Reading JSON Object from @RequestHeader

if you want a single http request header to be "injected" into your controller method (as an argument) by Spring try it this way:

@RequestMapping("/your-path")
public ResponseEntity<MyObject> getStuff(@RequestHeader("My-Header") String jsonValue) {
   //...
}

also see here: https://www.viralpatel.net/spring-requestheader-example/

you can also try to implement a custom converter, see here for an example:

https://stackoverflow.com/a/50996349/150623

the way to go would be to use an ObjectMapper instance from the Jackson lib to convert the JSON string to a java.util.Map object...

could work this way (not tested though):

import org.springframework.core.convert.converter.Converter;
import org.springframework.stereotype.Component;

@Component
public class JsonToMapConverter implements Converter<String, Map<String,String>> {

    private ObjectMapper objectMapper = new ObjectMapper();

    @Override
    public Map<String, String> convert(final String json) {
        try {
           return objectMapper.readValue(json, Map.class);
        } catch (IOException e) {
           //handle exception...
        }
    }
}

don't forget to add Jackson to your dependencies, e.g. in Maven:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.8</version>
</dependency>

No, you will need to de-serialise it yourself.

From the spring docs:

If the method parameter is Map<String, String>, MultiValueMap<String, String>, or HttpHeaders then the map is populated with all header names and values.

It will not extract and deserialise json from the map, instead you will need to do something like:

public ResponseEntity<MyObject> getStuff(@RequestHeader Map myHeader) { 
    String json = myHeader.get("My-Header");
    MyClass myClass = objectMapper.readValue(json, MyClass.class);

    ... 
}