Gson的使用--基础

翻译一篇来自javacreed的关于Gson的文章

基本用法

Gson gson = new GsonBuilder().create()
#或者 Gson gson = new Gson();
#Java Object转换为Json
gson.toJson("hello",System.out);
gson.toJson(123,System.out);

会输出
"hello"123

Java Object序列化到文件

FileWriter writer = new FileWriter("out.json");
Gson gson = new GsonBuilder().create();
gson.toJson("hell0",writer);
gson.toJson(123,writer);
writer.close();

从文件中读取Json并转换成Java Object

try(Reader reader = new 
InputStreamReader(this.class.getResourceAsStream("out.json"))){
  Gson gson = new GsonBuilder().create();
  Person p = gson.fromJson(reader, Person.class);
}

讨论一下嵌套的Json对象

{
  "name":"chico",
  "age":18,
  "exam":{
    "subject":"English",
    "score":100
  }
}

依然是Person类（必须有一个默认的构造函数）

public class Person{
  private String name;
  private int age;
  private Exam exam;
}

然后是Exam类

public class Exam{
  private String subject;
  private int score;
}

反序列化部分依然不变

try(Reader reader = new 
InputStreamRead(this.class.getResourceAsStream("out.json"))){
  Gson gson = new GsonBuilder().create();
  Person p = gson.fromJson(reader,Person.class);
}

常用的Gson解析类型

1.解析成list

[{"age":10,"name":"chico"},{"age":10,"name":"dong"}]

Gson gson = new GsonBuilder().create();
List<Person> list = gson.fromJson(jsonString,
  new TypeToke<List<Person>>(){}.getType());

2.解析成Map

{"p1":{"age":10,"name":"chico"},"p2":{"age":10,"name":"dong"}}

Gson gson = new GsonBuilder().create();
Map<String,Person> map =
  gson.fromJson(jsonString,
    new TypeToken<Map<String,Person>>(){}.getType());

3.解析节点

{"flag":true, "data":{"score":100,"name":"chico"}}

JsonParser  parser = new JsonParser();
JsonElement element = parser.parse(jsonString);
JsonObject root = element.getAsJsonObject();

JsonPrimitive jsonFlag = root.getAsJsonPrimitive("flag");
boolean flag = jsonFlag.getAsBoolean();

JsonObject jsonData = root.getAsJsonObject("data");
Data data = new Gson().fromJson(jsonData, Data.class);