How can I convert JSON to a HashMap using Gson

Question

I m requesting data from a server which returns data in the JSON format  Casting a HashMap into JSON when making the request wasn t hard at all but the other way seems to be a little tricky  The JSON response looks like this           header                alerts                                      AlertID     2                    TSExpires    null                   Target     1                    Text     woot                    Type     1                                                 AlertID     3                    TSExpires    null                   Target     1                    Text     woot                    Type     1                                    session     0bc8d0835f93ac3ebbf11560b2c5be9a              result     4be26bc400d3c      What way would be easiest to access this data  I m using the GSON module

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With google s Gson 2 7  probably earlier versions too  but I tested with the current version 2 7  it s as simple as   Map map   gson fromJson jsonString  Map class     Which returns a Map of type com google gson internal LinkedTreeMap and works recursively on nested objects  arrays  etc   I ran the OP example like so  simply replaced double- with single-quotes and removed whitespace    String jsonString      header     alerts      AlertID    2    TSExpires   null   Target    1    Text    woot    Type    1      AlertID    3    TSExpires   null   Target    1    Text    woot    Type    1      session    0bc8d0835f93ac3ebbf11560b2c5be9a     result    4be26bc400d3c     Map map   gson fromJson jsonString  Map class   System out println map getClass   toString     System out println map     And got the following output   class com google gson internal LinkedTreeMap  header  alerts   AlertID 2  TSExpires null  Target 1  Text woot  Type 1    AlertID 3  TSExpires null  Target 1  Text woot  Type 1    session 0bc8d0835f93ac3ebbf11560b2c5be9a   result 4be26bc400d3c

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Here s a one-liner that will do it   HashMap lt String  Object gt  myMap      gson fromJson yourJson  new TypeToken lt HashMap lt String  Object gt  gt      getType

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I used this code   Gson gson   new Gson    HashMap lt String  Object gt  fields   gson fromJson json  HashMap class

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JSONObject typically uses HashMap internally to store the data  So  you can use it as Map in your code    Example   JSONObject obj   JSONObject fromObject strRepresentation   Iterator i   obj entrySet   iterator    while  i hasNext         Map Entry e    Map Entry i next       System out println  Key      e getKey        System out println  Value      e getValue

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Try this  it will worked  I used it for Hashtable   public static Hashtable lt Integer  KioskStatusResource gt  parseModifued String json        JsonObject object    JsonObject  new com google gson JsonParser   parse json       Set lt Map Entry lt String  JsonElement gt  gt  set   object entrySet        Iterator lt Map Entry lt String  JsonElement gt  gt  iterator   set iterator         Hashtable lt Integer  KioskStatusResource gt  map   new Hashtable lt Integer  KioskStatusResource gt          while  iterator hasNext              Map Entry lt String  JsonElement gt  entry   iterator next             Integer key   Integer parseInt entry getKey             KioskStatusResource value   new Gson   fromJson entry getValue    KioskStatusResource class            if  value    null                map put key  value                        return map      Replace KioskStatusResource to your class and Integer to your key class

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Here is what I have been using   public static HashMap lt String  Object gt  parse String json        JsonObject object    JsonObject  parser parse json       Set lt Map Entry lt String  JsonElement gt  gt  set   object entrySet        Iterator lt Map Entry lt String  JsonElement gt  gt  iterator   set iterator        HashMap lt String  Object gt  map   new HashMap lt String  Object gt         while  iterator hasNext              Map Entry lt String  JsonElement gt  entry   iterator next            String key   entry getKey            JsonElement value   entry getValue            if   value isJsonPrimitive                  map put key  parse value toString                else               map put key  value getAsString                         return map

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This is more of addendum to Kevin Dolan s answer than a complete answer  but I was having trouble extracting the type from the Number  This is my solution   private Object handlePrimitive JsonPrimitive json      if json isBoolean          return json getAsBoolean        else if json isString        return json getAsString           Number num   element getAsNumber       if num instanceof Integer       map put fieldName  num intValue         else if num instanceof Long       map put fieldName  num longValue         else if num instanceof Float       map put fieldName  num floatValue         else         Double      map put fieldName  num doubleValue

