Go语言怎么使用标准库发起HTTP请求

GET /api/users HTTP/1.1

User-Agent: Mozilla/5.0 (windows NT 10.0; Win64; x64) AppleWEBKit/537.36 (Khtml, like Gecko) Chrome/58.0.3029.110 Safari/537.36
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.8

{"username":"admin","passWord":"123456"}

package main

import (
    "fmt"
    "io/ioutil"
    "net/http"
)

func main() {
    resp, err := http.Get("https://www.example.com")
    if err != nil {
        panic(err)
    }
    defer resp.Body.Close()

    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        panic(err)
    }

    fmt.Println(string(body))
}

package main

import (
    "bytes"
    "fmt"
    "io/ioutil"
    "net/http"
)

func main() {
    url := "http://www.example.com/api/login"
    data := []byte(`{"username":"admin","password":"123456"}`)
    req, err := http.NewRequest("POST", url, bytes.NewBuffer(data))
    if err != nil {
        panic(err)
    }
    req.Header.Set("Content-Type", "application/JSON")

    client := &http.Client{}
    resp, err := client.Do(req)
    if err != nil {
        panic(err)
    }
    defer resp.Body.Close()

    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        panic(err)
    }

    fmt.Println(string(body))
}

package main

import (
    "fmt"
    "github.com/go-resty/resty/v2"
)

func main() {
    client := resty.New()

    resp, err := client.R().
        EnableTrace().
        Get("https://www.example.com")
    if err != nil {
        panic(err)
    }

    fmt.Println(string(resp.Body()))
}