Parcels.java

package com..github.gfx.toolbox;

import android.os.Parcel;
import android.os.Parcelable;

import com.google.android.gms.common.annotation.KeepName;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;

import java.io.IOException;
import java.io.StringReader;
import java.io.StringWriter;
import java.util.Collection;
import java.util.List;

/**
 * original is here https://github.com/square/flow/blob/master/flow-sample/src/main/java/com/example/flow/GsonParcer.java
 */
public class Parcels {
    private Parcels() {
    }

    public static <T> Parcelable wrap(T instance) {
        try {
            String json = encode(instance);
            return new Wrapper(json);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public static <T> Parcelable wrap(List<T> instance) {
        try {
            String json = encode(instance);
            return new Wrapper(json);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public static <T> T unwrap(Parcelable parcelable) {
        Wrapper wrapper = (Wrapper) parcelable;
        try {
            return decode(wrapper.json);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public static <T, U> T unwrap(Parcelable parcelable, TypeToken<U> token) {
        Wrapper wrapper = (Wrapper) parcelable;
        try {
            return decode(wrapper.json, token);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public static <T> List<T> unwrapList(Parcelable parcelable) {
        TypeToken<Collection<T>> typeToken = new TypeToken<Collection<T>>() {
        };
        return unwrap(parcelable, typeToken);
    }

    private static <T> String encode(T instance) throws IOException {
        StringWriter stringWriter = new StringWriter();
        JsonWriter writer = new JsonWriter(stringWriter);

        try {
            Class<?> type = instance.getClass();

            writer.beginObject();
            writer.name(type.getName());
            GsonHolder.GSON.toJson(instance, type, writer);
            writer.endObject();

            return stringWriter.toString();
        } finally {
            writer.close();
        }
    }

    private static <T> T decode(String json) throws IOException {
        JsonReader reader = new JsonReader(new StringReader(json));
        try {
            reader.beginObject();
            Class<?> type = Class.forName(reader.nextName());
            return GsonHolder.GSON.fromJson(reader, type);
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        } finally {
            reader.close();
        }
    }

    private static <T, U> T decode(String json, TypeToken<U> token) throws IOException {
        JsonReader reader = new JsonReader(new StringReader(json));
        try {
            reader.beginObject();
            reader.nextName();
            return GsonHolder.GSON.fromJson(reader, token.getType());
        } finally {
            reader.close();
        }
    }

    private static class Wrapper implements Parcelable {
        private final String json;

        private Wrapper(String json) {
            this.json = json;
        }

        @Override
        public int describeContents() {
            return 0;
        }

        @Override
        public void writeToParcel(Parcel out, int flags) {
            out.writeString(json);
        }

        @KeepName
        public static final Creator<Wrapper> CREATOR = new Creator<Wrapper>() {
            @Override
            public Wrapper createFromParcel(Parcel in) {
                String json = in.readString();
                return new Wrapper(json);
            }

            @Override
            public Wrapper[] newArray(int size) {
                return new Wrapper[size];
            }
        };
    }
}