1. 实现目标

1. 优雅校验接口入参
2. 响应体格式统一处理
3. 异常统一处理

2. 统一状态码

• 创建状态码接口，所有状态码必须实现这个接口，统一标准

package com.example.mavendemo.enums;public interface StatusCode {int getCode();String getMsg();
}

• 定义状态码

package com.example.mavendemo.enums;import lombok.AllArgsConstructor;
import lombok.Getter;@Getter
@AllArgsConstructor
public enum ResponseCode implements StatusCode {SUCCESS(0, "请求成功"),FAILED(1, "请求失败"),VALIDATE_ERROR(2, "参数校验失败"),RESPONSE_ERROR(3, "返回失败"),APP_ERROR(40000,"服务内部异常"),BUSINESS_ERROR(40001,"业务异常");private int code;private String msg;
}

3. 统一响应体

• 响应结果统一使用ResultResponse进行包装，返回给前端

package com.example.mavendemo.dto;import com.example.mavendemo.enums.ResponseCode;
import com.example.mavendemo.enums.StatusCode;import lombok.AllArgsConstructor;
import lombok.Data;@Data
@AllArgsConstructor
public class ResultResponse {private int code;private String msg;private Object data;public static ResultResponse ok() {return new ResultResponse(ResponseCode.SUCCESS.getCode(), ResponseCode.SUCCESS.getMsg(), null);}public static ResultResponse ok(Object data) {return new ResultResponse(ResponseCode.SUCCESS.getCode(), ResponseCode.SUCCESS.getMsg(), data);}public static ResultResponse error(StatusCode statusCode) {return new ResultResponse(statusCode.getCode(), statusCode.getMsg(), null);}public static ResultResponse error(StatusCode statusCode, Object data) {return new ResultResponse(statusCode.getCode(), statusCode.getMsg(), data);}}

4. 统一异常

• 自定义一个异常类，对于特定错误，传入响应的状态码

package com.example.mavendemo.exception;import com.example.mavendemo.enums.ResponseCode;
import com.example.mavendemo.enums.StatusCode;import lombok.Getter;@Getter
public class ApiException extends RuntimeException {private StatusCode statusCode;public ApiException(String message) {super(message);this.statusCode = ResponseCode.APP_ERROR;}public ApiException(StatusCode statusCode, String message) {super(message);this.statusCode = statusCode;}}

5. 统一入参校验

• 需要引入hibernate-validator

<dependency><groupId>org.hibernate</groupId><artifactId>hibernate-validator</artifactId><version>6.1.7.Final</version>
</dependency>

• 定义实体类，对于需要校验的字段添加注解，例如@NotBlank，@Max

package com.example.mavendemo.model;import javax.validation.constraints.Max;
import javax.validation.constraints.NotBlank;import lombok.Data;@Data
public class User {@NotBlank(message = "姓名不能为空")private String name;@Max(value = 18, message = "年龄不能大于18")private Integer age;private String address;}

• 在传参时，使用@Valid，例如@RequestBody @Valid User user

6. 统一返回结果

• 如果不想统一响应体，可以定义一个注解，标记具体的接口进行排除

package com.example.mavendemo.annotation;import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface NotResponseAdvice {
}

• 实现ResponseBodyAdvice接口，重写supports和beforeBodyWrite方法，完成对response body的增强

package com.example.mavendemo.advice;import com.example.mavendemo.annotation.NotResponseAdvice;
import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.web.bind.annotation.RestControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;import com.example.mavendemo.dto.ResultResponse;/*** basePackages指定作用范围**/
@RestControllerAdvice(basePackages = {"com.example.mavendemo.controller"})
public class ControllerResponseAdvice implements ResponseBodyAdvice<Object> {/*** 校验是否执行beforeBodyWrite方法*/@Overridepublic boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {// 如果返回值已经是ResultResponse，或有NotResponseAdvice注解则不进行包装return !(returnType.getParameterType().isAssignableFrom(ResultResponse.class)|| returnType.hasMethodAnnotation(NotResponseAdvice.class));}/*** 对返回值进行处理*/@Overridepublic Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType,Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request,ServerHttpResponse response) {return ResultResponse.ok(body);}
}

