Keep the order of the JSON keys during JSON conversion to CSV

Question

I am using the JSON library provided here http   www json org java index html to convert a json string I have to CSV  But the problem I have is  the order of the keys is lost after conversion   This is the conversion code       JSONObject jo   new JSONObject someString       JSONArray ja   jo getJSONArray  items        String s   CDL toString ja       System out println s     This is the content of  someString           items                                WR   qwe                QU   asd                QA   end                WO   hasd                NO   qwer                       This is the result   WO QU WR QA NO hasd asd qwe end qwer   While what I expect is to keep the order of the keys   WR QU QA WO NO qwe asd end hasd qwer   Is there any way I can have this result using this library  If not  is there any other library that will provide the capability to keep the order of keys in the result

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Underscore-java keeps orders for elements while reading json  I am the maintainer of the project    String json      n                 items    n                 n                     n                         WR     qwe    n                         QU     asd    n                         QA     end    n                         WO     hasd    n                         NO     qwer   n                     n                 n               System out println U fromJson json         items   WR qwe  QU asd  QA end  WO hasd  NO qwer

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The most safe way is probably overriding keys method that is used to generate output   new JSONObject       Override   public Iterator keys        TreeSet lt Object gt  sortedKeys   new TreeSet lt Object gt         Iterator keys   super keys        while keys hasNext           sortedKeys add keys next               return sortedKeys iterator

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It is quite simple to maintain order  I had the same problem with maintaining the order from DB layer to UI Layer   Open JSONObject java file  It internally uses HashMap which doesn t maintain the order   Change it to LinkedHashMap         this map   new HashMap        this map   new LinkedHashMap      This worked for me  Let me know in the comments  I suggest the JSON library itself should have another JSONObject class which maintains order  like JSONOrderdObject java  I am very poor in choosing the names

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Your example          items                                WR   qwe                QU   asd                QA   end                WO   hasd                NO   qwer                                   add an element  itemorder          items                                WR   qwe                QU   asd                QA   end                WO   hasd                NO   qwer                                     itemorder    WR   QU   QA   WO   NO       This code generates the desired output without the column title line   JSONObject output   new JSONObject json   JSONArray docs   output getJSONArray  data    JSONArray names   output getJSONArray  itemOrder    String csv   CDL toString names docs

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JSONObject java takes whatever map you pass  It may be LinkedHashMap or TreeMap and  it will take hashmap only when the map is null    Here is the constructor of JSONObject java class that will do the checking of map    public JSONObject Map paramMap          this map    paramMap    null   new HashMap     paramMap         So before building a json object construct LinkedHashMap and then pass it to the constructor like this    LinkedHashMap lt String  String gt  jsonOrderedMap   new LinkedHashMap lt String  String gt      jsonOrderedMap put  1   red    jsonOrderedMap put  2   blue    jsonOrderedMap put  3   green     JSONObject orderedJson   new JSONObject jsonOrderedMap    JSONArray jsonArray   new JSONArray Arrays asList orderedJson     System out println  Ordered JSON Fianl CSV      CDL toString jsonArray      So there is no need to change the JSONObject java class    Hope it helps somebody

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Apache Wink has OrderedJSONObject  It keeps the order while parsing the String

