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How do I use GET method with sending json data in android?

API route in Python (Flask)
#app.route('/secret')
def secret():
if request.get_json(force=True)['key'] == 'secret key':
return jsonify(msg='Hello!')
It is working linux terminal
curl -iX GET -d '{"key":"secret key"}' localhost
Linux terminal output this
{"msg":"Hello!"}
It doesn't need to work in browser.
try{
HttpURLConnection connection = (HttpURLConnection)
new URL("http://<my local ip>/secret").openConnection();
connection.setRequestMethod("GET");
connection.setDoOutput(true);
connection.connect();
JSONObject jsonInput = new JSONObject();
jsonInput.put("key", "secret key");
OutputStream os = connection.getOutputStream();
byte[] input = jsonInput.toString().getBytes(StandardCharsets.UTF_8);
os.write(input, 0, input.length);
os.flush();
os.close();
BufferedReader br = new BufferedReader(new InputStreamReader(connection.getInputStream()));
StringBuilder response = new StringBuilder();
String responseLine = null;
while ((responseLine = br.readLine()) != null) {
response.append(responseLine.trim());
}
return response.toString();
} catch (IOException | JSONException e) {
Log.e("MainActivity", "Error: " + e.getMessage());
}
Although the GET method is set to the connection request in my codes, a POST request is being sent to the Python server.
Python Interpreter
Is it impossible to fix this?

Request Body is not recommended in HTTP GET requests. See HERE
A payload within a GET request message has no defined semantics;
sending a payload body on a GET request might cause some existing
implementations to reject the request.
When you try to write on a URL, you are implicitly POSTing on it despite you had set GET as the HTTP method. At below lines:
OutputStream os = connection.getOutputStream();
byte[] input = jsonInput.toString().getBytes(StandardCharsets.UTF_8);
os.write(input, 0, input.length);
For confirmation of my words see Writing to a URLConnection
writing to a URL is often called posting to a URL. The server
recognizes the POST request and reads the data sent from the client.

Receiving binary data over HTTP

I have a server which is sending a .png image to a client via a HTTP post request. The .png is stored inside a sqlite3 database, retrieved as a blob and this all works fine; I have tested saving the returned blob to disk and it can be opened as expected. When my client interprets the response, the payload has mysteriously grown in length from 16365 to 16367, inspecting the response string has shown there are some extra '?' characters intermittently in the stream
Testing the server using the ARC plug-in for Chrome has shown the response received there to be the right length, which leads me to believe there is a problem with my client code:
// request
URL url = new URL(targetURL);
conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("POST");
conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
conn.setRequestProperty("Content-Length", Integer.toString(parameters.getBytes().length));
conn.setRequestProperty("Content-Language", "en-US");
conn.setUseCaches(false);
conn.setDoOutput(true);
conn.getOutputStream().write(parameters.getBytes());
// response
Reader rd = new BufferedReader(new InputStreamReader(conn.getInputStream()));
StringBuilder sb = new StringBuilder();
for (int c; (c = rd.read()) >=0;)
sb.append((char)c);
String response = sb.toString();
// this String is of length 16367 when it should be 16365
Does anything jump out as being incorrect here? Note I am not doing any kind of character encoding on either side, should I be when using raw image data?

You can use DataInputStream to read the byte stream.
URL url = new URL("http://i.stack.imgur.com/ILTQq.png");
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
DataInputStream dis = new DataInputStream(conn.getInputStream());
FileOutputStream fw = new FileOutputStream(new File("/tmp/img.png"));
byte buffer[] = new byte[1024];
int offset = 0;
int bytes;
while ((bytes = dis.read(buffer, offset, buffer.length)) > 0) {
fw.write(buffer, 0, bytes);
}
fw.close();
Alternatively an instance of BufferedImage can be created directly from the URL using ImageIO.read(java.net.URL).
URL url = new URL("http://i.stack.imgur.com/ILTQq.png");
BufferedImage image = ImageIO.read(url);

Incorrect Json String was received on client while it was generated correctly on server side

I am working on a Server-Client application. For part of the requests, I need to generate a piece of Json String on Server side and send it to Client. The Json String was generated correctly on the server side according to the Server log. But on the Android client side, the String was changed and cannot be parsed as correct Json String.
Here are some related code.
Generate Json String on Server side:
#RequestMapping(value="/resourceList/{actType}/{type}/{id}")
#ResponseBody public Object personList(#PathVariable int actType, #PathVariable int type, #PathVariable int id){
ArrayList<ItemBase> list = new ArrayList();
......
return new ArrayList();
}
This generates following Json code:
[{"countryID":1,"locationID":5,"siteID":5,"brief":"shark point","userID":0,"status":"normal","rank":0.0,"id":2,"timestamp":1471494991000,"displayName":"shark point","pic":"2.jpg","actType":1,"type":64},{"countryID":1,"locationID":5,"siteID":5,"brief":"halik","userID":0,"status":"normal","rank":0.0,"id":3,"timestamp":1471495034000,"displayName":"halik","pic":"3.jpg","actType":1,"type":64}]
And receive it on Android client:
......
HttpURLConnection urlConnection = null;
try {
URL url = new URL(request);
urlConnection = (HttpURLConnection) url.openConnection();
InputStream in = new BufferedInputStream(urlConnection.getInputStream());
byte[] buffer = new byte[256];
int len = 0;
StringBuilder responseBuilder = new StringBuilder();
while ((len = in.read(buffer)) != -1) {
String str = new String(buffer, "utf-8");
responseBuilder.append(str);
}
String response = responseBuilder.toString().trim();
The response variable was written with value:
[{"countryID":1,"locationID":5,"siteID":5,"brief":"halik","userID":0,"status":"normal","rank":0.0,"id":3,"timestamp":1471495034000,"displayName":"halik","pic":"3.jpg","actType":1,471494991000,"displayName":"shark point","pic":"2.jpg","actType":1,"type":64},{"countryID":1,"locationID":5,"siteID":5,"brief":"halik","userID":0,"status":"normal","rank":0.0,"id":3,"timestamp":1471495034000,""type":64}]":"halik","pic":"3.jpg","actType":1,471494991000,"displayName":"shark point","pic":"2.jpg","actType":1,"type":64},{"countryID":1,"locationID":5,"siteID":5,"brief":"halik","userID":0,"status":"normal","rank":0.0,"id":3,"timestamp":1471495034000,"
Which cannot be parsed as Json String correctly with obvious errors.
Most methods which return a Json String to client request work fine as I expected except this one. But this method was implemented almost exactly the same as those ones work correctly. Thus I have no idea how this happened at all. Any one got any clew please help.

