java - 需要了解 java.sql.SQLException : No suitable driver found for jdbc:postgresql error 原因的建议

Question

我正在编写一个 Web 应用程序，我正在尝试使用 hibernate 连接到我项目中的 PostgreSQL 8.4.13 数据库。到目前为止我一直没有成功，我收到以下错误(java.sql.SQLException:找不到适合 jdbc 的驱动程序:postgresql://localhost:5432/mcappdb)- 跟踪在底部。我浏览了很多论坛，但没有找到解决我的问题的方法:

我已将以下依赖项包含到我的 pom.xml 中，并且构建成功。我正在使用“mvn jboss-as:deploy”部署到 jboss eap 6。

    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-core</artifactId>
        <version>4.2.5.Final</version>
    </dependency>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-entitymanager</artifactId>
        <version>4.2.5.Final</version>
    </dependency>  
    <dependency>
        <groupId>postgresql</groupId>
        <artifactId>postgresql</artifactId>
        <version>8.4-702.jdbc4</version>
    </dependency>

我已经配置了 persistence.xml 文件如下:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
         http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">

<persistence-unit name="mcappdb" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>

    <class>uk.co.metasphere.entities.userConfig</class>

    <properties>
        <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect"/>
        <property name="hibernate.connection.url" value="jdbc:postgresql://localhost:5432/mcappdb"/>
        <property name="hibernate.connection.username" value="mcapp"/>
        <property name="hibernate.connection.password" value="mc2000"/>
        <property name="hibernate.connection.driver_class" value="org.postgresql.Driver"/>
    </properties>
</persistence-unit>

此文件位于 src/main/resources/META-INF 目录中。

应用程序成功部署，但在尝试使用 hibernate 模式连接到数据库时引发错误。我的应用程序连接代码如下:

EntityManagerFactory emf = Persistence.createEntityManagerFactory("mcappdb");
EntityManager em1 = emf.createEntityManager();
userConfig uscon = em1.find(userConfig.class, 0);

错误是在调用 em1.find() 时引发的。

我已经阅读了很多论坛帖子。大多数表明错误要么是因为驱动程序不在类路径中，要么是定义的 url 错误。驱动程序 jar 文件位于/target/MCapp-1.0/WEB-INF/lib/postgresql-8.4-702.jdbc4.jar 中，我相信它与所有其他相关 jar 文件部署在同一位置(正确吗？)。如果我通过基本的 JBDC 连接(而不是 hibernate )进行连接，我使用的 url 就可以工作，所以我相信这也是可以的。

另一个建议是我需要使用以下代码加载驱动程序:

Class.forName("org.postgresql.Driver");

这也无济于事。

既然直接的 JDBC 连接工作正常，那么 Hibernate 似乎是问题所在？任何人都可以告诉我问题可能是什么或者我如何进一步调查它？ hibernate 在哪里/如何寻找数据库驱动程序？我是否需要将它部署到另一个目录或进行另一个配置步骤以便它可以找到它？

感谢收到的任何帮助。

错误痕迹:

