无法加载类 [org.postgresql.Driver]答案

【问题标题】：Unable to load class [org.postgresql.Driver]无法加载类 [org.postgresql.Driver]
【发布时间】：2017-12-18 17:38:32
【问题描述】：

Hibernate hibernate.cfg.xml Hibernate 4.3.11 和 Tomcat 7

下面

<?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>

我得到以下错误

   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

【问题讨论】：

似乎无法加载 org.postgresql.Driver 您可能需要自己从jdbc.postgresql.org 下载并安装在服务器的正确路径中。
我有 postgrsql 驱动 postgresql42.14.jar
鉴于该错误，PostgreSQL JDBC 驱动程序在运行时不在类路径中。
@MarkRotteveel 感谢您的 cmets 我已将 jar 添加到库中，如果我将其放入 src/
库不属于src文件夹，打包WAR时，库应包含在WEB-INF/lib文件夹中。

标签： java postgresql hibernate jdbc

【解决方案1】：

根据this post，您需要将postgresql-<version>.jar 直接放在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 放到 <TOMCAT_ROOT>/lib 下，您就应该准备就绪了。

你可以从here下载postgresql JDBC驱动

【讨论】：