How to convert hashmap to JSON object in Java

Question

How to convert or cast hashmap to JSON object in Java  and again convert JSON object to JSON string

User · Answer

Late to the party but here is my GSON adhoc writer for serializing hashmap. I had to write map of key-value pairs as json string attributes, expect one specific to be integer type. I did not want to create custom JavaBean wrapper for this simple usecase.

GSON JsonWriter class is easy to use serializer class containing few strongly typed writer.value() functions.

// write Map as JSON document to http servlet response
Map<String,String> sd = DAO.getSD(123);
res.setContentType("application/json; charset=UTF-8");
res.setCharacterEncoding("UTF-8");
JsonWriter writer = new JsonWriter(new OutputStreamWriter(res.getOutputStream(), "UTF-8"));
writer.beginObject();
for(String key : sd.keySet()) {
    String val = sd.get(key);
    writer.name(key);
    if (key.equals("UniqueID") && val!=null)
        writer.value(Long.parseLong(val));
    else
        writer.value(val);
}
writer.endObject();
writer.close();

If none of the custom types be needed I could have just use toJson() function. gson-2.2.4.jar library is just under 190KB without any brutal dependencies. Easy to use on any custom servlet app or standalone application without big framework integrations.

Gson gson = new Gson(); 
String json = gson.toJson(myMap);

User · Answer

we use Gson   Gson gson   new Gson    Type gsonType   new TypeToken lt HashMap gt      getType    String gsonString   gson toJson elements gsonType

User · Answer

Example using json   Map lt String  Object gt  data   new HashMap lt String  Object gt         data put   name    Mars         data put   age   32        data put   city    NY         JSONObject json   new JSONObject        json putAll  data        System out printf   JSON   s   json toString 2       output    JSON       age   32     name    Mars      city    NY      You can also try to use Google s GSON Google s GSON is the best library available to convert Java Objects into their JSON representation   http   code google com p google-gson

User · Answer

Gson way for a bit more complex maps and lists using TypeToken getParameterized method   We have a map that looks like this   Map lt Long  List lt NewFile gt  gt  map    We get the Type using the above mentioned getParameterized method like this   Type listOfNewFiles   TypeToken getParameterized ArrayList class  NewFile class  getType    Type mapOfList   TypeToken getParameterized LinkedHashMap class  Long class  listOfNewFiles  getType      And then use the Gson object fromJson method like this using the mapOfList object like this   Map lt Long  List lt NewFile gt  gt  map   new Gson   fromJson fileContent  mapOfList     The mentioned object NewFile looks like this   class NewFile       private long id      private String fileName       public void setId final long id                this id   id             public void setFileName final String fileName                this fileName   fileName            The deserialized JSON looks like this    x000D   x000D    x000D     1     x000D        x000D         id   12232  x000D         fileName    test html  x000D         x000D        x000D         id   12233  x000D         fileName    file txt  x000D         x000D        x000D         id   12234  x000D         fileName    obj json  x000D        x000D       x000D    2     x000D        x000D         id   122321  x000D         fileName    test2 html  x000D         x000D        x000D         id   122332  x000D         fileName    file2 txt  x000D         x000D        x000D         id   122343  x000D         fileName    obj2 json  x000D        x000D      x000D    x000D   x000D   x000D

User · Answer

You can use Gson  This library provides simple methods to convert Java objects to JSON objects and vice-versa    Example   GsonBuilder gb   new GsonBuilder    Gson gson   gb serializeNulls   create    gson toJson object     You can use a GsonBuilder when you need to set configuration options other than the default  In the above example  the conversion process will also serialize null attributes from object   However  this approach only works for non-generic types  For generic types you need to use toJson object  Type    More information about Gson here   Remember that the object must implement the Serializable interface

User · Answer

Underscore-java library can convert hash map or array list to json and vice verse   import com github underscore lodash U  import java util     public class Main        public static void main String   args             Map lt String  Object gt  map   new LinkedHashMap lt  gt             map put  1    a            map put  2    b             System out println U toJson map                                1    a                  2    b

User · Answer

If you don t really need HashMap then you can do something like that   String jsonString   new JSONObject        put  firstName   user firstName     put  lastName   user lastName      toString      Output        firstName    John      lastName    Doe

