Pfthb

Here is a simple example that submits a form then dumps the result page to System.out. Change the URL and the POST params as appropriate, of course:

import java.io.*;
import java.net.*;
import java.util.*;

class Test 
 public static void main(String args) throws Exception 
 URL url = new URL("http://example.net/new-message.php");
 Map<String,Object> params = new LinkedHashMap<>();
 params.put("name", "Freddie the Fish");
 params.put("email", "fishie@seamail.example.com");
 params.put("reply_to_thread", 10394);
 params.put("message", "Shark attacks in Botany Bay have gotten out of control. We need more defensive dolphins to protect the schools here, but Mayor Porpoise is too busy stuffing his snout with lobsters. He's so shellfish.");

 StringBuilder postData = new StringBuilder();
 for (Map.Entry<String,Object> param : params.entrySet()) 
 if (postData.length() != 0) postData.append('&');
 postData.append(URLEncoder.encode(param.getKey(), "UTF-8"));
 postData.append('=');
 postData.append(URLEncoder.encode(String.valueOf(param.getValue()), "UTF-8"));
 
 byte postDataBytes = postData.toString().getBytes("UTF-8");

 HttpURLConnection conn = (HttpURLConnection)url.openConnection();
 conn.setRequestMethod("POST");
 conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
 conn.setRequestProperty("Content-Length", String.valueOf(postDataBytes.length));
 conn.setDoOutput(true);
 conn.getOutputStream().write(postDataBytes);

 Reader in = new BufferedReader(new InputStreamReader(conn.getInputStream(), "UTF-8"));

 for (int c; (c = in.read()) >= 0;)
 System.out.print((char)c);
 

If you want the result as a String instead of directly printed out do:

 StringBuilder sb = new StringBuilder();
 for (int c; (c = in.read()) >= 0;)
 sb.append((char)c);
 String response = sb.toString();

I couldn't get Alan's example to actually do the post, so I ended up with this:

String urlParameters = "param1=a&param2=b&param3=c";
URL url = new URL("http://example.com/index.php");
URLConnection conn = url.openConnection();

conn.setDoOutput(true);

OutputStreamWriter writer = new OutputStreamWriter(conn.getOutputStream());

writer.write(urlParameters);
writer.flush();

String line;
BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));

while ((line = reader.readLine()) != null) 
 System.out.println(line);

writer.close();
reader.close(); 

I find HttpURLConnection really cumbersome to use. And you have to write a lot of boilerplate, error prone code. I needed a lightweight wrapper for my Android projects and came out with a library which you can use as well: DavidWebb.

The above example could be written like this:

Webb webb = Webb.create();
webb.post("http://example.com/index.php")
 .param("param1", "a")
 .param("param2", "b")
 .param("param3", "c")
 .ensureSuccess()
 .asVoid();

You can find a list of alternative libraries on the link provided.

I see some other answers have given the alternative, I personally think that intuitively you're doing the right thing ;). Sorry, at devoxx where several speakers have been ranting about this sort of thing.

That's why I personally use Apache's HTTPClient/HttpCore libraries to do this sort of work, I find their API to be easier to use than Java's native HTTP support. YMMV of course!

import java.net.*;

public class Demo

 public static void main()

 String data = "data=Hello+World!";
 URL url = new URL("http://localhost:8084/WebListenerServer/webListener");
 HttpURLConnection con = (HttpURLConnection) url.openConnection();
 con.setRequestMethod("POST");
 con.setDoOutput(true);
 con.getOutputStream().write(data.getBytes("UTF-8"));
 con.getInputStream();

 

i have read above answers and have created a utility class to simplify HTTP request. i hope it will help you.

Method Call

 // send params with Hash Map
 HashMap<String, String> params = new HashMap<String, String>();
 params.put("email","me@example.com");
 params.put("password","12345");

 //server url
 String url = "http://www.example.com";

 // static class "HttpUtility" with static method "newRequest(url,method,callback)"
 HttpUtility.newRequest(url,HttpUtility.METHOD_POST,params, new HttpUtility.Callback() 
 @Override
 public void OnSuccess(String response) 
 // on success
 System.out.println("Server OnSuccess response="+response);
 
 @Override
 public void OnError(int status_code, String message) 
 // on error
 System.out.println("Server OnError status_code="+status_code+" message="+message);
 
 );

Utility Class

import java.io.*;
import java.net.*;
import java.util.HashMap;
import java.util.Map;
import static java.net.HttpURLConnection.HTTP_OK;

public class HttpUtility 

 public static final int METHOD_GET = 0; // METHOD GET
 public static final int METHOD_POST = 1; // METHOD POST

