在单个Java对象中反序列化JSON的父级和子级节点数据

Question

I am new to Java and I am facing problem converting json data to java object. Lets say my json format is

{
  "totalSize" : 2,
  "done" : true,     
  "Id" : "xyz",
  "Name" : "P0000005239",
    "child" : {      
      "Type" : "someType",
      "Region" : "someRegion",      
      "Name" : "C001906"      
    },
    "Address_1" : "Address_1",
    "Address_2" : "Address_1" 
  }

If my java class structure is like this, deserialization is working

//Working class Structure
class Demo{
   int total_Size;
   boolean flag_done;
   String ID;
   String p_name;
   Child child; 
   String Address1;
   String Address2;

   //getter and setter
  }

But my class structure is(to which I am not able to map my json)

//Not Working
class Demo{
    int total_Size;
    boolean flag_done;
    String ID;
    String p_name;
    String c_type;
    String  c_region;
    String c_name;   
    String Address1;
    String Address2;

    //getter and setter
   }

Error

Invocation of init method failed; nested exception is 
com.google.gson.JsonParseException: The JsonDeserializer        
com.google.gson.DefaultTypeAdapters$CollectionTypeAdapter@4b28f983 failed to 
deserialized json object

How to create java object from json having all the data in single class(ie parent and child node data in single class without declaring separate child class)

I am using GSON with @SerializedName annotation for converting json into java object. Please let me know if you need more detail.

Answer 1

Try using fasterxml jackson

For this purpose you need to pass additional info in JSON:

@JsonTypeInfo(use=JsonTypeInfo.Id.NAME, 
  include=JsonTypeInfo.As.PROPERTY, property="@type")
class Base {
...
}

Then on serialization it will add @type field:

objectMapper.registerSubtypes(
        new NamedType(ConcreteAAdapter.class, "ConcreteA"),
        new NamedType(ConcreteBAdapter.class, "ConcreteB"),
        new NamedType(ConcreteCAdapter.class, "ConcreteC")
        );

// note, that for lists you need to pass TypeReference explicitly

objectMapper.writerWithType(new TypeReference<List<Base>>() {})
 .writeValueAsString(someList);




{
  "@type" : "ConcreteA",
  ...
  }
on deserialization it will be:



objectMapper.registerSubtypes(
        new NamedType(ConcreteA.class, "ConcreteA"),
        new NamedType(ConcreteB.class, "ConcreteB"),
        new NamedType(ConcreteC.class, "ConcreteC")
        );



objectMapper.readValue(....)

More here: http://wiki.fasterxml.com/JacksonPolymorphicDeserialization