parse_json.go

// Parsing arbitrary JSON using interfaces in Go // Demonstrates how to parse JSON with abritrary key names // See https://blog.golang.org/json-and-go for more info on generic JSON parsing package main import ( "encoding/json" "fmt" ) var jsonBytes = []byte(` { "key1":{ "Item1": "Value1", "Item2": 1}, "key2":{ "Item1": "Value2", "Item2": 2}, "key3":{ "Item1": "Value3", "Item2": 3} }`) // Item struct; we want to create these from the JSON above type Item struct { Item1 string Item2 int } // Implement the String interface for pretty printing Items func (i Item) String() string { return fmt.Sprintf("Item: %s, %d", i.Item1, i.Item2) } func main() { // Unmarshal using a generic interface var f interface{} err := json.Unmarshal(jsonBytes, &f) if err != nil { fmt.Println("Error parsing JSON: ", err) } // JSON object parses into a map with string keys itemsMap := f.(map[string]interface{}) // Loop through the Items; we're not interested in the key, just the values for _, v := range itemsMap { // Use type assertions to ensure that the value's a JSON object switch jsonObj := v.(type) { // The value is an Item, represented as a generic interface case interface{}: var item Item // Access the values in the JSON object and place them in an Item for itemKey, itemValue := range jsonObj.(map[string]interface{}) { switch itemKey { case "Item1": // Make sure that Item1 is a string switch itemValue := itemValue.(type) { case string: item.Item1 = itemValue default: fmt.Println("Incorrect type for", itemKey) } case "Item2": // Make sure that Item2 is a number; all numbers are transformed to float64 switch itemValue := itemValue.(type) { case float64: item.Item2 = int(itemValue) default: fmt.Println("Incorrect type for", itemKey) } default: fmt.Println("Unknown key for Item found in JSON") } } fmt.Println(item) // Not a JSON object; handle the error default: fmt.Println("Expecting a JSON object; got something else") } } }