 // Callback interface
 public interface Callback 
 // abstract methods
 public void OnSuccess(String response);
 public void OnError(int status_code, String message);
 
 // static method
 public static void newRequest(String web_url, int method, HashMap < String, String > params, Callback callback) 

 // thread for handling async task
 new Thread(new Runnable() 
 @Override
 public void run() 
 try 
 String url = web_url;
 // write GET params,append with url
 if (method == METHOD_GET && params != null) 
 for (Map.Entry < String, String > item: params.entrySet()) 
 String key = URLEncoder.encode(item.getKey(), "UTF-8");
 String value = URLEncoder.encode(item.getValue(), "UTF-8");
 if (!url.contains("?")) 
 url += "?" + key + "=" + value;
 else 
 url += "&" + key + "=" + value;
 
 
 

 HttpURLConnection urlConnection = (HttpURLConnection) new URL(url).openConnection();
 urlConnection.setUseCaches(false);
 urlConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); // handle url encoded form data
 urlConnection.setRequestProperty("charset", "utf-8");
 if (method == METHOD_GET) 
 urlConnection.setRequestMethod("GET");
 else if (method == METHOD_POST) 
 urlConnection.setDoOutput(true); // write POST params
 urlConnection.setRequestMethod("POST");
 

 //write POST data 
 if (method == METHOD_POST && params != null) 
 StringBuilder postData = new StringBuilder();
 for (Map.Entry < String, String > item: params.entrySet()) 
 if (postData.length() != 0) postData.append('&');
 postData.append(URLEncoder.encode(item.getKey(), "UTF-8"));
 postData.append('=');
 postData.append(URLEncoder.encode(String.valueOf(item.getValue()), "UTF-8"));
 
 byte postDataBytes = postData.toString().getBytes("UTF-8");
 urlConnection.setRequestProperty("Content-Length", String.valueOf(postDataBytes.length));
 urlConnection.getOutputStream().write(postDataBytes);

 
 // server response code
 int responseCode = urlConnection.getResponseCode();
 if (responseCode == HTTP_OK && callback != null) 
 BufferedReader reader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
 StringBuilder response = new StringBuilder();
 String line;
 while ((line = reader.readLine()) != null) 
 response.append(line);
 
 // callback success
 callback.OnSuccess(response.toString());
 reader.close(); // close BufferReader
 else if (callback != null) 
 // callback error
 callback.OnError(responseCode, urlConnection.getResponseMessage());
 

 urlConnection.disconnect(); // disconnect connection
 catch (IOException e) 
 e.printStackTrace();
 if (callback != null) 
 // callback error
 callback.OnError(500, e.getLocalizedMessage());
 
 
 
 ).start(); // start thread
 

GET and POST method set like this... Two types for api calling 1)get() and 2) post() . get() method to get value from api json array to get value & post() method use in our data post in url and get response.

 public class HttpClientForExample 

 private final String USER_AGENT = "Mozilla/5.0";

 public static void main(String args) throws Exception 

 HttpClientExample http = new HttpClientExample();

 System.out.println("Testing 1 - Send Http GET request");
 http.sendGet();

 System.out.println("nTesting 2 - Send Http POST request");
 http.sendPost();

 

 // HTTP GET request
 private void sendGet() throws Exception 

 String url = "http://www.google.com/search?q=developer";

 HttpClient client = new DefaultHttpClient();
 HttpGet request = new HttpGet(url);

 // add request header
 request.addHeader("User-Agent", USER_AGENT);

 HttpResponse response = client.execute(request);

 System.out.println("nSending 'GET' request to URL : " + url);
 System.out.println("Response Code : " + 
 response.getStatusLine().getStatusCode());

 BufferedReader rd = new BufferedReader(
 new InputStreamReader(response.getEntity().getContent()));

 StringBuffer result = new StringBuffer();
 String line = "";
 while ((line = rd.readLine()) != null) 
 result.append(line);
 

 System.out.println(result.toString());

 

 // HTTP POST request
 private void sendPost() throws Exception 

 String url = "https://selfsolve.apple.com/wcResults.do";

 HttpClient client = new DefaultHttpClient();
 HttpPost post = new HttpPost(url);

 // add header
 post.setHeader("User-Agent", USER_AGENT);

 List<NameValuePair> urlParameters = new ArrayList<NameValuePair>();
 urlParameters.add(new BasicNameValuePair("sn", "C02G8416DRJM"));
 urlParameters.add(new BasicNameValuePair("cn", ""));
 urlParameters.add(new BasicNameValuePair("locale", ""));
 urlParameters.add(new BasicNameValuePair("caller", ""));
 urlParameters.add(new BasicNameValuePair("num", "12345"));

 post.setEntity(new UrlEncodedFormEntity(urlParameters));

