Golang 【basic_leaming】结构体和 Json 相互转换序列化反序列化

雨点打透心脏的1/2处 2023-10-07 22:24 30阅读 0赞

#### 阅读目录 ####

*  一、关于JSON 数据
 *  二、结构体与JSON 序列化
 *   *  1、结构体对象转化成 Json 字符串
     *  2、Json 字符串转换成结构体对象
 *  三、结构体标签 Tag
 *  四、嵌套结构体和JSON 序列化反序列化

## 一、关于JSON 数据 ##

JSON(JavaScript Object Notation) 是一种轻量级的数据交换格式。

易于人阅读和编写。

同时也易于机器解析和生成。

RESTfull Api 接口中返回的数据都是json 数据。

Json 的基本格式如下：

{
        
    	"a": "Hello",
    	"b": "World"
    }

稍微复杂点的JSON。

{
        
    	"result": [{
        
    		"_id": "59f6ef443ce1fb0fb02c7a43",
    		"title": "笔记本电脑",
    		"status": "1",
    		"pic": "public\\upload\\UObZahqPYzFvx_C9CQjU8KiX.png",
    		"url": "12"
    	}, {
        
    		"_id": "5a012efb93ec4d199c18d1b4",
    		"title": "第二个轮播图",
    		"status": "1",
    		"pic": "public\\upload\\f3OtH11ZaPX5AA4Ov95Q7DEM.png"
    	}, {
        
    		"_id": "5a012f2433574208841e0820",
    		"title": "第三个轮播图",
    		"status": "1",
    		"pic": "public\\upload\\s5ujmYBQVRcLuvBHvWFMJHzS.jpg"
    	}, {
        
    		"_id": "5a688a0ca6dcba0ff4861a3d",
    		"title": "教程",
    		"status": "1",
    		"pic": "public\\upload\\Zh8EP9HOasV28ynDSp8TaGwd.png"
    	}]
    }

## 二、结构体与JSON 序列化 ##

比如我们Golang 要给App 或者小程序提供Api 接口数据，这个时候就需要涉及到结构体和Json 之间的相互转换。

Golang JSON 序列化是指把结构体数据转化成JSON 格式的字符串，Golang JSON 的反序列化是指把JSON 数据转化成Golang 中的结构体对象。

Golang 中的序列化和反序列化主要通过 “encoding/json” 包中 `json.Marshal()` 和 `json.Unmarshal()` 方法实现。

### 1、结构体对象转化成 Json 字符串 ###

package main
    
    import (
    	"encoding/json"
    	"fmt"
    )
    
    type Student struct {
        
    	ID     int
    	Gender string
    	name   string
    	//私有属性不能被json 包访问
    	Sno string
    }
    
    func main() {
        
    	var s1 = Student{
        
    		ID:     1,
    		Gender: "男",
    		name:   "李四",
    		Sno:    "s0001",
    	}
    	fmt.Printf("%#v\n", s1)
    	// main.Student{ID:1, Gender:"男", name:"李四", Sno:"s0001"}
    
    	var s, _ = json.Marshal(s1)
    	jsonStr := string(s)
    	fmt.Println(jsonStr)
    	// {"ID":1,"Gender":"男","Sno":"s0001"}
    }

### 2、Json 字符串转换成结构体对象 ###

package main
    
    import (
    	"encoding/json"
    	"fmt"
    )
    
    type Student struct {
        
    	ID     int
    	Gender string
    	Name   string
    	Sno    string
    }
    
    func main() {
        
    	// var jsonStr = "{\"ID\":1,\"Gender\":\"男\",\"Name\":\"李四\",\"Sno\":\"s0001\"}"
    	var jsonStr = `{"ID":1,"Gender":"男","Name":"李四","Sno":"s0001"}`
    	//定义一个Monster 实例
    	var student Student
    	err := json.Unmarshal([]byte(jsonStr), &student)
    	if err != nil {
        
    		fmt.Printf("unmarshal err=%v\n", err)
    	}
    	fmt.Printf("反序列化后student=%#v student.Name=%v \n", student, student.Name)
    	// 反序列化后student=main.Student{ID:1, Gender:"男", Name:"李四", Sno:"s0001"} student.Name=李四
    }

## 三、结构体标签 Tag ##

Tag 是结构体的元信息，可以在运行的时候通过反射的机制读取出来。

Tag 在结构体字段的后方定义，由一对反引号包裹起来，具体的格式如下：

`key1:"value1" key2:"value2"`

结构体 tag 由一个或多个键值对组成。

键与值使用冒号分隔，值用双引号括起来。同一个结构体字段可以设置多个键值对 tag，不同的键值对之间使用空格分隔。

> 注意事项：  
> 为结构体编写Tag 时，必须严格遵守键值对的规则。  
> 结构体标签的解析代码的容错能力很差，一旦格式写错，编译和运行时都不会提示任何错误，通过反射也无法正确取值。  
> 例如不要在key 和value 之间添加空格。

package main
    
    import (
    	"encoding/json"
    	"fmt"
    )
    
    type Student struct {
        
    	ID int `json:"id"`
    	//通过指定tag 实现json 序列化该字段时的key
    	Gender string `json:"gender"`
    	Name   string
    	Sno    string
    }
    
