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How to ensure that the JSON string is UTF-8 encoded in Java

I am working on a legacy web service client code where the JSON data is being sent to the web service. Recently it was found that for some requests in the JSON body, the service is giving HTTP 400 response due to invalid characters (non-UTF8) in the JSON Body.
Below is one example of the data which is causing the issue.
String value = "zu3z5eq tô‰U\f‹Á‹€z";
I am using org.json.JSONObject.toString() method to generate the JSON string. Can you please let me know how can I ensure that the JSON string is UTF-8 encoded?
I already tried few solutions like available online , like converting to byte array and then back, using java charset methods etc, but they did not work. Either they convert the valid values as well like chinese/japanese characters, or doesn't work at all.
Can you please provide some input on this?

You need to set the character encoding for OutputStreamWriter when you create it:
httpConn.connect();
wr = new OutputStreamWriter(httpConn.getOutputStream(), StandardCharsets.UTF_8);
wr.write(jsonObject.toString());
wr.flush();
Otherwise it defaults to the "platform default encoding," which is some encoding that has been used historically for text files on whatever system you are running.

Use Base64 encoding for converting the value to Byte[].
String value = "zu3z5eq tô‰U\f‹Á‹€z";
// WHILE SENDING ENCODE THE VALUE
byte[] encodedBytes = Base64.getEncoder().encode(value.getBytes("UTF-8"));
String encodedValue = new String(encodedBytes, "UTF-8");
// TRANSPORT....
// ON RECEIVING END DECODE THE VALUE
byte[] decodedBytes = Base64.getDecoder().decode(encodedValue.getBytes("UTF-8"));
System.out.println( new String(decodedBytes, "UTF-8"));

Android - Accessing JSON children from a URL

I'm in the process of converting my website to an Android app and one of the pages' data currently is populated via JSON in my website. The way it works is that the URL generates a different JSON data with the same structure based on the passed ID. I already have the logic for passing the ID to the URL. Now I want to read the data through Java code and parse the JSON children and its values in it.
I have a URL that leads to the JSON file in textual form, but I'm not sure how to go about reading the data from it and accessing the child nodes based on the JSON key.
So I guess what I'm asking is what is the usual approach for this procedure? I see a lot of different examples, but none of which are applicable to my problem.
Anyone have any suggestions as to how I should approach this?

JSONObject = new JSONObject(yourjsonstring);
Now you have your Json Object...
If your Json start with array use this:
JSONArray = new JSONArray(yourjsonarray);

You can use existing libraries to parse JSON, gson or Moshi are two solutions.
The way you go about parsing the JSON is as followed
First you need to make pojo's with the same structure as the JSON file.
then you can parse it to java code via the fromJSON() method, this will make new objects and fill it with the data from the JSON.
gson example for clarification:
Gson gson = new Gson();
Response response = gson.fromJson(jsonLine, Response.class);
where jsonLine = your json file and the Response.Class the pojo in which you want to json to load.
Now you have the JSON values as Java classes in response.
If you're using Retrofit and OkHTTP to perform the network calls i suggest you use Moshi as it's also from Square and claimed to work faster and better than gson. (if you want to know why you can leave a comment).

I think what you're trying to do is this
on post execute method do the following
#Override
protected void onPostExecute(String result) {
String status = "";
String message = "";
String tag = "";
String mail = "";
try {
JSONObject jsonResult = new JSONObject(result);
status = jsonResult.optString("status");
message = jsonResult.optString("message");
tag = jsonResult.optString("tag");
mail = jsonResult.optString("mail");
} catch (JSONException e) {
e.printStackTrace();
}
of course your json array contains different keys
Just reolace them with yours

Parsing Request as json with stackexchange API

I am struggling with some issue related with http, java and the stackexchange API
consider the following url as string:
private static final String URLSTRING_2 = "http://freegeoip.net/json/";
if I write this url in my browser I get this answer as json:
now im trying to do that with java and only native libs, for that am using the snippet below wich is working so far so good...
If I parse the json and i try to get the value for the key "country_name" then the snippet prints as spected "Singapore"
public static void main(String[] args) throws Exception {
// Connect to the URL using java's native library
final URL url = new URL(URLSTRING_2);
final HttpURLConnection request = (HttpURLConnection) url.openConnection();
request.connect();
// Convert to a JSON object to print data
final JsonParser jp = new JsonParser(); // from gson
final JsonElement root = jp.parse(new InputStreamReader((InputStream) request.getContent())); // Convert the input stream to a json
// element
final JsonObject rootobj = root.getAsJsonObject(); // May be an array, may be an object.
final String country = rootobj.get("country_name").getAsString(); // just grab the zipcode
System.out.println("country_name: " + country);
}
Now my question:
if I do the same with this link
https://api.stackexchange.com//2.2/users/22656?order=desc&sort=reputation&site=stackoverflow&filter=!T6oHjO_RIWkfWpoL5g
my browser outputs the following json:
but if I try to parse the json I get an exception because am getting from the request this:
ý•#‡ž¼ÚRìØ1ôX`»v?±h[‹-¹’/+ò........
for something that is not even human readable...
do you know why?
Thanks in advance

