针对每个应用部署的解决方案

这是一个侦听器，我写来解决这个问题:它自动检测驱动程序是否已经注册自己，并采取相应的行动

重要的是:它只能在驱动程序jar部署在WEB-INF/lib中使用，而不是像许多人建议的那样部署在Tomcat /lib中，这样每个应用程序都可以处理自己的驱动程序并在未受影响的Tomcat上运行。恕我直言，这才是应该的方式。

只需在web.xml中配置侦听器，然后再执行其他操作即可。

在web.xml顶部添加:

<listener>
    <listener-class>utils.db.OjdbcDriverRegistrationListener</listener-class>    
</listener>

保存为utils/db/OjdbcDriverRegistrationListener.java:

package utils.db;

import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Enumeration;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

import oracle.jdbc.OracleDriver;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Registers and unregisters the Oracle JDBC driver.
 * 
 * Use only when the ojdbc jar is deployed inside the webapp (not as an
 * appserver lib)
 */
public class OjdbcDriverRegistrationListener implements ServletContextListener {

    private static final Logger LOG = LoggerFactory
            .getLogger(OjdbcDriverRegistrationListener.class);

    private Driver driver = null;

    /**
     * Registers the Oracle JDBC driver
     */
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        this.driver = new OracleDriver(); // load and instantiate the class
        boolean skipRegistration = false;
        Enumeration<Driver> drivers = DriverManager.getDrivers();
        while (drivers.hasMoreElements()) {
            Driver driver = drivers.nextElement();
            if (driver instanceof OracleDriver) {
                OracleDriver alreadyRegistered = (OracleDriver) driver;
                if (alreadyRegistered.getClass() == this.driver.getClass()) {
                    // same class in the VM already registered itself
                    skipRegistration = true;
                    this.driver = alreadyRegistered;
                    break;
                }
            }
        }

        try {
            if (!skipRegistration) {
                DriverManager.registerDriver(driver);
            } else {
                LOG.debug("driver was registered automatically");
            }
            LOG.info(String.format("registered jdbc driver: %s v%d.%d", driver,
                    driver.getMajorVersion(), driver.getMinorVersion()));
        } catch (SQLException e) {
            LOG.error(
                    "Error registering oracle driver: " + 
                            "database connectivity might be unavailable!",
                    e);
            throw new RuntimeException(e);
        }
    }

    /**
     * Deregisters JDBC driver
     * 
     * Prevents Tomcat 7 from complaining about memory leaks.
     */
    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        if (this.driver != null) {
            try {
                DriverManager.deregisterDriver(driver);
                LOG.info(String.format("deregistering jdbc driver: %s", driver));
            } catch (SQLException e) {
                LOG.warn(
                        String.format("Error deregistering driver %s", driver),
                        e);
            }
            this.driver = null;
        } else {
            LOG.warn("No driver to deregister");
        }

    }

}

从版本6.0.24开始，Tomcat附带了内存泄漏检测特性，当web应用程序的/WEB-INF/lib中有JDBC 4.0兼容的驱动程序时，该驱动程序会在web应用程序启动期间使用ServiceLoader API自动注册自己，但在web应用程序关闭期间不会自动注销自己，这会导致此类警告消息。此消息完全是非正式的，Tomcat已经采取了相应的内存泄漏预防操作。

你能做什么?

Ignore those warnings. Tomcat is doing its job right. The actual bug is in someone else's code (the JDBC driver in question), not in yours. Be happy that Tomcat did its job properly and wait until the JDBC driver vendor get it fixed so that you can upgrade the driver. On the other hand, you aren't supposed to drop a JDBC driver in webapp's /WEB-INF/lib, but only in server's /lib. If you still keep it in webapp's /WEB-INF/lib, then you should manually register and deregister it using a ServletContextListener. Downgrade to Tomcat 6.0.23 or older so that you will not be bothered with those warnings. But it will silently keep leaking memory. Not sure if that's good to know after all. Those kind of memory leaks are one of the major causes behind OutOfMemoryError issues during Tomcat hotdeployments. Move the JDBC driver to Tomcat's /lib folder and have a connection pooled datasource to manage the driver. Note that Tomcat's builtin DBCP does not deregister drivers properly on close. See also bug DBCP-322 which is closed as WONTFIX. You would rather like to replace DBCP by another connection pool which is doing its job better then DBCP. For example HikariCP or perhaps Tomcat JDBC Pool.

这纯粹是mysql的驱动程序或tomcats webapp-classloader中的驱动程序注册/注销问题。复制mysql驱动到tomcats lib文件夹(所以它是由jvm直接加载，而不是由tomcat)，消息将会消失。这使得mysql jdbc驱动程序只有在JVM关闭时才会被卸载，没有人会关心内存泄漏。

这个错误发生在我使用JTDS Driver 1.3.0 (SQL Server)的Grails应用程序中。问题是SQL Server登录错误。解决这个问题后(在SQL Server)，我的应用程序被正确部署在Tomcat。提示:我在stacktrace.log中看到了错误

我在Tomcat版本6.026中发现了同样的问题。

我在WebAPP库和TOMCAT库中使用Mysql JDBC.jar。

要解决上述问题，请从TOMCAT lib文件夹中删除Jar。

因此，我所理解的是TOMCAT正在正确地处理JDBC内存泄漏。但是如果MYSQL Jdbc jar在WebApp和Tomcat Lib中被复制，Tomcat将只能处理Tomcat Lib文件夹中的jar。

在你的servlet上下文监听器contextDestroyed()方法中，手动注销驱动程序:

// This manually deregisters JDBC driver, which prevents Tomcat 7 from complaining about memory leaks wrto this class
Enumeration<Driver> drivers = DriverManager.getDrivers();
while (drivers.hasMoreElements()) {
    Driver driver = drivers.nextElement();
    try {
        DriverManager.deregisterDriver(driver);
        LOG.log(Level.INFO, String.format("deregistering jdbc driver: %s", driver));
    } catch (SQLException e) {
        LOG.log(Level.SEVERE, String.format("Error deregistering driver %s", driver), e);
    }
}