How to read json file into java with simple JSON library

Question

I want to read this JSON file with java using json simple library    My JSON file looks like this                        name   John            city   Berlin            cars                   audi                bmw                      job   Teacher                          name   Mark            city   Oslo            cars                   VW                Toyata                      job   Doctor            This is the java code I wrote to read this file   package javaapplication1  import java io FileNotFoundException  import java io FileReader  import java io IOException  import java util Iterator  import org json simple JSONArray  import org json simple JSONObject  import org json simple parser JSONParser  import org json simple parser ParseException   public class JavaApplication1       public static void main String   args             JSONParser parser   new JSONParser             try                    Object obj   parser parse new FileReader  c   file json                  JSONObject jsonObject     JSONObject  obj               String name    String  jsonObject get  name                System out println name                String city    String  jsonObject get  city                System out println city                String job    String  jsonObject get  job                System out println job                   loop array             JSONArray cars    JSONArray  jsonObject get  cars                Iterator lt String gt  iterator   cars iterator                while  iterator hasNext                   System out println iterator next                             catch  FileNotFoundException e                e printStackTrace              catch  IOException e                e printStackTrace              catch  ParseException e                e printStackTrace                        But I get the following exception      Exception in thread  main  java lang ClassCastException    org json simple JSONArray cannot be cast to org json simple JSONObject     at javaapplication1 JavaApplication1 main JavaApplication1 java 24    Can somebody tell me what I am doing wrong  The whole file is a array and there are objects and another array  cars  in the whole array of the file  But i dont know how I can parse the whole array into a java array  I hope somebody can help me with a code line which I am missing in my code   Thanks

User · Answer

Might be of help for someone else facing the same issue You can load the file as string and then can convert the string to jsonobject to access the values   import java util Scanner  import org json JSONObject  String myJson   new Scanner new File filename   useDelimiter    Z   next    JSONObject myJsonobject   new JSONObject myJson

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The whole file is an array and there are objects and other arrays  e g  cars  in the whole array of the file    As you say  the outermost layer of your JSON blob is an array   Therefore  your parser will return a JSONArray   You can then get JSONObjects from the array        JSONArray a    JSONArray  parser parse new FileReader  c   exer4-courses json        for  Object o   a          JSONObject person    JSONObject  o       String name    String  person get  name        System out println name        String city    String  person get  city        System out println city        String job    String  person get  job        System out println job        JSONArray cars    JSONArray  person get  cars         for  Object c   cars              System out println c                  For reference  see  Example 1  on the json-simple decoding example page

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Solution using Jackson library  Sorted this problem by verifying the json on JSONLint com and then using Jackson  Below is the code for the same    Main Class -  String jsonStr       r n              name      John    r n               city      Berlin    r n                                cars      r n                   FIAT    r n                 Toyata   r n                             r n            job      Teacher   r n           r n        r n                            name      Mark    r n               city      Oslo    r n               cars      r n                                VW    r n                   Toyata   r n             r n                            job      Doctor   r n           r n                  ObjectMapper mapper   new ObjectMapper             MyPojo jsonObj     mapper readValue jsonStr  MyPojo   class            for  MyPojo itr   jsonObj                 System out println  Val of getName is      itr getName                 System out println  Val of getCity is      itr getCity                 System out println  Val of getJob is      itr getJob                 System out println  Val of getCars is      itr getCars       n                POJO   public class MyPojo    private List lt String gt  cars   new ArrayList lt String gt      private String name   private String job   private String city   public List lt String gt  getCars         return cars     public void setCars List lt String gt  cars        this cars   cars     public String getName         return name     public void setName String name        this name   name     public String getJob         return job     public void setJob String job        this job   job     public String getCity         return city     public void setCity String city        this city   city         RESULT -          Val of getName is  John          Val of getCity is  Berlin          Val of getJob is  Teacher          Val of getCars is   FIAT  Toyata             Val of getName is  Mark           Val of getCity is  Oslo           Val of getJob is  Doctor           Val of getCars is   VW  Toyata

