当我使用web.xml作为应用程序中servlets的配置文件时，我无法启动Tomcat，这是文件的内容:
<?xml version="1.0" encoding="UTF-8"?>
<web-app
id="WebApp_ID" version="3.0"
xmlns="http://java.sun.com/xml/ns/j2ee"
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_3_0.xsd">
<servlet>
<servlet-name>AppLifeServlet</servlet-name>
<servlet-class>
com.example.application_lifecycle_chapter_4_7.ApplicatationLifecycleUI.Servlet
</servlet-class>
<init-param>
<param-name>UI</param-name>
<param-value>com.example.application_lifecycle_chapter_4_7.ApplicationLifecycleUI</param-value>
</init-param>
<async-supported>true</async-supported>
</servlet>
<servlet>
<servlet-name>MyPushyServlet</servlet-name>
<servlet-class>
com.example.application_lifecycle_chapter_4_7.MyPushyUI.Servlet
</servlet-class>
<init-param>
<param-name>UI</param-name>
<param-value>com.example.application_lifecycle_chapter_4_7.MyPushyUI</param-value>
</init-param>
<async-supported>true</async-supported>
</servlet>
<servlet-mapping>
<servlet-name>AppLifeServlet</servlet-name>
<url-pattern>/AppLife/*</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>AppLifeServlet</servlet-name>
<url-pattern>/VAADIN/*</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>MyPushyServlet</servlet-name>
<url-pattern>/MyPushyUI/*</url-pattern>
</servlet-mapping>
</web-app>
为什么它不起作用？ Tomcat 甚至不启动，而是返回异常:
SEVERE: Failed to destroy end point associated with ProtocolHandler ["ajp-nio-8009"]
java.lang.NullPointerException
at org.apache.tomcat.util.net.NioEndpoint.releaseCaches(NioEndpoint.java:307)
at org.apache.tomcat.util.net.NioEndpoint.unbind(NioEndpoint.java:482)
at org.apache.tomcat.util.net.AbstractEndpoint.destroy(AbstractEndpoint.java:795)
at org.apache.coyote.AbstractProtocol.destroy(AbstractProtocol.java:531)
at org.apache.catalina.connector.Connector.destroyInternal(Connector.java:1023)
at org.apache.catalina.util.LifecycleBase.destroy(LifecycleBase.java:305)
at org.apache.catalina.core.StandardService.destroyInternal(StandardService.java:588)
at org.apache.catalina.util.LifecycleBase.destroy(LifecycleBase.java:305)
at org.apache.catalina.core.StandardServer.destroyInternal(StandardServer.java:850)
at org.apache.catalina.util.LifecycleBase.destroy(LifecycleBase.java:305)
at org.apache.catalina.startup.Catalina.start(Catalina.java:629)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:351)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:485)
如果我禁用 web.xml 并使用 Servlet 的 3.0 API 注释一切正常...
web.xml 文件有什么问题？
编辑:这是 Tomcat 尝试启动时的完整异常输出:
SEVERE: A child container failed during start
java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/Application_Lifecycle_Chapter_4.7]]
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:192)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:917)
at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:868)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1409)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1399)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/Application_Lifecycle_Chapter_4.7]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:154)
... 6 more
Caused by: java.lang.IllegalArgumentException: The servlets named [AppLifeServlet] and [com.example.application_lifecycle_chapter_4_7.ApplicationLifecycleUI$Servlet] are both mapped to the url-pattern [/AppLife/*] which is not permitted
at org.apache.tomcat.util.descriptor.web.WebXml.addServletMapping(WebXml.java:308)
at org.apache.catalina.startup.ContextConfig.processAnnotationWebServlet(ContextConfig.java:2325)
at org.apache.catalina.startup.ContextConfig.processAnnotationsStream(ContextConfig.java:2007)
at org.apache.catalina.startup.ContextConfig.processAnnotationsWebResource(ContextConfig.java:1901)
at org.apache.catalina.startup.ContextConfig.processAnnotationsWebResource(ContextConfig.java:1896)
at org.apache.catalina.startup.ContextConfig.processAnnotationsWebResource(ContextConfig.java:1896)
at org.apache.catalina.startup.ContextConfig.processAnnotationsWebResource(ContextConfig.java:1896)
at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1139)
at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:771)
at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:305)
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:5095)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
... 6 more
Dec 07, 2014 7:49:30 PM 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.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:192)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:917)
at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:262)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.StandardService.startInternal(StandardService.java:439)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:760)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.startup.Catalina.start(Catalina.java:625)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:351)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:485)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:154)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1409)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1399)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
