Gson解析（6）——註冊TypeAdapter及處理Enum類型

枚舉類型給我們的程序帶來了好處,如何用Gson來實現與Json的互轉呢?請看本文.

本文重點掌握如何自己寫一個TypeAdapter及註冊TypeAdapter和處理Enum類型.

實體類:

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 + "]";
    }
}

自己寫一個轉換器實現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> {

    // 對象轉爲Json時調用,實現JsonSerializer<PackageState>接口
    @Override
    public JsonElement serialize(PackageState state, Type arg1,
            JsonSerializationContext arg2) {
        return new JsonPrimitive(state.ordinal());
    }

    // json轉爲對象時調用,實現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;
    }

}

測試類:

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);// 這個 state是枚舉值

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

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

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

輸出結果(結果中已經將state的對應枚舉類型轉爲了int類型):

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

文章轉自：http://blog.csdn.net/lk_blog/article/details/7685347

感謝博主的無私分享！