GsonBilder注册TypeAdapter及处理Enum类型

枚举类型给我们的程序带来了好处,如何用Gson来实现与Json的互转呢?请看本文.

本文重点掌握如何自己写一个TypeAdapter及注册TypeAdapter和处理Enum类型.

实体类:

 public enum PackageState {
     PLAY, UPDATE, UPDATING, DOWNLOAD, DOWNLOADING,
 }

 public class PackageItem {
     private String name;
     private PackageState state;
     private String size;

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public PackageState getState() {
         return state;
     }

     public void setState(PackageState state) {
         this.state = state;
     }

     public String getSize() {
         return size;
     }

     public void setSize(String size) {
         this.size = size;
     }

     @Override
     public String toString() {
         return "PackageItem [name=" + name + ", size=" + size + ", state="
                 + state + "]";
     }
 }

自己写一个转换器实现JsonSerializer<T>接口和jsonDeserializer<T>接口:

 mport java.lang.reflect.Type;

 import com.google.gson.JsonDeserializationContext;
 import com.google.gson.JsonDeserializer;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonParseException;
 import com.google.gson.JsonPrimitive;
 import com.google.gson.JsonSerializationContext;
 import com.google.gson.JsonSerializer;

 public class EnumSerializer implements JsonSerializer<PackageState>,
         JsonDeserializer<PackageState> {

     // 对象转为Json时调用,实现JsonSerializer<PackageState>接口
     @Override
     public JsonElement serialize(PackageState state, Type arg1,
             JsonSerializationContext arg2) {
         return new JsonPrimitive(state.ordinal());
     }

     // json转为对象时调用,实现JsonDeserializer<PackageState>接口
     @Override
     public PackageState deserialize(JsonElement json, Type typeOfT,
             JsonDeserializationContext context) throws JsonParseException {
         if (json.getAsInt() < PackageState.values().length)
             return PackageState.values()[json.getAsInt()];
         return null;
     }

 }

测试类:

 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;

 public class GsonTest6 {

     public static void main(String[] args) {
         GsonBuilder gsonBuilder = new GsonBuilder();
         gsonBuilder.registerTypeAdapter(PackageState.class,
                 new EnumSerializer());
         Gson gson = gsonBuilder.create();
         PackageItem item = new PackageItem();
         item.setName("item_name");
         item.setSize("500M");
         item.setState(PackageState.UPDATING);// 这个 state是枚举值

         String s = gson.toJson(item);
         System.out.println(s);

         System.out.println("--------------------------------");

         PackageItem retItem = gson.fromJson(s, PackageItem.class);
         System.out.println(retItem);
     }
 }

输出结果(结果中已经将state的对应枚举类型转为了int类型):

 {"name":"item_name","state":2,"size":"500M"}
 --------------------------------
 PackageItem [name=item_name, size=500M, state=UPDATING]