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:925)
at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:868)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
... 6 more
Dec 07, 2014 7:49:30 PM 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:154)
at org.apache.catalina.startup.Catalina.start(Catalina.java:625)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:351)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:485)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardService[Catalina]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:154)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:760)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
... 7 more
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:154)
at org.apache.catalina.core.StandardService.startInternal(StandardService.java:439)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
... 9 more
Caused by: org.apache.catalina.LifecycleException: A child container failed during start
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:925)
at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:262)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
... 11 more
Dec 07, 2014 7:49:30 PM org.apache.coyote.AbstractProtocol pause
INFO: Pausing ProtocolHandler ["http-nio-8080"]
Dec 07, 2014 7:49:30 PM org.apache.coyote.AbstractProtocol pause
INFO: Pausing ProtocolHandler ["ajp-nio-8009"]
Dec 07, 2014 7:49:30 PM org.apache.catalina.core.StandardService stopInternal
INFO: Stopping service Catalina
Dec 07, 2014 7:49:30 PM org.apache.coyote.AbstractProtocol destroy
INFO: Destroying ProtocolHandler ["http-nio-8080"]
Dec 07, 2014 7:49:30 PM org.apache.coyote.AbstractProtocol destroy
SEVERE: Failed to destroy end point associated with ProtocolHandler ["http-nio-8080"]
java.lang.NullPointerException
at org.apache.tomcat.util.net.NioEndpoint.releaseCaches(NioEndpoint.java:307)
at org.apache.tomcat.util.net.NioEndpoint.unbind(NioEndpoint.java:482)
at org.apache.tomcat.util.net.AbstractEndpoint.destroy(AbstractEndpoint.java:795)
at org.apache.coyote.AbstractProtocol.destroy(AbstractProtocol.java:531)
at org.apache.catalina.connector.Connector.destroyInternal(Connector.java:1023)
at org.apache.catalina.util.LifecycleBase.destroy(LifecycleBase.java:305)
at org.apache.catalina.core.StandardService.destroyInternal(StandardService.java:588)
at org.apache.catalina.util.LifecycleBase.destroy(LifecycleBase.java:305)
at org.apache.catalina.core.StandardServer.destroyInternal(StandardServer.java:850)
at org.apache.catalina.util.LifecycleBase.destroy(LifecycleBase.java:305)
at org.apache.catalina.startup.Catalina.start(Catalina.java:629)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:351)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:485)
Dec 07, 2014 7:49:30 PM org.apache.coyote.AbstractProtocol destroy
INFO: Destroying ProtocolHandler ["ajp-nio-8009"]
Dec 07, 2014 7:49:30 PM org.apache.coyote.AbstractProtocol destroy
SEVERE: Failed to destroy end point associated with ProtocolHandler ["ajp-nio-8009"]
java.lang.NullPointerException
at org.apache.tomcat.util.net.NioEndpoint.releaseCaches(NioEndpoint.java:307)
at org.apache.tomcat.util.net.NioEndpoint.unbind(NioEndpoint.java:482)
at org.apache.tomcat.util.net.AbstractEndpoint.destroy(AbstractEndpoint.java:795)
at org.apache.coyote.AbstractProtocol.destroy(AbstractProtocol.java:531)
at org.apache.catalina.connector.Connector.destroyInternal(Connector.java:1023)
at org.apache.catalina.util.LifecycleBase.destroy(LifecycleBase.java:305)
at org.apache.catalina.core.StandardService.destroyInternal(StandardService.java:588)
at org.apache.catalina.util.LifecycleBase.destroy(LifecycleBase.java:305)
at org.apache.catalina.core.StandardServer.destroyInternal(StandardServer.java:850)
at org.apache.catalina.util.LifecycleBase.destroy(LifecycleBase.java:305)
at org.apache.catalina.startup.Catalina.start(Catalina.java:629)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:351)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:485)
已解决:这是关键行:
Caused by: java.lang.IllegalArgumentException: The servlets named [AppLifeServlet] and
[com.example.application_lifecycle_chapter_4_7.ApplicationLifecycleUI$Servlet] are both
mapped to the url-pattern [/AppLife/*] which is not permitted
来自瓦丁之书:
You can use both a web.xml and WebServlet in the same application. Settings in the web.xml override the ones given in annotations.
这不是真的!在我的例子中，错误是由于这个短语造成的:我的 ApplicationLifecycleUI$Servlet 中有一个 @WebServlet 注释以及 web.xml 文件中的 servlet 映射。
这两个配置不能共存，所以必须选择URL映射是使用web.xml还是@WebServlet注解，否则启动时会报这个错 Tomcat 。
最佳答案
我发现@tonix 的评论实际上是正确的。注释和 web.xml 不能共存。如果您想保留注释，您只需删除 web.xml。
此外，只需检查您所有的 url 模式，无论它是在 web.xml 中还是在注释中，它们都应该是正确的，我的意思是通常它们应该以“/”(正斜杠)为前缀。
进行这些更改后，尝试重新启动 tomcat，它应该可以工作，我的情况非常相似。
关于java - 为什么 Tomcat 服务器不使用 web.xml 文件作为 Vaadin 7 应用程序中使用的 servlet 配置？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/27344048/