GO by example, part 5

5-go-by-example/50-json.go

@@ -0,0 +1,93 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+)
+
+// demonstrate encoding and decoding of custom types below
+type response1 struct {
+	Page   int
+	Fruits []string
+}
+
+// only exported fields will be encoded/decoded in JSON
+// Fields must start with capital letters to be exported
+type response2 struct {
+	Page   int      `json:"page"`
+	Fruits []string `json:"fruits"`
+}
+
+// Go offers built-in support for JSON encoding and decoding, including to and from built-in and custom data types
+func main() {
+	// encoding basic data types to JSON strings
+	bolB, _ := json.Marshal(true)
+	fmt.Println(string(bolB))
+
+	intB, _ := json.Marshal(1)
+	fmt.Println(string(intB))
+
+	fltB, _ := json.Marshal(2.34)
+	fmt.Println(string(fltB))
+
+	strB, _ := json.Marshal("gopher")
+	fmt.Println(string(strB))
+
+	// some for slices and maps, which encode to JSON arrays and objects
+	slcD := []string{"apple", "peach", "pear"}
+	slcB, _ := json.Marshal(slcD)
+	fmt.Println(string(slcB))
+
+	mapD := map[string]int{"apple": 5, "lettuce": 7}
+	mapB, _ := json.Marshal(mapD)
+	fmt.Println(string(mapB))
+
+	// the JSON package can automatically encode your custom data types
+	// it will only include exported fields in the encoded output and will by default use those names as the JSON keys
+	res1D := &response1{
+		Page:   1,
+		Fruits: []string{"apple", "peach", "pear"}}
+	res1B, _ := json.Marshal(res1D)
+	fmt.Println(string(res1B))
+
+	// use tags on struct field declarations to customize the encoded JSON key names
+	res2D := &response2{
+		Page:   1,
+		Fruits: []string{"apple", "peach", "pear"}}
+	res2B, _ := json.Marshal(res2D)
+	fmt.Println(string(res2B))
+
+	// generic decoding JSON data into Go values
+	byt := []byte(`{"num":6.13,"strs":["a","b"]}`)
+
+	// provide a variable where the JSON package can put the decoded data
+	var dat map[string]interface{}
+
+	// actual decoding, and a check for associated errors
+	if err := json.Unmarshal(byt, &dat); err != nil {
+		panic(err)
+	}
+	fmt.Println(dat)
+
+	// in order to use the values in the decoded map, convert them to their appropriate type
+	num := dat["num"].(float64)
+	fmt.Println(num)
+
+	// accessing nested data requires a series of conversions
+	strs := dat["strs"].([]interface{})
+	str1 := strs[0].(string)
+	fmt.Println(str1)
+
+	// decode JSON into custom data types
+	str := `{"page": 1, "fruits": ["apple", "peach"]}`
+	res := response2{}
+	json.Unmarshal([]byte(str), &res)
+	fmt.Println(res)
+	fmt.Println(res.Fruits[0])
+
+	// stream JSON encodings directly to os.Writers
+	enc := json.NewEncoder(os.Stdout)
+	d := map[string]int{"apple": 5, "lettuce": 7}
+	enc.Encode(d)
+}