Json转换利器Gson之实例六-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:

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public enum PackageState {

PLAY, UPDATE, UPDATING, DOWNLOAD, DOWNLOADING,

}

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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:

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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:

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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):

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{"name":"item_name","state":2,"size":"500M"}

--------------------------------

PackageItem [name=item_name, size=500M, state=UPDATING]

实例源码：Gson