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There are  hacky  ways to do it     but you shouldn t   In JSON  an object is defined thus      An object is an unordered set of name value pairs    See http   json org   Most implementations of JSON make no effort to preserve the order of an object s name value pairs  since it is  by definition  not significant   If you want order to be preserved  you need to redefine your data structure  e g          items                                 WR   qwe                  QU   asd                  QA   end                  WO   hasd                  NO   qwer                        or more simply          items                   WR   qwe              QU   asd              QA   end              WO   hasd              NO   qwer             FOLLOWUP     Thanks for the info  but I have no choice but to use JSON in my application and my application needs to keep the order of the keys regardless of the definition of JSON object    I am not allowed to change the format of the JSON file as well       You need to have a hard conversation with whoever designed that file structure and won t let you change it   It is   they are plain wrong   You need to convince them   If they really won t let you change it    You should insist on not calling it JSON      cos it isn t  You should point out that you are going to have to write   modify code specially to handle this  not JSON  format     unless you can find some JSON implementation that preserves the order   If they are a paying client  make sure that they pay for this extra work you have to do  You should point out that if the  not JSON  needs to be used by some other tool  it is going to be problematic   Indeed  this problem will occur over and over       This kind of thing as really bad   On the one hand  your software will be violating a well established   long standing specification that is designed to promote interoperability   On the other hand  the nit-wits who designed this lame  not JSON   file format are probably slagging off other people s systems etc  cos the systems cannot cope with their nonsense   UPDATE  It is also worth reading what the JSON RFC  RFC 7159  says on this subject   Here are some excerpts      In the years since the publication of RFC 4627  JSON has found very      wide use   This experience has revealed certain patterns  which       while allowed by its specifications  have caused interoperability      problems       JavaScript Object Notation  JSON  is a text format for the      serialization of structured data            JSON can represent four primitive types  strings  numbers  booleans       and null  and two structured types  objects and arrays        An object is an unordered collection of zero or more name value      pairs  where a name is a string and a value is a string  number       boolean  null  object  or array       JSON parsing libraries have been observed to differ as to whether or      not they make the ordering of object members visible to calling      software   Implementations whose behavior does not depend on member      ordering will be interoperable in the sense that they will not be      affected by these differences

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patchFor answer  gary        git diff JSONObject java                                                          diff --git a JSONObject java b JSONObject java index e28c9cd  e12b7a0 100755 --- a JSONObject java     b JSONObject java    -32 7  32 7    import java lang reflect Method   import java lang reflect Modifier   import java util Collection   import java util Enumeration  -import java util HashMap   import java util LinkedHashMap   import java util Iterator   import java util Locale   import java util Map     -152 7  152 9    public class JSONObject           Construct an empty JSONObject                public JSONObject     -        this map   new HashMap lt String  Object gt              this map   new HashMap lt String  Object gt                 I want to keep order of the given data           this map   new LinkedHashMap lt String  Object gt                         -243 7  245 7    public class JSONObject            throws JSONException               public JSONObject Map lt String  Object gt  map    -        this map   new HashMap lt String  Object gt              this map   new LinkedHashMap lt String  Object gt              if  map    null                 Iterator lt Entry lt String  Object gt  gt  i   map entrySet   iterator                 while  i hasNext

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Just stumbled upon the same problem  I believe the final solution used by the author consisted in using a custom ContainerFactory   public static Values parseJSONToMap String msgData        JSONParser parser   new JSONParser        ContainerFactory containerFactory   new ContainerFactory             Override         public Map createObjectContainer                 return new LinkedHashMap                        Override         public List creatArrayContainer                 return null                       try           return  Map lt String Object gt  parser parse msgData  containerFactory         catch  ParseException e            log warn  Exception parsing JSON string      msgData  e             return null        see  http   juliusdavies ca json-simple-1 1 1-javadocs org json simple parser JSONParser html parse java io Reader org json simple parser ContainerFactory

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Tested the wink solution  and working fine    Test public void testJSONObject         JSONObject jsonObject   new JSONObject        jsonObject put  bbb    xxx        jsonObject put  ccc    xxx        jsonObject put  aaa    xxx        jsonObject put  xxx    xxx        System out println jsonObject toString         assertTrue jsonObject toString   startsWith     xxx            Test public void testWinkJSONObject   throws JSONException       org apache wink json4j JSONObject jsonObject   new OrderedJSONObject        jsonObject put  bbb    xxx        jsonObject put  ccc    xxx        jsonObject put  aaa    xxx        jsonObject put  xxx    xxx        assertEquals     bbb     xxx     ccc     xxx     aaa     xxx     xxx     xxx      jsonObject toString

