表单验证，是最为常见的，今天演示的是利用hibernate-validtor进行校验，有的时候，虽然前端方面通过jQuery或者require.js校验框架进行校验，可以减轻服务器的压力和改善用户体验，但是比如第三方请求接口方面也需要校验，在Controller里面套着一大堆if-elseif-else等等，两层嵌套还好，三层或者三层以上就不好了，日子久了继续嵌套，就会导致后面变得难以维护。我有一个朋友在一家国企，据他所说，他遇到的最烂代码是if-else if里面套者十几层，而且一个类的代码居然上千行，正常合理情况，当达到上千行代码就要考虑抽象继承或者多态，再设计模式了。设计模式，我不懂，只是了解，这里就不提了，后续博文会讲到设计模式的。

这里说Validator的意义在于，通过注解减少if-else等重复判断代码，从而使Java代码行数减少，因为加载类中的代码是需要时间的。代码行数减少，意味着加载时间减少，从而提高代码效率。

演示示例如下:

一、导入maven依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>org.springframework</groupId><artifactId>gs-validating-form-input</artifactId><version>0.1.0</version><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>1.5.8.RELEASE</version></parent><properties><java.version>1.8</java.version></properties><build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId></plugin></plugins></build><dependencies><dependency><groupId>org.hibernate</groupId><artifactId>hibernate-validator</artifactId><version>5.4.1.Final</version>
</dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-thymeleaf</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.apache.tomcat.embed</groupId><artifactId>tomcat-embed-el</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency></dependencies></project>

二、编写实体

packagehello;importjavax.validation.constraints.Min;importjavax.validation.constraints.NotNull;importjavax.validation.constraints.Size;public classPersonForm {@NotNull@Size(min=2, max=30)privateString name;@NotNull@Min(18)privateInteger age;publicString getName() {return this.name;}public voidsetName(String name) {this.name =name;}publicInteger getAge() {returnage;}public voidsetAge(Integer age) {this.age =age;}publicString toString() {return "Person(Name: " + this.name + ", Age: " + this.age + ")";}
}

三、编写Controller

packagehello;importjava.util.List;importjavax.validation.Valid;importorg.springframework.format.FormatterRegistry;importorg.springframework.http.converter.HttpMessageConverter;importorg.springframework.stereotype.Controller;importorg.springframework.validation.BindingResult;importorg.springframework.validation.MessageCodesResolver;importorg.springframework.validation.Validator;importorg.springframework.web.bind.annotation.GetMapping;importorg.springframework.web.bind.annotation.PostMapping;importorg.springframework.web.method.support.HandlerMethodArgumentResolver;importorg.springframework.web.method.support.HandlerMethodReturnValueHandler;importorg.springframework.web.servlet.HandlerExceptionResolver;importorg.springframework.web.servlet.config.annotation.AsyncSupportConfigurer;importorg.springframework.web.servlet.config.annotation.ContentNegotiationConfigurer;importorg.springframework.web.servlet.config.annotation.CorsRegistry;importorg.springframework.web.servlet.config.annotation.DefaultServletHandlerConfigurer;importorg.springframework.web.servlet.config.annotation.InterceptorRegistry;importorg.springframework.web.servlet.config.annotation.PathMatchConfigurer;importorg.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;importorg.springframework.web.servlet.config.annotation.ViewControllerRegistry;importorg.springframework.web.servlet.config.annotation.ViewResolverRegistry;importorg.springframework.web.servlet.config.annotation.WebMvcConfigurer;@Controllerpublic class WebController implementsWebMvcConfigurer {@Overridepublic voidaddViewControllers(ViewControllerRegistry registry) {registry.addViewController("/results").setViewName("results");}@GetMapping("/")publicString showForm(PersonForm personForm) {return "form";}@PostMapping("/")publicString checkPersonInfo(@Valid PersonForm personForm, BindingResult bindingResult) {if(bindingResult.hasErrors()) {return "form";}return "/results";}@Overridepublic void addArgumentResolvers(List<HandlerMethodArgumentResolver>arg0) {//TODO Auto-generated method stub
}@Overridepublic voidaddCorsMappings(CorsRegistry arg0) {//TODO Auto-generated method stub
}@Overridepublic voidaddFormatters(FormatterRegistry arg0) {//TODO Auto-generated method stub
}@Overridepublic voidaddInterceptors(InterceptorRegistry arg0) {//TODO Auto-generated method stub
}@Overridepublic voidaddResourceHandlers(ResourceHandlerRegistry arg0) {//TODO Auto-generated method stub
}@Overridepublic void addReturnValueHandlers(List<HandlerMethodReturnValueHandler>arg0) {//TODO Auto-generated method stub
}@Overridepublic voidconfigureAsyncSupport(AsyncSupportConfigurer arg0) {//TODO Auto-generated method stub
}@Overridepublic voidconfigureContentNegotiation(ContentNegotiationConfigurer arg0) {//TODO Auto-generated method stub
}@Overridepublic voidconfigureDefaultServletHandling(DefaultServletHandlerConfigurer arg0) {//TODO Auto-generated method stub
}@Overridepublic void configureHandlerExceptionResolvers(List<HandlerExceptionResolver>arg0) {//TODO Auto-generated method stub
}@Overridepublic void configureMessageConverters(List<HttpMessageConverter<?>>arg0) {//TODO Auto-generated method stub
}@Overridepublic voidconfigurePathMatch(PathMatchConfigurer arg0) {//TODO Auto-generated method stub
}@Overridepublic voidconfigureViewResolvers(ViewResolverRegistry arg0) {//TODO Auto-generated method stub
}@Overridepublic void extendHandlerExceptionResolvers(List<HandlerExceptionResolver>arg0) {//TODO Auto-generated method stub
}@Overridepublic void extendMessageConverters(List<HttpMessageConverter<?>>arg0) {//TODO Auto-generated method stub
}@OverridepublicMessageCodesResolver getMessageCodesResolver() {//TODO Auto-generated method stubreturn null;}@OverridepublicValidator getValidator() {//TODO Auto-generated method stubreturn null;}
}

四、编写html代码

form.html

<htmlxmlns:th="http://www.thymeleaf.org"><body><formaction="#"th:action="@{/}"th:object="${personForm}"method="post"><table><tr><td>Name:</td><td><inputtype="text"th:field="*{name}" /></td><tdth:if="${#fields.hasErrors('name')}"th:errors="*{name}">Name Error</td></tr><tr><td>Age:</td><td><inputtype="text"th:field="*{age}" /></td><tdth:if="${#fields.hasErrors('age')}"th:errors="*{age}">Age Error</td></tr><tr><td><buttontype="submit">Submit</button></td></tr></table></form></body>
</html>

result.html

<htmlxmlns:th="http://www.thymeleaf.org"><body>Congratulations! You are old enough to sign up for this site.</body>
</html>

五、编写配置文件

application.properties

server.port=8080
spring.thymeleaf.cache=false
spring.thymeleaf.prefix=classpath:/templates/
spring.thymeleaf.check-template-location=true
spring.thymeleaf.suffix=.html
spring.thymeleaf.encoding=UTF-8
spring.thymeleaf.content-type=text/html
spring.thymeleaf.mode=HTML5

六、编写启动类

packagehello;importorg.springframework.boot.SpringApplication;importorg.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplicationpublic classApplication {public static void main(String[] args) throwsException {SpringApplication.run(Application.class, args);}}

最后运行main方法，在浏览器输入localhost:8080/

会出现对应的表单页面，输入不合法会出现提示，表示验证成功