- JSON 指的是 Javascript 对象表示法（JavaScript Object Notation）
- JSON 是轻量级的文本数据交换格式
- JSON 独立于语言：虽然JSON 使用 JS语法来描述对象，但是独立于语言和平台。
- JSON 解析器和 JSON 库支持不同的编程语言，(PHP，JSP，.NET，JAVA）等编程语言都支持JSON。
- JSON 具有自我描述性，它比比XML 更小、更快，更易解析
json字符串—>对象
// json字符串转换为JSONObject对象 JSONObject parseObject(String jsonString) // json字符串转换为JSONArray对象 JSONArray parseArray(String jsonString) // json字符串转换为javaBean T parseObject(String jsonString, Classclazz) List parseArray(String jsonString, Class clazz)
对象—>json字符串
String toJSONString(Object object)解析JSON字符串
{"112":{"name":"黄晓明","score":55},"113":{"name":"赵薇","score":63},"114":{"name":"陈坤","score":87},"115":{"name":"周迅","score":82}}
JSON格式：
{
"112": {
"name": "黄晓明",
"score": 55
},
"113": {
"name": "赵薇",
"score": 63
},
"114": {
"name": "陈坤",
"score": 87
},
"115": {
"name": "周迅",
"score": 82
}
}
首先要明白，以 { } 开头的是JSONObject，以 [ ] 开头的是JSONArray
@Test
public void testJson01() {
String str = "{"112":{"name":"黄晓明","score":55},"113":{"name":"赵薇","score":63},"114":{"name":"陈坤","score":87},"115":{"name":"周迅","score":82}}";
// 解析字符串，先将其转为JSONObject对象
JSONObject jsonObject = JSONObject.parseObject(str);
// 获取所有key的集合
Set keySet = jsonObject.keySet();
Iterator iterator = keySet.iterator();
// 迭代遍历
while (iterator.hasNext()){
JSONObject jb = jsonObject.getJSONObject(iterator.next());
System.out.print(jb.getString("name"));
System.out.println(jb.getInteger("score"));
}
}
运行结果：
[{"name":"Java","pId":100},{"name":"Spring框架","pId":888},{"name":"MySQL数据库","pId":999}]
JSON格式：
[
{
"name": "Java",
"pId": 100
},
{
"name": "Spring框架",
"pId": 888
},
{
"name": "MySQL数据库",
"pId": 999
}
]
Java代码实现：
@Test
public void testJson02() {
String str = "[{"name":"Java","pId":100},{"name":"Spring框架","pId":888},{"name":"MySQL数据库","pId":999}]";
// 解析字符串,将其转为JSONArray对象
JSONArray array = JSONObject.parseArray(str);
//迭代遍历方式A
for (int i = 0; i < array .size(); i++) {
JSONObject jb = array .getJSONObject(i);
System.out.println(jb.getString("name"));
System.out.println(jb.getString("pId"));
}
//迭代遍历方式B
for (Object o : array ) {
JSONObject s = (JSONObject)o;
System.out.println(s.getString("name"));
System.out.println(s.getString("pId"));
}
}
运行结果：
要解析的JSON字符串
{
"errcode": 0,
"errmsg": "ok",
"result": {
"auto_add_user": true,
"dept_id": 35,
"dept_permits": [],
"extention": "{"faceCount":"657"}",
"hide_dept": false,
"name": "layman",
"user_permits": []
},
"request_id": "iyptirsmnxy5"
}
解析复杂Json字符串
{'teacherName':'crystall','teacherAge':27,'course':{'courseName':'english','code':1270},'students':[{'studentName':'lily','studentAge':12},{'studentName':'lucy','studentAge':15}]}
Json格式：
{
"teacherName": "crystall",
"teacherAge": 27,
"course": {
"courseName": "english",
"code": 1270
},
"students": [
{
"studentName": "lily",
"studentAge": 12
},
{
"studentName": "lucy",
"studentAge": 15
}
]
}
java代码：
@Test
public void testJson03() {
String str = "{'teacherName':'layman','teacherAge':27,'course':{'courseName':'english','code':1270},'students':[{'studentName':'lily','studentAge':12},{'studentName':'lucy','studentAge':15}]}";
JSONObject jb = JSONObject.parseObject(str);
String teacherName = jb.getString("teacherName");
Integer teacherAge = jb.getInteger("teacherAge");
JSONObject course = jb.getJSONObject("course");
JSONArray students = jb.getJSONArray("students");
System.out.println(teacherName);
System.out.println(teacherAge);
System.out.println(course);
System.out.println(students);
}
把Json字符串直接转化为对象
以上面的复杂字符串为例子
{'teacherName':'crystall','teacherAge':27,'course':{'courseName':'english','code':1270},'students':[{'studentName':'lily','studentAge':12},{'studentName':'lucy','studentAge':15}]}
新建实体类teacher ：
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;
import java.util.List;
@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Teacher{
private String teacherName;
private Integer age;
private Course course;
private List Student;
}
新建实体类Student
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;
@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Student {
@JSONField(name = "studentName")
private String studentName;
@JSONField(name = "studentAge")
private Integer studentAge;
}
新建实体类Course
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;
@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Course {
private String name;
private Integer code;
}
转换方法：
@Test
public void testJson04() {
String str = "{'teacherName':'layman','teacherAge':27,'course':{'courseName':'english','code':1270},'students':[{'studentName':'lily','studentAge':12},{'studentName':'lucy','studentAge':15}]}";
// 解析字符串,将其转为JSONArray对象
Teacher teacher = JSON.parseObject(str, Teacher.class);
System.out.println(teacher);
}
运行结果：
可以看到，除了teacher中的teacherName属性有值外，其它的属性都没有值。
因为Json是根据key值去匹配变量名，如果变量名和key值不同，就会出现匹配不上，从而出现null值。
如何解决这个问题：
- key值和变量名一一对应
- 变量名上添加JSONField注解
进行teacher类的改造：
import com.alibaba.fastjson.annotation.JSONField;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;
import java.util.List;
@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Teacher{
@JSONField(name = "teacherAge")
private String name;
@JSONField(name = "teacherAge")
private Integer age;
private Course course;
private List Student;
}
改造Course类：
import com.alibaba.fastjson.annotation.JSONField;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;
@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Course {
@JSONField(name = "courseName")
private String name;
private Integer code;
}
重新运行，如下：
可以看到，Student这个类依然没有获取到。
为什么呢？
因为Json字符串中的key是：
students
而，Teacher类中的Field是
private List student;
students 和 List student并不匹配，少了个s
- tips：Field和key的值需要一一对应（不区分大小写）
在student添加注解
@JSONField(name = "students")
private List student;
修改后运行结果
推荐博客：
Jackson，Gson，Fastjson 的对比
Fastjson 汇总篇
JackSon使用篇
