json use mashal/unmashal to encode/decode

libo-ps · libo-ps · commit b4dd0e597d4f · 2018-04-28T13:14:19.000+08:00
diff --git a/go/json_marshal.go b/go/json_marshal.go
@@ -0,0 +1,142 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"reflect"
+)
+
+type Response1 struct {
+	Page   int
+	Fruits []string
+}
+type Response2 struct {
+	Page   int      `json:"page"`
+	Fruits []string `json:"fruits"`
+}
+
+func main() {
+	//encoding basic data types to JSON strings。
+	/**
+	:!go run a.go
+	[]uint8
+	[116 114 117 101]
+
+	[]uint8
+	1
+
+	[]uint8
+	3.12
+	[51 46 49 50]
+
+	[]uint8
+	"hello"
+	[34 104 101 108 108 111 34]
+	*/
+	bolB, _ := json.Marshal(true)
+	fmt.Println(reflect.TypeOf(bolB))
+	fmt.Println(bolB)
+
+	intB, _ := json.Marshal(1)
+	fmt.Println(reflect.TypeOf(intB))
+	fmt.Println(string(intB))
+
+	fltB, _ := json.Marshal(3.12)
+	fmt.Println(reflect.TypeOf(fltB))
+	fmt.Println(string(fltB))
+	fmt.Println(fltB)
+
+	strB, _ := json.Marshal("hello")
+	fmt.Println(reflect.TypeOf(strB))
+	fmt.Println(string(strB))
+	fmt.Println(strB)
+
+	//encoding slices and maps to JSON arrays and objects.
+	/** slice
+	[]uint8
+	["apple","orange"]
+	[91 34 97 112 112 108 101 34 44 34 111 114 97 110 103 101 34 93]
+	*/
+	slcD := []string{"apple", "orange"}
+	slcB, _ := json.Marshal(slcD)
+	fmt.Println(reflect.TypeOf(slcB))
+	fmt.Println(string(slcB))
+	fmt.Println(slcB)
+	/** map
+	[]uint8
+	{"apple":5,"orange":6}
+	[123 34 97 112 112 108 101 34 58 53 44 34 111 114 97 110 103 101 34 58 54 125]
+	*/
+	mapD := map[string]int{"apple": 5, "orange": 6}
+	mapB, _ := json.Marshal(mapD)
+	fmt.Println(reflect.TypeOf(mapB))
+	fmt.Println(string(mapB))
+	fmt.Println(mapB)
+
+	//encoding automatically your custom data types.
+	//{"Page":1,"Fruits":["apple","orange"]}
+	res1D := &Response1{
+		Page:   1,
+		Fruits: []string{"apple", "orange"},
+	}
+	res1B, _ := json.Marshal(res1D)
+	fmt.Println(string(res1B))
+	//use tags on struct field declarations to customize the encoded JSON key names.
+	//{"page":1,"fruits":["apple","orange"]}     [add tags to keys]
+	res2D := &Response2{
+		Page:   1,
+		Fruits: []string{"apple", "orange"},
+	}
+	res2B, _ := json.Marshal(res2D)
+	fmt.Println(string(res2B))
+
+	fmt.Println("DECODING JSON")
+	/***************************DECODING JSON**************************/
+	/**
+	1. provide a variable where the JSON package can put the decoded data.
+	2. map[string]interface()/ will hold/ a map of/ strings to arbitray data types.
+	*/
+	var dat map[string]interface{}
+	fmt.Println(reflect.TypeOf(dat)) //map[string]interface {}
+
+	byt := []byte(`{"num":6.13,"strs":["apple","orange"]}`)
+	//check for associated errors
+	/**
+	map[num:6.13 strs:[a b]]
+	map[string]interface {}
+	*/
+	if err := json.Unmarshal(byt, &dat); err != nil {
+		panic(err)
+	}
+	fmt.Println(dat)                 //map[num:6.13 strs:[a b]]
+	fmt.Println(reflect.TypeOf(dat)) //map[string]interface {}
+
+	// situation1: none-nested.  get value to get directly.
+	num := dat["num"].(float64)
+	fmt.Println(num)                 //6.13
+	fmt.Println(reflect.TypeOf(num)) //float64
+	// situation2: nested.  requires a series of casts.
+	strs := dat["strs"].([]interface{})
+	str1 := strs[0].(string)
+	fmt.Println(reflect.TypeOf(dat["strs"])) //[]interface {}
+	fmt.Println(reflect.TypeOf(strs))        //[]interface {}
+	fmt.Println(reflect.TypeOf(str1))        //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)           //{1 [apple peach]}
+	fmt.Println(res.Page)      //1
+	fmt.Println(res.Fruits[0]) //apple
+
+	/**
+	Except used bytes and strings as imtermediates between the data and JSON represation on standard out above.
+	We can also stream JSON encoding to os.Writer like os.Stdout or HTTP response bodies.
+	*/
+	enc := json.NewEncoder(os.Stdout)
+	d := map[string]int{"apple": 5, "orange": 7}
+	enc.Encode(d) //{"apple":5,"orange":7}
+}
