org.springframework.web.util.NestedServletException: Handler dispatch failed; nested exception is java.lang.NoClassDefFoundError: org/apache/commons/httpclient/HttpClient
Caused by: java.lang.ClassNotFoundException: org.apache.commons.httpclient.HttpClient
其实这样的报错信息内容已经很明确的告诉了我们为什么会报错，ClassNotFoundException（类没有找到异常），org.apache.commons.httpclient.HttpClient（这个就是需要找的类，但是没有找到，所以报类没有找到异常）。
一、背景描述
最近在开发一个项目，依赖了公司开发的jar包，然后按照模式把jar包引入进来，之后项目启动正常，就正常开发其他功能，等冒烟测试时才发现接口调用异常。
二、报错信息
把主要的报错信息摘取出来，如下：
org.springframework.web.util.NestedServletException: Handler dispatch failed; nested exception is java.lang.NoClassDefFoundError: org/apache/commons/httpclient/HttpClient
Caused by: java.lang.ClassNotFoundException: org.apache.commons.httpclient.HttpClient
详细报错信息内容如下：
org.springframework.web.util.NestedServletException: Handler dispatch failed; nested exception is java.lang.NoClassDefFoundError: org/apache/commons/httpclient/HttpClient at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1054) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:908) at javax.servlet.http.HttpServlet.service(HttpServlet.java:660) at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at com.alibaba.druid.support.http.WebStatFilter.doFilter(WebStatFilter.java:123) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:200) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:836) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1747) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:748) Caused by: java.lang.NoClassDefFoundError: org/apache/commons/httpclient/HttpClient at com.uiotsoft.shcs.thirws.client.api.ThirwsClient.reqestData(ThirwsClient.java:40) at com.uiotsoft.back.smarthome.skill.business.usercase.devicecontrol.DeviceControlV4.deviceControl(DeviceControlV4.java:110) at com.uiotsoft.back.smarthome.skill.business.usercase.devicecontrol.DeviceControlV4.execute(DeviceControlV4.java:50) at com.uiotsoft.back.smarthome.skill.business.usercase.devicecontrol.DeviceControlV4$$FastClassBySpringCGLIB$$40637e4d.invoke(<generated>) at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218) at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:749) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) at org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor.invoke(MethodBeforeAdviceInterceptor.java:56) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:88) at com.uiotsoft.framework.log.LogAspect.Around(LogAspect.java:49) at sun.reflect.GeneratedMethodAccessor107.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:644) at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:633) at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:70) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.aop.aspectj.AspectJAfterAdvice.invoke(AspectJAfterAdvice.java:47) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:93) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688) at com.uiotsoft.back.smarthome.skill.business.usercase.devicecontrol.DeviceControlV4$$EnhancerBySpringCGLIB$$841001a3.execute(<generated>) at com.uiotsoft.back.smarthome.skill.controller.api.TestDeviceControlControllerApi.deviceControl(TestDeviceControlControllerApi.java:35) 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:498) at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:892) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:797) at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1039) ... 46 common frames omitted Caused by: java.lang.ClassNotFoundException: org.apache.commons.httpclient.HttpClient at java.net.URLClassLoader.findClass(URLClassLoader.java:381) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349) at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ... 82 common frames omitted
三、解决方案
根据报错信息 org.apache.commons.httpclient.HttpClient 这个类没有找到，所以果断先去外部库中查找 org.apache.commons.httpclient 库里有没有 HttpClient 类，正如报错信息显示，确实没有找到这个 HttpClient 类，根据图中显示 外部库中连这个 jar包 都没有。而且连 commons 相关的包下也没有。
知道问题了，那就去找这个包吧，打开 https://mvnrepository.com/ 中央仓库的网站，去这里搜索 HttpClient 相关的包。
哇塞，好家伙，有572条结果，到底哪个才是呢，找与报错信息最相关的 org/apache/commons/httpclient/HttpClient ，而根据搜索结果 只有第二个 commons-httpclient » commons-httpclient 的 HttpClient 最符合，所以就先拿这个来试一下吧。
点击进去，找到使用最多的一个版本，Version 3.1，再点击进去，把 maven 依赖拷贝出来放到项目中，重新导入一个 maven 依赖，再次测试，一切正常。
完结！
