Failed to start component [StandardEngine[Catalina].StandardHost[localhost....

今天我用了近一天的时间研究一个错误，早上写代码是遇到一个 错误严重错误代码如下：

严重: ContainerBase.addChild: start:
org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/201110181]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:152)
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:812)
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:787)
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:607)
    at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1055)
    at org.apache.catalina.startup.HostConfig.deployDirectories(HostConfig.java:978)
    at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:472)
    at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1329)
    at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:311)
    at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
    at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
    at org.apache.catalina.util.LifecycleBase.setStateInternal(LifecycleBase.java:389)
    at org.apache.catalina.util.LifecycleBase.setState(LifecycleBase.java:334)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1041)
    at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:774)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:148)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1033)
    at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:291)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:148)
    at org.apache.catalina.core.StandardService.startInternal(StandardService.java:443)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:148)
    at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:727)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:148)
    at org.apache.catalina.startup.Catalina.start(Catalina.java:621)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:322)
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:450)
Caused by: java.lang.IllegalArgumentException: Servlet mapping specifies an unknown servlet name fDemoServlet
    at org.apache.catalina.core.StandardContext.addServletMapping(StandardContext.java:3151)
    at org.apache.catalina.core.StandardContext.addServletMapping(StandardContext.java:3130)
    at org.apache.catalina.deploy.WebXml.configureContext(WebXml.java:1301)
    at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1390)
    at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:896)
    at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:322)
    at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
    at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5103)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:148)
    ... 29 more
2011-10-18 15:21:19 org.apache.catalina.startup.HostConfig deployDirectory
严重: Error deploying web application directory 201110181
java.lang.IllegalStateException: ContainerBase.addChild: start: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/201110181]]
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:816)
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:787)
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:607)
    at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1055)
    at org.apache.catalina.startup.HostConfig.deployDirectories(HostConfig.java:978)
    at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:472)
    at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1329)
    at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:311)
    at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
    at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
    at org.apache.catalina.util.LifecycleBase.setStateInternal(LifecycleBase.java:389)
    at org.apache.catalina.util.LifecycleBase.setState(LifecycleBase.java:334)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1041)
    at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:774)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:148)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1033)
    at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:291)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:148)
    at org.apache.catalina.core.StandardService.startInternal(StandardService.java:443)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:148)
    at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:727)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:148)
    at org.apache.catalina.startup.Catalina.start(Catalina.java:621)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:322)
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:450)

错误分别是 ：

                    org.apache.catalina.LifecycleException:

                     java.lang.IllegalArgumentException:

                     java.lang.IllegalStateException:

       这三个错误原来见过，但是没有记住，今天让这三个错误纠结了我一天 现在我将错误的产生的原因给大家做个总结

现在正在学习 Servlet 我建立了三个文件 第一个文件Java文件

通过 New ----> Servlet 创建的 DemoServlet.java

package cn.cdn.web.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class DemoServlet extends HttpServlet {


    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        this.doPost(request, response);
    }


    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        /*设置编码*/
        request.setCharacterEncoding("UTF-8");
        System.out.println("==========-----------=============");

    }

}

 然后生成的 xml ：web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
    http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <display-name></display-name>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>DemoServlet</servlet-name>
    <servlet-class>cn.cdn.web.servlet.DemoServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>DemoServlet</servlet-name>//如果这里的名字定义错误 就会出现上面的错误！
    <url-pattern>/demo.do</url-pattern>
   </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

原因很简单，就是名字他找不到，所以就会报错，至于怎么解释我不清楚总之如果遇到这个错误大家就去这个地方找就行了

web.xml 中的 <servlet-name>DemoServlet</servlet-name>

                      <url-pattern>/demo.do</url-pattern>

看看是不是能解决！