java - 在这种情况下，为什么 Tomcat 无法从 WEB-INF/lib 加载类？

Question

我的应用程序使用jjwt来生成jwt token 。 jjwt 反过来使用 Jackson。我的 WEB-INF/lib 文件夹包含 jackson-core-2.8.10.jar 我已验证它包含 JsonProcessingException 类文件。当我到达代码中的特定点时，我仍然得到:

java.lang.NoClassDefFoundError: com/fasterxml/jackson/core/JsonProcessingException

这仍然很奇怪，因为当我的 friend 在 Windows(我使用的是 Linux)上的同一 Tomcat 版本(Apache Tomcat/8.5.23)中构建并运行相同的代码时，它不会给出错误。它甚至没有得到 JsonProcessingException。该代码运行相同的测试用例，没有任何问题。我正在我的机器上运行 java 版本“1.8.0_151”，以防相关。

代码段:

String jwt_token = Jwts.builder()
                .setClaims(claims)
                .signWith(SignatureAlgorithm.HS512, environment.getRequiredProperty("jwt.secret.key"))
                .compact();

当我尝试在 Jwts 调用周围放置 try catch block 以捕获异常时。我从 IDE 中收到以下错误:

Error:(61, 11) java: exception com.fasterxml.jackson.core.JsonProcessingException is never thrown in body of corresponding try statement

这是来自 catalina.out 的堆栈跟踪:

2017-10-26 05:23:22.110 ERROR 7422 --- [nio-8080-exec-2] o.s.boot.web.support.ErrorPageFilter     : Forwarding to error page from request [/token] due to exception [com/fasterxml/jackson/core/JsonProcessingException]

java.lang.NoClassDefFoundError: com/fasterxml/jackson/core/JsonProcessingException
    at io.jsonwebtoken.Jwts.builder(Jwts.java:116) ~[jjwt-0.8.0.jar:0.8.0]
    at com.myapp.rest.security.JwtGenerator.generate(JwtGenerator.java:58) ~[classes/:na]
    at com.myapp.rest.controller.JwtTokenController.generateJwt(JwtTokenController.java:40) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_151]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_151]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_151]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_151]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:133) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:661) ~[servlet-api.jar:na]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) ~[servlet-api.jar:na]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) [catalina.jar:8.5.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [catalina.jar:8.5.23]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-websocket.jar:8.5.23]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [catalina.jar:8.5.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [catalina.jar:8.5.23]
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:200) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [catalina.jar:8.5.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [catalina.jar:8.5.23]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:317) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:127) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:91) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:114) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:137) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:170) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:200) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:116) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.web.filter.CorsFilter.doFilterInternal(CorsFilter.java:96) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:64) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:105) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:214) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:177) ~[spring-security-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:347) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:263) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [catalina.jar:8.5.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [catalina.jar:8.5.23]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [catalina.jar:8.5.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [catalina.jar:8.5.23]
    at org.springframework.boot.web.support.ErrorPageFilter.doFilter(ErrorPageFilter.java:115) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
    at org.springframework.boot.web.support.ErrorPageFilter.access$000(ErrorPageFilter.java:59) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
    at org.springframework.boot.web.support.ErrorPageFilter$1.doFilterInternal(ErrorPageFilter.java:90) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.boot.web.support.ErrorPageFilter.doFilter(ErrorPageFilter.java:108) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [catalina.jar:8.5.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [catalina.jar:8.5.23]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199) [catalina.jar:8.5.23]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [catalina.jar:8.5.23]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478) [catalina.jar:8.5.23]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [catalina.jar:8.5.23]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) [catalina.jar:8.5.23]
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:650) [catalina.jar:8.5.23]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [catalina.jar:8.5.23]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [catalina.jar:8.5.23]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) [tomcat-coyote.jar:8.5.23]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-coyote.jar:8.5.23]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) [tomcat-coyote.jar:8.5.23]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459) [tomcat-coyote.jar:8.5.23]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-coyote.jar:8.5.23]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_151]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_151]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-util.jar:8.5.23]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_151]
Caused by: java.lang.ClassNotFoundException: com.fasterxml.jackson.core.JsonProcessingException
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381) ~[na:1.8.0_151]
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[na:1.8.0_151]
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[na:1.8.0_151]
    ... 91 common frames omitted

我相信这不是权限问题，因为我也使用 super 用户权限运行tomcat，但它仍然存在问题。我已经重新安装了Tomcat。没有帮助。我对此无计可施。由于我们无法达成一致，我们的开发进程已经停滞了一周。我在互联网上搜寻了数十个小时试图找到解决方案，但似乎没有任何效果。任何帮助将不胜感激。

Answer 1

我自己找到了问题的答案。事实证明，jvm/ext 文件夹中存在一个 jjwt 0.8 jar(我一定是在不久前放置的，无意或有意 - 无关紧要)，所以不是从 WEB-INF/lib 解析 jjwt jar在 jvm/ext 处得到解决。我之前已经注意到这一点，但假设该问题与此无关，因为我预计另一个 jar 会在其他地方找到。

事实证明，由于 jjwt 存在于 jvm/ext 文件夹中，类加载器在同一文件夹中查找其依赖项，而不在其他任何地方(例如 WEB-INF/lib)查找它。

这可能是因为类加载器在层次结构中工作，不同的加载器查看不同的级别。此实例中的引导加载程序在 jvm/ext 中查找类文件。负责 WEB/INF/lib 的加载器是 WebappX 加载器。 Class loading in Tomcat 。简而言之，我删除了 jvm/ext 中的 jar，一切又恢复正常了。