Develop Reference

Get Json / Resonse body from Curl Post Request in Java

This is the method I have written which sends a POST request to send an Email.
I am able to send the email and get the Response Code 200 Ok.
But I don't know how to get the JSON Response and convert it into an Object.
Can someone please tell me how to do this?
public void sendEmail() {
try {
URL url = new URL("https://mandrillapp.com/api/1.0/messages/send");
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.setRequestMethod("POST");
httpURLConnection.setDoOutput(true);
httpURLConnection.setRequestProperty("Content-Type", "application/json");
String data =
"{\"key\": \"" + mailchimpApiKey + "\", " +
"\"message\": {" +
"\"from_email\": \"from#gmail.com\", " +
"\"subject\": \"Hello World\", " +
"\"text\": \"Welcome to Mailchimp Transactional!\", " +
"\"to\": [{ \"email\": \"to#gmail.com\", \"type\": \"to\" }]}}";
byte[] out = data.getBytes(StandardCharsets.UTF_8);
OutputStream stream = httpURLConnection.getOutputStream();
stream.write(out);
System.out.println(httpURLConnection.getResponseCode() + " " + httpURLConnection.getResponseMessage());
httpURLConnection.disconnect();
} catch (IOException e) {
e.printStackTrace();
}
}

A basic search reveals: https://www.baeldung.com/httpurlconnection-post#8-read-the-response-from-input-stream
try(BufferedReader br = new BufferedReader(
new InputStreamReader(con.getInputStream(), "utf-8"))) {
StringBuilder response = new StringBuilder();
String responseLine = null;
while ((responseLine = br.readLine()) != null) {
response.append(responseLine.trim());
}
System.out.println(response.toString());
}
If the response is in JSON format, use any third-party JSON parsers such as Jackson library, Gson, or org.json to parse the response.

In addition to the answer by #mdre
I use the org.json library to convert responses into JSON Objects. The following method does exactly this:
import org.json.JSONException;
import org.json.JSONObject;
public static JSONObject convertResponseToJSONObject(String responseString) {
try {
JSONObject jsonObj = new JSONObject(responseString);
return jsonObj;
} catch (JSONException e) {
System.err.println(
"It is not possible to create a JSONObject from the input string, returning null. Exception:");
e.printStackTrace();
}
return null;
}
Note that the response only represents a JSON object if it starts with a {. If it starts with a [ the response represents a JSON array.

You can get errorStream or inputStream based on the response code you receive and get the response from it. Below example creates a BufferedReader from the stream
BufferedReader br = null;
if (100 <= httpURLConnection.getResponseCode() && httpURLConnection.getResponseCode() <= 399) {
br = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream()));
} else {
br = new BufferedReader(new InputStreamReader(httpURLConnection.getErrorStream()));
}
You can then read from the br and store data based on your requirement. Below will store data into StringBuilder
StringBuilder data = new StringBuilder();
String dataLine = null;
while ((dataLine = br.readLine()) != null) {
data.append(dataLine.trim());
}
System.out.println(data.toString());
Instead of printing as String you can also convert it into JSON by using JSON libraries. You may follow this guide

Json System.err: Unexpected character () at position 0. only from php

URL url = new URL(host);
urlConnection = (HttpURLConnection) url.openConnection();
int code = urlConnection.getResponseCode();
System.out.print(code);
if (code==200) {
InputStream in = new BufferedInputStream(urlConnection.getInputStream());
if (in != null) {
String content = in.toString();
System.out.print(content);
JSONParser jsonParser = new JSONParser();
JSONObject jsonObject = (JSONObject) jsonParser.parse(new InputStreamReader(in, "UTF-8"));
result = (String) jsonObject.get("name");
System.out.print(jsonObject);
}
in.close();
}
When I have a host string like http://www.example.com/json.txt it all works fine, but when I have host string like www.example.com/index.php?data=data&data2=data2 I get the following error:
W/System.err: Unexpected character () at position 0.
I/System.out: 200java.io.BufferedInputStream#8bc189fpp = [0, 700, 250, 700]
My PHP output in browser looks fine, when I copy it to json.txt it also works fine.
I try to play with urlConnection POST, GET, RAW without luck.
Any ideas?

Problem was probly BOM in php json.
I do:
URL url = new URL(host);
urlConnection = (HttpURLConnection) url.openConnection();
int code = urlConnection.getResponseCode();
System.out.print(code);
if(code==200){
InputStream in = new BufferedInputStream(urlConnection.getInputStream());
StringWriter writer = new StringWriter();
if (in != null) {
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(in));
String line = "";
while ((line = bufferedReader.readLine()) != null)
result += line;
result = result.substring(1);
JSONParser jsonParser = new JSONParser();
JSONObject jsonObject = (JSONObject)jsonParser.parse(result);
result=(String) jsonObject.get("name");
System.out.print(jsonObject);
}
in.close();
}
And it works.