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I have overcome a similar problem with a Custom JsonDeSerializer  I tried to make it a bit generic but still not enough  It is a solution though that fits my needs    First of all you need to implement a new JsonDeserializer for Map objects   public class MapDeserializer lt T  U gt  implements JsonDeserializer lt Map lt T  U gt  gt    And the deserialize method will look similar to this   public Map lt T  U gt  deserialize JsonElement json  Type typeOfT  JsonDeserializationContext context          throws JsonParseException            if   json isJsonObject                  return null                     JsonObject jsonObject   json getAsJsonObject            Set lt Entry lt String  JsonElement gt  gt  jsonEntrySet   jsonObject entrySet            Map lt T  U gt  deserializedMap   new HashMap lt T  U gt              for  Entry lt java lang String  JsonElement gt  entry   jsonEntrySet                try                   U value   context deserialize entry getValue    getMyType                     deserializedMap put  T  entry getKey    value                 catch  Exception ex                    logger info  Could not deserialize map    ex                                    return deserializedMap          The con with this solution  is that my Map s key is always of Type  String   However by chaning some things someone can make it generic  In addition  i need to say  that the value s class should be passed in the constructor  So the method getMyType   in my code returns the type of the Map s values  which was passed in the constructor   You can reference this post How do I write a custom JSON deserializer for Gson  in order to learn more about custom deserializers

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I had the exact same question and ended up here   I had a different approach that seems much simpler  maybe newer versions of gson         Gson gson   new Gson        Map jsonObject    Map  gson fromJson data  Object class     with the following json        map-00          array-00            entry-00          entry-01                value    entry-02           The following      Map map00    Map  jsonObject get  map-00        List array00    List  map00 get  array-00        String value    String  map00 get  value        for  int i   0  i  lt  array00 size    i              System out println  map-00 array-00     i           array00 get i              System out println  map-00 value       value     outputs  map-00 array-00 0   entry-00 map-00 array-00 1   entry-01 map-00 value   entry-02   You could dynamically check using instanceof when navigating your jsonObject   Something like  Map json   gson fromJson data  Object class   if json get  field   instanceof Map      Map field    Map json get  field      else if  json get  field   instanceof List      List field    List json get  field            It works for me  so it must work for you  -

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HashMap lt String  String gt  jsonToMap String JsonDetectionString  throws JSONException        HashMap lt String  String gt  map   new HashMap lt String  String gt         Gson gson   new Gson         map    HashMap lt String  String gt   gson fromJson JsonDetectionString  map getClass          return map

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You can use this class instead     handles even lists   nested lists and json   public class Utility        public static Map lt String  Object gt  jsonToMap Object json  throws JSONException            if json instanceof JSONObject              return  jsonToMap   JSONObject json             else if  json instanceof String                        JSONObject jsonObject   new JSONObject  String json                return  jsonToMap  jsonObject                      return null              private static Map lt String  Object gt   jsonToMap  JSONObject json  throws JSONException           Map lt String  Object gt  retMap   new HashMap lt String  Object gt              if json    JSONObject NULL                retMap   toMap json                     return retMap              private static Map lt String  Object gt  toMap JSONObject object  throws JSONException           Map lt String  Object gt  map   new HashMap lt String  Object gt              Iterator lt String gt  keysItr   object keys            while keysItr hasNext                  String key   keysItr next                Object value   object get key                if value instanceof JSONArray                    value   toList  JSONArray  value                              else if value instanceof JSONObject                    value   toMap  JSONObject  value                             map put key  value                     return map              public static List lt Object gt  toList JSONArray array  throws JSONException           List lt Object gt  list   new ArrayList lt Object gt             for int i   0  i  lt  array length    i                  Object value   array get i               if value instanceof JSONArray                    value   toList  JSONArray  value                              else if value instanceof JSONObject                    value   toMap  JSONObject  value                             list add value                     return list              To convert your JSON string to hashmap use this     HashMap lt String  Object gt  hashMap   new HashMap lt  gt  Utility jsonToMap response

