手写一个类似@RequestParam的注解（用来接收请求体的参数）

一、本文解决的痛点

按照大众认为的开发规范，一般post类型的请求参数应该传在请求body里面。但是我们有些post接口只需要传入一个字段，我们接受这种参数就得像下面这样单独创建一个类，类中再添加要传入的基本类型字段，配合@RequestBody来实现这种功能多少有点繁琐：

@Data
public class TextHolder {private String text;
}@PostMapping("test")
public ApiResponse test(@RequestBody TextHolder textHolder){....
}

那么我们能不能省略类的创建，实现一个类似@RequestParam的注解来实现请求体参数的直接接收呢？本文就是来解决这个问题的！

二、实现步骤

2.1定义我们这个增强版的请求体注解

@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
public @interface RequestBodyPlus {String value() default "";
}

2.2手写一个方法参数解析器

@Slf4j
public class RequestBodyPlusMethodHandler implements HandlerMethodArgumentResolver {public static final ThreadLocal<Map<String,Object>> requestBodyMap = new ThreadLocal<>();@Overridepublic boolean supportsParameter(MethodParameter methodParameter) {return methodParameter.hasParameterAnnotation(RequestBodyPlus.class);}@Overridepublic Object resolveArgument(MethodParameter methodParameter, ModelAndViewContainer modelAndViewContainer, NativeWebRequest nativeWebRequest, WebDataBinderFactory webDataBinderFactory) throws Exception {HttpServletRequest request  = nativeWebRequest.getNativeRequest(HttpServletRequest.class);RequestBodyPlus parameterAnnotation = methodParameter.getParameterAnnotation(RequestBodyPlus.class);String paramName = parameterAnnotation.value();if (StringUtils.isEmpty(paramName)) {paramName = methodParameter.getParameterName();}Map<String, Object> paramsMap = new HashMap<>();if (requestBodyMap.get() == null) {String requestBodyString = getRequestBodyString(request);paramsMap = JSON.parseObject(requestBodyString);// 需要把请求体Map放入ThreadLocal中，因为request中的inputStream读完一次，下次就读不了了，这也是原生的@RequestBody只能在方法参数中出现一次的原因！requestBodyMap.set(paramsMap);}else {paramsMap = requestBodyMap.get();}Object paramValue = paramsMap.get(paramName);// 有的参数需要databinder处理if (paramValue != null && webDataBinderFactory != null) {WebDataBinder binder = webDataBinderFactory.createBinder(nativeWebRequest, paramValue, paramName);paramValue = binder.convertIfNecessary(paramValue, methodParameter.getParameterType(), methodParameter);}return paramValue;}private String getRequestBodyString(final ServletRequest request){StringBuilder stringBuilder = new StringBuilder();try(InputStream inputStream = request.getInputStream();BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream, Charset.forName("UTF-8")));){String line = "";while((line = bufferedReader.readLine()) != null){stringBuilder.append(line);}}catch (IOException e){log.error("request的ServletInputStream转换失败",e);}finally {return stringBuilder.toString();}}}

2.3需要写一个拦截器，用来remove上面的threadLocal避免内存泄漏

public class RequestBodyPlusInterceptor implements HandlerInterceptor {@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {RequestBodyPlusMethodHandler.requestBodyMap.remove();}}

2.4需要把拦截器和参数解析器配置好才能生效

@Configuration
public class WebConfigurer extends WebMvcConfigurerAdapter {@Overridepublic void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {argumentResolvers.add(new RequestBodyPlusMethodHandler());}@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(new RequestBodyPlusInterceptor());super.addInterceptors(registry);}
}

三、使用案例

3.1测试代码：

@RestController
@RequestMapping("plus")
public class TestRequestBodyPlus {@PostMapping("one")public String test01(@RequestBodyPlus("dx") Integer dx, @RequestBodyPlus("ls") String ls, @RequestBodyPlus("jk") Date jk, @RequestBodyPlus("el") List<Long> el) {System.out.println(el);String format = "%d_______%s_______%s_________%d";return String.format(format, dx, ls, jk, el.size());}//有了下面这个方法，上面的接口的入参数就能传`2023-11-24`这种字符串@InitBinder //该注解底层的源码：RequestMappingHandlerAdapter#invokeHandlerMethodpublic void initBinder(WebDataBinder binder){SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");dateFormat.setLenient(false);binder.registerCustomEditor(Date.class,new CustomDateEditor(dateFormat,false));}//该方法的作用域仅在当前的controller，如果想全局生效，需要写在@ControllerAdvice所在的类中
}

3.2测试请求

POST localhost:8088/plus/one
{"dx" : 3,"ls" : "bbb","jk" : "2023-11-24","el" : [1,2,3,4,5]
}

3.3测试结果