User · Answer

I found another way to handle it   Map obj new HashMap        obj put  name   sonoo        obj put  age  new Integer 27        obj put  salary  new Double 600000       String jsonText   JSONValue toJSONString obj     System out print jsonText     Hope this helps   Thanks

User · Answer

You can convert Map to JSON using Jackson as follows   Map lt String Object gt  map   new HashMap lt  gt       You can convert any Object  String   value1   new String      value11    value12    value13     String   value2   new String      value21    value22    value23     map put  key1   value1   map put  key2   value2   map put  key3   string1    map put  key4   string2     String json   new ObjectMapper   writeValueAsString map   System out println json     Maven Dependencies for Jackson      lt dependency gt       lt groupId gt com fasterxml jackson core lt  groupId gt       lt artifactId gt jackson-core lt  artifactId gt       lt version gt 2 5 3 lt  version gt       lt scope gt compile lt  scope gt   lt  dependency gt    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 5 3 lt  version gt       lt scope gt compile lt  scope gt   lt  dependency gt    If you are using JSONObject library  you can convert map to JSON as follows   Map lt String  Object gt  map   new HashMap lt  gt        Convert a map having list of values  String   value1   new String      value11    value12    value13     String   value2   new String      value21    value22    value23     map put  key1   value1   map put  key2   value2    JSONObject json   new JSONObject map   System out println json     Maven Dependencies for JSONObject     lt dependency gt       lt groupId gt org json lt  groupId gt       lt artifactId gt json lt  artifactId gt       lt version gt 20140107 lt  version gt   lt  dependency gt    Hope this will help  Happy coding

User · Answer

If you use complex objects  you should apply enableComplexMapKeySerialization    as stated in https   stackoverflow com a 24635655 2914140 and https   stackoverflow com a 26374888 2914140   Gson gson   new GsonBuilder   enableComplexMapKeySerialization   create    Map lt Point  String gt  original   new LinkedHashMap lt Point  String gt     original put new Point 5  6    a    original put new Point 8  8    b    System out println gson toJson original      Output will be        5 6     a      8 8     b

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If you need use it in the code   Gson gsone   new Gson    JsonObject res   gsone toJsonTree sqlParams  getAsJsonObject

User · Answer

I m using Alibaba fastjson  easy and simple    lt dependency gt       lt groupId gt com alibaba lt  groupId gt       lt artifactId gt fastjson lt  artifactId gt       lt version gt VERSION CODE lt  version gt   lt  dependency gt    and import   import com alibaba fastjson JSON    Then   String text   JSON toJSONString obj      serialize VO vo   JSON parseObject          VO class     unserialize   Everything is ok

User · Answer

Gson can also be used to serialize arbitrarily complex objects    Here is how you use it    Gson gson   new Gson     String json   gson toJson myObject      Gson will automatically convert collections to JSON arrays  Gson can serialize private fields and automatically ignores transient fields

User · Answer

You can just enumerate the map and add the key-value pairs to the JSONObject  Method     private JSONObject getJsonFromMap Map lt String  Object gt  map  throws JSONException       JSONObject jsonData   new JSONObject        for  String key   map keySet              Object value   map get key           if  value instanceof Map lt      gt                 value   getJsonFromMap  Map lt String  Object gt   value                     jsonData put key  value             return jsonData

User · Answer

For those using org json simple JSONObject  you could convert the map to Json String and parse it to get the JSONObject   JSONObject object    JSONObject  new JSONParser   parse JSONObject toJSONString map

User · Answer

This solution works with complex JSONs   public Object toJSON Object object  throws JSONException       if  object instanceof HashMap            JSONObject json   new JSONObject            HashMap map    HashMap  object          for  Object key   map keySet                  json put key toString    toJSON map get key                       return json        else if  object instanceof Iterable            JSONArray json   new JSONArray            for  Object value     Iterable  object                 json put toJSON value                      return json            else           return object

User · Answer

import org json JSONObject       HashMap lt Object  Object gt  map   new HashMap lt  gt         String   list   Grader   Participant        String   list1   Assistant   intern        map put  TeachingAssistant  list       map put  Writer  list1       JSONObject jsonObject   new JSONObject map       System out printf jsonObject toString             Result    TeachingAssistant    Grader   Participant    Writer    Assistant   intern

