springMVC引入Validation的具体步骤详解

本文简单介绍如何引入validation的步骤，如何通过自定义validation减少代码量，提高生产力。特别提及：非基本类型属性的valid，GET方法的处理，validation错误信息的统一resolve。

本文中validation的实际实现委托给Hibernate validation处理

基本配置

pom引入maven依赖

<!-- validation begin -->
<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>5.4.0.Final</version>
</dependency>
<!-- validation end -->

增加validation配置

在spring-mvc-servlet.xml中增加如下配置:

<mvc:annotation-driven validator="validator">

<bean id="validator" class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean">
  <property name="providerClass" value="org.hibernate.validator.HibernateValidator" />
  <property name="validationMessageSource" ref="messageSource"/>
</bean>
//messageSource 为i18n资源管理bean，见applicationContext.xml配置

自定义exceptionHandler

个性化处理validation错误信息,返回给调用方的信息更加友好， 在applicationContext.xml中增加如下配置:

<!-- 加载i18n消息资源文件 -->
<bean id="messageSource" class="org.springframework.context.support.ResourceBundleMessageSource">
  <property name="basenames">
    <list>
      <value>errormsg</value>
      <value>validation_error</value>
    </list>
  </property>
</bean>

<bean id="validationExceptionResolver" class="com.*.exception.ValidationExceptionResovler"/>

在项目类路径上增加：validation_error_zh_CN.properties资源文件：

#the error msg for input validation
#common
field.can.not.be.null={field}不能为空
field.can.not.be.empty={field}不能为空或者空字符串
field.must.be.greater.than.min={field}不能小于{value}
field.must.be.letter.than.max={field}不能大于{value}

ValidationExceptionResovler实现：

ValidationExceptionResovler.java

@Slf4j
public class ValidationExceptionResovler extends AbstractHandlerExceptionResolver {
  public ValidationExceptionResovler() {
    // 设置order，在DefaultHandlerExceptionResolver之前执行
    this.setOrder(0);
  }
  /**
   * Handle the case where an argument annotated with {@code @Valid} such as
   * an {@link } or {@link } argument fails validation.
   * <p>
   * 自定义ValidationException 异常处理器
   * 获取到具体的validation 错误信息，并组装CommonResponse，返回给调用方。
   *
   * @param request current HTTP request
   * @param response current HTTP response
   * @param handler the executed handler
   * @return an empty ModelAndView indicating the exception was handled
   * @throws IOException potentially thrown from response.sendError()
   */
  @ResponseBody
  protected ModelAndView handleMethodArgumentNotValidException(BindingResult bindingResult,
                                 HttpServletRequest request,
                                 HttpServletResponse response,
                                 Object handler)
      throws IOException {

    List<ObjectError> errors = bindingResult.getAllErrors();
    StringBuffer errmsgBF = new StringBuffer();
    for (ObjectError error : errors) {
      String massage = error.getDefaultMessage();
      errmsgBF.append(massage);
      errmsgBF.append("||");
    }
    String errmsgString = errmsgBF.toString();
    errmsgString = errmsgString.length() > 2 ? errmsgString.substring(0, errmsgString.length() - 2) : errmsgString;
    log.error("Validation failed! {} ", errmsgString);

    Map<String, Object> map = new TreeMap<String, Object>();
    map.put("success", false);
    map.put("errorCode", "9999");
    map.put("errorMsg", errmsgString);

    ModelAndView mav = new ModelAndView();
    MappingJackson2JsonView view = new MappingJackson2JsonView();
    view.setAttributesMap(map);
    mav.setView(view);

    return mav;
  }

  @Override
  protected ModelAndView doResolveException(HttpServletRequest request,
                       HttpServletResponse response, Object handler,
                       Exception ex) {
    BindingResult bindingResult = null;
    if (ex instanceof MethodArgumentNotValidException) {
      bindingResult = ((MethodArgumentNotValidException) ex).getBindingResult();
    } else if(ex instanceof BindException) {
      bindingResult = ((BindException) ex).getBindingResult();
    } else {
      //other exception , ignore
    }

    if(bindingResult != null) {
      try {
        return handleMethodArgumentNotValidException(bindingResult, request, response, handler);
      } catch (IOException e) {
        log.error("doResolveException: ", e);
      }
    }
    return null;
  }
}

在controller中增加@Valid 

@RequestMapping("/buy")
@ResponseBody
public BaseResponse buy(@RequestBody @Valid BuyFlowerRequest request) throws Exception {
 //......
}

在request bean上为需要validation的属性增加validation注解

@Setter
@Getter
public class BuyFlowerRequest {

@NotEmpty(message = "{name.can.not.be.null}")
private String name;
} 

二级对象的validation

上面的写法，只能对BuyFlowerRequest在基本类型属性上做校验,但是没有办法对对象属性的属性进行validation,如果需要对二级对象的属性进行validation,则需要在二级对象及二级对象属性上同时添加@Valid 和 具体的validation注解.

