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

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。

我发现实现一个简单的destroy()方法来注销任何JDBC驱动程序工作得很好。

/**
 * Destroys the servlet cleanly by unloading JDBC drivers.
 * 
 * @see javax.servlet.GenericServlet#destroy()
 */
public void destroy() {
    String prefix = getClass().getSimpleName() +" destroy() ";
    ServletContext ctx = getServletContext();
    try {
        Enumeration<Driver> drivers = DriverManager.getDrivers();
        while(drivers.hasMoreElements()) {
            DriverManager.deregisterDriver(drivers.nextElement());
        }
    } catch(Exception e) {
        ctx.log(prefix + "Exception caught while deregistering JDBC drivers", e);
    }
    ctx.log(prefix + "complete");
}

我经常看到这个问题。是的，Tomcat 7会自动注销它，但这真的能控制你的代码吗?这是一个好的编码实践吗?当然，您希望知道您已经准备好了关闭所有对象、关闭数据库连接池线程和消除所有警告所需的所有正确代码。我当然喜欢。

我就是这么做的。

步骤1:注册监听器

web . xml

<listener>
    <listener-class>com.mysite.MySpecialListener</listener-class>
</listener>

步骤2:实现监听器

com.mysite.MySpecialListener.java

public class MySpecialListener implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        // On Application Startup, please…

        // Usually I'll make a singleton in here, set up my pool, etc.
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        // On Application Shutdown, please…

        // 1. Go fetch that DataSource
        Context initContext = new InitialContext();
        Context envContext  = (Context)initContext.lookup("java:/comp/env");
        DataSource datasource = (DataSource)envContext.lookup("jdbc/database");

        // 2. Deregister Driver
        try {
            java.sql.Driver mySqlDriver = DriverManager.getDriver("jdbc:mysql://localhost:3306/");
            DriverManager.deregisterDriver(mySqlDriver);
        } catch (SQLException ex) {
            logger.info("Could not deregister driver:".concat(ex.getMessage()));
        } 

        // 3. For added safety, remove the reference to dataSource for GC to enjoy.
        dataSource = null;
    }

}

请随意评论和/或添加…

尽管Tomcat会强制注销JDBC驱动程序，但在上下文破坏时清理webapp创建的所有资源是一个很好的实践，以防您移动到另一个servlet容器，该容器不像Tomcat那样执行内存泄漏预防检查。

但是，全面取消司机登记的方法是危险的。DriverManager.getDrivers()方法返回的一些驱动程序可能是由父类加载器(即servlet容器的类加载器)加载的，而不是webapp上下文的类加载器(例如，它们可能在容器的lib文件夹中，而不是webapp的，因此在整个容器中共享)。注销这些将会影响其他可能使用它们的web应用程序(甚至容器本身)。

因此，在取消注册之前，应该检查每个驱动程序的ClassLoader是否是web应用程序的ClassLoader。因此，在你的ContextListener的contextDestroyed()方法中:

public final void contextDestroyed(ServletContextEvent sce) {
    // ... First close any background tasks which may be using the DB ...
    // ... Then close any DB connection pools ...

    // Now deregister JDBC drivers in this context's ClassLoader:
    // Get the webapp's ClassLoader
    ClassLoader cl = Thread.currentThread().getContextClassLoader();
    // Loop through all drivers
    Enumeration<Driver> drivers = DriverManager.getDrivers();
    while (drivers.hasMoreElements()) {
        Driver driver = drivers.nextElement();
        if (driver.getClass().getClassLoader() == cl) {
            // This driver was registered by the webapp's ClassLoader, so deregister it:
            try {
                log.info("Deregistering JDBC driver {}", driver);
                DriverManager.deregisterDriver(driver);
            } catch (SQLException ex) {
                log.error("Error deregistering JDBC driver {}", driver, ex);
            }
        } else {
            // driver was not registered by the webapp's ClassLoader and may be in use elsewhere
            log.trace("Not deregistering JDBC driver {} as it does not belong to this webapp's ClassLoader", driver);
        }
    }
}