前言
本文中提到的解决方案，源码地址在：springboot-thymeleaf，希望可以帮你解决问题。
至于为什么已经写了一篇文章thymeleaf模板引擎调用java类中的方法，又多此一举的单独整理了这篇文章，是因为在解决此问题时首先搜索了一下关于此问题的文章，但是网上并没有搜到关于此问题的答案，因此自己做了整理。
问题描述
在springboot与thymeleaf整合过程中，出现了如下报错：
```
org.thymeleaf.exceptions.TemplateProcessingException: Exception evaluating SpringEL expression: "MethodTest.test()" (test:8)
at org.thymeleaf.spring4.expression.SpelVariableExpressionEvaluator.evaluate(SpelVariableExpressionEvaluator.java:161) ~[thymeleaf-spring4-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.standard.expression.VariableExpression.executeVariable(VariableExpression.java:154) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.standard.expression.SimpleExpression.executeSimple(SimpleExpression.java:59) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.standard.expression.Expression.execute(Expression.java:103) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.standard.expression.Expression.execute(Expression.java:133) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.standard.expression.Expression.execute(Expression.java:120) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.standard.processor.attr.AbstractStandardTextChildModifierAttrProcessor.getText(AbstractStandardTextChildModifierAttrProcessor.java:68) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.processor.attr.AbstractTextChildModifierAttrProcessor.getModifiedChildren(AbstractTextChildModifierAttrProcessor.java:59) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.processor.attr.AbstractChildrenModifierAttrProcessor.processAttribute(AbstractChildrenModifierAttrProcessor.java:59) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.processor.attr.AbstractAttrProcessor.doProcess(AbstractAttrProcessor.java:87) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.processor.AbstractProcessor.process(AbstractProcessor.java:212) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.dom.Node.applyNextProcessor(Node.java:1017) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.dom.Node.processNode(Node.java:972) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.dom.Node.processNode(Node.java:990) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.dom.Node.processNode(Node.java:990) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.dom.Node.processNode(Node.java:990) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.dom.Document.process(Document.java:93) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1155) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1060) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1011) ~[thymeleaf-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.spring4.view.ThymeleafView.renderFragment(ThymeleafView.java:335) ~[thymeleaf-spring4-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.thymeleaf.spring4.view.ThymeleafView.render(ThymeleafView.java:190) ~[thymeleaf-spring4-2.1.5.RELEASE.jar:2.1.5.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1271) ~[spring-webmvc-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1037) ~[spring-webmvc-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:980) ~[spring-webmvc-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897) ~[spring-webmvc-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) ~[spring-webmvc-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861) ~[spring-webmvc-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622) ~[tomcat-embed-core-8.5.11.jar:8.5.11]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) ~[spring-webmvc-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) ~[tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-embed-websocket-8.5.11.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:105) ~[spring-web-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81) ~[spring-web-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197) ~[spring-web-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.springframework.boot.web.support.ErrorPageFilter.doFilter(ErrorPageFilter.java:115) [spring-boot-1.5.1.RELEASE.jar:1.5.1.RELEASE]
at org.springframework.boot.web.support.ErrorPageFilter.access$000(ErrorPageFilter.java:59) [spring-boot-1.5.1.RELEASE.jar:1.5.1.RELEASE]
at org.springframework.boot.web.support.ErrorPageFilter$1.doFilterInternal(ErrorPageFilter.java:90) [spring-boot-1.5.1.RELEASE.jar:1.5.1.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.boot.web.support.ErrorPageFilter.doFilter(ErrorPageFilter.java:108) [spring-boot-1.5.1.RELEASE.jar:1.5.1.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:474) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:798) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1434) [tomcat-embed-core-8.5.11.jar:8.5.11]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.11.jar:8.5.11]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_121]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_121]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.11.jar:8.5.11]
at java.lang.Thread.run(Thread.java:745) [na:1.8.0_121]
Caused by: org.springframework.expression.spel.SpelEvaluationException: EL1011E: Method call: Attempted to call method test() on null context object
at org.springframework.expression.spel.ast.MethodReference.throwIfNotNullSafe(MethodReference.java:144) ~[spring-expression-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.expression.spel.ast.MethodReference.getValueRef(MethodReference.java:73) ~[spring-expression-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.expression.spel.ast.CompoundExpression.getValueRef(CompoundExpression.java:66) ~[spring-expression-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.expression.spel.ast.CompoundExpression.getValueInternal(CompoundExpression.java:87) ~[spring-expression-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.expression.spel.ast.SpelNodeImpl.getValue(SpelNodeImpl.java:120) ~[spring-expression-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:267) ~[spring-expression-4.3.6.RELEASE.jar:4.3.6.RELEASE]
at org.thymeleaf.spring4.expression.SpelVariableExpressionEvaluator.evaluate(SpelVariableExpressionEvaluator.java:139) ~[thymeleaf-spring4-2.1.5.RELEASE.jar:2.1.5.RELEASE]
... 80 common frames omitted
```
解决方案
通过异常栈可以得出有效信息：
Attempted to call method on null context object
调用的方法处于一个空对象中，即调用实例为空。
thymeleaf的context，即提供数据的地方，基于web的context，即WebContext相对context增加 param,session,application变量，并且自动将request atttributes添加到context variable map，可以在模板直接访问。
针对于此异常，需要将期望调用的java实例存入thymeleaf的context域中，代码层面即为：将实例对象存入Request对象中。
