interface{}类型通过json.Unmarshal之后的类型

一句话总结：所有JSON数值类型一律解析为float64类型，需手动转换；对于map类型需判断是否为nil再转换为所需类型。

interface{}类型在json.Unmarshal时，会自动将JSON转换为对应的数据类型：
JSON的boolean 转换为bool
JSON的数值 转换为float64
JSON的字符串 转换为string
JSON的Array 转换为[]interface{}
JSON的Object 转换为map[string]interface{}，也可以转为本身类型
JSON的null 转换为nil

package main

import (
    "encoding/json"
    "fmt"
)

type Person struct {
    Name string `json:"name"`
    Age  int    `json:"age"`
    Addr string `json:"addr,omitempty"`
}

func main() {
    var m map[string]interface{}     //声明变量，不分配内存
    m = make(map[string]interface{}) //必可不少，分配内存
    m["name"] = "simon"
    var age int = 12
    m["age"] = age
    m["addr"] = "China"
    print_map(m)
    fmt.Println()

    data, _ := json.Marshal(m)

    m1 := make(map[string]interface{})
    _ = json.Unmarshal(data, &m1)
    print_map(m1)
    fmt.Println()

    if m1["name"] != nil {
        fmt.Println(m1["name"].(string))
    }
    if m1["type"] != nil {
        fmt.Println(m1["type"].(string))
    } else {
        fmt.Println("there is not the key of type")
    }
    fmt.Println()

    p := Person{"simon", 22, "China"}
    data, _ = json.Marshal(p)
    p1 := Person{}
    _ = json.Unmarshal(data, &m1)
    _ = json.Unmarshal(data, &p1)
    fmt.Println("map m1:", m1)
    fmt.Println("person:", p1)
    fmt.Println(m1["name"], m1["age"], m1["addr"])
    fmt.Println(p1.Name, p1.Age, p1.Addr)
}

运行结果

name is string simon
age is int 12
addr is string China

addr is string China
age is float64 12
name is string simon

simon
there is not the key of type

map m1: map[addr:China age:22 name:simon]
person: {simon 22 China}
simon 22 China
simon 22 China

Process finished with exit code 0