JSON parsing class library Gson (2)---Generic object map, list, and JSON string interchange

JSON parsing class library Gson (2)---Generic object map, list, and JSON string interchange

---Gson class library to learn, generate and parse JSON data, and turn JSON strings to and from Java objects

First, the preface
This article extends the previous article and continues to introduce basic gson usage. In this article, we will describe how to implement Java generic objects such as map<>,list<> and JSON strings.
second, the basic use of Gson

serialization and deserialization of generic collection-type objects --------------------------------------------------------------------------------- ------------------ ◇ situation 1 "non-generic": Serialization and deserialization of Java arrays Unlike generics, arrays are not generics.
java Array = = = "JSON string JSON string = =" Java array

       
       
        
        GsonGson =NewGsonbuilder ()//. Setpretty Printing ()//Format output (serialization). Setdateformat ("Yyyy-mm-dd HH:mm:ss"
        
        

        
        
        
        
         
         //Serialization date formatted output. Create (); User user1 =NewUser ("1", "Wang Chongyang",NewDate ()); User user2 =NewUser ("2", "Guo Jing",NewDate ()); User User3 =NewUser ("3", "Huang Rong",NewDate ()); User[] Usersarray = {user1, user2, user3};
        
        
        
        
         
          Array Object/**
        
        
        
        
         
         * Serialized Array * *
        
        
        
        
         
         String jsonarrstring = Gson.tojson (Usersarray); System. out. println ("Array serialization  =="   " + jsonarrstring");
        
        
        
        
         
         /**  *  Array serialization  == " [   {     "I
        
        
        
        
         
         D ": " 1 ",     " name ": " Wang Chongyang ",
        
        
        
        
         
              "Birthday":  "2017-05-03 16:06:50"   }, &nbsp
        
        
        
        
         
         ;  {     "id":  "2",
        
        
        
        
         
              "name":  "Guo Jing",      "Birthday":  "2017-05-03 16:06:50"   },
        
        
        
        
         
           {      "id":  "3",      "NA" Me ": " Huang Rong ",     " Birthday ": " 2017-05-0
        
        
        
        
         
         3 16:06:50 "  }
        
        

        
        
         
         ]  */ /** a  * json string to deserialize an array of objects, the type parameters of which the arrays are deserialized can be straight
         
          Class that is connected to an array, asUser[].class* * user[] Usersarr = Gson.fromjson (jsonarrstring, user[).class); for (int i = 0; i < usersarr.length; i++) {Useru1 = Usersarr[i]; System. out. println ("JSON string deserializes an array of objects = =" + u1); * * User Object = = "User [id=1, name= Wang Chong, birthday=wed May 03 16:1 4:14 CST 2017] User Object = = "User [id=2, name= Guo Jing, birthday=wed May 16:14:14 CST 2017] User Object = = "User [id=3, name= Huang Rong, bi
        
        
        
        Rthday=wed may 16:14:14 CST 2017] */ }

Attention: The byte-code file of an array can reflect the object type in a specific array, but list<user> cannot be used directly with List<user>.class or List.class. Because generics compile to bytecode are erase type,list<user> and list<dept> are completely the same after being translated into bytecode, no difference.
The generic collection has to use the new TypeToken (list<user>) {}.gettype () as the second parameter of the inverse sequence.

◇ Case 2:java Map serialization and deserialization
Entity classes: