How Can I Parse Multiple JSON Objects in Go, Especially When They're Nested?

Parsing Multiple JSON Objects in Go: Addressing Nested Objects

When dealing with multiple JSON objects returned from a server in the form of nested objects, the standard encoding/json package may encounter difficulties. This article delves into a solution using a json.Decoder to handle such scenarios effectively.

Consider the following example:

{"something":"foo"}
{"something-else":"bar"}

Using the following code to parse this data:

correct_format := strings.Replace(string(resp_body), "}{", "},{", -1)
json_output := "[" + correct_format + "]"

results in an error.

Solution Using json.Decoder

To address this issue, we utilize a json.Decoder. A json.Decoder reads and decodes JSON data stream-like, sequentially decoding individual JSON objects from the input.

package main

import (
    "encoding/json"
    "fmt"
    "io"
    "log"
    "strings"
)

var input = `
{"foo": "bar"}
{"foo": "baz"}
`

type Doc struct {
    Foo string
}

func main() {
    dec := json.NewDecoder(strings.NewReader(input))
    for {
        var doc Doc

        err := dec.Decode(&doc)
        if err == io.EOF {
            // all done
            break
        }
        if err != nil {
            log.Fatal(err)
        }

        fmt.Printf("%+v\n", doc)
    }
}

In this solution:

• A json.Decoder is initialized to read from a string containing the JSON data.
• A loop iterates over the stream, decoding each JSON object into a Doc struct.
• Decoding continues until io.EOF (end of file) is encountered, indicating the end of the stream.
• Each successfully decoded object is printed.

Playground and Conclusion

You can try out this solution on the Go Playground: https://play.golang.org/p/ANx8MoMC0yq

By using a json.Decoder, we are able to parse multiple JSON objects, even when they are nested within a larger JSON structure.

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