Servlet：SEVERE：为servlet分配exception

下面的堆栈跟踪是我尝试访问servlet时得到的，这似乎从Tomcat管理器运行良好。

11 Sep, 2012 11:50:12 AM org.apache.catalina.core.ApplicationContext log INFO: Marking servlet LoginServlet as unavailable 11 Sep, 2012 11:50:12 AM org.apache.catalina.core.StandardWrapperValve invoke SEVERE: Allocate exception for servlet LoginServlet java.lang.Error: Unresolved compilation problems: The import javax.servlet cannot be resolved The import javax.servlet cannot be resolved The import javax.servlet cannot be resolved The import javax.servlet cannot be resolved The import javax.servlet cannot be resolved The import javax.servlet cannot be resolved HttpServlet cannot be resolved to a type ServletConfig cannot be resolved to a type ServletException cannot be resolved to a type HttpServlet cannot be resolved to a type ServletContext cannot be resolved to a type ServletException cannot be resolved to a type HttpServletRequest cannot be resolved to a type HttpServletResponse cannot be resolved to a type ServletException cannot be resolved to a type request cannot be resolved The method getLoggedin() from the type LoginHandler refers to the missing type ServletException The method destroy() of type LoginManager must override or implement a supertype method HttpServlet cannot be resolved to a type at com.login.servlets.LoginManager.(LoginManager.java:5) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at java.lang.Class.newInstance0(Unknown Source) at java.lang.Class.newInstance(Unknown Source) at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1149) at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:827) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:129) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293) at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:877) at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:594) at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1675) at java.lang.Thread.run(Unknown Source) 11 Sep, 2012 12:05:12 PM org.apache.catalina.core.ApplicationContext log INFO: Marking servlet Log4JInitServlet as unavailable 11 Sep, 2012 12:05:12 PM org.apache.catalina.core.StandardContext loadOnStartup SEVERE: Servlet /logintest threw load() exception java.lang.Error: Unresolved compilation problems: The import javax.servlet cannot be resolved The import javax.servlet cannot be resolved The import javax.servlet cannot be resolved The import javax.servlet cannot be resolved The import org.apache cannot be resolved The import org.apache cannot be resolved HttpServlet cannot be resolved to a type ServletConfig cannot be resolved to a type ServletException cannot be resolved to a type ServletContext cannot be resolved to a type BasicConfigurator cannot be resolved PropertyConfigurator cannot be resolved BasicConfigurator cannot be resolved at com.logger.WebLogger.(WebLogger.java:5) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at java.lang.Class.newInstance0(Unknown Source) at java.lang.Class.newInstance(Unknown Source) at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1149) at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:1026) at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:4421) at org.apache.catalina.core.StandardContext.start(StandardContext.java:4734) at org.apache.catalina.core.StandardContext.reload(StandardContext.java:3461) at org.apache.catalina.manager.ManagerServlet.reload(ManagerServlet.java:943) at org.apache.catalina.manager.HTMLManagerServlet.reload(HTMLManagerServlet.java:557) at org.apache.catalina.manager.HTMLManagerServlet.doGet(HTMLManagerServlet.java:121) at javax.servlet.http.HttpServlet.service(HttpServlet.java:617) at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.filters.CsrfPreventionFilter.doFilter(CsrfPreventionFilter.java:186) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:563) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293) at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:877) at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:594) at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1675) at java.lang.Thread.run(Unknown Source) 

在eclipse类路径中使用的所有jar都可以在Tomcat lib文件夹中使用。 webapp正在部署而没有任何错误日志，但是当我尝试访问一个servlet时，会发生此exception，并且我将其记录在tomcat日志中。 有人能帮忙吗？

 The package names are proper inside 'classes', also, the web.xml is proper. 

我不知道为什么会发生这种情况。 还有一些其他的webapps，几乎使用相同的libs运行良好。 期待一些人可以帮助我…

谢谢

Answer 1

最后，弄错了。 这是eclipse构建引起的问题。 由于构建不正确，类文件已损坏。 我清理了整个项目，采取了新的构建，现在它工作正常。 谢谢你的回复。

Answer 2

在查看了Exceptions之后，你得到了一些错误放置jar文件的地方

（servlet的api.jar文件）。 它应该在您的Project / WEB-INF / lib文件夹下。 我想会的

如果您的jar文件位于上面指定的路径中，则有效。

Answer 3

不知怎的，你错过了servlet-api.jar 。 它应该位于tomcat\lib文件夹中。

Answer 4

如果您收到此错误“SEVERE：为servlet分配exception”并加上“java.lang.InstantiationException”exception，请确保您的servlet类具有公共无参数构造函数，因为servlet容器需要能够实例化它。

如果您的servlet类没有定义明确的非零参数构造函数（通常就是这种情况），编译器提供的默认构造函数就足够了。

Answer 5

“ java.lang.Error: Unresolved compilation problems ：”

说应用程序编译不正确。 请将servlet-api.jar放在classpath中，而不仅仅放在项目的lib文件夹中，还要将它附加到classpath。

请确保tomcat/common/lib文件夹中也有相同的jar。

Answer 6

我有同样的问题！ 花了2个小时寻找解决方案！ 在这里！

WebContent（在Dynamic Web Project下） – > WEB-INF – > lib（它是空的 – 好吧） – >右键单击它（lib） – >构建路径 – >用作源文件夹。

DONE！

Answer 7

我还看到了这个exception，其中@Resource注释导致与两个技术相互踩踏的冲突（tomcat servlet api 3和spring）。

Answer 8

我的情况是使用J ava 8 lamda表达式和旧版本的Rest，它不是基于Java 8