Parsing JSON array into java util List with Gson

Question

I have a JsonObject named  mapping  with the following content          client    127 0 0 1        servers              8 8 8 8            8 8 4 4            156 154 70 1            156 154 71 1            I know I can get the array  servers  with   mapping get  servers   getAsJsonArray     And now I want to parse that JsonArray into a java util List     What is the easiest way to do this

User · Answer

Given you start with mapping get  servers   getAsJsonArray    if you have access to Guava Streams  you can do the below one-liner   List lt String gt  servers   Streams stream jsonArray iterator                                   map je - gt  je getAsString                                   collect Collectors toList       Note StreamSupport won t be able to work on JsonElement type  so it is insufficient

User · Answer

I read solution from official website of Gson at here  And this code for you       String json      client   127 0 0 1   servers    8 8 8 8   8 8 4 4   156 154 70 1   156 154 71 1           JsonObject jsonObject   new Gson   fromJson json  JsonObject class       JsonArray jsonArray   jsonObject getAsJsonArray  servers         String   arrName   new Gson   fromJson jsonArray  String   class        List lt String gt  lstName   new ArrayList lt  gt         lstName   Arrays asList arrName        for  String str   lstName            System out println str               Result show on monitor   8 8 8 8 8 8 4 4 156 154 70 1 156 154 71 1

User · Answer

Definitely the easiest way to do that is using Gson s default parsing function fromJson       There is an implementation of this function suitable for when you need to deserialize into any ParameterizedType  e g   any List   which is fromJson JsonElement json  Type typeOfT    In your case  you just need to get the Type of a List lt String gt  and then parse the JSON array into that Type  like this   import java lang reflect Type  import com google gson reflect TypeToken   JsonElement yourJson   mapping get  servers    Type listType   new TypeToken lt List lt String gt  gt       getType     List lt String gt  yourList   new Gson   fromJson yourJson  listType     In your case yourJson is a JsonElement  but it could also be a String  any Reader or a JsonReader   You may want to take a look at Gson API documentation

User · Answer

I was able to get the list mapping to work with just using  SerializedName for all fields   no logic around Type was necessary   Running the code - in step  4 below - through the debugger  I am able to observe that the List lt ContentImage gt  mGalleryImages object populated with the JSON data  Here s an example   1  The JSON            name    Some House        gallery                      description    Nice 300sqft  den jpg            photo url    image den jpg                            description    Floor Plan            photo url    image floor plan jpg                        2  Java class with the List  public class FocusArea         SerializedName  name       private String mName        SerializedName  gallery       private List lt ContentImage gt  mGalleryImages        3  Java class for the List items  public class ContentImage         SerializedName  description       private String mDescription        SerializedName  photo url       private String mPhotoUrl          getters setters          4  The Java code that processes the JSON      for  String key   focusAreaKeys             JsonElement sectionElement   sectionsJsonObject get key           FocusArea focusArea   gson fromJson sectionElement  FocusArea class

User · Answer

Below code is using com google gson JsonArray  I have printed the number of element in list as well as the elements in List  import java util ArrayList   import com google gson Gson  import com google gson JsonArray  import com google gson JsonObject  import com google gson JsonParser    public class Test        static String str                         client     127 0 0 1                       servers                            8 8 8 8                           8 8 4 4                           156 154 70 1                           156 154 71 1                                                     public static void main String   args               TODO Auto-generated method stub         try                JsonParser jsonParser   new JsonParser                JsonObject jo    JsonObject jsonParser parse str               JsonArray jsonArr   jo getAsJsonArray  servers                  jsonArr              Gson googleJson   new Gson                ArrayList jsonObjList   googleJson fromJson jsonArr  ArrayList class               System out println  List size is     jsonObjList size                         System out println  List Elements are      jsonObjList toString                 catch  Exception e                   TODO Auto-generated catch block             e printStackTrace                         OUTPUT  List size is   4  List Elements are     8 8 8 8  8 8 4 4  156 154 70 1  156 154 71 1

[java] Parsing JSON array into java.util.List with Gson

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