Passing a JSON structure to an external URL which is also a Vaadin app

Flow
1

Hi,

Is it possible to send a JSON structure to an external application (also a Vaadin Application) using something the following.

UI.getCurrent().getPage().setLocation("https://a.example.com/my-other-app")

I know you can build the URL by putting parameters on it but I want to send the JSON as POST data.

Is that possible?

Thanks, John.

2

Yes, it’s possible. I’d generally recommend going directly from server to server instead of having the browser act as a middle man. See for example this article: https://vaadin.com/learn/tutorials/consuming-rest-services-from-java-applications

3

I would use a [HttpClient]
(https://www.baeldung.com/httpclient-post-http-request) or [JAX-RS Client]
(https://www.baeldung.com/jersey-jax-rs-client) to send the post request. In the receiving Vaadin Application there should be a REST Controller to receive an handle the post request, for example with [Spring]
(https://www.baeldung.com/rest-with-spring-series).

4

Thanks both for your suggestions.

Just so that it is clear I think I need to explain what I am trying to do a bit better.

I need to redirect the user’s browser from the server they are on to a new server that runs my vaadin application.
At the moment I am using the following

            String QUERYLINK = "http://host.example.com/app/query?param1=abc?param2=123"
            UI.getCurrent().getPage().executeJavaScript("window.open(\"" + QUERYLINK + "\", \"_self\");");

This works just fine and the user is now on the new server and I have passed in the data and the called application retrieves it.

I want to do exactly the same thing except I don’t want to pass the data params on the URL.
I need to re-direct the users browser to the new application on a different server but I want to pass a JSON structure in the body of the request.

I can use httpClient to create the POST request and I get a response from the Vaadin application but how do I trigger the equivalent of the “window.open” piece so that the user browser re-directed to the new site as well and it is set up to engage with the vaadin application on the new server.

    doItButton.addClickListener(e-> {
            makePostRequest();
            // UI.getCurrent().getPage().executeJs("window.open(\"" + LINK + "\", \"_self\");");
        });

    /**
     * Create the post body. 
     * @return the the post body string
     */
    private String createPostBody() {
        final JsonObject l_payRequest = Json.createObjectBuilder()
                .add("bu", "M1")
                .add("cmt", "ABC")
                .build();
        MLOGGER.debug("Request: " + l_payRequest.toString());
        return l_payRequest.toString();
    }

    /**
     * makePostRequest.
     * @return boolean 200 OK = true else false
     */
    public final boolean makePostRequest() {
        int l_iHTTPResponse = 0;
        try {
            final HttpClient l_httpclient = HttpClientBuilder.create().build();
            final HttpPost l_httppost = new HttpPost("http://wc.sybernet.ie:8075/myapp-1.0.0/app");

            final StringEntity l_postbody = new StringEntity(createPostBody());
            l_postbody.setContentType("application/json");
            l_httppost.setEntity(l_postbody);
            //Execute and get the response.
            final HttpResponse response = l_httpclient.execute(l_httppost);
            MLOGGER.info("HTTP response " + response.getStatusLine().getStatusCode());
            l_iHTTPResponse = response.getStatusLine().getStatusCode();
            if (l_iHTTPResponse == HttpURLConnection.HTTP_OK) {
                final String l_sResponse = EntityUtils.toString(response.getEntity());
                // System.out.println("response: " + l_sResponse);
            } else {
                throw new Exception("makePayment(): Did not get 200 back from executeMethod");
            }
        } catch (Exception e) {
            MLOGGER.error("MakeSSLPostRequest() Exception : " + e.getMessage());
        }
        return (l_iHTTPResponse == HttpURLConnection.HTTP_OK);
    }
5

Oh thats a very different situation that was originally asked. Using a Client here will not help you. But neither will setting the location of the page, as that will not make a POST request.

I can only think of one way to navigate in a browser with a POST request and that is [submitting a form]
(https://stackoverflow.com/q/1651197/3441504). I think it should be possible to add hidden input fields in the form holding the values you want to post, and make your button the submit button of the form.

I don’t think there is a Form component for Vaadin, but I found [this code example]
(https://vaadin.com/forum/thread/17959073/17968751) that should help you with all aspects of this issue

6

Kaspar,

Thanks a million for the pointer - that works just perfectly!

Best Regards
John.