json基础

• json表示法是一种轻量级的基于文本的开放标准
• json是javascript object notation的缩写
• json的网络媒体格式是 application/json
• 容易阅读和编写
• 语言无关性

json的几种数据格式

• 对象

  An object is an unordered set of name/value pairs. An object begins with { (left brace) and ends with } (right brace). Each name is followed by : (colon) and the name/value pairs are separated by .

  object

• 数组

An array is an ordered collection of values. An array begins with [ (left bracket) and ends with ] (right bracket). Values are separated by ,

array

• 值

  A value can be a string in double quotes, or a number, or true or false or null, or an object or an array. These structures can be nested.

  value

json语法

• 数据使用键值对表示
• 使用大括号表示对象，每个名称后面跟着一个:，键值对之间使用,分割
• 使用方括号[]保存数组，数组值使用,分割

{
    "book": [
        {
            "id":"01",
            "language": "Java",
            "edition": "third",
            "author": "Herbert Schildt"
        },
        {
            "id":"07",
            "language": "C++",
            "edition": "second"
            "author": "E.Balagurusamy"
    }]
}

book为键，它对应的又是一个json数组对象,json数组用[]包起来：

[ 
    {
        "id":"01",
        "language": "Java",
        "edition": "third",
        "author": "Herbert Schildt"
    },
    {
        "id":"07",
        "language": "C++",
        "edition": "second"
        "author": "E.Balagurusamy"
    }
]

数组元素是一个json对象，对象之间使用,隔开：

{ 
    "id":"01",
    "language": "Java",
    "edition": "third",
    "author": "Herbert Schildt"
}

java中使用json

下载 json .jar

    /**
     * 测试生成json对象
     * @throws JSONException
     */
    @Test
    public void testBuildJsonObject() throws JSONException {
        JSONObject jsonObject = new JSONObject();
        jsonObject.put("id",1);
        jsonObject.put("name","shixu");
        jsonObject.put("age",23);
        jsonObject.put("id",2); //JsonObject底层是维护一个map,所以不能有重复的键,这里会把之前的值覆盖掉
        System.out.println(jsonObject);
        System.out.println("id:"+jsonObject.get("id"));
        System.out.println("name:"+jsonObject.get("name"));
        System.out.println("age:"+jsonObject.get("age"));
      
      
        HashMap map = new HashMap<>();
        map.put("id",1);
        map.put("name","shixu");
        JSONObject jsonObjectMap= new JSONObject(map);  //使用map初始化
        System.out.println(jsonObjectMap);
        System.out.println("id:"+jsonObjectMap.get("id"));
        System.out.println("name:"+jsonObjectMap.get("name"));
    }

结果：

{"id":2,"age":23,"name":"shixu"}
id:2
name:shixu
age:23
{"id":1,"name":"shixu"}
id:1

   /**
     * 测试生成JSONArray ,用于存放jsonObject
     * @throws JSONException
     */
    @Test
    public void testBuildJsonArray() throws JSONException {
        JSONArray jsonArray = new JSONArray();
        HashMap map = new HashMap<>();
        map.put("id",1);
        map.put("name","shixu");
        JSONObject jsonObjectMap= new JSONObject(map);  //使用map初始化
        jsonArray.put(jsonObjectMap);
        jsonArray.put(jsonObjectMap);
        System.out.println(jsonArray);
        System.out.println(jsonArray.getJSONObject(0));
        System.out.println(jsonArray.getJSONObject(1));
    }

结果：

[{"id":1,"name":"shixu"},{"id":1,"name":"shixu"}]

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

将一个json字符串解析为json对象

/**
 * 将一个json字符串解析为json对象
 * @throws JSONException
 */
@Test
public void testJsonStrToJsonObject() throws JSONException {
    String jsonStr = "[{\"id\":1,\"name\":\"shixu\"},{\"id\":2,\"name\":\"suntime\"}]";
    JSONTokener jsonTokener = new JSONTokener(jsonStr);
    JSONArray jsonArray = new JSONArray(jsonTokener);
    for (int i = 0; i <jsonArray.length() ; i++) {
        JSONObject jsonObject = jsonArray.getJSONObject(i);
        System.out.println(jsonObject);
        System.out.print("id:"+jsonObject.get("id"));
        System.out.println("\tname:"+jsonObject.get("name"));
    }
}

结果：

{"id":1,"name":"shixu"}
id:1 name:shixu
{"id":2,"name":"suntime"}
id:2 name:suntime

总结