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 ,
-
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