• 这里需要注意String类型的返回值，使用上面的代码会报错java.lang.ClassCastException: cannot be cast to java.lang.String
• 需要介绍一下HttpMessageConverter接口，负责将请求信息转换为一个java对象，将java对象输出为响应信息；所以在触发@ResponseBody注解时，Spring都会遍历这个HttpMessageConverter列表，然后选择第一个符合返回值类型的转换器然后进行转换。
• HttpMessageConverter如下

• String类型会优先使用StringHttpMessageConverter转换器。实际上String类型既可以使用MappingJackson2HttpMessageConverter，也可以使用StringHttpMessageConverter来解析。所以可以将HttpMessageConverter列表反转，调换MappingJackson2HttpMessageConverter和StringHttpMessageConverter的顺序来解决。
• 实现WebMvcConfigurer，重写configureMessageConverters方法

package com.example.mavendemo.advice;import java.util.Collections;
import java.util.List;import org.springframework.context.annotation.Configuration;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;@Configuration
public class WebResponseConfig implements WebMvcConfigurer {/*** 反转HttpMessageConverter集合，将MappingJackson2HttpMessageConverter移到StringHttpMessageConverter前面*/@Overridepublic void configureMessageConverters(List<HttpMessageConverter<?>> converters) {Collections.reverse(converters);}}

7. 统一异常处理

• 使用@RestControllerAdvice注解对Controller进行增强，配合@ExceptionHandler使用，统一处理异常

package com.example.mavendemo.advice;import com.example.mavendemo.exception.ApiException;
import org.springframework.web.bind.MethodArgumentNotValidException;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.RestControllerAdvice;import com.example.mavendemo.dto.ResultResponse;
import com.example.mavendemo.enums.ResponseCode;@RestControllerAdvice
public class ControllerExceptionAdvice {/*** 参数错误异常*/@ExceptionHandler(MethodArgumentNotValidException.class)public ResultResponse methodArgumentNotValidExceptionHandler(MethodArgumentNotValidException e) {return ResultResponse.error(ResponseCode.VALIDATE_ERROR,e.getBindingResult().getAllErrors().get(0).getDefaultMessage());}/*** 自定义异常*/@ExceptionHandler(ApiException.class)public ResultResponse apiExceptionHandler(ApiException e) {return ResultResponse.error(e.getStatusCode(), e.getMessage());}/*** 异常兜底*/@ExceptionHandler(Exception.class)public ResultResponse exceptionHandler(Exception e) {return ResultResponse.error(ResponseCode.FAILED, e.getMessage());}}

8. 验证

• 测试类

package com.example.mavendemo.controller;import javax.validation.Valid;import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;import com.example.mavendemo.annotation.NotResponseAdvice;
import com.example.mavendemo.enums.ResponseCode;
import com.example.mavendemo.exception.ApiException;
import com.example.mavendemo.model.User;@RestController
public class HelloController {/*** 测试入参校验和统一响应体*/@PostMapping("/hello")public User hello(@RequestBody @Valid User user) {return user;}/*** 测试String类型返回值的响应体*/@GetMapping("/name")public String getName(String name) {return name;}/*** 测试不统一响应体和统一异常处理情况*/@NotResponseAdvice@GetMapping("/findUser")public User getAddress(String name, Integer age) {if (age > 18) {throw new ApiException(ResponseCode.BUSINESS_ERROR, "查无此人");}User user = new User();user.setName(name);user.setAge(age);user.setAddress("北京市王府井大街1号");return user;}}

• 验证参数校验

• 验证统一响应体

1. 返回值是java对象

2. 返回值是String类型

• 验证不需要统一的响应体

• 验证统一异常处理