CustomBodyAnnotationApplication.java

package com.example.custombodyannotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.util.List;

import javax.servlet.http.HttpServletRequest;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.core.MethodParameter;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.util.Assert;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.ModelAndViewContainer;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@SpringBootApplication
public class CustomBodyAnnotationApplication {

    public static void main(String[] args) {
        SpringApplication.run(CustomBodyAnnotationApplication.class, args);
    }

    @Bean
    WebMvcConfigurer webMvcConfigurer(ObjectMapper objectMapper) {
        return new WebMvcConfigurer() {

            @Override public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {
                resolvers.add(new JsonParameterHandlerMethodArgumentResolver(objectMapper));
            }
        };
    }
}

class JsonParameterHandlerMethodArgumentResolver implements HandlerMethodArgumentResolver {
    private final ObjectMapper objectMapper;

    JsonParameterHandlerMethodArgumentResolver(ObjectMapper objectMapper) {
        this.objectMapper = objectMapper;
    }

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

    @Override public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
            NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        JsonParameter parameterAnnotation = parameter.getParameterAnnotation(JsonParameter.class);
        HttpInputMessage inputMessage = this.createInputMessage(webRequest);
        JsonNode jsonNode = objectMapper.readTree(inputMessage.getBody());
        return jsonNode.get(parameterAnnotation.value()).asText();
    }

    private ServletServerHttpRequest createInputMessage(NativeWebRequest webRequest) {
        HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);
        Assert.state(servletRequest != null, "No HttpServletRequest");
        return new ServletServerHttpRequest(servletRequest);
    }
}

@RestController
class HelloCtrl {

    @PostMapping("/foo")
    void foo(@JsonParameter("title") String title) {
        System.out.println(title);
    }

}

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.PARAMETER)
@interface JsonParameter {
    String value();
}