细说Golang的JSON解析

json.Marshal()

解析简单JSON

package main

import (
    "fmt"
    "encoding/json"
    "time"
    
)

func main() {
    type FruitBasket struct {
        Name    string 
        Fruit   []string
        Id      int64 `json:"ref"`// 声明对应的json key
        Created time.Time
    }

    jsonData := []byte(`
    {
        "Name": "Standard",
        "Fruit": [
             "Apple",
            "Banana",
            "Orange"
        ],
        "ref": 999,
        "Created": "2018-04-09T23:00:00Z"
    }`)

    var basket FruitBasket
    err := json.Unmarshal(jsonData, &basket)
    if err != nil {
         fmt.Println(err)
    }
    fmt.Println(basket.Name, basket.Fruit, basket.Id)
    fmt.Println(basket.Created)
}

json.UnMarshal()c := []byte(s)

解析内嵌对象的JSON

"Fruit" : {"Name", "Apple", "PriceTag": "$1"}

    jsonData := []byte(`
    {
        "Name": "Standard",
        "Fruit" : {"Name": "Apple", "PriceTag": "$1"},
        "ref": 999,
        "Created": "2018-04-09T23:00:00Z"
    }`)

那么结构体类型应该这么声明

type Fruit struct {
    Name string `json":Name"`
    PriceTag string `json:"PriceTag"`
}

type FruitBasket struct {
    Name    string 
    Fruit   Fruit
    Id      int64 `json:"ref"`// 声明对应的json key
    Created time.Time
}

解析内嵌对象数组的JSON(Embed Array of Object)

如果上面JOSN对象里的Fruit值现在变成了

"Fruit" : [
    {
        "Name": "Apple",
            "PriceTag": "$1"
    },
    {
        "Name": "Pear",
        "PriceTag": "$1.5"
    }
]

[]Fruit

type Fruit struct {
    Name string `json:"Name"`
    PriceTag string `json:"PriceTag"`
}

type FruitBasket struct {
    Name    string 
    Fruit   []Fruit
    Id      int64 `json:"ref"`// 声明对应的json key
    Created time.Time
}

解析具有动态Key的对象（Parse a JSON object with dynamic key)

下面再做一下复杂的变通，如果把上面的对象数组变为Key为水果ID的对象（object of object）比如

"Fruit" : {
    "1": {
        "Name": "Apple",
        "PriceTag": "$1"
    },
    "2": {
        "Name": "Pear",
        "PriceTag": "$1.5"
    }
}

每个Key的名字在声明结构体的时候是不知道值的，这样该怎么声明呢，答案是把Fruit字段的类型声明为一个key为string类型值为Fruit类型的map

type Fruit struct {
    Name string `json:"Name"`
    PriceTag string `json:"PriceTag"`
}

type FruitBasket struct {
    Name    string 
    Fruit   map[string]Fruit
    Id      int64 `json:"ref"`// 声明对应的json key
    Created time.Time
}

示例代码

package main

import (
    "fmt"
    "encoding/json"
    "time"
    
)

func main() {
    type Fruit struct {
        Name string `json:"Name"`
        PriceTag string `json:"PriceTag"`
    }

    type FruitBasket struct {
        Name    string 
        Fruit   map[string]Fruit
        Id      int64 `json:"ref"`// 声明对应的json key
        Created time.Time

    }    
    jsonData := []byte(`
    {
        "Name": "Standard",
        "Fruit" : {
        "1": {
        "Name": "Apple",
        "PriceTag": "$1"
        },
        "2": {
        "Name": "Pear",
        "PriceTag": "$1.5"
        }
        },
        "ref": 999,
        "Created": "2018-04-09T23:00:00Z"
    }`)

    var basket FruitBasket
    err := json.Unmarshal(jsonData, &basket)
    if err != nil {
         fmt.Println(err)
    }
    for _, item := range basket.Fruit {
    fmt.Println(item.Name, item.PriceTag)
    }
}

解析包含任意层级的数组和对象的JSON数据(arbitrary arrays and objects)

encode\jsonencoding\json

• map[string]interface{} 存储JOSN对象
• []interface 存储JOSN数组

json.Unmarshl

示例代码:

jsonData := []byte(`{"Name":"Eve","Age":6,"Parents":["Alice","Bob"]}`)

var v interface{}
json.Unmarshal(jsonData, &v)
data := v.(map[string]interface{})

for k, v := range data {
    switch v := v.(type) {
    case string:
        fmt.Println(k, v, "(string)")
    case float64:
        fmt.Println(k, v, "(float64)")
    case []interface{}:
        fmt.Println(k, "(array):")
        for i, u := range v {
            fmt.Println("    ", i, u)
        }
    default:
        fmt.Println(k, v, "(unknown)")
    }
}

虽然将JSON数据存储到空接口类型的值中可以用来解析任意结构的JSON数据，但是在实际应用中发现还是有不可控的地方，比如将数字字符串的值转换成了float类型的值，所以经常会在运行时报类型断言的错误，所以在JSON结构确定的情况下还是优先使用结构体类型声明，将JSON数据到结构体中的方式来解析JSON。