jartomcat:java。sql。SQLException:无法加载类：com。mysql。jdbc。类加载器的驱动程序

Question

在服务器上运行web应用程序时，我遇到以下异常：

使用的服务器：ApacheTomcat 8.5

异常：java。sql。SQLException:无法加载类：com。mysql。jdbc。ClassLoader的驱动程序

我试过很多东西，包括放ojdbc6。WEB-INF/lib文件夹中的jar， 将jar放入ApacheTomcat lib文件夹中，在项目的构建路径中，我手动添加了jar，这也是基于谷歌的发现，我尝试了一些在我的案例中没有成功的转变

从web应用程序的角度来看，类或资源加载按以下顺序查看存储库：

1. JVM的引导类
2. /WEB应用程序的WEB-INF/类
3. /WEB-INF/lib/*。web应用程序的jar
4. 系统类加载器类（如上所述）
5. 通用类加载器类（如上所述）

我把jar放在/WEB-INF/lib/文件夹中

Complete stack trace.

java.sql.SQLException: Unable to load class: com.mysql.jdbc.Driver from ClassLoader:java.net.URLClassLoader@76ed5528;ClassLoader:ParallelWebappClassLoader
  context: ROOT
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@76ed5528

    at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:283)
    at org.apache.tomcat.jdbc.pool.PooledConnection.connect(PooledConnection.java:203)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.createConnection(ConnectionPool.java:718)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.borrowConnection(ConnectionPool.java:650)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.init(ConnectionPool.java:468)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.<init>(ConnectionPool.java:143)
    at org.apache.tomcat.jdbc.pool.DataSourceProxy.pCreatePool(DataSourceProxy.java:118)
    at org.apache.tomcat.jdbc.pool.DataSourceProxy.createPool(DataSourceProxy.java:107)
    at org.apache.tomcat.jdbc.pool.DataSourceFactory.createDataSource(DataSourceFactory.java:554)
    at org.apache.tomcat.jdbc.pool.DataSourceFactory.getObjectInstance(DataSourceFactory.java:241)
    at org.apache.naming.factory.FactoryBase.getObjectInstance(FactoryBase.java:94)
    at javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:321)
    at org.apache.naming.NamingContext.lookup(NamingContext.java:839)
    at org.apache.naming.NamingContext.lookup(NamingContext.java:173)
    at org.apache.catalina.core.NamingContextListener.addResource(NamingContextListener.java:1091)
    at org.apache.catalina.core.NamingContextListener.createNamingContext(NamingContextListener.java:661)
    at org.apache.catalina.core.NamingContextListener.lifecycleEvent(NamingContextListener.java:249)
    at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:94)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5087)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1404)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1394)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.ClassNotFoundException: Unable to load class: com.mysql.jdbc.Driver from ClassLoader:java.net.URLClassLoader@76ed5528;ClassLoader:ParallelWebappClassLoader
  context: ROOT
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@76ed5528

    at org.apache.tomcat.jdbc.pool.ClassLoaderUtil.loadClass(ClassLoaderUtil.java:56)
    at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:271)
    ... 25 more
Caused by: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1285)
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1119)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:348)
    at org.apache.tomcat.jdbc.pool.ClassLoaderUtil.loadClass(ClassLoaderUtil.java:38)
    ... 26 more

May 07, 2019 4:04:12 PM org.apache.naming.NamingContext lookup
WARNING: Unexpected exception resolving reference
java.sql.SQLException: Unable to load class: com.mysql.jdbc.Driver from ClassLoader:java.net.URLClassLoader@76ed5528;ClassLoader:ParallelWebappClassLoader
  context: ROOT
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@76ed5528