Can not find the Json object (Using org.json)

Microsoft Academic provided an API to get some general information from Microsoft academic. The response type is a Json Object. Using org.Json and following code, I have tried to read the response object but I have failed (need to download these jars + common-logging and common-codec) :
URIBuilder builder = new URIBuilder("https://api.projectoxford.ai/academic/v1.0/evaluate?");
builder.setParameter("expr", "Composite(AA.AuN=='jaime teevan')");
builder.setParameter("count", "100");
builder.setParameter("attributes", "Ti,CC");
URI uri = builder.build();
HttpGet request = new HttpGet(uri);
request.setHeader("Ocp-Apim-Subscription-Key", "Your-Key");
HttpClient httpclient = HttpClients.createDefault();
HttpResponse response = httpclient.execute(request);
HttpEntity entity = response.getEntity();
if (entity != null) {
JSONObject obj = new JSONObject(entity);
JSONArray arr = obj.getJSONArray("entities");
for (int i = 0; i < arr.length(); i++){
String post_id = arr.getJSONObject(i).getString("Ti");
System.out.println(post_id);
}
System.out.println(EntityUtils.toString(entity));
}
Which returns the following exception:
Exception in thread "main" org.json.JSONException: JSONObject["entities"] not found.
at org.json.JSONObject.get(JSONObject.java:471)
at org.json.JSONObject.getJSONArray(JSONObject.java:618)
How to fix this?
EDIT
Although it is easy to see an example of the response from the link I provided at the beginning of my question (Microsoft Academic), but for ease of readers I show it in here:
{
"expr": "Composite(AA.AuN=='jaime teevan')",
"entities":
[
{
"logprob": -15.08,
"Ti": "personalizing search via automated analysis of interests and activities",
"CC": 372,
},
{
"logprob": -15.389,
"Ti": "the perfect search engine is not enough a study of orienteering behavior in directed search",
"CC": 237,
}
]
}

Seems like the problem to me is you are not converting your response to string , you need to convert your response to string before passing it to JSONObject
HttpEntity entity = response.getEntity();
ByteArrayOutputStream os = new ByteArrayOutputStream();
try {
entity.writeTo(os);
} catch (IOException e1) {
}
String contentString = new String(os.toByteArray());
or other way is
InputStream instream = entity.getContent();
BufferedReader reader = new BufferedReader(new InputStreamReader(instream));
StringBuilder sb = new StringBuilder();
String line = null;
try {
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
String contentString = sb.toString(); // you can pass sb.toString() directly to jsonobject as well
and now pass contentString to JSONObject
JSONObject obj = new JSONObject(contentString);
JSONArray arr = obj.getJSONArray("entities");
Update : your can also use this which is also suggested by #Ömer Fadıl Usta
but i would strongly recommend to use HttpURLConnection for security and performance

Try to pass string JsonData to JSONObject :
if (entity != null) {
String jsonData = EntityUtils.toString(entity);
JSONObject obj = new JSONObject(jsonData);
........
.....
}

Java String to JSON conversion

i am getting data from restful api in String variable now i want to convert to JSON object but i am having problem while conversion it throws exception .Here is my code :
URL url = new URL("SOME URL");
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setRequestProperty("Accept", "application/json");
BufferedReader br = new BufferedReader(new InputStreamReader(
(conn.getInputStream())));
String output;
System.out.println("Output from Server .... \n");
while ((output = br.readLine()) != null) {
System.out.println(output);
}
conn.disconnect();
JSONObject jObject = new JSONObject(output);
String projecname=(String) jObject.get("name");
System.out.print(projecname);
MY string contain
{"data":{"name":"New Product","id":1,"description":"","is_active":true,"parent":{"id":0,"name":"All Projects"}}}
this is the string which i want in json but it shows me Exception in thread "main"
java.lang.NullPointerException
at java.io.StringReader.<init>(Unknown Source)
at org.json.JSONTokener.<init>(JSONTokener.java:83)
at org.json.JSONObject.<init>(JSONObject.java:310)
at Main.main(Main.java:37)

