从零搭建开发脚手架 自定义HandlerMethodArgumentResolver-注解@JsonArg和实体CurrentUser

前言

参数绑定时springmvc会对从前端传来的参数自动转化成方法定义的参数的类型，我们可自己定义此接口来实现自己的类型的转换。

HandlerMethodArgumentResolver是什么？它是springmvc提供的入参解析器，像平常应用的注解@RequestParam @PathVariable @ModelAttribute …等等修饰在@RequestMapping下的参数上都可以用HandlerMethodArgumentResolver来解析。

public interface HandlerMethodArgumentResolver {
	// 参数是否符合条件，反回true会调用下面的方法
	boolean supportsParameter(MethodParameter parameter);
	// 对修饰的参数解析赋值等
	Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;
}
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有很多内置实现，我们可以去参考，例如：RequestParamMethodArgumentResolver.java

场景1 自定义参数映射注解JsonArg

1.创建自定义注解

@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
public @interface JsonArg {
    String value() default "";
}
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2.创建自定义HandlerMethodArgumentResolver

public class JsonArgumentResolver implements HandlerMethodArgumentResolver {

    private static final String JSON_BODY_ATTRIBUTE = "JSON_REQUEST_BODY";

    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.hasParameterAnnotation(JsonArg.class);
    }

    @Override
    public Object resolveArgument(
      MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest,
      WebDataBinderFactory binderFactory) 
      throws Exception {
        String body = getRequestBody(webRequest);
        String jsonPath = Objects.requireNonNull(
          Objects.requireNonNull(parameter.getParameterAnnotation(JsonArg.class)).value());
        Class<?> parameterType = parameter.getParameterType();
        return JsonPath.parse(body).read(jsonPath, parameterType);
    }

    private String getRequestBody(NativeWebRequest webRequest) {
        HttpServletRequest servletRequest = Objects.requireNonNull(
          webRequest.getNativeRequest(HttpServletRequest.class));
        String jsonBody = (String) servletRequest.getAttribute(JSON_BODY_ATTRIBUTE);
        if (jsonBody == null) {
            try {
                jsonBody = IOUtils.toString(servletRequest.getInputStream());
                servletRequest.setAttribute(JSON_BODY_ATTRIBUTE, jsonBody);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return jsonBody;
    }
}
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3.注册自定义HandlerMethodArgumentResolver

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
        JsonArgumentResolver jsonArgumentResolver = new JsonArgumentResolver();
        argumentResolvers.add(jsonArgumentResolver);
    }
}
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4.使用示例

@PostMapping("/process/custompojo")
public ResponseEntity process(
  @JsonArg("firstName") String firstName, 
  @JsonArg("lastName") String lastName,
  @JsonArg("address") AddressDto address) {
    ...
}
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该节来自：https://www.baeldung.com/spring-mvc-json-param-mapping

场景2 自定义类型接收分页参数

参考：PageableHandlerMethodArgumentResolver.java

1.创建自定义类型

public class PageRequest {
	private int page;
	private int size;
    private List<Order> orders;
    public static class Order {
        private String property;
        private String direction;
    }
}
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2.创建自定义HandlerMethodArgumentResolver

public class PageRequestArgumentResolver implements HandlerMethodArgumentResolver {
    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return PageRequest.class.equals(parameter.getParameterType());
    }

    @Override
    public Object resolveArgument(
            MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest,
            WebDataBinderFactory binderFactory)
            throws Exception {
        PageRequest.PageRequestBuilder builder = PageRequest.builder();
        String page = webRequest.getParameter("page");
        String pageSize = webRequest.getParameter("size");
        String[] directionParameter = webRequest.getParameterValues("sort");
        List<PageRequest.Order> allOrders = new ArrayList<>();
        builder.page(Integer.valueOf(page))
                .size(Integer.valueOf(pageSize))
                .orders(allOrders);
        if (ArrayUtil.isNotEmpty(directionParameter)) {
            for (String part : directionParameter) {
                if (part == null) {
                    continue;
                }
                String[] elements = Arrays.stream(part.split(",")) //
                        .toArray(String[]::new);
                allOrders.add(PageRequest.Order.builder()
                        .property(elements[0])
                        .direction(elements.length > 1 ? elements[1] : "asc")
                        .build());
            }
        }
        return builder.build();
    }
}
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3.注册自定义HandlerMethodArgumentResolver

@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
        argumentResolvers.add(new PageRequestArgumentResolver());
    }
}
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4.使用示例

/api/v1/users?page=1&size=2&sort=name,email,asc
/api/v1/users?page=1&size=2&sort=name,desc&sort=email,asc&sort=jack,asc
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@GetMapping
public void get(PageRequest page) {
    log.info(page);
}
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结果日志：

PageRequest(page=1, size=2, 
            orders=[PageRequest.Order(property=name, direction=desc),
                    PageRequest.Order(property=email, direction=asc), 
                    PageRequest.Order(property=jack, direction=asc)])
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场景3 自定义注解+类型接收当前登陆人

1.创建自定义类型和自定义注解

public class CurrentUser {
    private String id;
    private String username;
    private String displayName;
}

@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
public @interface Auth {
}
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2.创建自定义HandlerMethodArgumentResolver

public class AuthInfoArgumentResolver implements HandlerMethodArgumentResolver {
 		@Override
        public boolean supportsParameter(MethodParameter parameter) {
            return CurrentUser.class.equals(parameter.getParameterType()) &&
                	parameter.hasParameterAnnotation(Auth.class);
        }

        @Override
        public Object resolveArgument(
                    MethodParameter parameter,
                    ModelAndViewContainer mvContainer,
                    NativeWebRequest nativeWebRequest,
                    WebDataBinderFactory webDataBinderFactory) throws Exception {
            HttpServletRequest request = nativeWebRequest.getNativeRequest(HttpServletRequest.class);
            if (request == null) {
                return null;
            }
                // CurrentUser  = from request
            return CurrentUser.builder().id(StpUtil.getLoginId().toString()).build();
        }
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3.注册自定义HandlerMethodArgumentResolver

同上

4.使用示例

/api/v1/users
-hearder token
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@RestController
public class HelloController {
    @PostMapping
    public void test(@RequestBody City city, @Auth CurrentUser user) {
        ...
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参数类型转换总结

• 对于单个简单类型到对象的转换，使用Converter实现。

  从零搭建开发脚手架 SpringMvc使用Converter中枚举类型参数的序列化和反序列化

• 为了封装一系列对象的转换逻辑，使用ConverterFactory实现。

• 对于任何数据，间接出现或需要应用其他逻辑来检索关联的数据，使用HandlerMethodArgumentResolver实现。