今日在重新部署项目时出现此问题，虽然对项目无影响，但问题就是问题。完整信息如下（使用idea工具）：
十二月 05, 2015 11:44:27 上午 org.apache.catalina.startup.HostConfig undeploy
信息: Undeploying context []
2015-12-05 11:44:27 JRebel: Reloading class 'com.shyy.web.controller.anntation.UserController'.
2015-12-05 11:44:27 JRebel-Spring: Reconfiguring bean 'userController' [com.shyy.web.controller.anntation.UserController]
2015-12-05 11:44:27 JRebel-Spring: Reconfiguring bean 'userController' [com.shyy.web.controller.anntation.UserController]
十二月 05, 2015 11:44:27 上午 org.apache.catalina.loader.WebappClassLoader clearReferencesJdbc
严重: The web application [] registered the JDBC driver [com.mysql.jdbc.Driver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.
十二月 05, 2015 11:44:27 上午 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
严重: The web application [] appears to have started a thread named [Abandoned connection cleanup thread] but has failed to stop it. This is very likely to create a memory leak.
[2015-12-05 11:44:28,265] Artifact shuyangyang:war: Artifact is being deployed, please wait...
十二月 05, 2015 11:44:51 上午 org.apache.catalina.loader.WebappClassLoader validateJarFile
信息: validateJarFile(E:Tomcat-7.0.59apache-tomcat-7.0.59webappsROOTWEB-INFlibjavax.el-api-2.2.4.jar) - jar not loaded. See Servlet Spec 3.0, section 10.7.2. Offending class: javax/el/Expression.class
十二月 05, 2015 11:44:51 上午 org.apache.catalina.loader.WebappClassLoader validateJarFile
信息: validateJarFile(E:Tomcat-7.0.59apache-tomcat-7.0.59webappsROOTWEB-INFlibservlet-api-3.0.20100224.jar) - jar not loaded. See Servlet Spec 3.0, section 10.7.2. Offending class: javax/servlet/Servlet.class
log4j:WARN No appenders could be found for logger (org.springframework.web.context.ContextLoader).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
2015-12-05 11:44:55 JRebel-Spring: Monitoring Spring bean definitions in 'E:Spring3shuyangyang argetclassesapplicationContext.xml'.
2015-12-05 11:44:56 JRebel-Spring: Monitoring Spring bean definitions in 'E:Spring3shuyangyang argetclassesdispatcher-servlet.xml'.
[2015-12-05 11:44:58,500] Artifact shuyangyang:war: Artifact is deployed successfully
[2015-12-05 11:44:58,500] Artifact shuyangyang:war: Deploy took 30,235 milliseconds
分析：
1.十二月 05, 2015 11:44:27 上午 org.apache.catalina.startup.HostConfig undeploy
在http://blog.csdn.net/aesop_wubo/article/details/7907047文章这样介绍HostConfig ：“HostConfig是一个生命周期监听器类，在tomcat加载配置文件的时候被添加到Host之上。”但是这里的信息是undeploy,是表明HostConfig 未部署或者说是部署失败？——但这样解释也很矛盾，因为后面出现了“Artifact is deployed successfully”。
2.严重: The web application [] registered the JDBC driver [com.mysql.jdbc.Driver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.
这里说的是mysql驱动注册失败，原因是为了阻止内存泄露。关于memory leak,百度百科上有解释，但不懂。
3.严重: The web application [] appears to have started a thread named [Abandoned connection cleanup thread] but has failed to stop it. This is very likely to create a memory leak.
这里说的是web 容器重启一个叫Abandoned connection cleanup thread的线程失败。原因可能是这很像创建了一个内存泄露。
真正原因及解决方案待续。。