    func main() {
        
    	var s1 = Student{
        
    		ID:     1,
    		Gender: "男",
    		Name:   "李四",
    		Sno:    "s0001",
    	}
    	fmt.Printf("%#v\n", s1)
    	// main.Student{ID:1, Gender:"男", Name:"李四", Sno:"s0001"}
    
    	var s, _ = json.Marshal(s1)
    	jsonStr := string(s)
    	fmt.Println(jsonStr)
    	// {"id":1,"gender":"男","Name":"李四","Sno":"s0001"}
    }

package main
    
    import (
    	"encoding/json"
    	"fmt"
    )
    
    type Student struct {
        
    	ID int `json:"id"`
    	//通过指定tag 实现json 序列化该字段时的key
    	Gender string `json:"gender"`
    	Name   string
    	Sno    string
    }
    
    func main() {
        
    	var s2 Student
    	var str = "{\"id\":1,\"gender\":\"男\",\"Name\":\"李四\",\"Sno\":\"s0001\"}"
    	err := json.Unmarshal([]byte(str), &s2)
    	if err != nil {
        
    		fmt.Println(err)
    	}
    	fmt.Printf("%#v", s2)
    	// main.Student{ID:0, Gender:"", Name:"", Sno:""}
    }

## 四、嵌套结构体和JSON 序列化反序列化 ##

package main
    
    import (
    	"encoding/json"
    	"fmt"
    )
    
    // Student 学生
    type Student struct {
        
    	ID     int
    	Gender string
    	Name   string
    }
    
    // Class 班级
    type Class struct {
        
    	Title    string
    	Students []Student
    }
    
    func main() {
        
    	c := &Class{
        
    		Title:    "001",
    		Students: make([]Student, 0, 200),
    	}
    	for i := 0; i < 10; i++ {
        
    		stu := Student{
        
    			Name:   fmt.Sprintf("stu%02d", i),
    			Gender: "男",
    			ID:     i,
    		}
    		c.Students = append(c.Students, stu)
    	}
    	//JSON 序列化：结构体-->JSON 格式的字符串
    	data, err := json.Marshal(c)
    	if err != nil {
        
    		fmt.Println("json marshal failed")
    		return
    	}
    	fmt.Printf("json:%s\n", data)
    }

{
        
    	"Title": "001",
    	"Students": [{
        
    		"ID": 0,
    		"Gender": "男",
    		"Name": "stu00"
    	}, {
        
    		"ID": 1,
    		"Gender": "男",
    		"Name": "stu01"
    	}, {
        
    		"ID": 2,
    		"Gender": "男",
    		"Name": "stu02"
    	}, {
        
    		"ID": 3,
    		"Gender": "男",
    		"Name": "stu03"
    	}, {
        
    		"ID": 4,
    		"Gender": "男",
    		"Name": "stu04"
    	}, {
        
    		"ID": 5,
    		"Gender": "男",
    		"Name": "stu05"
    	}, {
        
    		"ID": 6,
    		"Gender": "男",
    		"Name": "stu06"
    	}, {
        
    		"ID": 7,
    		"Gender": "男",
    		"Name": "stu07"
    	}, {
        
    		"ID": 8,
    		"Gender": "男",
    		"Name": "stu08"
    	}, {
        
    		"ID": 9,
    		"Gender": "男",
    		"Name": "stu09"
    	}]
    }

package main
    
    import (
    	"encoding/json"
    	"fmt"
    )
    
    // Student 学生
    type Student struct {
        
    	ID     int
    	Gender string
    	Name   string
    }
    
    // Class 班级
    type Class struct {
        
    	Title    string
    	Students []Student
    }
    
    func main() {
        
    	str := `{"Title":"001","Students":[{"ID":0,"Gender":"男","Name":"stu00"},{"ID":1,"Gender":"男","Name":"stu01"},{"ID":2,"Gender":"男","Name":"stu02"},{"ID":3,"Gender":"男","Name":"stu03"},{"ID":4,"Gender":"男","Name":"stu04"},{"ID":5,"Gender":"男","Name":"stu05"},{"ID":6,"Gender":"男","Name":"stu06"},{"ID":7,"Gender":"男","Name":"stu07"},{"ID":8,"Gender":"男","Name":"stu08"},{"ID":9,"Gender":"男","Name":"stu09"}]}`
    	c1 := &Class{
        }
    	err := json.Unmarshal([]byte(str), c1)
    	if err != nil {
        
    		fmt.Println("json unmarshal failed!")
    		return
    	}
    	fmt.Printf("%#v\n", c1)
    }

running...
    &main.Class{Title:"001", Students:[]main.Student{main.Student{ID:0, Gender:"男", Name:"stu00"}, main.Student{ID:1, Gender:"男", Name:"stu01"}, main.Student{ID:2, Gender:"男", Name:"stu02"}, main.Student{ID:3, Gender:"男", Name:"stu03"}, main.Student{ID:4, Gender:"男", Name:"stu04"}, main.Student{ID:5, Gender:"男", Name:"stu05"}, main.Student{ID:6, Gender:"男", Name:"stu06"}, main.Student{ID:7, Gender:"男", Name:"stu07"}, main.Student{ID:8, Gender:"男", Name:"stu08"}, main.Student{ID:9, Gender:"男", Name:"stu09"}}}