How to set up a JSON upload with POST?

Question

I need to make an API that captures some data from the machine (OS name, cpu usage, network usage etc.) and send as JSON. I was able to capture the data and have it displayed on the console in the form of JSON, however, I never messed with the data SEND. I did some research on Httprequest, but I didn’t understand how to use it. Remembering, I’ve only been dealing with Java for about 3 months, so if you can help me understand how I can do this sending, I really appreciate it!

Guys, that’s the code I’m in right now. I’m returning a STRING with the CPUINFO class Json, but if some application "pulls" it, it will pull in String format, and not Json, right? I have how to make it return in Json?

public class ServerHTTP {

    static CPUINFO infocpu = new CPUINFO();

    public static void main(String[] args) throws IOException {
        HttpServer server = HttpServer.create(new InetSocketAddress(9080), 0);
        System.out.println("Executando");
        server.createContext("/teste", new MyHandler());
        server.createContext("/", new HomeHandler());
        server.createContext("/dados", new dataHandler());
        server.setExecutor(null);
        server.start();

    }

    static class MyHandler implements HttpHandler {
        public void handle(HttpExchange t) throws IOException {

            Headers h = t.getResponseHeaders();
            h.add("Content-Type", "application/json");

            String response = "<h1> Hello World! </h1>";
            t.sendResponseHeaders(200, response.length());
            OutputStream os = t.getResponseBody();
            os.write(response.getBytes());
            os.close();
        }
    }

    static class HomeHandler implements HttpHandler {
        public void handle(HttpExchange t) throws IOException {

            Headers h = t.getResponseHeaders();
            h.add("Access-Control-Allow-Origin", "*");
            h.add("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");

            String response = "<h> Homepage </h>";
            t.sendResponseHeaders(200, response.length());
            OutputStream os = t.getResponseBody();
            os.write(response.getBytes());
            os.close();
        }
    }

    static class dataHandler implements HttpHandler {
        public void handle(HttpExchange he) throws IOException {
            Headers h = he.getResponseHeaders();
            h.add("Access-Control-Allow-Origin", "*");
            h.add("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
            String response = infocpu + "";
            he.sendResponseHeaders(200, response.length());
            OutputStream os = he.getResponseBody();
            os.write(response.toString().getBytes());
            os.close();
        }
    }

Answer 1

Here’s an example of how to do a Java post using Json as the request body:

String payload = "data={" +
            "\"username\": \"admin\", " +
            "\"first_name\": \"System\", " +
            "\"last_name\": \"Administrator\"" +
            "}";
StringEntity entity = new StringEntity(payload, ContentType.APPLICATION_FORM_URLENCODED);

HttpClient httpClient = HttpClientBuilder.create().build();
HttpPost request = new HttpPost("http://localhost:8080/endpoint");
request.setEntity(entity);

HttpResponse response = httpClient.execute(request);
System.out.println(response.getStatusLine().getStatusCode());

Dependencia Maven:

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.3</version>
</dependency>