【转】 Json转换利器Gson之实例五-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]