdoc.controller.AddUser] in context with path [/pgdoc] threw exception
    org.hibernate.boot.registry.classloading.spi.ClassLoadingException: Unable to load class [org.postgresql.Driver]
        at org.hibernate.boot.registry.classloading.internal.ClassLoaderServiceImpl.classForName(ClassLoaderServiceImpl.java:245)
        at org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl.loadDriverIfPossible(DriverManagerConnectionProviderImpl.java:200)
        at org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl.buildCreator(DriverManagerConnectionProviderImpl.java:156)
        at org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl.configure(DriverManagerConnectionProviderImpl.java:95)
        at org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.configureService(StandardServiceRegistryImpl.java:111)
        at org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:234)
        at org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:206)
        at org.hibernate.engine.jdbc.internal.JdbcServicesImpl.buildJdbcConnectionAccess(JdbcServicesImpl.java:260)
        at org.hibernate.engine.jdbc.internal.JdbcServicesImpl.configure(JdbcServicesImpl.java:94)
        at org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.configureService(StandardServiceRegistryImpl.java:111)
        at org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:234)
        at org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:206)
        at org.hibernate.cfg.Configuration.buildTypeRegistrations(Configuration.java:1887)
        at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1845)
        at com.pgdoc.controller.AddUser.doPost(AddUser.java:53)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
        at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:445)
        at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1115)
        at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
        at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Unknown Source)
    Caused by: java.lang.ClassNotFoundException: Could not load requested class : org.postgresql.Driver
        at org.hibernate.boot.registry.classloading.internal.ClassLoaderServiceImpl$AggregatedClassLoader.findClass(ClassLoaderServiceImpl.java:230)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Unknown Source)
        at org.hibernate.boot.registry.classloading.internal.ClassLoaderServiceImpl.classForName(ClassLoaderServiceImpl.java:242)
        ... 36 more

- Rajarshi Das

---

似乎无法加载org.postgresql.Driver，您可能需要从https://jdbc.postgresql.org/自行下载并将其安装在服务器的正确路径中。 - Eelke

我有PostgreSQL驱动程序postgresql42.14.jar。 - Rajarshi Das

根据错误提示，运行时未在类路径上找到PostgreSQL JDBC驱动程序。 - Mark Rotteveel

@MarkRotteveel 谢谢你的评论，我已将 jar 添加到 libraries 中，我应该将它放在 src/ 中吗？ - Rajarshi Das

在打包WAR文件时，库文件不应该放在src文件夹中，而应该包含在WEB-INF/lib文件夹中。 - Mark Rotteveel

Answer 1

根据这篇帖子，您需要将postgresql-<version>.jar直接放在您servlet容器的lib文件夹中。例如，如果您正在使用Apache Tomcat，只需将您的jar放在<TOMCAT_ROOT>/lib下即可完成设置。您可以从这里下载postgresql JDBC驱动程序。

- Pipo