User · Answer

your json file look like this  import java io    import java util    import org json simple    import org json simple parser    public class JSONReadFromTheFileTest      public static void main String   args          JSONParser parser   new JSONParser          try            Object obj   parser parse new FileReader  quot  Users User Desktop course json quot              JSONObject jsonObject    JSONObject obj           String name    String jsonObject get  quot Name quot             String course    String jsonObject get  quot Course quot             JSONArray subjects    JSONArray jsonObject get  quot Subjects quot             System out println  quot Name   quot    name            System out println  quot Course   quot    course            System out println  quot Subjects  quot             Iterator iterator   subjects iterator             while  iterator hasNext                  System out println iterator next                        catch Exception e             e printStackTrace                    the output is Name  Raja Course  MCA Subjects  subject1  MIS subject2  DBMS subject3  UML  took it from here

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Sample Json          per page   3       total   12       data                   last name    Bluth                id   1               avatar    https   s3 amazonaws com uifaces faces twitter calebogden 128 jpg                first name    George                                    last name    Weaver                id   2                 avatar    https   s3 amazonaws com uifaces faces twitter josephstein 128 jpg                first name    Janet                                    last name    Wong                id   3                 avatar    https   s3 amazonaws com uifaces faces twitter olegpogodaev 128 jpg                first name    Emma                        page   1       total pages   4       First If statement will convert the single data from the body Second if statement will differentiate the JsonArray object  public static String getvalueJpath JSONObject responseJson  String Jpath             Object obj   responseJson          for String s   Jpath split                   if  s isEmpty                    if   s contains         s contains                            obj     JSONObject  obj  get s                   else                     if s contains         s contains                               obj     JSONArray   JSONObject obj  get s split        0    get Integer parseInt s split        1  replaceAll                      return obj toString

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You can use readAllBytes   return String Files readAllBytes Paths get filePath   StandardCharsets UTF 8

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You can use  Gson for this  GSON is a Java library that can be used to convert Java Objects into their JSON representation  It can also be used to convert a JSON string to an equivalent Java object   Take a look of this Converting JSON to Java

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Use google-simple library    lt dependency gt       lt groupId gt com googlecode json-simple lt  groupId gt       lt artifactId gt json-simple lt  artifactId gt       lt version gt 1 1 1 lt  version gt   lt  dependency gt    Please find the sample code below   public static void main String   args        try           JSONParser parser   new JSONParser              Use JSONObject for simple JSON and JSONArray for array of JSON          JSONObject data    JSONObject  parser parse                new FileReader   resources config json      path to the JSON file           String json   data toJSONString          catch  IOException   ParseException e            e printStackTrace              Use JSONObject for simple JSON like   id   1   name   ankur   and JSONArray for array of JSON like    id   1   name   ankur     id   2   name   mahajan

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import java io FileNotFoundException  import java io FileReader  import java io IOException   import org json simple JSONArray  import org json simple JSONObject  import org json simple parser JSONParser  import org json simple parser ParseException   public class Delete 01       public static void main String   args  throws FileNotFoundException              IOException  ParseException            JSONParser parser   new JSONParser            JSONArray jsonArray    JSONArray  parser parse new FileReader                   delete 01 json              for  Object o   jsonArray                JSONObject person    JSONObject  o               String strName    String  person get  name                System out println  Name        strName                String strCity    String  person get  city                System out println  City        strCity                JSONArray arrays    JSONArray  person get  cars                for  Object object   arrays                    System out println  cars        object                             String strJob    String  person get  job                System out println  Job        strJob               System out println

