Server Tomcat v7.0 Server at localhost failed to start.

今天在复习servlet的时候创建Web项目之后，启动项目报错如下：

SEVERE: A child container failed during start
java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/day045]]
    at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:252)
    at java.util.concurrent.FutureTask.get(FutureTask.java:111)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1120)
    at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:819)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1572)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1562)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
    at java.util.concurrent.FutureTask.run(FutureTask.java:166)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:722)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/day045]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:153)
    ... 7 more
Caused by: java.lang.IllegalArgumentException: The servlets named [re] and [controller.RegisterServlet] are both mapped to the url-pattern [/RegisterServlet] which is not permitted
    at org.apache.catalina.deploy.WebXml.addServletMapping(WebXml.java:293)
    at org.apache.catalina.startup.ContextConfig.processAnnotationWebServlet(ContextConfig.java:2462)
    at org.apache.catalina.startup.ContextConfig.processAnnotationsStream(ContextConfig.java:2137)
    at org.apache.catalina.startup.ContextConfig.processAnnotationsFile(ContextConfig.java:2098)
    at org.apache.catalina.startup.ContextConfig.processAnnotationsFile(ContextConfig.java:2090)
    at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1304)
    at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:889)
    at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:386)
    at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:117)
    at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5472)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
    ... 7 more

七月 13, 2017 3:07:00 下午 org.apache.catalina.core.ContainerBase startInternal
SEVERE: A child container failed during start
java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost]]
    at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:252)
    at java.util.concurrent.FutureTask.get(FutureTask.java:111)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1120)
    at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:300)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
    at org.apache.catalina.core.StandardService.startInternal(StandardService.java:444)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
    at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:738)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
    at org.apache.catalina.startup.Catalina.start(Catalina.java:693)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:294)
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:428)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:153)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1572)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1562)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
    at java.util.concurrent.FutureTask.run(FutureTask.java:166)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:722)
Caused by: org.apache.catalina.LifecycleException: A child container failed during start
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1128)
    at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:819)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
    ... 7 more

七月 13, 2017 3:07:00 下午 org.apache.catalina.startup.Catalina start
SEVERE: The required Server component failed to start so Tomcat is unable to start.
org.apache.catalina.LifecycleException: Failed to start component [StandardServer[8005]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:153)
    at org.apache.catalina.startup.Catalina.start(Catalina.java:693)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:294)
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:428)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardService[Catalina]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:153)
    at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:738)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
    ... 7 more
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:153)
    at org.apache.catalina.core.StandardService.startInternal(StandardService.java:444)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
    ... 9 more
Caused by: org.apache.catalina.LifecycleException: A child container failed during start
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1128)
    at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:300)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
    ... 11 more
由上面红色划线部分可知，说是我在web中配置的的两个路径冲突，我Web.xml配置如下

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>com.jy.day04</display-name>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>re</servlet-name>
    <servlet-class>controller/RegisterServlet</servlet-class>
  </servlet>
 <servlet-mapping>
    <servlet-name>re</servlet-name>
    <url-pattern>/RegisterServlet</url-pattern>
  </servlet-mapping>

</web-app>

平常也是这样配置没有出现问题，经过一系列的百度谷歌之后，得到结论如下：

原因：It seems that you have mixed @WebServlet annotation based and web.xml based configuration.----------说是把基础注解和web.xml中的配置混合了。

解决方法：1.删除该项目，重建项目即可。

2.不删除项目的话，只需将web.xml中的<servlet></servlet>    和  <servlet-mapping></servlet-mapping> 删除一个就行了。web.xml修改如下：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>com.jy.day04</display-name>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>re</servlet-name>
    <servlet-class>controller/RegisterServlet</servlet-class>
  </servlet>
 <!-- <servlet-mapping>
    <servlet-name>re</servlet-name>
    <url-pattern>/RegisterServlet</url-pattern>
  </servlet-mapping> -->

</web-app>