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I know this is a fairly old question  but I was searching for a solution to generically deserialize nested JSON to a Map lt String  Object gt   and found nothing   The way my yaml deserializer works  it defaults JSON objects to Map lt String  Object gt  when you don t specify a type  but gson doesn t seem to do this   Luckily you can accomplish it with a custom deserializer   I used the following deserializer to naturally deserialize anything  defaulting JsonObjects to Map lt String  Object gt  and JsonArrays to Object  s  where all the children are similarly deserialized   private static class NaturalDeserializer implements JsonDeserializer lt Object gt      public Object deserialize JsonElement json  Type typeOfT         JsonDeserializationContext context        if json isJsonNull    return null      else if json isJsonPrimitive    return handlePrimitive json getAsJsonPrimitive         else if json isJsonArray    return handleArray json getAsJsonArray    context       else return handleObject json getAsJsonObject    context         private Object handlePrimitive JsonPrimitive json        if json isBoolean          return json getAsBoolean        else if json isString          return json getAsString        else         BigDecimal bigDec   json getAsBigDecimal             Find out if it is an int type       try           bigDec toBigIntegerExact            try   return bigDec intValueExact              catch ArithmeticException e             return bigDec longValue            catch ArithmeticException e              Just return it as a double       return bigDec doubleValue                private Object handleArray JsonArray json  JsonDeserializationContext context        Object   array   new Object json size         for int i   0  i  lt  array length  i          array i    context deserialize json get i   Object class       return array        private Object handleObject JsonObject json  JsonDeserializationContext context        Map lt String  Object gt  map   new HashMap lt String  Object gt         for Map Entry lt String  JsonElement gt  entry   json entrySet          map put entry getKey    context deserialize entry getValue    Object class        return map          The messiness inside the handlePrimitive method is for making sure you only ever get a Double or an Integer or a Long  and probably could be better  or at least simplified if you re okay with getting BigDecimals  which I believe is the default   You can register this adapter like   GsonBuilder gsonBuilder   new GsonBuilder    gsonBuilder registerTypeAdapter Object class  new NaturalDeserializer     Gson gson   gsonBuilder create      And then call it like   Object natural   gson fromJson source  Object class     I m not sure why this is not the default behavior in gson  since it is in most other semi-structured serialization libraries

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Below is supported since gson 2 8 0  public static Type getMapType Class keyType  Class valueType       return TypeToken getParameterized HashMap class  keyType  valueType  getType       public static   lt K V gt  HashMap lt K V gt  fromMap String json  Class lt K gt  keyType  Class lt V gt  valueType       return gson fromJson json  getMapType keyType valueType

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This code works   Gson gson   new Gson     String json       k1     v1     k2     v2      Map lt String Object gt  map   new HashMap lt String Object gt     map    Map lt String Object gt   gson fromJson json  map getClass

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Here you go   import java lang reflect Type  import com google gson reflect TypeToken   Type type   new TypeToken lt Map lt String  String gt  gt      getType    Map lt String  String gt  myMap   gson fromJson    k1   apple   k2   orange     type

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Update for new Gson lib  You now can parse nested Json to Map directly  but you should be aware in case you try to parse Json to Map lt String  Object gt  type  it will raise exception  To fix this  just declare the result as LinkedTreeMap type   Example below  String nestedJSON    quot    quot id  quot    quot 1  quot    quot message  quot    quot web didload  quot    quot content  quot     quot success  quot  1   quot   Gson gson   new Gson    LinkedTreeMap result   gson fromJson nestedJSON   LinkedTreeMap class

[java] How can I convert JSON to a HashMap using Gson?

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