1. 实现目标

优雅校验接口入参
响应体格式统一处理
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
     */
    @Override
    public 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
     */
    @Override
    public 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

在这里插入图片描述

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
     */
    @Override
    public 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;
    }

}