User · Answer

First convert all your objects into valid Strings  HashMap lt String  String gt  params   new HashMap lt  gt     params put  arg1     lt b gt some text lt  b gt     params put  arg2   someObject toString       Then insert the entire map into a org json JSONObject  JSONObject postData   new JSONObject params     Now you can get the JSON by simply calling the object s toString  postData toString       arg1    lt b gt some text lt   b gt    arg2   object output     Create a new JSONObject  JSONObject o   new JSONObject postData toString       Or as a byte array for sending over HTTP  postData toString   getBytes  UTF-8

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In my case I didn t want any dependancies  Using Java 8 you can get JSON as a string this simple   Map lt String  Object gt  map   new HashMap lt  gt     map put  key    value    map put  key2    value2    String json       map entrySet   stream        map e - gt        e getKey                    String valueOf e getValue                 collect Collectors joining

User · Answer

This is typically the work of a Json library  you should not try to do it yourself  All json libraries should implement what you are asking for  and you can find a list of Java Json libraries on json org  at the bottom of the page

User · Answer

You can use XStream - it is really handy  See the examples here  package com thoughtworks xstream json test   import com thoughtworks xstream XStream  import com thoughtworks xstream io json JettisonMappedXmlDriver   public class WriteTest        public static void main String   args           HashMap lt String String gt  map   new HashMap lt String String gt           map add  1    a          map add  2    b          XStream xstream   new XStream new JettisonMappedXmlDriver            System out println xstream toXML map

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Better be late than never  I used GSON to convert list of HashMap to string if in case you want to have a serialized list   List lt HashMap lt String  String gt  gt  list   new ArrayList lt  gt     HashMap lt String String gt  hashMap   new HashMap lt  gt     hashMap add  key    value    hashMap add  key    value    hashMap add  key    value    list add hashMap    String json   new Gson   toJson list     This json produces    key   value   key   value   key   value

User · Answer

If you are using JSR 374  Java API for JSON Processing   javax json   This seems to do the trick       JsonObjectBuilder job   Json createObjectBuilder  Map lt String  Object gt   obj       JsonObject jsonObject   job build

User · Answer

If you are using net sf json JSONObject then you won t find a JSONObject map  constructor in it  You have to use the public static JSONObject fromObject  Object object   method  This method accepts JSON formatted strings  Maps  DynaBeans and JavaBeans   JSONObject jsonObject   JSONObject fromObject myMap

User · Answer

No need for Gson or JSON parsing libraries  Just using new JSONObject Map lt String  JSONObject gt   toString    e g          convert target map to JSON string        param map the target map     return JSON string of the map      NonNull public String toJson  NonNull Map lt String  Target gt  map        final Map lt String  JSONObject gt  flatMap   new HashMap lt  gt         for  String key   map keySet              try               flatMap put key  toJsonObject map get key               catch  JSONException e                e printStackTrace                        try              2 indentSpaces for pretty printing         return new JSONObject flatMap  toString 2         catch  JSONException e            e printStackTrace            return

User · Answer

I faced a similar problem when deserializing the Response from custom commands in selenium  The response was json  but selenium internally translates that into a java util HashMap String  Object   If you are familiar with scala and use the play-API for JSON  you might benefit from this   import play api libs json  JsValue  Json  import scala collection JavaConversions mapAsScalaMap   object JsonParser      def parse map  Map String  Any    JsValue         val values   for  key  value   lt - map  yield         value match           case m  java util Map String      unchecked   gt  Json obj key - gt  parse m toMap           case m  Map String      unchecked   gt  Json obj key - gt  parse m           case int  Int   gt  Json obj key - gt  int          case str  String   gt  Json obj key - gt  str          case bool  Boolean   gt  Json obj key - gt  bool                     values foldLeft Json obj     temp  obj    gt          temp deepMerge obj                 Small code description   The code recursively traverses through the HashMap until basic types  String  Integer  Boolean  are found  These basic types can be directly wrapped into a JsObject  When the recursion is unfolded  the deepmerge concatenates the created objects     unchecked  takes care of type erasure warnings

User · Answer

Here my single-line solution with GSON   myObject   new Gson   fromJson new Gson   toJson myHashMap   MyClass class

User · Answer

this works for me    import groovy json JsonBuilder properties   new Properties   properties put  name    zhangsan    println new JsonBuilder properties  toPrettyString

User · Answer

You can use   new JSONObject map     Caution  This will only work for a Map lt String  String gt    Other functions you can get from its documentation http   stleary github io JSON-java index html

[java] How to convert hashmap to JSON object in Java

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