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Reading from JsonFile  public static ArrayList lt Employee gt  readFromJsonFile String fileName           ArrayList lt Employee gt  result   new ArrayList lt Employee gt              try              String text   new String Files readAllBytes Paths get fileName    StandardCharsets UTF 8                JSONObject obj   new JSONObject text               JSONArray arr   obj getJSONArray  employees                 for int i   0  i  lt  arr length    i                     String name   arr getJSONObject i  getString  name                    short salary   Short parseShort arr getJSONObject i  getString  salary                     String position   arr getJSONObject i  getString  position                    byte years in company   Byte parseByte arr getJSONObject i  getString  years in company                      if  position compareToIgnoreCase  manager      0                       result add new Manager name  salary  position  years in company                                      else                      result add new OrdinaryEmployee name  salary  position  years in company                                                                 catch Exception ex               System out println ex toString                       return result

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You can use jackson library and simply use these 3 lines to convert your json file to Java Object   ObjectMapper mapper   new ObjectMapper    InputStream is   Test class getResourceAsStream   test json    testObj   mapper readValue is  Test class

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This issue occurs when you are importing the org  json library for JSONObject class  Instead you need to import org json simple library

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Hope this example helps too  I have done java coding in a similar way for the below json array example as follows    following is the json data format   stored as  EMPJSONDATA json      EMPNO  275172  EMP NAME   Rehan   DOB   29-02-1992   DOJ   10-06-2013   ROLE   JAVA DEVELOPER       EMPNO  275173  EMP NAME   G K   DOB   10-02-1992   DOJ   11-07-2013   ROLE   WINDOWS ADMINISTRATOR       EMPNO  275174  EMP NAME   Abiram   DOB   10-04-1992   DOJ   12-08-2013   ROLE   PROJECT ANALYST      EMPNO  275174  EMP NAME   Mohamed Mushi   DOB   10-04-1992   DOJ   12-08-2013   ROLE   PROJECT ANALYST     public class Jsonminiproject    public static void main String   args           JSONParser parser   new JSONParser         try           JSONArray a    JSONArray  parser parse new FileReader  F  JSON DATA EMPJSONDATA json             for  Object o   a                        JSONObject employee    JSONObject  o               Long no    Long  employee get  EMPNO                System out println  Employee Number       no                String st    String  employee get  EMP NAME                System out println  Employee Name       st                String dob    String  employee get  DOB                System out println  Employee DOB       dob                String doj    String  employee get  DOJ                System out println  Employee DOJ       doj                String role    String  employee get  ROLE                System out println  Employee Role       role                System out println   n                       catch  FileNotFoundException e               TODO Auto-generated catch block         e printStackTrace          catch  IOException e               TODO Auto-generated catch block         e printStackTrace          catch  ParseException e               TODO Auto-generated catch block         e printStackTrace

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Add Jackson databind    lt dependency gt       lt groupId gt com fasterxml jackson core lt  groupId gt       lt artifactId gt jackson-databind lt  artifactId gt       lt version gt 2 9 0 pr2 lt  version gt   lt  dependency gt    Create DTO class with related fields and read JSON file   ObjectMapper objectMapper   new ObjectMapper    ExampleClass example   objectMapper readValue new File  example json    ExampleClass class

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package com json   import java io FileNotFoundException  import java io FileReader  import java io IOException  import java util Iterator   import org json simple JSONArray  import org json simple JSONObject  import org json simple parser JSONParser  import org json simple parser ParseException   public class ReadJSONFile        public static void main String   args             JSONParser parser   new JSONParser             try               Object obj   parser parse new FileReader  C  My Workspace JSON Test file json                  JSONArray array    JSONArray  obj              JSONObject jsonObject    JSONObject  array get 0                String name    String  jsonObject get  name                System out println name                String city    String  jsonObject get  city                System out println city                String job    String  jsonObject get  job                System out println job                   loop array             JSONArray cars    JSONArray  jsonObject get  cars                Iterator lt String gt  iterator   cars iterator                while  iterator hasNext                      System out println iterator next                             catch  FileNotFoundException e                e printStackTrace              catch  IOException e                e printStackTrace              catch  ParseException e                e printStackTrace

[java] How to read json file into java with simple JSON library

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