注意：是否实例化Gson对象都可以实现转换的操作

Map to String

Map<String, String> data = new HashMap<>();
data.put("name", "edmond");
data.put("age", "22");
data.put("email", "bogendihong@163.com");
System.out.println(data); // {name=edmond, age=22, email=bogendihong@163.com}

String jsonStr = new Gson().toJson(data);
System.out.println(jsonStr); // {"name":"edmond","age":"22","email":"bogendihong@163.com"}

String to JsonObject

String jsonStr = "{\"name\":\"edmond\",\"age\":\"22\",\"email\":\"bogendihong@163.com\"}";
JsonObject jsonObject = new Gson().fromJson(jsonStr, JsonObject.class);
System.out.println(jsonObject); // {"name":"edmond","age":"22","email":"bogendihong@163.com"}

String to Bean类

class User {
    String name;
    int age;
    String email;
    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", email='" + email + '\'' +
                '}';
    }
}

String jsonStr = "{\"name\":\"edmond\",\"age\":\"22\",\"email\":\"bogendihong@163.com\"}";
User user = new Gson().fromJson(jsonStr, User.class);
System.out.println(user); // User{name='edmond', age=22, email='bogendihong@163.com'}

Map to JsonObject

Map<String, String> data = new HashMap<>();
        data.put("name", "edmond");
        data.put("age", "22");
        data.put("email", "bogendihong@163.com");
        System.out.println(data);

        // 转换为String
        String jsonStr = new Gson().toJson(data);
        // 将String再转化为JsonObject
        JsonObject jsonObject = new Gson().fromJson(jsonStr, JsonObject.class).getAsJsonObject();
        System.out.println(jsonObject); // {"name":"edmond","age":"22","email":"bogendihong@163.com"}

List<Map> to JsonArray

List<Map<String, Object>> list = new ArrayList<>();
        Map<String, Object> map1 = new HashMap<>();
        map1.put("name", "John");
        map1.put("age", 30);
        list.add(map1);

        Map<String, Object> map2 = new HashMap<>();
        map2.put("name", "Mary");
        map2.put("age", 25);
        list.add(map2);

        String jsonStr = new Gson().toJson(list);
        JsonElement element = new Gson().fromJson(jsonStr, JsonElement.class);
        JsonArray jsonArray = element.getAsJsonArray();
        System.out.println(jsonArray); // [{"name":"John","age":30},{"name":"Mary","age":25}]

Json数组字符串 to List

String jsonStr = "[{\"name\":\"John\",\"age\":30},{\"name\":\"Mary\",\"age\":25}]";
        JsonElement element = new Gson().fromJson(jsonStr, JsonElement.class);
        JsonArray jsonArray = element.getAsJsonArray();
        List<Map<String, Object>> list = new ArrayList<>();
        for (JsonElement jsonElement : jsonArray) {
            Map<String, Object> map = new Gson().fromJson(jsonElement, new TypeToken<Map<String, Object>>() {}.getType());
            list.add(map);
        }
        System.out.println(list); //[{name=John, age=30.0}, {name=Mary, age=25.0}]

Bean类 to JsonObject

User user = new User("edmond", 22, "bogendihong@163.com");
        JsonObject jsonObject = new Gson().toJsonTree(user).getAsJsonObject();
        System.out.println(jsonObject); // {"name":"edmond","age":22,"email":"bogendihong@163.com"}