    at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:283)
    at org.apache.tomcat.jdbc.pool.PooledConnection.connect(PooledConnection.java:203)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.createConnection(ConnectionPool.java:718)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.borrowConnection(ConnectionPool.java:650)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.init(ConnectionPool.java:468)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.<init>(ConnectionPool.java:143)
    at org.apache.tomcat.jdbc.pool.DataSourceProxy.pCreatePool(DataSourceProxy.java:118)
    at org.apache.tomcat.jdbc.pool.DataSourceProxy.createPool(DataSourceProxy.java:107)
    at org.apache.tomcat.jdbc.pool.DataSourceFactory.createDataSource(DataSourceFactory.java:554)
    at org.apache.tomcat.jdbc.pool.DataSourceFactory.getObjectInstance(DataSourceFactory.java:241)
    at org.apache.naming.factory.FactoryBase.getObjectInstance(FactoryBase.java:94)
    at javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:321)
    at org.apache.naming.NamingContext.lookup(NamingContext.java:839)
    at org.apache.naming.NamingContext.lookup(NamingContext.java:173)
    at org.apache.catalina.core.NamingContextListener.addResource(NamingContextListener.java:1091)
    at org.apache.catalina.core.NamingContextListener.createNamingContext(NamingContextListener.java:661)
    at org.apache.catalina.core.NamingContextListener.lifecycleEvent(NamingContextListener.java:249)
    at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:94)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5087)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1404)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1394)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.ClassNotFoundException: Unable to load class: com.mysql.jdbc.Driver from ClassLoader:java.net.URLClassLoader@76ed5528;ClassLoader:ParallelWebappClassLoader
  context: ROOT
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@76ed5528

    at org.apache.tomcat.jdbc.pool.ClassLoaderUtil.loadClass(ClassLoaderUtil.java:56)
    at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:271)
    ... 25 more
Caused by: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1285)
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1119)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:348)
    at org.apache.tomcat.jdbc.pool.ClassLoaderUtil.loadClass(ClassLoaderUtil.java:38)
    ... 26 more

May 07, 2019 4:04:12 PM org.apache.catalina.core.NamingContextListener addResource
WARNING: Failed to register in JMX: javax.naming.NamingException: Unable to load class: com.mysql.jdbc.Driver from ClassLoader:java.net.URLClassLoader@76ed5528;ClassLoader:ParallelWebappClassLoader
  cont8ext: ROOT
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@76ed552

预期结果：它不能抛出jar的任何异常，因为jar已经存在于/WEB-INF/lib/以及tomcat/lib文件夹中

实际结果：如上所述，它正在抛出异常

Answer 1

我想在头脑风暴之后发布一个答案（至少在我的案例中是这样）

WEB-INF/lib folder should contains both jars, if in case it is not picked from there by class loader in some strange scenario(my case), copy the same in tomcat/lib folder.

这对我来说很有效，所以在发布答案时，我对任何其他观点都持开放态度

Answer 2

在Debian 10中处理Java项目时，我遇到了这个错误

问题是我有多个。MySQL JDBC连接器的jar文件，即：

mysql-connector-java-5.1.27.jar
mysql-connector-java-5.1.27.jar-1

下面是我如何修复它的：

我只是从主文件开始删除了两个文件：

sudo rm -rf mysql-connector-java-5.1.27.jar
sudo rm -rf mysql-connector-java-5.1.27.jar-1

然后，我再次将该文件的副本下载到tomcat（/opt/tomcat/lib）的lib目录中：

sudo wget https://repo1.maven.org/maven2/mysql/mysql-connector-java/5.1.27/mysql-connector-java-5.1.27.jar

一切又恢复正常了

就这些

我希望这有帮助

Answer 3

显然，您正试图从Oracle JDBC JAR文件（ojdbc6.jar）加载MySQL JDBC驱动程序类（com.mysql.jdbc.Driver）

这行不通

如果您试图与Oracle数据库通信，则需要使用Oracle JDBC的Driver类名

如果您试图与MySQL数据库通信，则需要使用适当的JConnector驱动程序

---

根据您的评论，问题在于您将JDBC驱动程序JAR文件放错了位置。如果您使用的是Tomcat的JNDI Datasource配置机制，那么驱动程序JAR需要位于$CATALINA_HOME/lib。。。按照说明

这是因为驱动程序是通过核心Tomcat代码加载的，而不是通过你的webapp加载的。你的webapp的WEB-INF/lib目录将不在核心类加载器的类路径上