Question

I am developing a Spring Rest application. One of my methods is that:

@RequestMapping(method = RequestMethod.GET)
public @ResponseBody
Collection<Configuration> getConfigurationInJSON() {
    Collection<Configuration> confList = new ArrayList<Configuration>();
...

I fill my confList and send it for GET request, it works. However when I want to keep that confList in a HashMap and send it after got it’s entrySet as like that:

@RequestMapping(method = RequestMethod.GET)
public
@ResponseBody
Collection<Configuration> getAllConfigurationsInJSON() {
    return configurationMap.values();
}

It gives me 406 error, so it means there is a wrong. What are the differences between that collections and why the second one is not same with first example?

Answer 1

For the sake of simplicity, can you just copy the values() collection?

new ArrayList<Configuration>(configurationMap.values());

Only thing that comes to my mind is that Spring expects mutable collection, but don’t really understand why. Hard to say without debugging, try enabling org.springframework.web full logging.