tomcat 启动错误

故事梗概：

　　学习servlet尽然能碰到服务器起不来的，百思不得其解，然后我百度，我FQgoogle，找stackoverflow。找到了不少答案，比如stackoverflow给出说是在

1	<workspace-directory>.metadata.pluginsorg.eclipse.core.resources

　　中有个.snap文件删掉，就可解决这个问题，我试了不行。stackoverflow的链接如下：http://stackoverflow.com/questions/13244233/server-tomcat-v7-0-server-at-localhost-failed-to-start-without-stack-trace-whi。

百度下，Myexception网给出答案是1、端口被占用，2、启动时间不够，3、eclipse引发的问题，4、重新启动电脑（最笨的办法，如果不停的出现，不停的重起会烦死的。）。下面是原文链接。这答案给的没有一个是我要的，所以，以后还是尽量谷歌，百度感觉真心不靠谱。

故事真相：

　　在eclipse这个强大的软件中，我们省略很多手动写代码的时间，过程如下：

在上图中点击finish后就生成下面的代码。

比如在eclipse中，我们建一个新的 servlet文件后，代码中会生成如下一大块代码。

 1 import java.io.IOException;
 2 import javax.servlet.ServletException;
 3 import javax.servlet.annotation.WebServlet;
 4 import javax.servlet.http.HttpServlet;
 5 import javax.servlet.http.HttpServletRequest;
 6 import javax.servlet.http.HttpServletResponse;
 7 
 8 /**
 9  * Servlet implementation class ServletDemo
10  */
11 @WebServlet("/ServletDemo")
12 public class ServletDemo extends HttpServlet {
13     private static final long serialVersionUID = 1L;
14        
15     /**
16      * @see HttpServlet#HttpServlet()
17      */
18     public ServletDemo() {
19         super();
20         // TODO Auto-generated constructor stub
21     }
22 
23     /**
24      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
25      */
26     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
27         // TODO Auto-generated method stub
28         response.getWriter().append("Served at: ").append(request.getContextPath());
29     }
30 
31     /**
32      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
33      */
34     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
35         // TODO Auto-generated method stub
36         doGet(request, response);
37     }
38 
39 }

而这里面，留意下有个注解

@WebServlet("/ServletDemo")

这个注解是eclipse帮我们生成好的，而问题恰恰就出在这。我们知道，每次我们新建一个servlet后会在web.xml文件中配置映射关系，这样才能在浏览器敲入一个地址后，地址发来的请求能让服务器接收到请求并将该请求交给指定的Servlet去处理。web.xml的作用就在此，它的代码如下：

<?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" version="3.0">
  <servlet>
    <servlet-name>ServletDemo</servlet-name>
    <servlet-class>com.vivizhang.servlet.HelloWorldServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ServletDemo</servlet-name>
    <url-pattern>/HelloServlet</url-pattern>
  </servlet-mapping>
</web-app>

所以问题的真相就是配置和自动生成的注解冲突了，导致如下的错误（截取）：

 A child container failed during start
java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/ServletDemo]]
    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[/HelloServlet]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:153)
    ... 7 more
Caused by: java.lang.IllegalArgumentException: The servlets named [ServletDemo] and [com.vivizhang.servlet.ServletDemo] are both mapped to the url-pattern [/ServletDemo] 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.processAnnotationsFile(ContextConfig.java:2090)
    at org.apache.catalina.startup.ContextConfig.processAnnotationsFile(ContextConfig.java:2090)
    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

九月 18, 2016 4:40:37 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

九月 18, 2016 4:40:37 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[8006]]
    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

这里的问题出在：

The servlets named [ServletDemo] and [com.vivizhang.servlet.ServletDemo] are both mapped to the url-pattern [/ServletDemo] which is not permitted

故事解决办法：

　　可以选择删除web.xml中的映射，也可以选择将自动生成的注解注释掉，这样就不会有冲突了，二者选其一留下即可。