eclipse中启动tomcat访问项目时，报的第一个错误A child container failed during start. 然后依次查看console中的内容，通过caused by发现具体错误：The servlets named [AServlet] and [cn.itcast.servlet.AServlet] are both mapped to the url-pattern [/AServlet] which is not permitted.
百度A child container failed during start.解决办法，没有一个是可以解决我的问题的，这句话只是个笼统的问题，还要通过caused by寻找具体的问题。
The servlets named [AServlet] and [cn.itcast.servlet.AServlet] are both mapped to the url-pattern [/AServlet] which is not permitted. 意思是说/AServlet名为AServlet和cn.itcast.servlet.AServlet的servlet相关联，这是不可取的。通过百度，我知道在创建Servlet时，在类上面有一行代码@WebServlet("/AServlet")（图如下）
报错时console里的报错内容如下：
五月 06, 2018 4:31:51 下午 org.apache.tomcat.util.digester.SetPropertiesRule begin
警告: [SetPropertiesRule]{Server/Service/Engine/Host/Context} Setting property 'source' to 'org.eclipse.jst.jee.server:Servlet_2' did not find a matching property.
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: Server version: Apache Tomcat/7.0.77
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: Server built: Mar 28 2017 16:01:48 UTC
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: Server number: 7.0.77.0
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: OS Name: Windows 7
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: OS Version: 6.1
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: Architecture: amd64
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: Java Home: C:\Program Files\Java\jdk1.7.0_80\jre
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: JVM Version: 1.7.0_80-b15
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: JVM Vendor: Oracle Corporation
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: CATALINA_BASE: C:\Users\Administrator\eclipse-workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp3
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: CATALINA_HOME: F:\Study_Data\softWare\tomcat\apache-tomcat-7.0.77
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: Command line argument: -Dcatalina.base=C:\Users\Administrator\eclipse-workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp3
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: Command line argument: -Dcatalina.home=F:\Study_Data\softWare\tomcat\apache-tomcat-7.0.77
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: Command line argument: -Dwtp.deploy=C:\Users\Administrator\eclipse-workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp3\wtpwebapps
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: Command line argument: -Djava.endorsed.dirs=F:\Study_Data\softWare\tomcat\apache-tomcat-7.0.77\endorsed
五月 06, 2018 4:31:51 下午 org.apache.catalina.startup.VersionLoggerListener log
信息: Command line argument: -Dfile.encoding=GBK
五月 06, 2018 4:31:51 下午 org.apache.catalina.core.AprLifecycleListener lifecycleEvent
信息: The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: C:\Program Files\Java\jdk1.7.0_80\bin;C:\Windows\Sun\Java\bin;C:\Windows\system32;C:\Windows;C:\ProgramData\Oracle\Java\javapath;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Program Files (x86)\Microsoft SQL Server\100\Tools\Binn\;C:\Program Files\Microsoft SQL Server\100\Tools\Binn\;C:\Program Files\Microsoft SQL Server\100\DTS\Binn\;C:\Program Files (x86)\Microsoft SQL Server\100\Tools\Binn\VSShell\Common7\IDE\;C:\Program Files (x86)\Microsoft Visual Studio 9.0\Common7\IDE\PrivateAssemblies\;C:\Program Files (x86)\Microsoft SQL Server\100\DTS\Binn\;.
五月 06, 2018 4:31:52 下午 org.apache.coyote.AbstractProtocol init
信息: Initializing ProtocolHandler ["http-bio-8080"]
五月 06, 2018 4:31:52 下午 org.apache.coyote.AbstractProtocol init
信息: Initializing ProtocolHandler ["ajp-bio-8009"]
五月 06, 2018 4:31:52 下午 org.apache.catalina.startup.Catalina load
信息: Initialization processed in 2506 ms
五月 06, 2018 4:31:52 下午 org.apache.catalina.core.StandardService startInternal
信息: Starting service Catalina
五月 06, 2018 4:31:52 下午 org.apache.catalina.core.StandardEngine startInternal
信息: Starting Servlet Engine: Apache Tomcat/7.0.77
五月 06, 2018 4:31:53 下午 org.apache.catalina.core.ContainerBase startInternal
严重: A child container failed during start
java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/Servlet_2]]
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:188)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1119)
at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:819)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1571)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1561)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
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:745)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/Servlet_2]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:162)
... 6 more
Caused by: java.lang.IllegalArgumentException: The servlets named [AServlet] and [cn.itcast.servlet.AServlet] are both mapped to the url-pattern [/AServlet] which is not permitted
at org.apache.catalina.deploy.WebXml.addServletMapping(WebXml.java:293)
at org.apache.catalina.startup.ContextConfig.processAnnotationWebServlet(ContextConfig.java:2458)
at org.apache.catalina.startup.ContextConfig.processAnnotationsStream(ContextConfig.java:2133)
at org.apache.catalina.startup.ContextConfig.processAnnotationsFile(ContextConfig.java:2094)
at org.apache.catalina.startup.ContextConfig.processAnnotationsFile(ContextConfig.java:2086)
at org.apache.catalina.startup.ContextConfig.processAnnotationsFile(ContextConfig.java:2086)
at org.apache.catalina.startup.ContextConfig.processAnnotationsFile(ContextConfig.java:2086)
at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1303)
at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:888)
at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:388)
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:5522)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
... 6 more
五月 06, 2018 4:32:13 下午 org.apache.catalina.startup.TldConfig execute
信息: At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
五月 06, 2018 4:32:13 下午 org.apache.catalina.util.SessionIdGeneratorBase createSecureRandom
信息: Creation of SecureRandom instance for session ID generation using [SHA1PRNG] took [159] milliseconds.
五月 06, 2018 4:32:14 下午 org.apache.catalina.core.ContainerBase startInternal
严重: 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.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:188)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1119)
at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:300)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
at org.apache.catalina.core.StandardService.startInternal(StandardService.java:444)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:758)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
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:606)
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:162)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1571)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1561)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.catalina.LifecycleException: A child container failed during start
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1127)
at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:819)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
... 6 more
五月 06, 2018 4:32:14 下午 org.apache.catalina.startup.Catalina start
严重: 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:162)
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:606)
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:162)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:758)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
... 7 more
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:162)
at org.apache.catalina.core.StandardService.startInternal(StandardService.java:444)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
... 9 more
Caused by: org.apache.catalina.LifecycleException: A child container failed during start
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1127)
at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:300)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
... 11 more
五月 06, 2018 4:32:14 下午 org.apache.coyote.AbstractProtocol pause
信息: Pausing ProtocolHandler ["http-bio-8080"]
五月 06, 2018 4:32:14 下午 org.apache.coyote.AbstractProtocol pause
信息: Pausing ProtocolHandler ["ajp-bio-8009"]
五月 06, 2018 4:32:14 下午 org.apache.catalina.core.StandardService stopInternal
信息: Stopping service Catalina
五月 06, 2018 4:32:14 下午 org.apache.coyote.AbstractProtocol destroy
信息: Destroying ProtocolHandler ["http-bio-8080"]
五月 06, 2018 4:32:14 下午 org.apache.coyote.AbstractProtocol destroy
信息: Destroying ProtocolHandler ["ajp-bio-8009"]