The StackOverflow API GZIP-compresses its response. The reason you see that string of non-human-readable characters is that you are trying to read GZIP-compressed data without first decompressing it.
Your browser is capable of reading this header and doing the decompression itself. Your code isn't yet.
You can confirm that GZIP compression is used by displaying the value of the Content-Encoding header in the response. Adding the line
System.out.println(request.getContentEncoding());
will print out
gzip
Fortunately, fixing the problem is fairly straightforward. You need to wrap the InputStream you get from the request in a GZIPInputStream:
final JsonElement root = jp.parse(new InputStreamReader(new GZIPInputStream((InputStream) request.getContent()))); // Convert the input stream to a json
However, instead of the built-in Java classes, I'd recommend using a library such as Apache HTTPComponents Client for making your HTTP requests. In particular, a library such as this will automatically detect the content-encoding and do the decompression for you.

Simple JSON-String Query

I am developing a web-app using AJAX requests on the client-side and Servlets on the server-side.
My aim is to send objects of Javascript to server, then do some manipulations there and send it back to show here.
Let's say my js object is
var obj={hero:"Spiderman",name:"Peter Parker"};
My Approach
1.Convert obj to JSON string and send
var str= JSON.stringify(obj);
xmlhttp.open("POST",myurl,true);
xmlhttp.setRequestHeader("Content-Type","application/json",true);
xmlhttp.send("data="+str);
2. Recieve string,convert this back to JSON, manipulate "name" to "Bruce Wayne" and send it back as string
3.Recieve and convert back to Json
var data= JSON.parse(xmlhttp.responseText);
I am struggling at second point.I am using org.json for it .I searched and read docs but could not find satisfied answer for converting string to json and vica-versa in JAVA in my context.
It would be really helpful one could provide simple working code or point to some links where I can study.
P.S :
I cannot use Jquery as I am using AngularJS. See Why?
I will always send valid JSON string.
I can use other JSON lib. if its good than org.json and satisfy my needs.
Please provide its jar download link.

Assuming you are able to pull out data in your server code
This is how you can do it using org.json:
JSONParser parser = new JSONParser();
JSONObject requestObj = (JSONObject) parser.parse(data);
String name = (string)requestObj.get("name");
name = "Bruce Wayne";
Code to create the response can look something like this:
JSONObject response = new JSONObject();
response.put("name",name);
return response.toJSONString();
This assumes your server method returns a String type
And in case if you are using Servlet you can use HttpServletResponse object res to create response like:
res.setContentType("application/json");
OutputStream os = res.getOutputStream();
os.write(response.toString().getBytes());
os.close();

ISO-8859-1 encoded strings out of /into JSON in Java

My application has a Java servlet that reads a JSONObject out of the request and constructs some Java objects that are used elsewhere. I'm running into a problem because there are strings in the JSON that are encoded in ISO-8859-1. When I extract them into Java strings, the encoding appears to get interpreted as UTF-16. I need to be able to get the correctly encoded string back at some point to put into another JSON object.
I've tried mucking around with ByteBuffers and CharBuffers, but then I don't get any characters at all. I can't change the encoding, as I have to play nicely with other applications that use ISO-8859-1.
Any tips would be greatly appreciated.
It's a legacy application using Struts 1.3.8. I'm using net.sf.json 2.2.4 for JSONObject and JSONArray.
A snippet of the parsing code is:
final JSONObject a = (JSONObject) i;
final JSONObject attr = a.getJSONObject("attribute");
final String category = attr.getString("category");
final String value = attr.getString("value");
I then create POJOs using that information, that are retrieved by another action class to create JSON to pass to the client for display, or to pass to other applications.
So to clarify, if the JSON contains the string "Juan Guzmán", the Java String contains something like Juan Guzm?_An (I don't have the exact one in front of me). I'm not sure how to get the correct diacritical back. I believe that if I can get a Java String that contains the correct representation, that Mezzie's solution, below, will allow me to create the string with the correct encoding to put back into the JSON to serve back.

I had the same issue and I am using the same technology as you are. In our case, it was UTF 8. so just change that to UTF-16
public static String UTF8toISO( String str )
{
try
{
return new String( str.getBytes( "ISO-8859-1" ), "UTF-8" );
}
catch ( UnsupportedEncodingException e )
{
e.printStackTrace();
}
return str;
}