 HttpResponse response = client.execute(post);
 System.out.println("nSending 'POST' request to URL : " + url);
 System.out.println("Post parameters : " + post.getEntity());
 System.out.println("Response Code : " + 
 response.getStatusLine().getStatusCode());

 BufferedReader rd = new BufferedReader(
 new InputStreamReader(response.getEntity().getContent()));

 StringBuffer result = new StringBuffer();
 String line = "";
 while ((line = rd.readLine()) != null) 
 result.append(line);
 

 System.out.println(result.toString());

 

I had the same issue. I wanted to send data via POST.
I used the following code:

 URL url = new URL("http://example.com/getval.php");
 Map<String,Object> params = new LinkedHashMap<>();
 params.put("param1", param1);
 params.put("param2", param2);

 StringBuilder postData = new StringBuilder();
 for (Map.Entry<String,Object> param : params.entrySet()) 
 if (postData.length() != 0) postData.append('&');
 postData.append(URLEncoder.encode(param.getKey(), "UTF-8"));
 postData.append('=');
 postData.append(URLEncoder.encode(String.valueOf(param.getValue()), "UTF-8"));
 
 String urlParameters = postData.toString();
 URLConnection conn = url.openConnection();

 conn.setDoOutput(true);

 OutputStreamWriter writer = new OutputStreamWriter(conn.getOutputStream());

 writer.write(urlParameters);
 writer.flush();

 String result = "";
 String line;
 BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));

 while ((line = reader.readLine()) != null) 
 result += line;
 
 writer.close();
 reader.close()
 System.out.println(result);

I used Jsoup for parse:

 Document doc = Jsoup.parseBodyFragment(value);
 Iterator<Element> opts = doc.select("option").iterator();
 for (;opts.hasNext();) 
 Element item = opts.next();
 if (item.hasAttr("value")) 
 System.out.println(item.attr("value"));
 
 

Try this pattern:

public static PricesResponse getResponse(EventRequestRaw request) 

 // String urlParameters = "param1=a&param2=b&param3=c";
 String urlParameters = Piping.serialize(request);

 HttpURLConnection conn = RestClient.getPOSTConnection(endPoint, urlParameters);

 PricesResponse response = null;

 try 
 // POST
 OutputStreamWriter writer = new OutputStreamWriter(conn.getOutputStream());
 writer.write(urlParameters);
 writer.flush();

 // RESPONSE
 BufferedReader reader = new BufferedReader(new InputStreamReader((conn.getInputStream()), StandardCharsets.UTF_8));
 String json = Buffering.getString(reader);
 response = (PricesResponse) Piping.deserialize(json, PricesResponse.class);

 writer.close();
 reader.close();

 catch (Exception e) 
 e.printStackTrace();
 

 conn.disconnect();

 System.out.println("PricesClient: " + response.toString());

 return response;


public static HttpURLConnection getPOSTConnection(String endPoint, String urlParameters) 

 return RestClient.getConnection(endPoint, "POST", urlParameters);




public static HttpURLConnection getConnection(String endPoint, String method, String urlParameters) 

 System.out.println("ENDPOINT " + endPoint + " METHOD " + method);
 HttpURLConnection conn = null;

 try 
 URL url = new URL(endPoint);
 conn = (HttpURLConnection) url.openConnection();
 conn.setRequestMethod(method);
 conn.setDoOutput(true);
 conn.setRequestProperty("Content-Type", "text/plain");

 catch (IOException e) 
 e.printStackTrace();
 

 return conn;

here i sent jsonobject as parameter //jsonobject="name":"lucifer","pass":"abc"//serverUrl = "http://192.168.100.12/testing" //host=192.168.100.12

 public static String getJson(String serverUrl,String host,String jsonobject)

 StringBuilder sb = new StringBuilder();

 String http = serverUrl;

 HttpURLConnection urlConnection = null;
 try 
 URL url = new URL(http);
 urlConnection = (HttpURLConnection) url.openConnection();
 urlConnection.setDoOutput(true);
 urlConnection.setRequestMethod("POST");
 urlConnection.setUseCaches(false);
 urlConnection.setConnectTimeout(50000);
 urlConnection.setReadTimeout(50000);
 urlConnection.setRequestProperty("Content-Type", "application/json");
 urlConnection.setRequestProperty("Host", host);
 urlConnection.connect();
 //You Can also Create JSONObject here 
 OutputStreamWriter out = new OutputStreamWriter(urlConnection.getOutputStream());
 out.write(jsonobject);// here i sent the parameter
 out.close();
 int HttpResult = urlConnection.getResponseCode();
 if (HttpResult == HttpURLConnection.HTTP_OK) 
 BufferedReader br = new BufferedReader(new InputStreamReader(
 urlConnection.getInputStream(), "utf-8"));
 String line = null;
 while ((line = br.readLine()) != null) 
 sb.append(line + "n");
 
