Java 11标准的HTTP客户端API，实现了HTTP/2和Web Socket，可以在java.net.HTTP找到。*:

String payload = "{\"name\": \"myname\", \"age\": \"20\"}";
HttpClient client = HttpClient.newHttpClient();

HttpRequest request = HttpRequest.newBuilder(URI.create("www.site.com"))
            .header("content-type", "application/json")
            .POST(HttpRequest.BodyPublishers.ofString(payload))
            .build();
    
HttpResponse<String> response = client.send(request, BodyHandlers.ofString());

@momo对Apache HttpClient的回答，4.3.1版本或更高版本。我使用JSON- java构建我的JSON对象:

JSONObject json = new JSONObject();
json.put("someKey", "someValue");    

CloseableHttpClient httpClient = HttpClientBuilder.create().build();

try {
    HttpPost request = new HttpPost("http://yoururl");
    StringEntity params = new StringEntity(json.toString());
    request.addHeader("content-type", "application/json");
    request.setEntity(params);
    httpClient.execute(request);
// handle response here...
} catch (Exception ex) {
    // handle exception here
} finally {
    httpClient.close();
}

对于Java 11，你可以使用新的HTTP客户端:

HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
    .uri(URI.create("http://localhost/api"))
    .header("Content-Type", "application/json")
    .POST(ofInputStream(() -> getClass().getResourceAsStream(
        "/some-data.json")))
    .build();

client.sendAsync(request, BodyHandlers.ofString())
    .thenApply(HttpResponse::body)
    .thenAccept(System.out::println)
    .join();

你可以使用InputStream, String, File中的发布者。将JSON转换为字符串或IS可以用Jackson完成。

Java 11标准的HTTP客户端API，实现了HTTP/2和Web Socket，可以在java.net.HTTP找到。*:

String payload = "{\"name\": \"myname\", \"age\": \"20\"}";
HttpClient client = HttpClient.newHttpClient();

HttpRequest request = HttpRequest.newBuilder(URI.create("www.site.com"))
            .header("content-type", "application/json")
            .POST(HttpRequest.BodyPublishers.ofString(payload))
            .build();
    
HttpResponse<String> response = client.send(request, BodyHandlers.ofString());

Java 8与apache httpClient 4

CloseableHttpClient client = HttpClientBuilder.create().build();
HttpPost httpPost = new HttpPost("www.site.com");


String json = "details={\"name\":\"myname\",\"age\":\"20\"} ";

        try {
            StringEntity entity = new StringEntity(json);
            httpPost.setEntity(entity);

            // set your POST request headers to accept json contents
            httpPost.setHeader("Accept", "application/json");
            httpPost.setHeader("Content-type", "application/json");

            try {
                // your closeablehttp response
                CloseableHttpResponse response = client.execute(httpPost);

                // print your status code from the response
                System.out.println(response.getStatusLine().getStatusCode());

                // take the response body as a json formatted string 
                String responseJSON = EntityUtils.toString(response.getEntity());

                // convert/parse the json formatted string to a json object
                JSONObject jobj = new JSONObject(responseJSON);

                //print your response body that formatted into json
                System.out.println(jobj);

            } catch (IOException e) {
                e.printStackTrace();
            } catch (JSONException e) {

                e.printStackTrace();
            }

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }

使用HttpURLConnection可能是最简单的。

http://www.xyzws.com/Javafaq/how-to-use-httpurlconnection-post-data-to-web-server/139

你将使用JSONObject或其他东西来构造JSON，但不是用来处理网络;你需要序列化它，然后将它传递给一个HttpURLConnection到POST。