How to return a set of objects with Spring Boot?

I did a lesson about Spring Boot and it works perfectly. But what if I want to return a set of objects ? I tried doing this but it doesn’t work. How can I do it correctly ?

With one object (it works):

@RequestMapping("/greeting")
public Greeting greeting(@RequestParam(value="name", defaultValue = "World") String name) {
    return new Greeting(counter.incrementAndGet(),
            String.format(template, name));
}

With many objects (it doesn’t work):

@RequestMapping(value = "/greeting", method = RequestMethod.GET, consumes = MediaType.APPLICATION_JSON_VALUE, produces = MediaType.APPLICATION_JSON_VALUE)
public @ResponseBody List<Greeting> greeting() {
    Greeting greeting1 = new Greeting(1, "One");
    Greeting greeting2 = new Greeting(2, "Two");
    List<Greeting> list = new ArrayList<>();
    list.add(greeting1);
    list.add(greeting2);
    return list;
}

Answer

If you compare your original method to your newly made one (with a List), you’ll notice a few differences.

First of all, within the @RequestMapping annotation you’re now using the properties consumes and produces. produces is not a problem here, because you are producing a response that should be JSON. However you’re not consuming anything, so you should leave away the consumes.

@RequestMapping(value = "/greeting", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
public @ResponseBody List<Greeting> greeting() {
    Greeting greeting1 = new Greeting(1, "One");
    Greeting greeting2 = new Greeting(2, "Two");
    List<Greeting> list = new ArrayList<>();
    list.add(greeting1);
    list.add(greeting2);
    return list;
}

As a sidenote, you might also notice that you used the @ResponseBody annotation. Putting it here won’t cause any errors, but it is not necessary, because if you followed the Spring tutorial correctly, you should have annotated your controller with @RestController and by doing that, you already tell Spring that it will use a response body.