How to deserialize a list using GSON or another JSON library in Java

Question

I can serialize a List lt Video gt  in my servlet on GAE  but I can t deserialize it   What am I doing wrong   This is my class Video in GAE  which is serialized   package legiontube   import java util Date   import javax jdo annotations IdGeneratorStrategy  import javax jdo annotations IdentityType  import javax jdo annotations PersistenceCapable  import javax jdo annotations Persistent  import javax jdo annotations PrimaryKey    PersistenceCapable identityType   IdentityType APPLICATION  public class Video         PrimaryKey     private String id        Persistent     private String titulo        Persistent     private String descricao        Persistent     private Date date       public Video        public Video String id  String titulo  String descricao  Date date        super      this id   id    this titulo   titulo    this descricao   descricao    this date   date       public String getId       return id       public void setId String id      this id   id       public String getTitulo       return titulo       public void setTitulo String titulo      this titulo   titulo       public String getDescricao       return descricao       public void setDescricao String descricao      this descricao   descricao       public Date getDate       return date       public void setDate Date date      this date   date          This is my class Video in my other application  where I try to deserialize   package classes   import java util Date   public class Video    private String id   private String titulo   private String descricao   private Date date    public Video String id  String titulo  String descricao  Date date        super      this id   id    this titulo   titulo    this descricao   descricao    this date   date       public String getId       return id      public void setId String id      this id   id      public String getTitulo       return titulo      public void setTitulo String titulo      this titulo   titulo      public String getDescricao       return descricao      public void setDescricao String descricao      this descricao   descricao      public Date getDate       return date      public void setDate Date date      this date   date

User · Answer

Be careful using the answer provide by  DevNG  Arrays asList   returns internal implementation of ArrayList that doesn t implement some useful methods like add    delete    etc  If you call them an UnsupportedOperationException will be thrown  In order to get real ArrayList instance you need to write something like this   List lt Video gt    new ArrayList lt  gt  Arrays asList videoArray

User · Answer

I recomend this one-liner List lt Video gt  videos   Arrays asList new Gson   fromJson json  Video   class     Warning  the list of videos  returned by Arrays asList is immutable - you can t insert new values  If you need to modify it  wrap in new ArrayList lt  gt         Reference   Method Arrays asList Constructor Gson Method Gson fromJson  source json may be of type JsonElement  Reader  or String  Interface List JLS - Arrays JLS - Generic Interfaces

User · Answer

Another way is to use an array as a type  e g    Video   videoArray   gson fromJson json  Video   class     This way you avoid all the hassle with the Type object  and if you really need a list you can always convert the array to a list  e g    List lt Video gt  videoList   Arrays asList videoArray     IMHO this is much more readable     In Kotlin this looks like this   Gson   fromJson jsonString  Array lt Video gt   class java    To convert this array into List  just use  toList   method

User · Answer

With Gson  you d just need to do something like   List lt Video gt  videos   gson fromJson json  new TypeToken lt List lt Video gt  gt      getType       You might also need to provide a no-arg constructor on the Video class you re deserializing to

[java] How to deserialize a list using GSON or another JSON library in Java?

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