How to parse a JSON Input stream

Question

I am using java to call a url that returns a JSON object   url   new URL  my URl    urlInputStream   url openConnection   getInputStream      How can I convert the response into string form and parse it

User · Answer

Kotlin version with Gson

to read the response JSON:

val response = BufferedReader(
                   InputStreamReader(conn.inputStream, "UTF-8")
               ).use { it.readText() }

to parse response we can use Gson:

val model = Gson().fromJson(response, YourModelClass::class.java)

User · Answer

I would suggest you have to use a Reader to convert your InputStream in    BufferedReader streamReader   new BufferedReader new InputStreamReader in   UTF-8      StringBuilder responseStrBuilder   new StringBuilder     String inputStr  while   inputStr   streamReader readLine       null      responseStrBuilder append inputStr   new JSONObject responseStrBuilder toString       I tried in toString   but it returns    getClass   getName           Integer toHexString hashCode       like documentation says it derives to toString from Object

User · Answer

This example reads all objects from a stream of objects  it is assumed that you need CustomObjects instead of a Map           ObjectMapper mapper   new ObjectMapper            JsonParser parser   mapper getFactory   createParser  source            if parser nextToken      JsonToken START ARRAY              throw new IllegalStateException  Expected an array                      while parser nextToken      JsonToken START OBJECT                 read everything from this START OBJECT to the matching END OBJECT              and return it as a tree model ObjectNode           ObjectNode node   mapper readTree parser             CustomObject custom   mapper convertValue  node  CustomObject class                  do whatever you need to do with this object           System out println       custom                      parser close      This answer was composed by using   Use Jackson To Stream Parse an Array of Json Objects and Convert JsonNode into Object

User · Answer

I suggest use javax json Json factory as less verbose possible solution  JsonObject json   Json createReader yourInputStream  readObject     Enjoy

User · Answer

use jackson to convert json  input stream to the map or object http   jackson codehaus org   there are also some other usefull libraries for json  you can google  json java

User · Answer

All the current answers assume that it is okay to pull the entire JSON into memory where the advantage of an InputStream is that you can read the input little by little   If you would like to avoid reading the entire Json file at once then I would suggest using the Jackson library  which is my personal favorite but I m sure others like Gson have similar functions    With Jackson you can use a JsonParser to read one section at a time   Below is an example of code I wrote that wraps the reading of an Array of JsonObjects in an Iterator   If you just want to see an example of Jackson  look at the initJsonParser  initFirstElement  and initNextObject methods   public class JsonObjectIterator implements Iterator lt Map lt String  Object gt  gt   Closeable       private static final Logger LOG   LoggerFactory getLogger JsonObjectIterator class        private final InputStream inputStream      private JsonParser jsonParser      private boolean isInitialized       private Map lt String  Object gt  nextObject       public JsonObjectIterator final InputStream inputStream            this inputStream   inputStream          this isInitialized   false          this nextObject   null             private void init             this initJsonParser            this initFirstElement            this isInitialized   true             private void initJsonParser             final ObjectMapper objectMapper   new ObjectMapper            final JsonFactory jsonFactory   objectMapper getFactory             try               this jsonParser   jsonFactory createParser inputStream             catch  final IOException e                LOG error  There was a problem setting up the JsonParser      e getMessage    e               throw new RuntimeException  There was a problem setting up the JsonParser      e getMessage    e                        private void initFirstElement             try                  Check that the first element is the start of an array             final JsonToken arrayStartToken   this jsonParser nextToken                if  arrayStartToken    JsonToken START ARRAY                    throw new IllegalStateException  The first element of the Json structure was expected to be a start array token  but it was      arrayStartToken                                 Initialize the first object             this initNextObject              catch  final Exception e                LOG error  There was a problem initializing the first element of the Json Structure      e getMessage    e               throw new RuntimeException  There was a problem initializing the first element of the Json Structure      e getMessage    e                         private void initNextObject             try               final JsonToken nextToken   this jsonParser nextToken                    Check for the end of the array which will mean we re done             if  nextToken    JsonToken END ARRAY                    this nextObject   null                  return                                Make sure the next token is the start of an object             if  nextToken    JsonToken START OBJECT                    throw new IllegalStateException  The next token of Json structure was expected to be a start object token  but it was      nextToken                                 Get the next product and make sure it s not null             this nextObject   this jsonParser readValueAs new TypeReference lt Map lt String  Object gt  gt                      if  this nextObject    null                    throw new IllegalStateException  The next parsed object of the Json structure was null                            catch  final Exception e                LOG error  There was a problem initializing the next Object      e getMessage    e               throw new RuntimeException  There was a problem initializing the next Object      e getMessage    e                         Override     public boolean hasNext             if   this isInitialized                this init                       return this nextObject    null              Override     public Map lt String  Object gt  next                This method will return the current object and initialize the next object so hasNext will always have knowledge of the current state             Makes sure we re initialized first         if   this isInitialized                this init                          Store the current next object for return         final Map lt String  Object gt  currentNextObject   this nextObject              Initialize the next object         this initNextObject             return currentNextObject              Override     public void close   throws IOException           IOUtils closeQuietly this jsonParser           IOUtils closeQuietly this inputStream              If you don t care about memory usage  then it would certainly be easier to read the entire file and parse it as one big Json as mentioned in other answers

User · Answer

If you like to use Jackson Databind  which Spring uses by default for its HttpMessageConverters   then you may use the ObjectMapper readTree InputStream  API  For example   ObjectMapper mapper   new ObjectMapper    JsonNode json   mapper readTree myInputStream

User · Answer

InputStream is   HTTPClient get url       InputStreamReader reader   new InputStreamReader is       JSONTokener tokenizer   new JSONTokener reader       JSONObject jsonObject   new JSONObject tokenizer

User · Answer

Use a library    GSON Jackson or one of many other JSON libraries that are out there

User · Answer

For those that pointed out the fact that you can t use the toString method of InputStream like this see https   stackoverflow com a 5445161 1304830    My correct answer would be then    import org json JSONObject   public static String convertStreamToString java io InputStream is        java util Scanner s   new java util Scanner is  useDelimiter    A        return s hasNext     s next                 JSONObject json   new JSONObject convertStreamToString url openStream

User · Answer

if you have JSON file you can set it on assets folder then call it using this code  InputStream in   mResources getAssets   open  fragrances json        where mResources object from Resources class

[java] How to parse a JSON Input stream

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