md2k · March 14, 2018 15:05 · Dec 14, 2015
diff --git a/parse_json.go b/parse_json.go
@@ -0,0 +1,85 @@
+// 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")
+		}
+	}
+
+}