解码大数据流JSON [英] Decode large stream JSON

问题描述

我在文件("file.json")中存储了一个庞大的JSON数组 我需要遍历数组并对每个元素进行一些操作.

I have a massive JSON array stored in a file ("file.json") I need to iterate through the array and do some operation on each element.

err = json.Unmarshal(dat, &all_data)

造成内存不足-我猜是因为它首先将所有内容加载到内存中.

Causes an out of memory - I'm guessing because it loads everything into memory first.

有没有一种方法可以逐个元素地传输JSON元素?

Is there a way to stream the JSON element by element?

推荐答案

这里有一个这样的例子: https://golang.org/pkg/encoding/json/#example_Decoder_Decode_stream .

There is an example of this sort of thing here: https://golang.org/pkg/encoding/json/#example_Decoder_Decode_stream.

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\n", 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\n", m.Name, m.Text)
    }

    // read closing bracket
    t, err = dec.Token()
    if err != nil {
        log.Fatal(err)
    }
    fmt.Printf("%T: %v\n", t, t)

}

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