How to access plain json body in Spring rest controller?

Having the following code:

@RequestMapping(value = "/greeting", method = POST, consumes = APPLICATION_JSON_VALUE, produces = APPLICATION_JSON_VALUE)
@ResponseBody
public String greetingJson(@RequestBody String json) {
    System.out.println("json = " + json); // TODO json is null... how to retrieve plain json body?
    return "Hello World!";
}

The String json argument is always null despite json being sent in the body.

Note that I don't want automatic type conversion, I just want the plain json result.

This for example works:

@RequestMapping(value = "/greeting", method = POST, consumes = APPLICATION_JSON_VALUE, produces = APPLICATION_JSON_VALUE)
@ResponseBody
public String greetingJson(@RequestBody User user) {
    return String.format("Hello %s!", user);
}

Probably I can use the use the ServletRequest or InputStream as argument to retrieve the actual body, but I wonder if there is an easier way?

Best way I found until now is:

@RequestMapping(value = "/greeting", method = POST, consumes = APPLICATION_JSON_VALUE, produces = APPLICATION_JSON_VALUE)
@ResponseBody
public String greetingJson(HttpEntity<String> httpEntity) {
    String json = httpEntity.getBody();
    // json contains the plain json string

Let me know if there are other alternatives.

You can just use

@RequestBody String pBody

Only HttpServletRequest worked for me. HttpEntity gave null string.

import java.io.IOException;
import javax.servlet.http.HttpServletRequest;
import org.apache.commons.io.IOUtils;

@RequestMapping(value = "/greeting", method = POST, consumes = APPLICATION_JSON_VALUE, produces = APPLICATION_JSON_VALUE)
@ResponseBody
public String greetingJson(HttpServletRequest request) throws IOException {
    final String json = IOUtils.toString(request.getInputStream(), StandardCharsets.UTF_8);
    System.out.println("json = " + json);
    return "Hello World!";
}

simplest way that works for me is

@RequestMapping(value = "/greeting", method = POST, consumes = MediaType.ALL_VALUE, produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
@ResponseBody
public String greetingJson(String raw) {
    System.out.println("json = " + raw);
    return "OK";
}

If you have dozens of Methods that need to get HTTP body as JSON and convert it to custom data type, it is a better way to implement the support on the framework

public static class Data {
    private String foo;
    private String bar;
}

//convert http body to Data object.
//you can also use String parameter type to get the raw json text.
@RequestMapping(value = "/greeting")
@ResponseBody
public String greetingJson(@JsonBody Data data) {
    System.out.println(data);
    return "OK";
}

notice that we using user defined annotation @JsonBody.

// define custom annotation
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.PARAMETER)
public @interface JsonBody {
    String encoding() default "utf-8";
}

//annotation processor for JsonBody 
@Slf4j
public class JsonBodyArgumentResolver implements HandlerMethodArgumentResolver {

    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.getParameterAnnotation(JsonBody.class) != null;
    }

    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest,
                              WebDataBinderFactory binderFactory) throws Exception {
        JsonBody annotation = parameter.getParameterAnnotation(JsonBody.class);
        assert annotation != null;
        ServletRequest servletRequest = webRequest.getNativeRequest(ServletRequest.class);
        if (servletRequest == null) {
            throw new Exception("can not get ServletRequest from NativeWebRequest");
        }
        String copy = StreamUtils.copyToString(servletRequest.getInputStream(), Charset.forName(annotation.encoding()));
        return new Gson().fromJson(copy, parameter.getGenericParameterType());
    }
}

// register the annotation processor
@Component
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {
        resolvers.add(new JsonBodyArgumentResolver());
    }
}

As of 4.1 you can now use RequestEntity<String> requestEntity and access the body by requestEntity.getBody()

https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/http/RequestEntity.html