json - REST with Spring and Jackson full data binding

Question

I'm using Spring MVC to handle JSON POST requests. Underneath the covers I'm using the MappingJacksonHttpMessageConverter built on the Jackson JSON processor and enabled when you use the mvc:annotation-driven.

One of my services receives a list of actions:

@RequestMapping(value="/executeActions", method=RequestMethod.POST)
    public @ResponseBody String executeActions(@RequestBody List<ActionImpl> actions) {
        logger.info("executeActions");
        return "ACK";
    }

I have found that Jackson maps the requestBody to a List of java.util.LinkedHashMap items (simple data binding). Instead, I would like the request to be bound to a List of typed objects (in this case "ActionImpl").

I know this is easy to do if you use Jackson's ObjectMapper directly:

List<ActionImpl> result = mapper.readValue(src, new TypeReference<List<ActionImpl>>() { }); 

but I was wondering what's the best way to achieve this when using Spring MVC and MappingJacksonHttpMessageConverter. Any hints?

Thanks

question from:https://stackoverflow.com/questions/4441557/rest-with-spring-and-jackson-full-data-binding

Answer 1

I suspect problem is due to type erasure, i.e. instead of passing generic parameter type, maybe only actions.getClass() is passed; and this would give type equivalent of List< ?>.

If this is true, one possibility would be to use an intermediate sub-class, like:

public class ActionImplList extends ArrayList<ActionImpl> { }

because this will the retain type information even if only class is passed. So then:

public @ResponseBody String executeActions(@RequestBody ActionImplList actions)

would do the trick. Not optimal but should work.

I hope someone with more Spring MVC knowledge can shed light on why parameter type is not being passed (perhaps it's a bug?), but at least there is a work around.