15:12:53,932 ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/MCapp-1.0].[Mcapp Application]] (http-/0.0.0.0:8080-1) Servlet.service() for servlet Mcapp Application threw exception: java.sql.SQLException: No suitable driver found for jdbc:postgresql://localhost:5432/mcappdb
at java.sql.DriverManager.getConnection(DriverManager.java:596) [rt.jar:1.7.0_25]
at java.sql.DriverManager.getConnection(DriverManager.java:187) [rt.jar:1.7.0_25]
at org.hibernate.service.jdbc.connections.internal.DriverManagerConnectionProviderImpl.getConnection(DriverManagerConnectionProviderImpl.java:193) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.internal.AbstractSessionImpl$NonContextualJdbcConnectionAccess.obtainConnection(AbstractSessionImpl.java:278) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.obtainConnection(LogicalConnectionImpl.java:297) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.getConnection(LogicalConnectionImpl.java:169) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.engine.jdbc.internal.proxy.ConnectionProxyHandler.extractPhysicalConnection(ConnectionProxyHandler.java:82) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.engine.jdbc.internal.proxy.ConnectionProxyHandler.continueInvocation(ConnectionProxyHandler.java:138) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.engine.jdbc.internal.proxy.AbstractProxyHandler.invoke(AbstractProxyHandler.java:81) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at com.sun.proxy.$Proxy17.prepareStatement(Unknown Source)
at org.hibernate.engine.jdbc.internal.StatementPreparerImpl$5.doPrepare(StatementPreparerImpl.java:147) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.engine.jdbc.internal.StatementPreparerImpl$StatementPreparationTemplate.prepareStatement(StatementPreparerImpl.java:166) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.engine.jdbc.internal.StatementPreparerImpl.prepareQueryStatement(StatementPreparerImpl.java:145) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.loader.Loader.prepareQueryStatement(Loader.java:1711) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.loader.Loader.doQuery(Loader.java:828) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:289) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:259) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.loader.Loader.loadEntity(Loader.java:2033) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:82) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:72) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.persister.entity.AbstractEntityPersister.load(AbstractEntityPersister.java:3719) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.event.internal.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:449) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.event.internal.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:418) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.event.internal.DefaultLoadEventListener.load(DefaultLoadEventListener.java:204) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.event.internal.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:251) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.event.internal.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:148) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.internal.SessionImpl.fireLoad(SessionImpl.java:1079) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.internal.SessionImpl.access$2200(SessionImpl.java:172) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.load(SessionImpl.java:2425) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.internal.SessionImpl.get(SessionImpl.java:975) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.ejb.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:802) [hibernate-entitymanager-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at org.hibernate.ejb.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:776) [hibernate-entitymanager-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
at uk.co.metasphere.McappUI.init(McappUI.java:210) [classes:]
at com.vaadin.ui.UI.doInit(UI.java:607) [vaadin-server-7.1.5.jar:7.1.5]
at com.vaadin.server.communication.UIInitHandler.getBrowserDetailsUI(UIInitHandler.java:223) [vaadin-server-7.1.5.jar:7.1.5]
at com.vaadin.server.communication.UIInitHandler.synchronizedHandleRequest(UIInitHandler.java:73) [vaadin-server-7.1.5.jar:7.1.5]
at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:37) [vaadin-server-7.1.5.jar:7.1.5]
at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1371) [vaadin-server-7.1.5.jar:7.1.5]
at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:238) [vaadin-server-7.1.5.jar:7.1.5]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.1.Final-redhat-1.jar:1.0.1.Final-redhat-1]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:329) [jbossweb-7.0.16.Final-redhat-1.jar:]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:248) [jbossweb-7.0.16.Final-redhat-1.jar:]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:275) [jbossweb-7.0.16.Final-redhat-1.jar:]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:161) [jbossweb-7.0.16.Final-redhat-1.jar:]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:489) [jbossweb-7.0.16.Final-redhat-1.jar:]
at org.jboss.as.jpa.interceptor.WebNonTxEmCloserValve.invoke(WebNonTxEmCloserValve.java:50) [jboss-as-jpa-7.1.2.Final-redhat-1.jar:7.1.2.Final-redhat-1]
at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:153) [jboss-as-web-7.1.2.Final-redhat-1.jar:7.1.2.Final-redhat-1]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:155) [jbossweb-7.0.16.Final-redhat-1.jar:]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) [jbossweb-7.0.16.Final-redhat-1.jar:]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) [jbossweb-7.0.16.Final-redhat-1.jar:]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:368) [jbossweb-7.0.16.Final-redhat-1.jar:]
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:877) [jbossweb-7.0.16.Final-redhat-1.jar:]
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:679) [jbossweb-7.0.16.Final-redhat-1.jar:]
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:931) [jbossweb-7.0.16.Final-redhat-1.jar:]
at java.lang.Thread.run(Thread.java:724) [rt.jar:1.7.0_25]

Answer 1

将您的驱动程序放在应用服务器的 lib 文件夹中。您正在使用的 JPA 库在您的应用程序服务器(而不是您的应用程序)中。您的应用程序服务器无法访问您应用程序中的类。参见 here