We Keep Coding

OutputStream os = con.getOutputStream() throws NullPointerException

I am trying to build an android app for a website and I need to post some value to this page first.
Here is my code:
private void sendPOST(String user,String pass) throws IOException {
String POST_PARAMS = "username="+user+"&password="+pass;
URL obj = new URL("http://xx.xx.xx.xx/mysite/test.php");
HttpURLConnection con = (HttpURLConnection) obj.openConnection();
con.setRequestMethod("POST");
con.setRequestProperty("User-Agent", "Mozilla/5.0");
//----------------------------------------------------------- For POST only - START---------------------------------------------
con.setDoOutput(true);
OutputStream os = con.getOutputStream();
os.write(POST_PARAMS.getBytes());
os.flush();
os.close();
// ------------------------------------------------------------For POST only - END----------------------------------------------------
int responseCode = con.getResponseCode();
if (responseCode == HttpURLConnection.HTTP_OK) { //success
BufferedReader in = new BufferedReader(new InputStreamReader(
con.getInputStream()));
String inputLine;
StringBuffer response = new StringBuffer();
while ((inputLine = in.readLine()) != null) {
response.append(inputLine);
}
in.close();
// print result
Toast.makeText(getApplicationContext(), response.toString()==""?"No Result":response.toString(), Toast.LENGTH_LONG).show();
} else {
Toast.makeText(getApplicationContext(),"POST request failed", Toast.LENGTH_LONG).show();
}
}
when this line is executed OutputStream os = con.getOutputStream();
a null exception occurs.
I am unable to proceed further. Please suggest what i must do to remove this exception.

put your delevelopment server in another locatation other than localhost (try using the real IP, something like: 192.168.0.1).
sometimes you will receive a successfull connection from HttpUrlConnection.openConnection() (it returns non null object) and this not guarantee the subsequents calls to success. In other words, when you call con.getOutputStream() it throws an exception no matter if con is non-null.

It's the old question but I might have to answer on it because I have face to it today. When you ping http (instead https) have to put in manifest -> application: android:usesCleartextTraffic="true"

I think this would helped you years ago...
try(OutputStream os = con.getOutputStream()) {
byte[] input = POST_PARAMS.getBytes("utf-8");
os.write(input, 0, input.length);
}

maybe you should try to "connect" first before doing anything with your created HttpURLConnection con.
HttpURLConnection con = (HttpURLConnection) obj.openConnection();
con.connect();
do more stuff with con...
I hope this helps you :)

URL obj = new URL("http://xx.xx.xx.xx/mysite/test.php");
URL Class object "obj" can't reach to your mentioned URL properly.
Try this instead:
URL obj = new URL("http://"+"xx.xx.xx.xx/mysite/test.php");

HTTP URL connection response

I am trying to hit the URL and get the response from my Java code.
I am using URLConnection to get this response. And writing this response in html file.
When opening this html in browser after executing the java class, I am getting only google home page and not with the results.
Whats wrong with my code, my code here,
FileWriter fWriter = null;
BufferedWriter writer = null;
URL url = new URL("https://www.google.co.in/?gfe_rd=cr&ei=aS-BVpPGDOiK8Qea4aKIAw&gws_rd=ssl#q=google+post+request+from+java");
byte[] encodedBytes = Base64.encodeBase64("root:pass".getBytes());
String encoding = new String(encodedBytes);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.setRequestProperty("User-Agent", "Mozilla/5.0");
connection.setRequestProperty("Accept-Charset", "UTF-8");
connection.setDoInput(true);
connection.setRequestProperty("Authorization", "Basic " + encoding);
connection.connect();
InputStream content = (InputStream) connection.getInputStream();
BufferedReader in = new BufferedReader(new InputStreamReader(content));
String line;
try {
fWriter = new FileWriter(new File("f:\\fileName.html"));
writer = new BufferedWriter(fWriter);
while ((line = in.readLine()) != null) {
String s = line.toString();
writer.write(s);
}
writer.close();
} catch (Exception e) {
e.printStackTrace();
}
}
Same code works couple of days back, but not now.

The reason is that this url does not return search results it self. You have to understand google's working process to understand it. Open this url in your browser and view its source. You will only see lots of javascript there.
Actually, in a short summary, google uses Ajax requests to process search queries.
To perform required task you either have to use a headless browser (the hard way) which can execute javascript/ajax OR better use google search api as directed by anand.

This method of searching is not advised is supposed to fail, you must use google search APIs for this kind of work.
Note: Google uses some redirection and uses token, so even if you will find a clever way to handle it, it is ought to fail in long run.
Edit:
This is a sample of how using Google search APIs you can get your work done in reliable way; please do refer to the source for more information.
public static void main(String[] args) throws Exception {
String google = "http://ajax.googleapis.com/ajax/services/search/web?v=1.0&q=";
String search = "stackoverflow";
String charset = "UTF-8";
URL url = new URL(google + URLEncoder.encode(search, charset));
Reader reader = new InputStreamReader(url.openStream(), charset);
GoogleResults results = new Gson().fromJson(reader, GoogleResults.class);
// Show title and URL of 1st result.
System.out.println(results.getResponseData().getResults().get(0).getTitle());
System.out.println(results.getResponseData().getResults().get(0).getUrl());
}

how to get response from php file?