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Another hacky solution using reflect   JSONObject json   new JSONObject    Field map   json getClass   getDeclaredField  map    map setAccessible true    because the field is private final    map set json  new LinkedHashMap lt  gt      map setAccessible false    return flag

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Solved   I used the JSON simple library from here https   code google com p json-simple  to read the JSON string to keep the order of keys and use JavaCSV library from here http   sourceforge net projects javacsv  to convert to CSV format

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You can use the following code to do custom ORDERED serialization and deserialization of JSON Array  This example assumes you are ordering Strings but can be applied to all types    Serialization  JSONArray params   new JSONArray    int paramIndex   0   for  String currParam   mParams        JSONObject paramObject   new JSONObject        paramObject put  index   paramIndex       paramObject put  value   currParam        params put paramObject         paramIndex     json put  orderedArray   params     Deserialization  JSONArray paramsJsonArray   json optJSONArray  orderedArray    if  null    paramsJsonArray        ArrayList lt String gt  paramsArr   new ArrayList lt  gt         for  int i   0  i  lt  paramsJsonArray length    i                  JSONObject param   paramsJsonArray optJSONObject i           if  null    param                        int paramIndex   param optInt  index   -1               String paramValue   param optString  value   null                if  paramIndex  gt  -1  amp  amp  null    paramValue                                paramsArr add paramIndex  paramValue

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A more verbose  but broadly applicable solution to this sort of problem is to use a pair of data structures  a list to contain the ordering  and a map to contain the relations   For Example          items                                WR   qwe                QU   asd                QA   end                WO   hasd                NO   qwer                         itemOrder             WR    QU    QA    WO    NO       You iterate the itemOrder list  and use those to look up the map values   Ordering is preserved  with no kludges   I have used this method many times

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In the real world  an application will almost always have java bean or domain that is to be serialized de-serialized to from JSON  Its already mentioned that JSON Object specification does not guarantee order and any manipulation to that behavior does not justify the requirement   I had the same scenario in my application where I needed to preserve order just for the sack of readability purpose  I used standard jackson way to serialize my java bean to JSON   Object object   getObject       the source java bean that needs conversion String jsonString   new com fasterxml jackson databind ObjectMapper   writeValueAsString object     In order to make the json with an ordered set of elements I just use JSON property annotation in the the Java bean I used for conversion  An example below    JsonInclude JsonInclude Include NON NULL   JsonPropertyOrder   name   phone   city   id    public class SampleBean implements Serializable       private int id      private String name      private String city      private String phone            standard getters and setters     the getObject   used above   public SampleBean getObject        SampleBean bean    new SampleBean        bean setId  100        bean setName  SomeName        bean setCity  SomeCity        bean setPhone  1234567890        return bean      The output shows as per Json property order annotation         name   SomeName       phone   1234567890       city   SomeCity       id  100

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I know this is solved and the question was asked long time ago  but as I m dealing with a similar problem  I would like to give a totally different approach to this   For arrays it says  An array is an ordered collection of values   at http   www json org  - but objects   An object is an unordered set of name value pairs    aren t ordered   I wonder why that object is in an array - that implies an order that s not there      items                    WR   qwe            QU   asd            QA   end            WO   hasd            NO   qwer               So a solution would be to put the keys in a  real  array and add the data as objects to each key like this      items           WR     data    qwe           QU     data    asd           QA     data    end           WO     data    hasd           NO     data    qwer          So this is an approach that tries to rethink the original modelling and its intent  But I haven t tested  and I wonder  if all involved tools would preserve the order of that original JSON array

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instead of using jsonObject try using CsvSchema its way easier and directly converts object to csv   CsvSchema schema   csvMapper schemaFor MyClass class  withHeader            csvMapper writer schema  writeValueAsString myClassList     and it mentains the order id your pojo has  JsonPropertyOrder in it

[java] Keep the order of the JSON keys during JSON conversion to CSV

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