wells wells - 1 year ago 84
JSON Question

How to parse a complicated JSON with Go lang unmarshal?


the standard package encoding/json exposes
function to parse JSON.

It's possible to either unmarshal the JSON string in a predefined
, or use the
and iterate the result for unexpected JSON data structure.

That said, I can't parse complex JSON properly. Can someone tell me how to achieve this?

"k1" : "v1",
"k2" : "v2",
"k3" : 10,
"result" : [
["v4", v5, {"k11" : "v11", "k22" : "v22"}]
, ... ,
["v4", v5, {"k33" : "v33", "k44" : "v44"}

Answer Source

Citing from JSON and Go:

Without knowing this data's structure, we can decode it into an interface{} value with Unmarshal:

b := []byte(`{
   "k1" : "v1", 
   "k3" : 10,
   result:["v4",12.3,{"k11" : "v11", "k22" : "v22"}]
var f interface{}
err := json.Unmarshal(b, &f)

At this point the Go value in f would be a map whose keys are strings and whose values are themselves stored as empty interface values:

f = map[string]interface{}{
    "k1": "v1",
    "k3":  10,
    "result": []interface{}{

To access this data we can use a type assertion to access f's underlying map[string]interface{}:

m := f.(map[string]interface{})

We can then iterate through the map with a range statement and use a type switch to access its values as their concrete types:

for k, v := range m {
    switch vv := v.(type) {
    case string:
        fmt.Println(k, "is string", vv)
    case int:
        fmt.Println(k, "is int", vv)
    case []interface{}:
        fmt.Println(k, "is an array:")
        for i, u := range vv {
            fmt.Println(i, u)
        fmt.Println(k, "is of a type I don't know how to handle")

In this way you can work with unknown JSON data while still enjoying the benefits of type safety.

More information about Go and JSON can be found in the original article. I changed the code snippets slightly to be more similar to the JSON in the question.

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