【数据解析入门系列】-初探Json

定义

JSON是一种轻量级的数据交换格式，采用完全独立于编程语言的文本格式来存储和表示数据。简洁和清晰的层次结构使得 JSON 成为理想的数据交换语言。 易于阅读和编写，同时也易于解析和生成，并有效地提升网络传输效率。

语法

数据在名称/值对中

数据由逗号分隔

花括号保存对象

方括号保存数组

{
　　"employees": [
　　　　{ "firstName":"John" , "lastName":"Doe" },
　　　　{ "firstName":"Anna" , "lastName":"Smith" },
　　　　{ "firstName":"Peter" , "lastName":"Jones" }
　　]
}

 实例分析

public static void jsonChange() throws IOException {
        
        /**
         * 方式1：传统方式 org.json
         * Json数据转换成实体对象存在缺陷，性能和功能不够完善
         */
        // JSONObject/JSONArray与String相互转换
        String jsonStr = "{"age":25,"name":"小明","sex":"男"}";
        JSONObject jsonObject = new JSONObject(jsonStr);
        System.out.println("name="+jsonObject.getString("name"));
        System.out.println("age="+jsonObject.getInt("age"));
        System.out.println("sex="+jsonObject.getString("sex"));
        System.out.println(jsonObject.toString());
        jsonStr = "[{"age":25,"name":"小明","sex":"男"},{"age":20,"name":"小红","sex":"女"}]";
        JSONArray jsonArray = new JSONArray(jsonStr);
        System.out.println(jsonArray.toString());
        for (int i=0; i<jsonArray.length();i++){
            jsonObject = (JSONObject) jsonArray.get(i);
            System.out.println(jsonObject.toString());
        }

        // 对象转JSONObject/JSONArray（org.json是不支持JSONObject/JSONArray转对象）
        jsonObject = new JSONObject(new Person("小明",25,"男"));
        System.out.println(jsonObject);
        List<Person> list = new ArrayList<>();
        list.add(new Person("小明",25,"男"));
        jsonArray = new JSONArray(list);
        System.out.println(jsonArray.toString());

        /**
         * 方式2：fastjson
         * 复杂的实体类转换成Json数据存在缺陷，解析json的速度最优
         */
        // String转对象
        jsonStr = "{"age":25,"name":"小明","sex":"男"}";
        Person person = JSON.parseObject(jsonStr,Person.class);
        System.out.println(person.toString());
        jsonStr = "[{"age":25,"name":"小明","sex":"男"},{"age":20,"name":"小红","sex":"女"}]";
        list = JSON.parseArray(jsonStr,Person.class);
        System.out.println(list.toString());

        // 对象转String
        jsonStr = JSON.toJSONString(person);
        System.out.println(jsonStr);
        jsonStr = JSON.toJSONString(list);
        System.out.println(jsonStr);

        /**
         * 方式3：Jackson
         * 复杂的Json数据转换成实体类存在缺陷，性能和功能优于传统方式
         */
        // String转对象
        ObjectMapper mapper=new ObjectMapper();
        jsonStr = "{"age":25,"name":"小明","sex":"男"}";
        person = mapper.readValue(jsonStr, Person.class);
        System.out.println(person.toString());
        jsonStr = "[{"age":25,"name":"小明","sex":"男"},{"age":20,"name":"小红","sex":"女"}]";
        list =  mapper.readValue(jsonStr,mapper.getTypeFactory().constructParametricType(ArrayList.class, Person.class));
        System.out.println(list.toString());

        // 对象转String
        jsonStr = mapper.writeValueAsString(person);
        System.out.println(jsonStr);
        jsonStr = mapper.writeValueAsString(list);
        System.out.println(jsonStr);

        /**
         * 方式4：Gson
         * 功能方面在几种方式中最优，性能方面不如Jackson方式
         */
        // String转对象
        String json = "{"age":25,"name":"小明","sex":"男"}";
        Gson gson = new Gson();
        person = gson.fromJson(json,Person.class);
        System.out.println(person.toString());
        json = "[{"age":25,"name":"小明","sex":"男"},{"age":20,"name":"小红","sex":"女"}]";
        list = gson.fromJson(json,new TypeToken<ArrayList<Person>>(){}.getType());
        System.out.println(list.toString());

        // 对象转String
        json = gson.toJson(person);
        System.out.println(json);
        json = gson.toJson(list);
        System.out.println(json);
    }