在 web.xml 中添加一个 servlet

【问题标题】：Adding a servlet in web.xml在 web.xml 中添加一个 servlet
【发布时间】：2014-03-07 12:09:13
【问题描述】：

我有一个名为 DBServlet 的 servlet 项目，它位于包 DB 中。我的xml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">
  <display-name>Lab4DWP</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>DB.DBServlet</servlet-name>
    <servlet-class>DB.DBServlet</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>DB.DBervlet</servlet-name>
    <url-pattern>/DB.DBServlet</url-pattern>
</servlet-mapping>
</web-app>

当我尝试运行它时。控制台输出如下：

SEVERE: A child container failed during start
java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/Lab4DWP]]
    at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:222)
    at java.util.concurrent.FutureTask.get(FutureTask.java:83)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1123)
    at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:800)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1549)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
    at java.util.concurrent.FutureTask.run(FutureTask.java:138)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
    at java.lang.Thread.run(Thread.java:695)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/Lab4DWP]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:154)
    ... 7 more
Caused by: java.lang.IllegalArgumentException: Servlet mapping specifies an unknown servlet name DB.DBervlet
    at org.apache.catalina.core.StandardContext.addServletMapping(StandardContext.java:3241)
    at org.apache.catalina.core.StandardContext.addServletMapping(StandardContext.java:3220)
    at org.apache.catalina.deploy.WebXml.configureContext(WebXml.java:1367)
    at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1346)
    at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:878)
    at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:376)
    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:5322)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    ... 7 more
10.02.2014 14:42:11 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$Sync.innerGet(FutureTask.java:222)
    at java.util.concurrent.FutureTask.get(FutureTask.java:83)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1123)
    at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:302)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.StandardService.startInternal(StandardService.java:443)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:732)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.startup.Catalina.start(Catalina.java:691)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:322)
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:456)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:154)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1549)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
    at java.util.concurrent.FutureTask.run(FutureTask.java:138)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
    at java.lang.Thread.run(Thread.java:695)
Caused by: org.apache.catalina.LifecycleException: A child container failed during start
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1131)
    at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:800)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    ... 7 more
10.02.2014 14:42:11 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:691)
    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:456)
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:732)
    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:443)
    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:1131)
    at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:302)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    ... 11 more
10.02.2014 14:42:11 org.apache.coyote.AbstractProtocol pause
INFO: Pausing ProtocolHandler ["http-bio-8080"]
10.02.2014 14:42:11 org.apache.coyote.AbstractProtocol pause
INFO: Pausing ProtocolHandler ["ajp-bio-8009"]
10.02.2014 14:42:11 org.apache.catalina.core.StandardService stopInternal
INFO: Stopping service Catalina
10.02.2014 14:42:11 org.apache.coyote.AbstractProtocol destroy
INFO: Destroying ProtocolHandler ["http-bio-8080"]
10.02.2014 14:42:11 org.apache.coyote.AbstractProtocol destroy
INFO: Destroying ProtocolHandler ["ajp-bio-8009"]

我想我在将 servlet 添加到 web.xml 时做错了，但在示例中我使用它就像我发布的那样。有什么解决办法吗？

【问题讨论】：

  • 从你的xml中删除servlet配置，然后再次尝试启动tomcat，看看你服务器的其他配置是否有问题。
  • 您是否尝试过在名称中不使用点？
  • 试过没有点，是的。

标签： java xml eclipse servlets derby


【解决方案1】：

您没有将包名称放在 servlet 名称之前。

<servlet>
<description></description>
<display-name>GetCascadParamServlet</display-name>
<servlet-name>GetCascadParamServlet</servlet-name>
<servlet-class>com.agileinfotech.bsviewer.servlet.GetCascadParamServlet</servlet-class> // this is package of where my servlet is created.
</servlet>

<servlet-mapping>
     <servlet-name>GetCascadParamServlet</servlet-name>
     <url-pattern>/GetCascadParamServlet</url-pattern>
</servlet-mapping>

【讨论】：

    【解决方案2】：

    映射中的 servlet 名称错误。它应该是 DB.DBServlet，并且您已经编写了 DB.DBervlet。您指定的内容缺少“S”。请再试一次。

    另外， 命名包时请避免使用大写字母。从您的配置看来 DB 是包名。

    【讨论】：

      【解决方案3】：

      错字（缺少S）：

      <servlet-name>DB.DBervlet</servlet-name>

      如异常消息中所述：

      Caused by: java.lang.IllegalArgumentException: Servlet mapping specifies an unknown servlet name DB.DBervlet

      改为：

      <servlet-name>DB.DBServlet</servlet-name>

      【讨论】：

      • 好收获。典型的“错误是可怕的”失明。给 OP 的提示：例外是您的朋友，请仔细阅读。
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