Create a java REST client to call a spring boot REST API

Question

I have a springboot project that takes only POST JSON String which I'm converting to HashMap using gson. I tested using Postman as a POST and add the body as props with a json string like {'fistname': 'John', 'lastname' : 'Doe'}, translates to props = {'fistname': 'John', 'lastname' : 'Doe'}. its working as expected

@RequestMapping(value = "/rest", method = RequestMethod.POST)
    protected String parse(@RequestParam("props") String props) {
    Gson gson = new Gson();
    Map<String, String> params = new HashMap<String, String>();
    params = gson.fromJson(props, Map.class);

    // Rest of the process
}

On the other hand, I have a JavaEE project, which needs to call this API

protected void callREST() {

      try {
            String json = someClass.getDate() //retrieved from database which is stored as json structure
            Map<String, String> props = gson.fromJson(json, Map.class);

            URL url = new URL("http://localhost:9090/myApp/rest");
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setDoOutput(true);
            conn.setRequestMethod("POST");
            conn.setRequestProperty("Content-Type", "application/json");

            DataOutputStream wr = new DataOutputStream( conn.getOutputStream());

            System.out.println(props.toString());
            wr.writeBytes(json.toString());
            wr.flush();
            wr.close();
            if(conn.getResponseCode() != HttpURLConnection.HTTP_CREATED) {
                throw new RuntimeException("Failed :: HTTP error code : " + conn.getResponseCode());
            }

            BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String output;
            System.out.println("Output from Server ... \n");
            while((output = br.readLine()) != null) {
                System.out.println(output);
            }

            conn.disconnect();

       } catch(Exception e) {
          //print stack trace
       }
 }

I get Failed :: HTTP error code : 400. I suspect the spring boot is not receiving the data in props variable since its a POST request. What should i add in the client code to pass the props and the data to make this call successful ?

Note: JavaEE is running on tomcat :8080, Springboot is running on different tomcat :9090

Have a look at Spring"s RestTemplate class, it is very useful for this. — Arnaud
– Arnaud, Commented Aug 16, 2017 at 15:56

Vlad Bochenin · Accepted Answer · 2017-08-16 16:02:56Z

1

@RequestParam means that server awaits param in request URL http://localhost:9090/myApp/rest?param=..... but in you client you are writing JSON in body of request.

Try to use @RequestBody annotation in your endpoint

protected String parse(@RequestBody String props) {...}

answered Aug 16, 2017 at 16:02

Vlad Bochenin

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1 Comment

user525146 Over a year ago

How can I make this async ?

JB Nizet · Accepted Answer · 2017-08-16 16:03:25Z

1

Your resources expects to get form parameters (i.e. key value pairs, using x-www-form-urlencoded encoding), where the value happens to be JSON (although what you posted is not valid JSON).

But your client Java code sets the content type to application/json, and sends the JSON as the body, instead of sending it as the value of the key "props" of a x-www-form-urlencoded body.

So that can't work.

If you can change the server, then do that. Accept JSON as the body directly:

@RequestMapping(value = "/rest", method = RequestMethod.POST)
public String parse(@RequestBody Map<String, String> map) {
     ...
}

If not, you'll need to send the correct key value pair, and make sure the value is properly url-encoded.

answered Aug 16, 2017 at 16:03

JB Nizet

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