Gson转换|Gson转换 — json数据转换为Object实体公共方法 Gson转换—json数据转换为Objec

Gson转换 — json数据转换为Object实体

最近在做远程接口调用时，需要对数据进行加解密，因此返回的参数统一为以下json格式

{ "code":0, "msg":"成功", "sign":"abcdefghijkl", "timestamp":1491897441000, "data":{} }

首先，我们假设传输过程中的对象实体是
user.java

public class User {private int id; private String name; ...省略get set...@Override public String toString() { return "User [id=" + id + ", name=" + name + "]"; }}

当返回的数据转成对象时，可能存在三种情况：

1. User 对象 2. List list 对象 3. Page page

Page.java

public class Page {private int page; private int size; private int total; private List data; ...省略 get set...@Override public String toString() { return "User [page=" + page + ", size=" + size + ", total=" + total + ", data="https://www.it610.com/article/+ data +"]"; }}

因此返回data的json可能为以下三种：
1.对象实体的json json -> User

{ "id":1, "name":"eric" }

2.对象实体列表的json json -> List list

[ { "id":1, "name":"eric" }, { "id":2, "name":"john" } ]

3.分页的实体json json -> Page page

{ "page":1, "size":10, "total":2, "data":[ { "id":1, "name":"eric" }, { "id":2, "name":"john" } ] }

因此我们需要写一个公共类解决上述转换问题
GsonUtils.java

public class GsonUtils {private GsonUtils() {}public static T fromJson(String json,Class type){ Gson gson = new Gson(); return gson.fromJson(json,type); }public static List listFromJson(String json){ Gson gson = new Gson(); return gson.fromJson(json, new TypeToken>(){}.getType()); }}

测试：

public class Main {public static void main(String[] args) {String json1 = "{\"id\":1,\"name\":\"eric\"}"; String json2 = "[{\"id\":1,\"name\":\"eric\"},{\"id\":2,\"name\":\"john\"}]"; String json3 = "{\"page\":1,\"size\":10,\"total\":2,\"data\":[{\"id\":1,\"name\":\"eric\"},{\"id\":2,\"name\":\"john\"}]}"; User user = GsonUtils.fromJson(json1, User.class); List lists = GsonUtils.listFromJson(json2); Page page = GsonUtils.fromJson(json3, Page.class); System.out.println("user:" + user); System.out.println("lists:" + lists); System.out.println("page:" + page); }}

运行后的结果：

user:User [id=1, name=eric] lists:[{id=1.0, name=eric}, {id=2.0, name=john}] page:User [page=1, size=10, total=2, list=[{id=1.0, name=eric}, {id=2.0, name=john}]]

此时已经成功将三种格式的json转化为Object，但是这里有个问题如下：如果我们用一下方法获取user，就会报错，因为处理Java反射TypeToken泛型运行时类型擦除

User user = lists.get(0);

Exception in thread "main" java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to swun.test.entity.User at swun.test.Main.main(Main.java:27)

因此我们将方法listFromJson修改为

public static List listFromJson(String json,Type type){ Gson gson = new Gson(); return gson.fromJson(json, type); }

在调用的时候，将具体的Type传入

public class Main {public static void main(String[] args) {String json1 = "{\"id\":1,\"name\":\"eric\"}"; String json2 = "[{\"id\":1,\"name\":\"eric\"},{\"id\":2,\"name\":\"john\"}]"; String json3 = "{\"page\":1,\"size\":10,\"total\":2,\"data\":[{\"id\":1,\"name\":\"eric\"},{\"id\":2,\"name\":\"john\"}]}"; User user = GsonUtils.fromJson(json1, User.class); List lists = GsonUtils.listFromJson(json2,new TypeToken>(){}.getType()); Page page = GsonUtils.fromJson(json3, Page.class); System.out.println("user:" + user); System.out.println("lists:" + lists); System.out.println("page:" + page); User user1 = lists.get(0); System.out.println("user1:" + user1); }}

【Gson转换|Gson转换 — json数据转换为Object实体公共方法】运行结果如下：

user:User [id=1, name=eric] lists:[User [id=1, name=eric], User [id=2, name=john]] page:User [page=1, size=10, total=2, data=https://www.it610.com/article/[{id=1.0, name=eric}, {id=2.0, name=john}]] user1:User [id=1, name=eric]