How to fix Thymeleaf th:field unexpected error-CodePudding

I am new to Spring Boot and Thymeleaf. I tried to follow some example but got error as below with no any ideas...

My Spring Boot version is 2.7.1 and Java 17

entity:

@Data
public class Taco {
    private String name;
    private List<Ingredient> ingredients;
}

controller:

@Slf4j
@Controller
@RequestMapping("/design")
@SessionAttributes("tacoOrder")
public class DesignTacoController {

    @ModelAttribute
    public void addIngredientsToModel(Model model) {
        List<Ingredient> ingredients = Arrays.asList(
                new Ingredient("FLTO", "Flour Tortilla", Type.WRAP),
                new Ingredient("COTO", "Corn Tortilla", Type.WRAP),
                new Ingredient("GRBF", "Ground Beef", Type.PROTEIN),
                new Ingredient("CARN", "Carnitas", Type.PROTEIN),
                new Ingredient("TMTO", "Diced Tomatoes", Type.VEGGIES),
                new Ingredient("LETC", "Lettuce", Type.VEGGIES),
                new Ingredient("CHED", "Cheddar", Type.CHEESE),
                new Ingredient("JACK", "Monterrey Jack", Type.CHEESE),
                new Ingredient("SLSA", "Salsa", Type.SAUCE),
                new Ingredient("SRCR", "Sour Cream", Type.SAUCE)
        );

        Type[] types = Ingredient.Type.values();
        for (Type type : types) {
            model.addAttribute(type.toString().toLowerCase(),
                    filterByType(ingredients, type));
        }
    }

    @GetMapping
    public String showDesignForm(Model model) {
        model.addAttribute("taco", new Taco());
        return "design";
    }
    private Iterable<Ingredient> filterByType(
            List<Ingredient> ingredients, Type type) {
        return ingredients
                .stream()
                .filter(x -> x.getType().equals(type))
                .collect(Collectors.toList());
    }
}

view:

<form method="POST" th:object="${design}">
    <div>
        <h3>Name your taco creation:</h3>
        <input type="text" th:field="*{name}"/><br/>
        <button>Submit your taco</button>
    </div>
</form>

The th:field will get 500 internal error when I open this web page....

I've google and take a look in Thymeleaf document, but seems the th:field usage is correct.

org.thymeleaf.exceptions.TemplateInputException: An error happened during template parsing (template: "class path resource [templates/design.html]")
    at org.thymeleaf.templateparser.markup.AbstractMarkupTemplateParser.parse(AbstractMarkupTemplateParser.java:241)
    at org.thymeleaf.templateparser.markup.AbstractMarkupTemplateParser.parseStandalone(AbstractMarkupTemplateParser.java:100)
    at org.thymeleaf.engine.TemplateManager.parseAndProcess(TemplateManager.java:666)
    at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1098)
    at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1072)
    at org.thymeleaf.spring5.view.ThymeleafView.renderFragment(ThymeleafView.java:366)
    at org.thymeleaf.spring5.view.ThymeleafView.render(ThymeleafView.java:190)
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1401)
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1145)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1084)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:655)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:764)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:360)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:890)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1787)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
    at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: org.attoparser.ParseException: Error during execution of processor 'org.thymeleaf.spring5.processor.SpringInputGeneralFieldTagProcessor' (template: "design" - line 15, col 28)
    at org.attoparser.MarkupParser.parseDocument(MarkupParser.java:393)
    at org.attoparser.MarkupParser.parse(MarkupParser.java:257)
    at org.thymeleaf.templateparser.markup.AbstractMarkupTemplateParser.parse(AbstractMarkupTemplateParser.java:230)
    ... 48 more
Caused by: org.thymeleaf.exceptions.TemplateProcessingException: Error during execution of processor 'org.thymeleaf.spring5.processor.SpringInputGeneralFieldTagProcessor' (template: "design" - line 15, col 28)
    at org.thymeleaf.processor.element.AbstractAttributeTagProcessor.doProcess(AbstractAttributeTagProcessor.java:117)
    at org.thymeleaf.processor.element.AbstractElementTagProcessor.process(AbstractElementTagProcessor.java:95)
    at org.thymeleaf.util.ProcessorConfigurationUtils$ElementTagProcessorWrapper.process(ProcessorConfigurationUtils.java:633)
    at org.thymeleaf.engine.ProcessorTemplateHandler.handleStandaloneElement(ProcessorTemplateHandler.java:918)
    at org.thymeleaf.engine.TemplateHandlerAdapterMarkupHandler.handleStandaloneElementEnd(TemplateHandlerAdapterMarkupHandler.java:260)
    at org.thymeleaf.templateparser.markup.InlinedOutputExpressionMarkupHandler$InlineMarkupAdapterPreProcessorHandler.handleStandaloneElementEnd(InlinedOutputExpressionMarkupHandler.java:256)
    at org.thymeleaf.standard.inline.OutputExpressionInlinePreProcessorHandler.handleStandaloneElementEnd(OutputExpressionInlinePreProcessorHandler.java:169)
    at org.thymeleaf.templateparser.markup.InlinedOutputExpressionMarkupHandler.handleStandaloneElementEnd(InlinedOutputExpressionMarkupHandler.java:104)
    at org.attoparser.HtmlElement.handleStandaloneElementEnd(HtmlElement.java:79)
    at org.attoparser.HtmlMarkupHandler.handleStandaloneElementEnd(HtmlMarkupHandler.java:241)
    at org.attoparser.MarkupEventProcessorHandler.handleStandaloneElementEnd(MarkupEventProcessorHandler.java:327)
    at org.attoparser.ParsingElementMarkupUtil.parseStandaloneElement(ParsingElementMarkupUtil.java:96)
    at org.attoparser.MarkupParser.parseBuffer(MarkupParser.java:706)
    at org.attoparser.MarkupParser.parseDocument(MarkupParser.java:301)
    ... 50 more
Caused by: java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'design' available as request attribute
    at org.springframework.web.servlet.support.BindStatus.<init>(BindStatus.java:153)
    at org.springframework.web.servlet.support.RequestContext.getBindStatus(RequestContext.java:903)
    at org.thymeleaf.spring5.context.webmvc.SpringWebMvcThymeleafRequestContext.getBindStatus(SpringWebMvcThymeleafRequestContext.java:227)
    at org.thymeleaf.spring5.util.FieldUtils.getBindStatusFromParsedExpression(FieldUtils.java:306)
    at org.thymeleaf.spring5.util.FieldUtils.getBindStatus(FieldUtils.java:253)
    at org.thymeleaf.spring5.util.FieldUtils.getBindStatus(FieldUtils.java:227)
    at org.thymeleaf.spring5.processor.AbstractSpringFieldTagProcessor.doProcess(AbstractSpringFieldTagProcessor.java:174)
    at org.thymeleaf.processor.element.AbstractAttributeTagProcessor.doProcess(AbstractAttributeTagProcessor.java:74)
    ... 63 more

CodePudding user response：

From incomplete template code I'm asuming the error is due to the fact that you only set a taco attriubte in your controller model.addAttribute("taco", new Taco()); but call a design object in view <form method="POST" th:object="${design}"> You'd either have to change the ${design} to ${taco} or define a seperate design attirbute