Getting a RESTful webservice with Spring to understand a JSON-string

Question

I'm very new to using Spring, and all the things involved, but I'm trying to get through this.

I'm trying to make a service, using the Spring MVN and Gradle, to understand a JSON-formatted String. It's all made in Java. But I can't get it to work as it should, at all.

This

@RequestMapping(value = "/toggle")
public @ResponseBody String sendCommand(@RequestParam(value="IP") String IP){
//body
}

Is a method in my Controller, but, when I send the following JSON-formatted String

{"IP":"192.168.1.9"}

I still get the Response Code 400.

I've tried different variations, one example using a @RequestBody instead, with an own class for the indata. And another where I recieve a HttpEntity, to watch whether the String was recieved correctly. While the String is recieved correctly, I can't get my code to "read" it.

I can go to localhost:8080/toggle, and through HTTP set the variables, say:

http://localhost:8080/toggle?IP=192.168.1.9

works.

Where would you suggest to continue troubleshooting? Thanks in advance!

---

EDIT: Wow. Thanks a lot for quick replies, I was expecting a day or two to go without replies, instead I got your help within minutes. I knew this site was good, but you are great, thanks!

That said, I made a new class called Ident, which has only a private String variable, with constructor, setter and getter. Now I have

@RequestMapping(value = "/toggle")
public @ResponseBody String sendCommand(@RequestBody Ident ident) {
//body
}

I still get 400 sending the same String though.

And while it would work using a @PathVariable, I'd like getting this to work, because now I'm only experimenting with it. It will be used to send more than only the IP later on.

I'm using @ComponentScan @EnableAutoConfiguration in the main-file, might that have something to do with things - that it gets set up wrong?

Answer 1

You are mixing to different thing (request parameters and json objects).

In order to catch the POSTed {"IP":"192.168.1.9"} you need to do something like the following:

@RequestMapping(value = "/toggle")
public @ResponseBody String sendCommand(@RequestBody String json){
   final YourObject yourObject = mapJsonToObject(json);
   final String ip = yourObject.getIp();
//body
}

You also need to create a class that corresponds to the json and map that json to the class (using a library like jackson).

If you want to forgo the creation of the intermediate object (which I do not propose you do since it makes the code cleaner), you could just extract the IP from the json String using standard JDK methods

Answer 2

Your Method Should be like,

 @RequestMapping(value = "/toggle/{IP}")
 public @ResponseBody String sendCommand(@PathVariable String IP){
   //body
 }

here IP is placeholder that can accommodate any passed IP.

and your URL request should be like

http ://localhost:8080/toggle/192.168.1.9 // [as per RESTful URL principle ]