The name is present inside the data. You need to parse a JSON hierarchically to be able to fetch the data properly.
JSONObject jObject = new JSONObject(output); // json
JSONObject data = jObject.getJSONObject("data"); // get data object
String projectname = data.getString("name"); // get the name from data.
Note: This example uses the org.json.JSONObject class and not org.json.simple.JSONObject.
As "Matthew" mentioned in the comments that he is using org.json.simple.JSONObject, I'm adding my comment details in the answer.
Try to use the org.json.JSONObject instead. But then if you can't change your JSON library, you can refer to this example which uses the same library as yours and check the how to read a json part from it.
Sample from the link provided:
JSONObject jsonObject = (JSONObject) obj;
String name = (String) jsonObject.get("name");

You are getting NullPointerException as the "output" is null when the while loop ends. You can collect the output in some buffer and then use it, something like this-
StringBuilder buffer = new StringBuilder();
String output;
System.out.println("Output from Server .... \n");
while ((output = br.readLine()) != null) {
System.out.println(output);
buffer.append(output);
}
output = buffer.toString(); // now you have the output
conn.disconnect();

Converting the String to JsonNode using ObjectMapper object :
ObjectMapper mapper = new ObjectMapper();
// For text string
JsonNode = mapper.readValue(mapper.writeValueAsString("Text-string"), JsonNode.class)
// For Array String
JsonNode = mapper.readValue("[\"Text-Array\"]"), JsonNode.class)
// For Json String
String json = "{\"id\" : \"1\"}";
ObjectMapper mapper = new ObjectMapper();
JsonFactory factory = mapper.getFactory();
JsonParser jsonParser = factory.createParser(json);
JsonNode node = mapper.readTree(jsonParser);

Instead of JSONObject , you can use ObjectMapper to convert java object to json string
ObjectMapper mapper = new ObjectMapper();
String requestBean = mapper.writeValueAsString(yourObject);

Send data using POST to java server from Android client and get JSON response

I am completely new to Android programming. I have come across the following problem -
I want to validate the credentials of the user who uses the application. For this I want to use POST method to send the Login details to the server. From there I want to get response in JSON format. I don't know how to receive the response. I am using Java for server side programming.
P.S. I would deal with security concerns bit later.
Following is my Android code. I know it is a mess.. Please help.
HttpURLConnection connection;
OutputStreamWriter request = null;
URL url = null;
String response = null;
String parameters = "username="+mUsername+"&password="+mPassword;
try
{
url = new URL("address");
connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("POST");
connection.setDoInput(true);
connection.setDoOutput(true);
connection.connect();
request = new OutputStreamWriter(connection.getOutputStream());
request.write(parameters);
request.flush();
request.close();
String line = "";
InputStreamReader isr = new InputStreamReader(connection.getInputStream());
BufferedReader reader = new BufferedReader(isr);
StringBuilder sb = new StringBuilder();
while ((line = reader.readLine()) != null)
{
sb.append(line);
}
// Response from server after login process will be stored in response variable.
response = sb.toString();
// You can perform UI operations here
Toast.makeText(this,"Message from Server: \n"+ response, 0).show();
isr.close();
reader.close();
}
catch(IOException e)
{
// Error
return -1;
}

There's an open source class you can use for just this, and you can easily browse the code to see how it works. There are actually many open source libs that do this, but the following is among the cleanest and easiest to work with in my opinion.
https://github.com/kevinsawicki/http-request/blob/master/lib/src/main/java/com/github/kevinsawicki/http/HttpRequest.java
And your code will probably look something like this:
Map<String, String> params = new HashMap<String, String>();
params.put("username", mUsername);
params.put("password", mPassword);
String response = HttpRequest.post(url).form(params).body();
EDIT
My original answer including the params map in to post method would have sent the request as a POST but the params in the url. The corrected version (form method) sends the params in the body.

You can convert your json response to a JSONObject class.
Look this app, the code is very simple.
#Override
public List<User> getRanking() {
final List<User> result = new ArrayList<User>();
String url = "http://quiz-exmo.rhcloud.com/rest/user/ranking/";
String json = HttpUtil.doGet(url);
try {
final JSONObject resultJsonObject = new JSONObject(json);
final JSONArray jsonArray = resultJsonObject.getJSONArray("users");
for (int index = 0, total = jsonArray.length(); index < total; index++) {
final JSONObject jsonObject = jsonArray.getJSONObject(index);
final User user = new User();
user.name = jsonObject.getString("name");
user.email = jsonObject.getString("email");
user.score = jsonObject.getInt("points");
result.add(user);
}
} catch (JSONException e) {
throw new RuntimeException(e);
}
return result;
}
https://github.com/exmo/equizmo-android/blob/master/maven/equizmo/src/main/java/br/gov/serpro/quiz/service/rest/UserServiceRest.java