How to Parse JSON Array with Gson

Question

I want to parse JSON arrays and using gson  Firstly  I can log JSON output  server is responsing to client clearly    Here is my JSON output                         id    1              title   sample title                                               id    2              title   sample title                                          I tried this structure for parsing  A class  which depends on single array and ArrayList for all JSONArray    public class PostEntity          private ArrayList lt Post gt  postList   new ArrayList lt Post gt            public List lt Post gt  getPostList                 return postList                  public void setPostList List lt Post gt  postList                this postList    ArrayList lt Post gt  postList                 Post class    public class Post          private String id        private String title            getters  amp  setters         When I try to use gson no error  no warning and no log    GsonBuilder gsonb   new GsonBuilder     Gson gson   gsonb create      PostEntity postEnt   JSONObject jsonObj   new JSONObject jsonOutput    postEnt   gson fromJson jsonObj toString    PostEntity class     Log d  postLog   postEnt getPostList   get 0  getId       What s wrong  how can I solve

User · Answer

id    1              title   sample title                                               id    2              title   sample title                                          Check Easy code for this output   Gson gson new GsonBuilder   create                    List lt Post gt  list  Arrays asList gson fromJson yourResponse toString Post   class

User · Answer

To conver in Object Array   Gson gson new Gson    ElementType    refVar gson fromJson jsonString ElementType   class     To convert as post type  Gson gson new Gson    Post    refVar gson fromJson jsonString Post   class     To read it as List of objects TypeToken can be used  List lt Post gt  posts  List lt Post gt  gson fromJson jsonString                        new TypeToken lt List lt Post gt  gt      getType

User · Answer

You can parse the JSONArray directly  don t need to wrap your Post class with PostEntity one more time and don t need new JSONObject   toString   either   Gson gson   new Gson    String jsonOutput    Your JSON String   Type listType   new TypeToken lt List lt Post gt  gt      getType    List lt Post gt  posts   gson fromJson jsonOutput  listType     Hope that helps

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I was looking for a way to parse object arrays in a more generic way  here is my contribution   CollectionDeserializer java   import java lang reflect ParameterizedType  import java lang reflect Type  import java util ArrayList  import java util Collection  import java util Iterator   import com google gson Gson  import com google gson JsonArray  import com google gson JsonDeserializationContext  import com google gson JsonDeserializer  import com google gson JsonElement  import com google gson JsonParseException   public class CollectionDeserializer implements JsonDeserializer lt Collection lt   gt  gt          Override     public Collection lt   gt  deserialize JsonElement json  Type typeOfT              JsonDeserializationContext context  throws JsonParseException           Type realType     ParameterizedType typeOfT  getActualTypeArguments   0            return parseAsArrayList json  realType                          param serializedData         param type         return              SuppressWarnings  unchecked       public  lt T gt  ArrayList lt T gt  parseAsArrayList JsonElement json  T type            ArrayList lt T gt  newArray   new ArrayList lt T gt             Gson gson   new Gson             JsonArray array  json getAsJsonArray            Iterator lt JsonElement gt  iterator   array iterator             while iterator hasNext                 JsonElement json2    JsonElement iterator next                T object    T  gson fromJson json2   Class lt   gt  type               newArray add object                      return newArray             JSONParsingTest java   public class JSONParsingTest        List lt World gt  worlds        Test     public void grantThatDeserializerWorksAndParseObjectArrays             String worldAsString       worlds                         name     name1     id   1                      name     name2     id   2                      name     name3     id   3                            GsonBuilder builder   new GsonBuilder            builder registerTypeAdapter Collection class  new CollectionDeserializer             Gson gson   builder create            Object decoded   gson fromJson  String worldAsString  JSONParsingTest class            assertNotNull decoded           assertTrue JSONParsingTest class isInstance decoded             JSONParsingTest decodedObject    JSONParsingTest decoded          assertEquals 3  decodedObject worlds size             assertEquals  Long 2L  decodedObject worlds get 1  getId               World java   public class World       private String name      private Long id       public void setName String name            this name   name             public String getName             return name             public Long getId             return id             public void setId Long id            this id   id

User · Answer

Some of the answers of this post are valid  but using TypeToken  the Gson library generates a Tree objects whit unreal types for your application   To get it I had to read the array and convert one by one the objects inside the array  Of course this method is not the fastest and I don t recommend to use it if you have the array is too big  but it worked for me   It is necessary to include the Json library in the project  If you are developing on Android  it is included          Convert JSON string to a list of objects     param sJson String sJson to be converted     param tClass Class     return List lt T gt  list of objects generated or null if there was an error     public static  lt T gt  List lt T gt  convertFromJsonArray String sJson  Class lt T gt  tClass        try          Gson gson   new Gson            List lt T gt  listObjects   new ArrayList lt  gt                read each object of array with Json library         JSONArray jsonArray   new JSONArray sJson           for int i 0  i lt jsonArray length    i                    get the object             JSONObject jsonObject   jsonArray getJSONObject i                  get string of object from Json library to convert it to real object with Gson library             listObjects add gson fromJson jsonObject toString    tClass                         return list with all generated objects         return listObjects        catch Exception e           e printStackTrace                 error  return null     return null

User · Answer

you can get List value without using Type object   EvalClassName   evalClassName  ArrayList lt EvalClassName gt  list  evalClassName  new Gson   fromJson JSONArrayValue toString   EvalClassName   class   list   new ArrayList lt  gt  Arrays asList evalClassName      I have tested it and it is working

User · Answer

Type listType   new TypeToken lt List lt Post gt  gt       getType    List lt Post gt  posts   new Gson   fromJson jsonOutput toString    listType

User · Answer

You can easily do this in Kotlin using the following code   val fileData    your json string  val gson   GsonBuilder   create   val packagesArray   gson fromJson fileData   Array lt YourClass gt   class java  toList     Basically  you only need to provide an Array of YourClass objects

User · Answer

in Kotlin   val jsonArrayString    quot   A   B   C   quot   val gson   Gson    val listType  Type   object   TypeToken lt List lt String  gt   gt       getType    val stringList   List lt String gt    gson fromJson                              jsonArrayString                              listType

[java] How to Parse JSON Array with Gson

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