tomcat启动报错原因分析及解决
拿到catalina.log的启动日志
2015-8-13 15:24:02 org.apache.catalina.core.StandardContext start
严重: Error listenerStart
2015-8-13 15:24:02 org.apache.catalina.core.StandardContext start
严重: Context [/callback] startup failed due to previous errors
2015-8-13 15:24:02 org.apache.catalina.loader.WebappClassLoader clearReferencesJdbc
严重: The web application [/callback] registered the JDBC driver [com.alibaba.druid.proxy.DruidDriver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.
2015-8-13 15:24:02 org.apache.catalina.loader.WebappClassLoader clearReferencesJdbc
严重: The web application [/callback] registered the JDBC driver [oracle.jdbc.driver.OracleDriver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.
2015-8-13 15:24:02 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
严重: The web application [/callback] appears to have started a thread named [Thread-2] but has failed to stop it. This is very likely to create a memory leak.
2015-8-13 15:24:02 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
严重: The web application [/callback] appears to have started a thread named [Thread-3] but has failed to stop it. This is very likely to create a memory leak.
2015-8-13 15:24:02 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
严重: The web application [/callback] appears to have started a thread named [commons-pool-EvictionTimer] but has failed to stop it. This is very likely to create a memory leak.
2015-8-13 15:24:03 org.apache.catalina.startup.HostConfig deployDirectory
信息: Deploying web application directory ROOT
2015-8-13 15:24:03 org.apache.coyote.http11.Http11Protocol start
信息: Starting Coyote HTTP/1.1 on http-8920
2015-8-13 15:24:03 org.apache.jk.common.ChannelSocket init
信息: JK: ajp13 listening on /0.0.0.0:8009
2015-8-13 15:24:03 org.apache.jk.server.JkMain start
信息: Jk running ID=0 time=0/18 config=null
2015-8-13 15:24:03 org.apache.catalina.startup.Catalina start
信息: Server startup in 48288 ms刚开始分析，怀疑是数据库有异常
The web application [/callback] registered the JDBC driver [com.alibaba.druid.proxy.DruidDriver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.
然后通过DBA分析，发现数据库所有的连接都是正常的，没有未释放的链接。然后立即转向，发现这样一句：
严重: Context [/callback] startup failed due to previous errors不过这里没有发现报错日志，然后立即去查localhost.log，看到报错日志
2015-8-13 15:23:17 org.apache.catalina.core.ApplicationContext log信息: Initializing Logback from [/u1pf_bgwghttp/tomcat_bgw/webapps/callback/WEB-INF/logback.xml]然后打开logback.xml配置文件，看到如下配置：
[%d{yyyy-MM-dd HH:mm:ss.SSS}] [%thread] [%-5level] [%logger{36}] - %msg%n
INFO
DEBUG
到这一步，基本定位到原因了，下一步，就要看下为啥报错了。spring解析logback.xml要访问
http://www.w3.org/2002/xmlspec/dtd/2.10/xmlspec.dtd然后ping www.w3.org 不通，怀疑是最近主机组做了网络限制。
3.遗留疑问
3.1 为什么spring解析logback.xml要调用 http://www.w3.org/2002/xmlspec/dtd/2.10/xmlspec.dtd
答：待研究
3.2
http://www.w3.org/2002/xmlspec/dtd/2.10/xmlspec.dtd在这里到底做什么用？
答：DTD是一种保证XML文档格式正确的有效方法，可以比较XML文档和DTD文件来看文档是否符合规范，元素和标签使用是否正确。一个DTD文档包含：元素的定义规则，元素间关系的定义规则，元素可使用的属性，可使用的实体或符号规则。
DTD分为内部DTD与外部DTD,内部DTD包含在XML文档中,外部DTD则通过URL引用.一个DTD文件是以.dtd结尾的文本文件
DTD分为内部DTD与外部DTD,内部DTD包含在XML文档中,外部DTD则通过URL引用.一个DTD文件是以.dtd结尾的文本文件