如下写法:

@Setter
@Getter
public class BuyFlowerRequest {
  @NotEmpty(field = "花名")
  private String name;

  @Min(field = "价格", value = 1)
  private int price;

  @NotNull
  private List<PayType> payTypeList;

} 

@Setter
@Getter
public class PayType {

  @Valid
  @Min(value = 1)
  private int payType;

  @Valid
  @Min(value = 1)
  private int payAmount;
}

进一步减少编码量

为了减少编码工作量,通过自定义Validation注解,尝试将validation作用的filed名称传递到 错误信息的资源文件中,从而避免为每个域编写不同的message模版.

下面以重写的@NotNull为例讲解:

1、定义Validation注解,注意相比原生注解增加了field(),用于传递被validated的filed名字

NotNull.java

@Target( { ElementType.METHOD, ElementType.FIELD, ElementType.ANNOTATION_TYPE, ElementType.CONSTRUCTOR, ElementType.PARAMETER })
@Constraint(validatedBy = { NotNullValidator.class })
@Retention(RetentionPolicy.RUNTIME)
public @interface NotNull {
  String field() default "";
  String message() default "{field.can.not.be.null}";
  Class<?>[] groups() default {};
  Class<? extends Payload>[] payload() default {};
}

2、定义Validator,所有的Validator均实现ConstraintValidator接口:

NotNullValidator.java

public class NotNullValidator implements ConstraintValidator<NotNull, Object> {

  @Override
  public void initialize(NotNull annotation) {

  }

  @Override
  public boolean isValid(Object str, ConstraintValidatorContext constraintValidatorContext) {
    return str != null;
  }
}

3、在filed上加入Validation注解,注意指定filed值,message如果没有个性化需求，可以不用指明，validation组件会自行填充default message。

BuyFlowerRequest.java

@Setter
@Getter
public class BuyFlowerRequest {

  @NotEmpty(field = "花名")
  private String name;

  @Min(field = "价格", value = 1)
  private int price;
}

注：@NotNull注解已经支持对list的特殊校验，对于List类型节点，如果list==null || list.size() == 0都会返回false，validation失败。目前已按照此思路自定义实现了@NotNull、@NotEmpty、@Min、@Max注解,在goods工程中可以找到.

支持GET请求

上面的示例都是POST请求，@RequestBody可以 resolve POST请求，但是不支持GET请求，阅读spring的文档和源码，发现@ModelAttribute可以将GET请求resolve成Bean，且支持Validation。具体可以翻阅spring源码：ModelAttributeMethodProcessor.resolveArgument()方法。

使用示例：

@RequestMapping(value = "/buy", method = RequestMethod.GET)
@ResponseBody
public BaseResponse detail(@Valid @ModelAttribute DetailFlowerRequest request) throws Exception {

  DetailFlowerResponse response = new DetailFlowerResponse();
  response.setName(request.getName());

  return ResultFactory.success(response, BaseResponse.class);
}

TODO

1、根据业务场景扩展validation,如:日期格式、金额等

2、支持多个field关系校验的validation

附：spring validation实现关键代码

@RequestBody

实现类：RequestResponseBodyMethodProcessor.java

public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
 Object arg = this.readWithMessageConverters(webRequest, parameter, parameter.getGenericParameterType());
 String name = Conventions.getVariableNameForParameter(parameter);
 WebDataBinder binder = binderFactory.createBinder(webRequest, arg, name);
 if (arg != null) {
 this.validateIfApplicable(binder, parameter);
 if (binder.getBindingResult().hasErrors() && this.isBindExceptionRequired(binder, parameter)) {
  throw new MethodArgumentNotValidException(parameter, binder.getBindingResult());
 }
 }
 mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, binder.getBindingResult());
 return arg;
}

@ModelAttibute

实现类：ModelAttributeMethodProcessor.java

public final Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
 String name = ModelFactory.getNameForParameter(parameter);
 Object attribute = mavContainer.containsAttribute(name) ? mavContainer.getModel().get(name) : this.createAttribute(name, parameter, binderFactory, webRequest);
 if (!mavContainer.isBindingDisabled(name)) {
 ModelAttribute ann = (ModelAttribute)parameter.getParameterAnnotation(ModelAttribute.class);
 if (ann != null && !ann.binding()) {
  mavContainer.setBindingDisabled(name);
 }
 }
 WebDataBinder binder = binderFactory.createBinder(webRequest, attribute, name);
 if (binder.getTarget() != null) {
 if (!mavContainer.isBindingDisabled(name)) {
  this.bindRequestParameters(binder, webRequest);
 }
 this.validateIfApplicable(binder, parameter);
 if (binder.getBindingResult().hasErrors() && this.isBindExceptionRequired(binder, parameter)) {
  throw new BindException(binder.getBindingResult());
 }
 }
 Map<String, Object> bindingResultModel = binder.getBindingResult().getModel();
 mavContainer.removeAttributes(bindingResultModel);
 mavContainer.addAllAttributes(bindingResultModel);
 return binder.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter);
}

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