I'm currently trying to connect my phpmyadmin server with android studio.
I'm using the emulator if it matters.
I made some php files to receive data and change data in my database.
checkuserexist.php
<?php
require('con1.php');
if (isset($_GET['username'])) {
$username = mysqli_real_escape_string($link,$_GET['username']);
if (!empty($username)) {
$username_query = mysqli_query($link,"SELECT * FROM users WHERE username='".$username."'");
$username_result = mysqli_num_rows($username_query);
if($username_result == 0)
print $existornot = "NotExist";
else print $existornot = "Exist";
}
}
?>
And in my Android Studio program:
URL url = new URL("http://10.0.2.2:8080/fives/checkuserexist.php?username=yariv");
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
InputStream stream = conn.getInputStream();
InputStreamReader isReader = new InputStreamReader(stream );
//put output stream into a string
BufferedReader br = new BufferedReader(isReader );
String result = "";
String line;
while ((line = br.readLine()) != null) {
System.out.println(line);
result += line;
}
br.close();
InputStream stream = conn.getInputStream();
return an exeption:
failed to connect to /10.0.2.2 (port 8080): connect failed: ETIMEDOUT (Connection timed out)
How to solve this exeption?

You could echo out some JSON in the PHP file and use the JSONObject/JSONArray classes in android

should check the emulator network setting to see what is your main machine IP address.
second way :
open run menu, type cmd and again type ipconfig.
you can also try other IP v4 addresses found in the here:

HttpURLConnection to Tomcat

I am trying to connect from a java desktop application to a jsp Servlet to send a file.
Clientcoding:
HttpURLConnection urlConnection = null;
URL url = null;
url = new URL("http://127.0.0.1:8080/emobile/AddTripMobile");
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setDoOutput(true);
OutputStream out = new BufferedOutputStream(
urlConnection.getOutputStream());
out.write(12); //The data to send
out.flush();
If I connect with the desktop application to the server nothing happens.
(I set a breakpoint in the doGet and doPost)
Any suggestions?

You need to add the following :
InputStream is = urlConnection.getInputStream();
out.write(12); //The data to send
out.flush();

Try closing the output stream.

TCP connection is not reused for HTTP requests with HttpURLConnection

I'm have created an application which sends GET requests to a URL, and then downloads the full content of that page.
The client sends a GET to e.g. stackoverflow.com, and forwards the response to a parser, which has the resposibility to find all the sources from the page that needs to be downloaded with subsequent GET requests.
The method below is used to send those GET requests. It is called many times consecutively, with the URLs returned by the parser. Most of those URLs are located on the same host, and should be able to share the TCP connection.
public static void sendGetRequestToSubObject(String RecUrl)
{
URL url = new URL(recUrl.toString());
URLConnection connection = url.openConnection ();
InputStreamReader isr = new InputStreamReader(connection.getInputStream());
}
Each time this method is called, a new TCP connection is created (with a TCP 3-way handshake) and the GET is then sent on that connection. But I want to reuse the TCP connections, to improve performance.
I guess that since I create a new URL object each time the method is called, this is the way it going to work...
Maybe someone can help me do this in a better way?
Thanks!

HttpURLConnection will reuse connections if it can!
For this to work, several preconditions need to be fulfilled, mostly on the server side. Those preconditions are described in the article linked to above.

Found the problem! I was not reading the input stream properly. This caused the input stream objects to hang, and they could not be reused.
I only defined it, like this:
InputStreamReader isr = new InputStreamReader(connection.getInputStream());
but I never read from it :-)
I changed the read method as well. Instead of a buffered reader I stole this:
InputStream in = null;
String queryResult = "";
try {
URL url = new URL(archiveQuery);
HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();
HttpURLConnection httpConn = (HttpURLConnection) urlConn;
httpConn.setAllowUserInteraction(false);
httpConn.connect();
in = httpConn.getInputStream();
BufferedInputStream bis = new BufferedInputStream(in);
ByteArrayBuffer baf = new ByteArrayBuffer(50);
int read = 0;
int bufSize = 512;
byte[] buffer = new byte[bufSize];
while(true){
read = bis.read(buffer);
if(read==-1){
break;
}
baf.append(buffer, 0, read);
}
queryResult = new String(baf.toByteArray());
} catch (MalformedURLException e) {
// DEBUG
Log.e("DEBUG: ", e.toString());
} catch (IOException e) {
// DEBUG
Log.e("DEBUG: ", e.toString());
}
}
From here: Reading HttpURLConnection InputStream - manual buffer or BufferedInputStream?