You're building String the wrong way.
Try this instead:
// …
HttpURLConnection urlConnection = null;
try {
URL url = new URL(request);
urlConnection = (HttpURLConnection) url.openConnection();
InputStream in = new BufferedInputStream(urlConnection.getInputStream());
BufferedInputStream bis = new BufferedInputStream(in);
ByteArrayOutputStream buf = new ByteArrayOutputStream();
int result = bis.read();
while(result != -1) {
buf.write((byte) result);
result = bis.read();
}
String response = buf.toString();
// …

Base64 image data is not getting in android

I am using HTTPURLConnection to connect to server and my response contains Base64 image data. When trying to read the response using getInputStream its not reading the complete response, breaks in between. My response contains list of objects in JSON format and each object contains BASE64 image data. Reading breaks while trying to read the first image data from the first object. Though its not showing any error it displays till half of the image data.How do i get the full response?? Here is my code
InputStream is = httpURLConnection.getInputStream();
byte[] b = new byte[1024];
StringBuffer buffer=new StringBuffer();
while ( is.read(b) != -1){
buffer.append(new String(b));
System.out.println("Read= "+is.read());
}
System.out.println(buffer);

Have you tried the example code from Google?
URL url = new URL("http://www.android.com/");
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
try {
InputStream in = new BufferedInputStream(urlConnection.getInputStream());
readStream(in);
} finally {
urlConnection.disconnect();
}
where readStream is your own method.
Reading from a BufferedInputStream is easier and faster.

Getting JSON response as part of Rest call in Java

I am trying to make Rest service call in Java. I am new to web and Rest service. I have Rest service which returns JSON as response. I have the following code but I think it's incomplete because I don't know how to process output using JSON.
public static void main(String[] args) {
try {
URL url = new URL("http://example.com:7000/test/db-api/processor");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setDoOutput(true);
connection.setInstanceFollowRedirects(false);
connection.setRequestMethod("PUT");
connection.setRequestProperty("Content-Type", "application/json");
OutputStream os = connection.getOutputStream();
//how do I get json object and print it as string
os.flush();
connection.getResponseCode();
connection.disconnect();
} catch(Exception e) {
throw new RuntimeException(e);
}
}
I am new to Rest services and JSON.

Since this is a PUT request you're missing a few things here:
OutputStream os = conn.getOutputStream();
os.write(input.getBytes()); // The input you need to pass to the webservice
os.flush();
...
BufferedReader br = new BufferedReader(new InputStreamReader(
(conn.getInputStream()))); // Getting the response from the webservice
String output;
System.out.println("Output from Server .... \n");
while ((output = br.readLine()) != null) {
System.out.println(output); // Instead of this, you could append all your response to a StringBuffer and use `toString()` to get the entire JSON response as a String.
// This string json response can be parsed using any json library. Eg. GSON from Google.
}
Have a look at this to have a more clear idea on hitting webservices.

Your code is mostly correct, but there is mistake about OutputStream.
As R.J said OutputStream is needed to pass request body to the server.
If your rest service doesn't required any body you don't need to use this one.
For reading the server response you need use InputStream(R.J also show you example) like that:
try (InputStream inputStream = connection.getInputStream();
ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();) {
byte[] buf = new byte[512];
int read = -1;
while ((read = inputStream.read(buf)) > 0) {
byteArrayOutputStream.write(buf, 0, read);
}
System.out.println(new String(byteArrayOutputStream.toByteArray()));
}
This way is good if you don't want to depends on third-part libraries. So I recommend you to take a look on Jersey - very nice library with huge amount of very useful feature.
Client client = JerseyClientBuilder.newBuilder().build();
Response response = client.target("http://host:port").
path("test").path("db-api").path("processor").path("packages").
request().accept(MediaType.APPLICATION_JSON_TYPE).buildGet().invoke();
System.out.println(response.readEntity(String.class));

Since your Content-Type is application/json, you could directly cast the response to a JSON object for example
JSONObject recvObj = new JSONObject(response);

JsonKey jsonkey = objectMapper.readValue(new URL("http://echo.jsontest.com/key/value/one/two"), JsonKey.class);
System.out.println("jsonkey.getOne() : "+jsonkey.getOne())