Server Tomcat v7.0 Server at localhost failed to start.錯誤可能原因之一

故事由來：

　　學Servlet中，突然發現啟動Tomcat時出現這個問題

故事梗概：

　　學習servlet盡然能碰到服務器起不來的，百思不得其解，然后我百度，我翻牆google，找stackoverflow。找到了不少答案，比如stackoverflow給出說是在

<workspace-directory>\.metadata\.plugins\org.eclipse.core.resources

　　中有個.snap文件刪掉，就可解決這個問題，我試了不行。stackoverflow的鏈接如下：http://stackoverflow.com/questions/13244233/server-tomcat-v7-0-server-at-localhost-failed-to-start-without-stack-trace-whi。

百度下，Myexception網給出答案是1、端口被占用，2、啟動時間不夠，3、eclipse引發的問題，4、重新啟動電腦（最笨的辦法，如果不停的出現，不停的重起會煩死的。）。下面是原文鏈接。這答案給的沒有一個是我要的，所以，以后還是盡量谷歌，百度感覺真心不靠譜。

故事真相：

　　在eclipse這個強大的軟件中，我們省略很多手動寫代碼的時間，過程如下：

 

在上圖中點擊finish后就生成下面的代碼。

比如在eclipse中，我們建一個新的 servlet文件后，代碼中會生成如下一大塊代碼。

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class ServletDemo
 */
@WebServlet("/ServletDemo")
public class ServletDemo extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public ServletDemo() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.getWriter().append("Served at: ").append(request.getContextPath());
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

而這里面，留意下有個注解

@WebServlet("/ServletDemo")

這個注解是eclipse幫我們生成好的，而問題恰恰就出在這。我們知道，每次我們新建一個servlet后會在web.xml文件中配置映射關系，這樣才能在瀏覽器敲入一個地址后，地址發來的請求能讓服務器接收到請求並將該請求交給指定的Servlet去處理。web.xml的作用就在此，它的代碼如下：

<?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>

所以問題的真相就是配置和自動生成的注解沖突了，導致如下的錯誤（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

這里的問題出在：

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

故事解決辦法：

　　可以選擇刪除web.xml中的映射，也可以選擇將自動生成的注解注釋掉，這樣就不會有沖突了，二者選其一留下即可。

故事后續：

　　如果在其他問題都沒出錯的情況下，可能就是xml文件和注解出現了沖突，當然，出現這個問題的原因不止這一個，會有其他很多原因，去google吧，希望我的文章能幫助你解決實際的問題。