我必须在哪里放置 Tomcat 连接池的 JDBC 驱动程序? [英] Where do I have to place the JDBC driver for Tomcat's connection pool?
问题描述
所以我已经弄清楚了我的错误,现在我只是想了解一下到底发生了什么.我使用的是 Apache Tomcat 7.0.32 版.我正在使用
另见:
- 臭名昭著的 java.sql.SQLException:没有合适的驱动程序找到
- 我该怎么做在基于 servlet 的应用程序中连接到 JDBC 数据库/数据源?
- 在多线程系统中使用静态 java.sql.Connection 实例是否安全?
So I've figured out my error, now I'm just looking for some insight as to what is going on exactly. I am using Apache Tomcat Version 7.0.32. I am using this tutorial to set up pooling for JDBC. In my META-INF folder I made a context.xml file and put this in there.
<?xml version="1.0" encoding="UTF-8"?>
<Context>
<Resource type="javax.sql.DataSource" name="jdbc/gmustudent"
factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"
driverClassName="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost:3306/official"
username="root" password="root"
maxActive="100" maxIdle="20" minIdle="15" initialSize="15" maxWait="10000" />
</Context>
I got this error when I wrote this
WARNING: Unexpected exception resolving reference
java.sql.SQLException: com.mysql.jdbc.Driver
at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:254)
at org.apache.tomcat.jdbc.pool.PooledConnection.connect(PooledConnection.java:182)
at org.apache.tomcat.jdbc.pool.ConnectionPool.createConnection(ConnectionPool.java:699)
at org.apache.tomcat.jdbc.pool.ConnectionPool.borrowConnection(ConnectionPool.java:631)
at org.apache.tomcat.jdbc.pool.ConnectionPool.init(ConnectionPool.java:485)
at org.apache.tomcat.jdbc.pool.ConnectionPool.<init>(ConnectionPool.java:143)
at org.apache.tomcat.jdbc.pool.DataSourceProxy.pCreatePool(DataSourceProxy.java:116)
at org.apache.tomcat.jdbc.pool.DataSourceProxy.createPool(DataSourceProxy.java:103)
at org.apache.tomcat.jdbc.pool.DataSourceFactory.createDataSource(DataSourceFactory.java:539)
at org.apache.tomcat.jdbc.pool.DataSourceFactory.getObjectInstance(DataSourceFactory.java:237)
at org.apache.naming.factory.ResourceFactory.getObjectInstance(ResourceFactory.java:143)
at javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:304)
at org.apache.naming.NamingContext.lookup(NamingContext.java:843)
at org.apache.naming.NamingContext.lookup(NamingContext.java:154)
at org.apache.naming.NamingContext.lookup(NamingContext.java:831)
at org.apache.naming.NamingContext.lookup(NamingContext.java:168)
at org.apache.catalina.core.NamingContextListener.addResource(NamingContextListener.java:1061)
at org.apache.catalina.core.NamingContextListener.createNamingContext(NamingContextListener.java:671)
at org.apache.catalina.core.NamingContextListener.lifecycleEvent(NamingContextListener.java:270)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5173)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1549)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:680)
Caused by: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:247)
at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:246)
... 29 more
Oct 31, 2012 11:23:25 AM org.apache.catalina.core.NamingContextListener addResource
WARNING: Failed to register in JMX: javax.naming.NamingException: com.mysql.jdbc.Driver
Oct 31, 2012 11:23:25 AM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["http-bio-8086"]
Oct 31, 2012 11:23:25 AM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["ajp-bio-8009"]
Oct 31, 2012 11:23:25 AM org.apache.catalina.startup.Catalina start
INFO: Server startup in 794 ms
This error only comes up when I have this statement in my context.xml file. When I remove it no error.
factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"
The reason I want to make sure that I have it is because in the apache tomcat tutorial it says
factory is required, and the value should be org.apache.tomcat.jdbc.pool.DataSourceFactory
So then I did a little bit of research on SO and found a post saying that you need to add this jar to your lib folder if you have an older version of tomcat. So I added the jar and now it works but I would like to have some information as to what on earth is going on because I am using the newest tomcat version. So why when I specify a factory do I get an error. And what is this jar that I'm adding in and why is there very little documentation about it? Any information about what is going on here would be greatly appreciated.
The JDBC driver has to be visible to the same classloader as the data source factory itself. The data source factory library is placed in Tomcat's own /lib
folder and thus loaded by Tomcat's "common" classloader.
Your problem sounds much like that you dropped the JDBC driver in webapp's /WEB-INF/lib
. The webapp's /WEB-INF/lib
is invisible to the "common" classloader. So technically, you have to place the JDBC driver in Tomcat's own /lib
folder (or, at least, in a configurable path as specified by common.loader
setting in /conf/catalina.properties
) in order to make it visible to the data source factory.
Or, as you attempted, copying the data source factory into /WEB-INF/lib
will also fix it. The webapp's /WEB-INF/lib
has namely higher precedence in classloading than Tomcat's /lib
folder. So if the data source factory is found in /WEB-INF/lib
, it will be loaded from there. As the JDBC driver is also there, it will be seen. This is however not the right solution to your concrete problem, this is more a workaround, so you shouldn't do this.
There isn't exactly documentation which is specifically targeted to this issue. The Tomcat Class Loader HOW-TO will however help in understanding the class loading hierarchy in Tomcat.
See also:
- The infamous java.sql.SQLException: No suitable driver found
- How should I connect to JDBC database / datasource in a servlet based application?
- Is it safe to use a static java.sql.Connection instance in a multithreaded system?
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