How do I parse JSON from a Java HTTPResponse?

Question

I have an HttpResponse object for a web request I just made. The response is in the JSON format, so I need to parse it. I can do it in an absurdly complex way, but it seems like there must be a better way.

Is this really the best I can do?

    HttpResponse response; // some response object
    Reader in = new BufferedReader(
        new InputStreamReader(response.getEntity().getContent(), "UTF-8"));
    StringBuilder builder= new StringBuilder();
    char[] buf = new char[1000];
    int l = 0;
    while (l >= 0) {
        builder.append(buf, 0, l);
        l = in.read(buf);
    }
    JSONTokener tokener = new JSONTokener( builder.toString() );
    JSONArray finalResult = new JSONArray( tokener );

I'm on Android if that makes any difference.

Answer 1

Two things which can be done more efficiently:

1. Use StringBuilder instead of StringBuffer since it's the faster and younger brother.
2. Use BufferedReader#readLine() to read it line by line instead of reading it char by char.

---

HttpResponse response; // some response object
BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent(), "UTF-8"));
StringBuilder builder = new StringBuilder();
for (String line = null; (line = reader.readLine()) != null;) {
    builder.append(line).append("\n");
}
JSONTokener tokener = new JSONTokener(builder.toString());
JSONArray finalResult = new JSONArray(tokener);

If the JSON is actually a single line, then you can also remove the loop and builder.

HttpResponse response; // some response object
BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent(), "UTF-8"));
String json = reader.readLine();
JSONTokener tokener = new JSONTokener(json);
JSONArray finalResult = new JSONArray(tokener);

Answer 2

Use JSON Simple,

http://code.google.com/p/json-simple/

Which has a small foot-print, no dependencies so it's perfect for Android.

You can do something like this,

Object obj=JSONValue.parse(buffer.tString());
JSONArray finalResult=(JSONArray)obj;

Answer 3

You can use the Gson library for parsing

void getJson() throws IOException {
    HttpClient  httpClient = new DefaultHttpClient();
    HttpGet httpGet = new HttpGet("some url of json");
    HttpResponse httpResponse = httpClient.execute(httpGet);
    String response = EntityUtils.toString(httpResponse.getEntity());

    Gson gson = new Gson();
    MyClass myClassObj = gson.fromJson(response, MyClass.class);

}

here is sample json file which is fetchd from server

{
"id":5,
"name":"kitkat",
"version":"4.4"
}

here is my class

class MyClass{
int id;
String name;
String version;
}

refer this

Answer 4

Jackson appears to support some amount of JSON parsing straight from an InputStream. My understanding is that it runs on Android and is fairly quick. On the other hand, it is an extra JAR to include with your app, increasing download and on-flash size.

Answer 5

Instead of doing

Reader in = new BufferedReader(
    new InputStreamReader(response.getEntity().getContent(), "UTF-8"));
StringBuilder builder= new StringBuilder();
char[] buf = new char[1000];
int l = 0;
while (l >= 0) {
    builder.append(buf, 0, l);
    l = in.read(buf);
}
JSONTokener tokener = new JSONTokener( builder.toString() );

You can do:

JSONTokener tokener = new JSONTokener(
                           IOUtils.toString(response.getEntity().getContent()) );

where IOUtils is from the commons IO library.

Answer 6

For Android, and using Apache's Commons IO Library for IOUtils:

// connection is a HttpURLConnection
InputStream inputStream = connection.getInputStream()
ByteArrayOutputStream baos = new ByteArrayOutputStream();
IOUtils.copy(inputStream, baos);
JSONObject jsonObject = new JSONObject(baos.toString()); // JSONObject is part of Android library

Answer 7

There is no need to do the reader loop yourself. The JsonTokener has this built in. E.g.

ttpResponse response; // some response object
BufferedReader reader = new BufferedReader(new    
JSONTokener tokener = new JSONTokener(reader);
JSONArray finalResult = new JSONArray(tokener);