SpringBoot實戰(九)之Validator

表單驗證，是最為常見的，今天示範的是利用hibernate-validtor進行校驗，有的時候，雖然前端方面通過jQuery或者require.js校驗架構進行校驗，可以減輕伺服器的壓力和改善使用者體驗，但是比如第三方請求接口方面也需要校驗，在Controller裡面套着一大堆if-elseif-else等等，兩層嵌套還好，三層或者三層以上就不好了，日子久了繼續嵌套，就會導緻後面變得難以維護。我有一個朋友在一家國企，據他所說，他遇到的最爛代碼是if-else if裡面套者十幾層，而且一個類的代碼居然上千行，正常合理情況，當達到上千行代碼就要考慮抽象繼承或者多态，再設計模式了。設計模式，我不懂，隻是了解，這裡就不提了，後續博文會講到設計模式的。

這裡說Validator的意義在于，通過注解減少if-else等重複判斷代碼，進而使Java代碼行數減少，因為加載類中的代碼是需要時間的。代碼行數減少，意味着加載時間減少，進而提高代碼效率。

示範示例如下:

一、導入maven依賴

<?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、編寫實體

package hello;

import javax.validation.constraints.Min;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;

public class PersonForm {

    @NotNull
    @Size(min=2, max=30)
    private String name;

    @NotNull
    @Min(18)
    private Integer age;

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String toString() {
        return "Person(Name: " + this.name + ", Age: " + this.age + ")";
    }
}      

三、編寫Controller

package hello;

import java.util.List;

import javax.validation.Valid;

import org.springframework.format.FormatterRegistry;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.stereotype.Controller;
import org.springframework.validation.BindingResult;
import org.springframework.validation.MessageCodesResolver;
import org.springframework.validation.Validator;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.servlet.HandlerExceptionResolver;
import org.springframework.web.servlet.config.annotation.AsyncSupportConfigurer;
import org.springframework.web.servlet.config.annotation.ContentNegotiationConfigurer;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.DefaultServletHandlerConfigurer;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.PathMatchConfigurer;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.ViewControllerRegistry;
import org.springframework.web.servlet.config.annotation.ViewResolverRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;


@Controller
public class WebController implements WebMvcConfigurer {

    @Override
    public void addViewControllers(ViewControllerRegistry registry) {
        registry.addViewController("/results").setViewName("results");
    }

    @GetMapping("/")
    public String showForm(PersonForm personForm) {
        return "form";
    }

    @PostMapping("/")
    public String checkPersonInfo(@Valid PersonForm personForm, BindingResult bindingResult) {

        if (bindingResult.hasErrors()) {
            return "form";
        }

        return "/results";
    }

    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void addCorsMappings(CorsRegistry arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void addFormatters(FormatterRegistry arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void addInterceptors(InterceptorRegistry arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void addResourceHandlers(ResourceHandlerRegistry arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void addReturnValueHandlers(List<HandlerMethodReturnValueHandler> arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void configureAsyncSupport(AsyncSupportConfigurer arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void configureContentNegotiation(ContentNegotiationConfigurer arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void configureDefaultServletHandling(DefaultServletHandlerConfigurer arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void configurePathMatch(PathMatchConfigurer arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void configureViewResolvers(ViewResolverRegistry arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void extendMessageConverters(List<HttpMessageConverter<?>> arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public MessageCodesResolver getMessageCodesResolver() {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public Validator getValidator() {
        // TODO Auto-generated method stub
        return null;
    }
}      

四、編寫html代碼

form.html

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

result.html

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

五、編寫配置檔案

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、編寫啟動類

package hello;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Application {

    public static void main(String[] args) throws Exception {
        SpringApplication.run(Application.class, args);
    }

}      

最後運作main方法，在浏覽器輸入localhost:8080/

會出現對應的表單頁面，輸入不合法會出現提示，表示驗證成功