1，现象，从页面访问某个url的时候，从后端的catalina.out里面没有找到相应的错误，页面只是显示500错误
2，在开发者模式中，看response里面的返回，返回如下
HTTP Status 500 - Handler processing failed; nested exception is java.lang.NoSuchMethodError: com.alibaba.fastjson.JSON.parseObject(Ljava/io/InputStream;Ljava/nio/charset/Charset;Ljava/lang/reflect/Type;Lcom/alibaba/fastjson/parser/ParserConfig;Lcom/alibaba/fastjson/parser/deserializer/ParseProcess;I[Lcom/alibaba/fastjson/parser/Feature;)Ljava/lang/Object;
type Exception report
message Handler processing failed; nested exception is java.lang.NoSuchMethodError: com.alibaba.fastjson.JSON.parseObject(Ljava/io/InputStream;Ljava/nio/charset/Charset;Ljava/lang/reflect/Type;Lcom/alibaba/fastjson/parser/ParserConfig;Lcom/alibaba/fastjson/parser/deserializer/ParseProcess;I[Lcom/alibaba/fastjson/parser/Feature;)Ljava/lang/Object;
description The server encountered an internal error that prevented it from fulfilling this request.
exception
org.springframework.web.util.NestedServletException: Handler processing failed; nested exception is java.lang.NoSuchMethodError: com.alibaba.fastjson.JSON.parseObject(Ljava/io/InputStream;Ljava/nio/charset/Charset;Ljava/lang/reflect/Type;Lcom/alibaba/fastjson/parser/ParserConfig;Lcom/alibaba/fastjson/parser/deserializer/ParseProcess;I[Lcom/alibaba/fastjson/parser/Feature;)Ljava/lang/Object;
org.springframework.web.servlet.DispatcherServlet.triggerAfterCompletionWithError(DispatcherServlet.java:1260)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:939)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:851)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:953)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:855)
javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:829)
javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
net.bull.javamelody.MonitoringFilter.doFilter(MonitoringFilter.java:186)
net.bull.javamelody.MonitoringFilter.doFilter(MonitoringFilter.java:230)
net.bull.javamelody.MonitoringFilter.doFilter(MonitoringFilter.java:202)
org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:61)
org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)
org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)
org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)
org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)
org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)
org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)
org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:449)
org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365)
org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90)
org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83)
org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:383)
org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:362)
org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:343)
org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:260)
org.jasig.cas.client.session.SingleSignOutFilter.doFilter(SingleSignOutFilter.java:76)
org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:106)
root cause
java.lang.NoSuchMethodError: com.alibaba.fastjson.JSON.parseObject(Ljava/io/InputStream;Ljava/nio/charset/Charset;Ljava/lang/reflect/Type;Lcom/alibaba/fastjson/parser/ParserConfig;Lcom/alibaba/fastjson/parser/deserializer/ParseProcess;I[Lcom/alibaba/fastjson/parser/Feature;)Ljava/lang/Object;
com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter.readType(FastJsonHttpMessageConverter.java:263)
com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter.read(FastJsonHttpMessageConverter.java:237)
org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver.readWithMessageConverters(AbstractMessageConverterMethodArgumentResolver.java:143)
org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.readWithMessageConverters(RequestResponseBodyMethodProcessor.java:180)
org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.resolveArgument(RequestResponseBodyMethodProcessor.java:95)
org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:77)
org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:157)
org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:124)
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:745)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:685)
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:919)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:851)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:953)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:855)
javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:829)
javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
net.bull.javamelody.MonitoringFilter.doFilter(MonitoringFilter.java:186)
net.bull.javamelody.MonitoringFilter.doFilter(MonitoringFilter.java:230)
net.bull.javamelody.MonitoringFilter.doFilter(MonitoringFilter.java:202)
org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:61)
org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)
org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)
org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)
org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)
org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)
org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)
org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:449)
org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365)
org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90)
org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83)
org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:383)
org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:362)
org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:343)
org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:260)
org.jasig.cas.client.session.SingleSignOutFilter.doFilter(SingleSignOutFilter.java:76)
org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:106)
note The full stack trace of the root cause is available in the Apache Tomcat/7.0.72 logs.
Apache Tomcat/7.0.72
3，仔细对比了fastjon的版本，发现版本是fastjson-1.2.58.jar
4，解决思路：既然tomcat的访问，后台日志里面根本没有查到，而项目的lib里面的jar包也正常，里面的fastjson的版本也是有这个方法的
有可能就是tomcat会另外加载其他的jar包，顺着这个思路，去看catalina.sh的配置，发现有如下配置
#cloudwise_javaAgent
#if [ "$1" = "start" -o "$1" = "run" ]; then
#export JAVA_OPTS="$JAVA_OPTS -javaagent:/home/app_user/cloudwise/JavaAgent_2.1.2/lib/CAgent-1.0.0.jar=/home/app_user/cloudwise/JavaAgent_2.1.2/"
#fi
在JavaAgent_2.1.2/里面的CAgent-1.0.0.jar 反编译看到
5，问题定位，就是catalina.sh先默认加载了一个1.2.42的jar包。里面的fastjson的JSON里面没有相应的方法，而1.2.58的方法是有的，将catalina.sh里面的cloudwise的配置去掉就可以了
6，扩展分析; 可以使用 java -verbose:class，看类的加载情况，可以分析出来，某个类先怎么加载的，以及加载的jar包是什么
java -verbose:gc 可以用来跟踪虚拟机内存回收情况
java –verbose:jni 可以用来跟踪java调用本地native方法调用的情况