jackJson

Posted 2022-12-01 再来半包

JackJson

• jackJson
• • 将javaBean对象转换为json字符串
  • 将json字符串写入文件
  • 将json字符串转换成实体类对象
  • 将List转换为json字符串

jackJson

将javaBean对象转换为json字符串

1、先创建一个jackJson的核心对象 ObjectMapper以及实体类对象

ObjectMapper om=new ObjectMapper();	
User user=new User("才春磊",20,"[e-mail]");

2、把实体类转换成json格式的字符串

try 
            String userstr = om.writeValueAsString(user);
            System.out.println(userstr);
         catch (IOException e) 
            e.printStackTrace();
        
/*
打印结果
"name":"才春磊","age":20,"email":"[e-mail]"
*/

通过ObjectMapper中的writeValueAsString()方法将实体类的对象转换成了Json字符串

将json字符串写入文件

try 
            om.writeValue(new File("D:\\\\json.txt"),user);
         catch (IOException e) 
            e.printStackTrace();
        

通过ObjectMapper中的writeValue()方法将实体类转换的Json字符串写入文件中

注解：

@JsonIgnore    写在实体类中，表示在将对象转换为Json字符串的时候忽略这个属性	
@JsonFormat(pattern = "yyyy-MM-dd")     写在实体类中，表示将实体类对象转换为Json字符串的时候，日期类属性，以什么形式转换为Json字符串

将json字符串转换成实体类对象

public static void main(String[] args) 
    //把Json格式的字符串转换成指定的实体类对象
    //创建jackJson的核心类ObjectMapper
    ObjectMapper om =new ObjectMapper();
    //创建User实体类对象
    User user=new User("才春磊",20,"asdf");
    try 
    	//将实体类对象转换成Json字符串
        String userStr = om.writeValueAsString(user);
        System.out.println(userStr);
        //将User类转换过来的Json字符串转回Json对象
        //User.class反射的方法
        User user1 = om.readValue(userStr, User.class);
        System.out.println(user);
     catch (IOException e) 
        e.printStackTrace();
    

/*
运行结果
"name":"才春磊","age":20,"email":"asdf"
Username='才春磊', age=20, email='asdf'
*/

将List转换为json字符串

public static void main(String[] args) 
        ObjectMapper om =new ObjectMapper();
        User user=new User("才春磊",20,"aaaa");
        User user2=new User("才春磊1",21,"bbbb");
        User user3=new User("才春磊2",22,"cccc");
        List<User> list=new ArrayList<User>();
        list.add(user);
        list.add(user2);
        list.add(user3);
        //把list集合转换成json字符串
        try 
            String listStr = om.writeValueAsString(list);
            System.out.println(listStr);
         catch (IOException e) 
            e.printStackTrace();
        
    
/*
运行结果为
["name":"才春磊","age":20,"email":"aaaa",
"name":"才春磊1","age":21,"email":"bbbb",
"name":"才春磊2","age":22,"email":"cccc"]
*/

将Map转换为json字符串

public static void main(String[] args) 
        ObjectMapper om=new ObjectMapper();
        Map<String,Object> map=new HashMap<String,Object>();
        map.put("name","才春磊");
        map.put("sex","男");
        map.put("age",20);
        try 
            String jsonMap = om.writeValueAsString(map);
            System.out.println(jsonMap);
         catch (IOException e) 
            e.printStackTrace();
        
    
/*
运行结果
"sex":"男","name":"才春磊","age":20
*/