dongxia8656
2019-01-22 20:46
浏览 26
已采纳

将很大的json解码为结构数组

I have a web application which have a REST API, get JSON as input and perform transformations of this JSON.

Here is my code:

func (a *API) getAssignments(w http.ResponseWriter, r *http.Request) {

   var document DataPacket
   err := json.NewDecoder(r.Body).Decode(&document)
   if err != nil {
       a.handleJSONParseError(err, w)
      return
   }

   // transformations

JSON which I get is a collection of structs. External application use my application and send me very big json files (300-400MB). Decode this json at the one moment of time takes a very big time and amount of memory.

Is there any way to work with this json as stream and decode structs from this collection one by one ?

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1条回答 默认 最新

  • dounianxie2058 2019-01-22 20:50
    已采纳

    First, read the documentation.


    Package json

    import "encoding/json"

    func (*Decoder) Decode

    func (dec *Decoder) Decode(v interface{}) error
    

    Decode reads the next JSON-encoded value from its input and stores it in the value pointed to by v.

    Example (Stream): This example uses a Decoder to decode a streaming array of JSON objects.

    Playground: https://play.golang.org/p/o6hD-UV85SZ

    package main
    
    import (
        "encoding/json"
        "fmt"
        "log"
        "strings"
    )
    
    func main() {
        const jsonStream = `
        [
            {"Name": "Ed", "Text": "Knock knock."},
            {"Name": "Sam", "Text": "Who's there?"},
            {"Name": "Ed", "Text": "Go fmt."},
            {"Name": "Sam", "Text": "Go fmt who?"},
            {"Name": "Ed", "Text": "Go fmt yourself!"}
        ]
    `
        type Message struct {
            Name, Text string
        }
        dec := json.NewDecoder(strings.NewReader(jsonStream))
    
        // read open bracket
        t, err := dec.Token()
        if err != nil {
            log.Fatal(err)
        }
        fmt.Printf("%T: %v
    ", t, t)
    
        // while the array contains values
        for dec.More() {
            var m Message
            // decode an array value (Message)
            err := dec.Decode(&m)
            if err != nil {
                log.Fatal(err)
            }
    
            fmt.Printf("%v: %v
    ", m.Name, m.Text)
        }
    
        // read closing bracket
        t, err = dec.Token()
        if err != nil {
            log.Fatal(err)
        }
        fmt.Printf("%T: %v
    ", t, t)
    
    }
    
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