 br.close();
 Log.e("new Test", "" + sb.toString());
 return sb.toString();
 else 
 Log.e(" ", "" + urlConnection.getResponseMessage());
 
 catch (MalformedURLException e) 
 e.printStackTrace();
 catch (IOException e) 
 e.printStackTrace();
 catch (JSONException e) 
 e.printStackTrace();
 finally 
 if (urlConnection != null)
 urlConnection.disconnect();
 
 return null;

I higly recomend http-request built on apache http api.

For your case you can see example:

private static final HttpRequest<String.class> HTTP_REQUEST = 
 HttpRequestBuilder.createPost("http://example.com/index.php", String.class)
 .responseDeserializer(ResponseDeserializer.ignorableDeserializer())
 .build();

public void sendRequest(String request)
 String parameters = request.split("\?")[1];
 ResponseHandler<String> responseHandler = 
 HTTP_REQUEST.executeWithQuery(parameters);

 System.out.println(responseHandler.getStatusCode());
 System.out.println(responseHandler.get()); //prints response body

If you are not interested in the response body

private static final HttpRequest<?> HTTP_REQUEST = 
 HttpRequestBuilder.createPost("http://example.com/index.php").build();

public void sendRequest(String request)
 ResponseHandler<String> responseHandler = 
 HTTP_REQUEST.executeWithQuery(parameters);

For general sending post request with http-request: Read the documentation and see my answers HTTP POST request with JSON String in JAVA, Sending HTTP POST Request In Java, HTTP POST using JSON in Java

Hello pls use this class to improve your post method

public static JSONObject doPostRequest(HashMap<String, String> data, String url) UnsupportedEncodingException e) 

 JSONObject jsonObject=new JSONObject();

 try 
 jsonObject.put("status","false");
 jsonObject.put("message",e.getLocalizedMessage());
 catch (JSONException e1) 
 e1.printStackTrace();
 
 Log.e(TAG, "Error: " + e.getLocalizedMessage());
 catch (Exception e) 
 e.printStackTrace();
 JSONObject jsonObject=new JSONObject();

 try 
 jsonObject.put("status","false");
 jsonObject.put("message",e.getLocalizedMessage());
 catch (JSONException e1) 
 e1.printStackTrace();
 
 Log.e(TAG, "Other Error: " + e.getLocalizedMessage());
 
 return null;

This answer covers the specific case of the POST Call using a Custom Java POJO.

Using maven dependency for Gson to serialize our Java Object to JSON.

Install Gson using the dependency below.

<dependency>
 <groupId>com.google.code.gson</groupId>
 <artifactId>gson</artifactId>
 <version>2.8.5</version>
 <scope>compile</scope>
</dependency>

For those using gradle can use the below

dependencies 
implementation 'com.google.code.gson:gson:2.8.5'

Other imports used:

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.*;
import org.apache.http.impl.client.CloseableHttpClient;
import com.google.gson.Gson;

Now, we can go ahead and use the HttpPost provided by Apache

private CloseableHttpClient httpclient = HttpClients.createDefault();
HttpPost httppost = new HttpPost("https://example.com");

Product product = new Product(); //custom java object to be posted as Request Body
 Gson gson = new Gson();
 String client = gson.toJson(product);

 httppost.setEntity(new StringEntity(client, ContentType.APPLICATION_JSON));
 httppost.setHeader("RANDOM-HEADER", "headervalue");
 //Execute and get the response.
 HttpResponse response = null;
 try 
 response = httpclient.execute(httppost);
 catch (IOException e) 
 throw new InternalServerErrorException("Post fails");
 
 Response.Status responseStatus = Response.Status.fromStatusCode(response.getStatusLine().getStatusCode());
 return Response.status(responseStatus).build();

The above code will return with the response code received from the POST Call

I took Boann's answer and used it to create a more flexible query string builder that supports lists and arrays, just like php's http_build_query method:

public static byte httpBuildQueryString(Map<String, Object> postsData) throws UnsupportedEncodingException 
 StringBuilder postData = new StringBuilder();
 for (Map.Entry<String,Object> param : postsData.entrySet()) 
 if (postData.length() != 0) postData.append('&');

 Object value = param.getValue();
 String key = param.getKey();

 if(value instanceof Object 
 return postData.toString().getBytes("UTF-8");