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.

如果您从Maven构建的war中获得此消息，则将JDBC驱动程序的作用域更改为已提供，并将其副本放在lib目录中。是这样的:

<dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
  <version>5.1.18</version>
  <!-- put a copy in /usr/share/tomcat7/lib -->
  <scope>provided</scope>
</dependency>

要防止这种内存泄漏，只需在上下文关闭时注销驱动程序。

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.mywebsite</groupId>
    <artifactId>emusicstore</artifactId>
    <version>1.0-SNAPSHOT</version>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.7.0</version>
                <configuration>
                    <source>1.9</source>
                    <target>1.9</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

    <dependencies>
        <!-- ... -->

        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>4.0.1.Final</version>
        </dependency>

        <dependency>
            <groupId>org.hibernate.javax.persistence</groupId>
            <artifactId>hibernate-jpa-2.0-api</artifactId>
            <version>1.0.1.Final</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.11</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/javax.servlet/servlet-api -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>

</project>

MyWebAppContextListener.java

package com.emusicstore.utils;

import com.mysql.cj.jdbc.AbandonedConnectionCleanupThread;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Enumeration;

public class MyWebAppContextListener implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        System.out.println("************** Starting up! **************");
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        System.out.println("************** Shutting down! **************");
        System.out.println("Destroying Context...");
        System.out.println("Calling MySQL AbandonedConnectionCleanupThread checkedShutdown");
        AbandonedConnectionCleanupThread.checkedShutdown();

        ClassLoader cl = Thread.currentThread().getContextClassLoader();

        Enumeration<Driver> drivers = DriverManager.getDrivers();
        while (drivers.hasMoreElements()) {
            Driver driver = drivers.nextElement();

            if (driver.getClass().getClassLoader() == cl) {
                try {
                    System.out.println("Deregistering JDBC driver {}");
                    DriverManager.deregisterDriver(driver);

                } catch (SQLException ex) {
                    System.out.println("Error deregistering JDBC driver {}");
                    ex.printStackTrace();
                }
            } else {
                System.out.println("Not deregistering JDBC driver {} as it does not belong to this webapp's ClassLoader");
            }
        }
    }

}

web . xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                             http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">

    <listener>
        <listener-class>com.emusicstore.utils.MyWebAppContextListener</listener-class>
    </listener>

<!-- ... -->

</web-app>

这个bug修复的灵感来源。

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。

我也遇到了类似的问题，但除此之外，每当我在运行Tomcat服务器的情况下修改/保存JSP页面时，我都会得到一个Java堆空间错误，因此上下文没有完全充电。

我的版本是Apache Tomcat 6.0.29和JDK 6u12。

根据URL http://wiki.apache.org/tomcat/MemoryLeakProtection的参考部分的建议，将JDK升级到6u21解决了Java堆空间问题(上下文现在重新加载OK)，尽管仍然出现JDBC驱动程序错误。

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);
        }
    }
}