json.Unmarshal json string to object is empty result [duplicate]

问题

This question already has answers here:

Printing Empty Json as a result [duplicate] (1 answer)

json.Marshal(struct) returns “{}” (2 answers)

Closed 4 months ago.

I've got a very simple program like this:

package main

import (
    "encoding/json"
    "fmt"
)

type RunCommand struct{
    level string `json:"level"`
    caller string `json:"caller"`
    msg string `json:"msg"`
    cmd string `json:"cmd"`
}

func main() {
    content := `{"level":"info","caller":"my.go:10","msg":"run","cmd":"--parse"}`
    runCommand := RunCommand{}
    e := json.Unmarshal([]byte(content), &runCommand)
    if e != nil {
        fmt.Println("Unmarshal error")
    }
    fmt.Println(runCommand.level)
}

I wish that I could parse out all the json fields inside "content" into "runCommand" object, but actually, the final "fmt.Println" prints nothing. Where did I get wrong?

回答1:

You have to have exported fields, like this:

type RunCommand struct{
    Level string `json:"level"`
    Caller string `json:"caller"`
    Msg string `json:"msg"`
    Cmd string `json:"cmd"`
}

and now you can use: fmt.Println(runCommand.Level) otherwise json.Unmarshal will ignore non-exported fields.

来源：https://stackoverflow.com/questions/57908166/json-unmarshal-json-string-to-object-is-empty-result