Parse JSON from HttpURLConnection object

Question

I am doing basic http auth with the HttpURLConnection object in Java           URL urlUse   new URL url           HttpURLConnection conn   null          conn    HttpURLConnection  urlUse openConnection            conn setRequestMethod  GET            conn setRequestProperty  Content-length    0            conn setUseCaches false           conn setAllowUserInteraction false           conn setConnectTimeout timeout           conn setReadTimeout timeout           conn connect             if conn getResponseCode    201    conn getResponseCode    200                        success   true              I am expecting a JSON object  or string data in the format of a valid JSON object  or HTML with simple plain text that is valid JSON  How do I access that from the HttpURLConnection after it returns a response

User · Answer

Define the following function  not mine  not sure where I found it long ago    private static String convertStreamToString InputStream is     BufferedReader reader   new BufferedReader new InputStreamReader is    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            return sb toString         Then   String jsonReply  if conn getResponseCode    201    conn getResponseCode    200                success   true          InputStream response   conn getInputStream            jsonReply   convertStreamToString response               Do JSON handling here

User · Answer

In addition  if you wish to parse your object in case of http error  400-5   codes   You can use the following code   just replace   getInputStream  with  getErrorStream        BufferedReader rd   new BufferedReader              new InputStreamReader conn getErrorStream          StringBuilder sb   new StringBuilder        String line      while   line   rd readLine       null            sb append line             rd close        return sb toString

User · Answer

The JSON string will just be the body of the response you get back from the URL you have called  So add this code      BufferedReader in   new BufferedReader new InputStreamReader                              conn getInputStream      String inputLine  while   inputLine   in readLine       null       System out println inputLine   in close      That will allow you to see the JSON being returned to the console  The only missing piece you then have is using a JSON library to read that data and provide you with a Java representation   Here s an example using JSON-LIB

User · Answer

You can get raw data using below method  BTW  this pattern is for Java 6  If you are using Java 7 or newer  please consider try-with-resources pattern   public String getJSON String url  int timeout        HttpURLConnection c   null      try           URL u   new URL url           c    HttpURLConnection  u openConnection            c setRequestMethod  GET            c setRequestProperty  Content-length    0            c setUseCaches false           c setAllowUserInteraction false           c setConnectTimeout timeout           c setReadTimeout timeout           c connect            int status   c getResponseCode             switch  status                case 200              case 201                  BufferedReader br   new BufferedReader new InputStreamReader c getInputStream                      StringBuilder sb   new StringBuilder                    String line                  while   line   br readLine       null                        sb append line   n                                      br close                    return sb toString                     catch  MalformedURLException ex            Logger getLogger getClass   getName    log Level SEVERE  null  ex         catch  IOException ex            Logger getLogger getClass   getName    log Level SEVERE  null  ex         finally          if  c    null              try                 c disconnect                catch  Exception ex                 Logger getLogger getClass   getName    log Level SEVERE  null  ex                                  return null      And then you can use returned string with Google Gson to map JSON to object of specified class  like this   String data   getJSON  http   localhost authmanager php    AuthMsg msg   new Gson   fromJson data  AuthMsg class   System out println msg     There is a sample of AuthMsg class   public class AuthMsg       private int code      private String message       public int getCode             return code            public void setCode int code            this code   code             public String getMessage             return message            public void setMessage String message            this message   message            JSON returned by http   localhost authmanager php must look like this     code  1  message   Logged in     Regards

User · Answer

This function will be used get the data from url in form of HttpResponse object    public HttpResponse getRespose String url  String your auth code   HttpClient client   new DefaultHttpClient    HttpPost postForGetMethod   new HttpPost url   postForGetMethod addHeader  Content-type    Application JSON    postForGetMethod addHeader  Authorization   your auth code   return client execute postForGetMethod       Above function is called here and we receive a String form of the json using the Apache library Class And in following statements we try to make simple pojo out of the json we received   String jsonString            EntityUtils toString getResponse  http   echo jsontest com title ipsum content     blah   Your auth if you need one   getEntity     UTF-8    final GsonBuilder gsonBuilder   new GsonBuilder    gsonBuilder registerTypeAdapter JsonJavaModel  class  new    CustomJsonDeserialiser     final Gson gson   gsonBuilder create    JsonElement json   new JsonParser   parse jsonString   JsonJavaModel pojoModel   gson fromJson                      jsonElementForJavaObject  JsonJavaModel class     This is a simple java model class for incomming json      public class JsonJavaModel      String content      String title        This is a custom deserialiser   public class CustomJsonDeserialiserimplements JsonDeserializer lt JsonJavaModel gt              Override public JsonJavaModel deserialize JsonElement json  Type type                                   JsonDeserializationContext arg2  throws    JsonParseException       final JsonJavaModel jsonJavaModel  new JsonJavaModel        JsonObject object   json getAsJsonObject         try        jsonJavaModel content   object get  Content   getAsString        jsonJavaModel title   object get  Title   getAsString          catch  Exception e             e printStackTrace              return jsonJavaModel      Include Gson library and org apache http util EntityUtils

[java] Parse JSON from HttpURLConnection object

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