异常

SpringBoot执行报错：Property or field 'username' cannot be found on object of type 'java.lang.Boolean' - maybe not public or not valid?

2021-06-25 16:27:10.433 ERROR 19176 --- [nio-8080-exec-2] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.thymeleaf.exceptions.TemplateProcessingException: Exception evaluating SpringEL expression: "user.username" (template: "table" - line 10, col 13)] with root cause

org.springframework.expression.spel.SpelEvaluationException: EL1008E: Property or field 'username' cannot be found on object of type 'java.lang.Boolean' - maybe not public or not valid?
	at org.springframework.expression.spel.ast.PropertyOrFieldReference.readProperty(PropertyOrFieldReference.java:217) ~[spring-expression-5.3.8.jar:5.3.8]
	at org.springframework.expression.spel.ast.PropertyOrFieldReference.getValueInternal(PropertyOrFieldReference.java:104) ~[spring-expression-5.3.8.jar:5.3.8]
	at org.springframework.expression.spel.ast.PropertyOrFieldReference.access$000(PropertyOrFieldReference.java:51) ~[spring-expression-5.3.8.jar:5.3.8]
	at org.springframework.expression.spel.ast.PropertyOrFieldReference$AccessorLValue.getValue(PropertyOrFieldReference.java:406) ~[spring-expression-5.3.8.jar:5.3.8]
	at org.springframework.expression.spel.ast.CompoundExpression.getValueInternal(CompoundExpression.java:92) ~[spring-expression-5.3.8.jar:5.3.8]
	at org.springframework.expression.spel.ast.SpelNodeImpl.getValue(SpelNodeImpl.java:112) ~[spring-expression-5.3.8.jar:5.3.8]
	at org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:337) ~[spring-expression-5.3.8.jar:5.3.8]
	at org.thymeleaf.spring5.expression.SPELVariableExpressionEvaluator.evaluate(SPELVariableExpressionEvaluator.java:265) ~[thymeleaf-spring5-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.standard.expression.VariableExpression.executeVariableExpression(VariableExpression.java:166) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.standard.expression.SimpleExpression.executeSimple(SimpleExpression.java:66) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.standard.expression.Expression.execute(Expression.java:109) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.standard.expression.Expression.execute(Expression.java:138) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.standard.processor.AbstractStandardExpressionAttributeTagProcessor.doProcess(AbstractStandardExpressionAttributeTagProcessor.java:144) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.processor.element.AbstractAttributeTagProcessor.doProcess(AbstractAttributeTagProcessor.java:74) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.processor.element.AbstractElementTagProcessor.process(AbstractElementTagProcessor.java:95) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.util.ProcessorConfigurationUtils$ElementTagProcessorWrapper.process(ProcessorConfigurationUtils.java:633) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.engine.ProcessorTemplateHandler.handleOpenElement(ProcessorTemplateHandler.java:1314) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.engine.OpenElementTag.beHandled(OpenElementTag.java:205) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.engine.Model.process(Model.java:282) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.engine.Model.process(Model.java:290) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.engine.IteratedGatheringModelProcessable.processIterationModel(IteratedGatheringModelProcessable.java:367) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.engine.IteratedGatheringModelProcessable.process(IteratedGatheringModelProcessable.java:221) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.engine.ProcessorTemplateHandler.handleCloseElement(ProcessorTemplateHandler.java:1640) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.engine.CloseElementTag.beHandled(CloseElementTag.java:139) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.engine.TemplateModel.process(TemplateModel.java:136) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.engine.TemplateManager.parseAndProcess(TemplateManager.java:661) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1098) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1072) ~[thymeleaf-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.spring5.view.ThymeleafView.renderFragment(ThymeleafView.java:366) ~[thymeleaf-spring5-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.thymeleaf.spring5.view.ThymeleafView.render(ThymeleafView.java:190) ~[thymeleaf-spring5-3.0.12.RELEASE.jar:3.0.12.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1396) ~[spring-webmvc-5.3.8.jar:5.3.8]
	at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1141) ~[spring-webmvc-5.3.8.jar:5.3.8]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1080) ~[spring-webmvc-5.3.8.jar:5.3.8]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963) ~[spring-webmvc-5.3.8.jar:5.3.8]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.8.jar:5.3.8]
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.3.8.jar:5.3.8]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:626) ~[tomcat-embed-core-9.0.46.jar:4.0.FR]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.8.jar:5.3.8]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) ~[tomcat-embed-core-9.0.46.jar:4.0.FR]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227) ~[tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.46.jar:9.0.46]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.8.jar:5.3.8]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.8.jar:5.3.8]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.8.jar:5.3.8]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.8.jar:5.3.8]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.8.jar:5.3.8]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.8.jar:5.3.8]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) [tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542) [tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143) [tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) [tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357) [tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374) [tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:893) [tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1707) [tomcat-embed-core-9.0.46.jar:9.0.46]
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.46.jar:9.0.46]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_151]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_151]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.46.jar:9.0.46]
	at java.lang.Thread.run(Thread.java:748) [na:1.8.0_151]

 

错误代码

    @Autowired
    private UserMapper userMapper;

    @GetMapping("/mybatis")
    public String table(String username,Model model){
        User user = userMapper.selectByUsername(username);
        model.addAttribute("users",new ArrayList<>().add(user));
        return "table";
    }

原因

我们来断点调试，查看原因

我们这里必须连着前台的代码一起看，前端是遍历users，来渲染数据成一个表格，本意是users应该是一个List，但是这里却是一个布尔类型。

为什么会保存为一个布尔类型呢？

因为从数据库获取只有一条记录，要添加到List集合中，为了偷懒，所以使用了匿名内部类。

add()方法返回的就是一个布尔值，而不是我们期望的List集合。

而boolean类型前端的Thymeleaf无法按照List集合进行解析。

解决

创建一个List结合，单独调用add()方法添加元素，再传递list集合作为参数。

正确代码

然后就能访问成功了