Spring实战第五版第二章

2.3 校验表单输入

在编写”/design”页面post处理逻辑时，按照书本上直接’return “design”; ‘方式，会报如下错误：

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

个人猜测post请求时，model数据模型中的数据被清空，导致重新请求视图时，绑定的“design”对象为空，在渲染输入框中“design”对象属性时报错。可采用redirect方式重新请求“/design”的get方法，或重新设置model。

   @PostMapping
    public String processDesign(@Valid Taco design, Errors error,Model model){
        //若校验不生效，则检查valid依赖包是否引入完整
        if(error.hasErrors()){
            model.addAttribute("design",new Taco());
            return "design";//直接请求视图报错,可能因为model中的map.design为空
//            return "redirect:design";

        }
        log.info("processing design :"+design);
        return "redirect:/orders/current";//type=Not Found, status=404
//        return "/orders/current";//直接请求视图，未编辑网页时报错模板不存在
    }

通过传入model的方式解决报错后，请求校验不通过时前后页面变化如下图，原“ingredients”信息不再存在，进一步证实model中数据未在视图中保存。

ps:字段校验不生效，需检查javax.validation依赖包是否完整导入

<dependency>
    <groupId>javax.validation</groupId>
    <artifactId>validation-api</artifactId>
    <version>1.1.0.Final</version>
</dependency>

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-validator</artifactId>
    <version>5.4.1.Final</version>
</dependency>
<dependency>
    <groupId>org.jboss.logging</groupId>
    <artifactId>jboss-logging</artifactId>
    <version>3.3.0.Final</version>
</dependency>
<dependency>
    <groupId>com.fasterxml</groupId>
    <artifactId>classmate</artifactId>
    <version>1.3.3</version>
</dependency>