[FIXED] Java Servlet send form data to REST API

Issue

I have a simple HTML form to send a request to a REST API. It works well, when I submit, it sends the form data to API and displays the response in the browser.

<form name="theForm" action="localhost:8080/App/rest/consumeForm" method="post">
    <input name="userName" value="Bob Smith" /><br/>
    <input type="submit" value="submit"/>
</form>

Browser shows:

{"address": "12 First St.", "city": "Toronto"}

I would like to capture the response. Any ideas? (no ajax or javascript, just plain old Servlet or JSP please)

PART 2: I now POST my form to a servlet I created, which handles the request and response from the REST API. It works nicely, but it needs the form data URLEncoded. Anyone know if there is a way to convert form data to such a string, or even convert form data to JSON directly?

String charset = java.nio.charset.StandardCharsets.UTF_8.name();
String userName = "Bob Smith";
String country = "Canada";

String queryString = String.format("userName=%s&country=%s" 
        ,URLEncoder.encode(userName, charset) 
        ,URLEncoder.encode(country, charset)            
        );

Can I build the above queryString dynamically?

//// send request
URLConnection connection = new URL("localhost:8080/App/rest/consumeForm").openConnection();
connection.setDoOutput(true); // Triggers POST.
connection.setRequestProperty("Accept-Charset", charset);
connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded;charset=" + charset);
try (OutputStream output = connection.getOutputStream()) {
    output.write(queryString.getBytes(charset));
}       

//// get response
BufferedReader apiResponse = new BufferedReader(new InputStreamReader((connection.getInputStream())));
String output;
System.out.println("\n\n\nrecieved....");
while ((output = apiResponse.readLine()) != null) {
    System.out.println(output);
}

Solution

It turns out that submitting to a servlet using POST and communicating with the REST API using the servlet works for me. There may be better ways, but this seems relatively clean for junior developers to follow and maintain. (I'm still open to other options).

I build a queryString with the form data (req is the HttpServletRequest)

String theQueryString="domainId=1";
for(Entry<String, String[]> qsParm:req.getParameterMap().entrySet()) {
  theQueryString+="&"+qsParm.getKey()+"="+URLEncoder.encode(req.getParameter(qsParm.getKey()), charset);   
}

// set up connection to use as API interaction
URLConnection connection = new URL("localhost:8080/App/rest/consumeForm").openConnection();
connection.setDoOutput(true); // Triggers POST apparently
connection.setRequestProperty("Accept-Charset", java.nio.charset.StandardCharsets.UTF_8.name());
connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded;charset=" + java.nio.charset.StandardCharsets.UTF_8.name());
        
// send request to API via connection OutputStream
try (OutputStream output = connection.getOutputStream()) {
  output.write(theQueryString.getBytes(java.nio.charset.StandardCharsets.UTF_8.name()));  // this sends the request to the API url
}       

// get response from connection InputStream and read as JSON
ObjectMapper mapper = new ObjectMapper();
JsonNode jsonMap = mapper.readTree(connection.getInputStream());

// now the response can be worked with in at least two ways that I have tried
String user1 = jsonMap.get("userName").asText();
String user2 = jsonMap.at("user").getValueAsText();

Answered By - Jake v1
Answer Checked By - Gilberto Lyons (JavaFixing Admin)