Go语言设置JSON的默认值操作

package main
import (
 "encoding/json"
 "fmt"
 "net"
 "net/http"
)
type JsonTest struct {
 Test1  string   `json:"test1"`
 Test2  []string  `json:"test2"`
}
//定义自己的路由器
type MyMux1 struct {
}
//实现http.Handler这个接口的唯一方法
func (mux *MyMux1) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 urlPath := r.URL.Path
 switch urlPath {
 case "/test":
 mux.testJson(w, r)
 default:
 http.Error(w, "没有此url路径", http.StatusBadRequest)
 }
}
func (mux *MyMux1) testJson(w http.ResponseWriter, r *http.Request) {
 if r.Method != "GET" {
 http.Error(w, "the method is not allowed", http.StatusMethodNotAllowed)
 }
 jsontest := &JsonTest{}
 //只初始化Test1字段
 jsontest.Test1 = "value1"
 
 jsondata,_ := json.Marshal(jsontest)
 w.Header().Set("Content-Type", "application/json")
 fmt.Fprintf(w, "%s", jsondata)
}
func main() {
 //实例化路由器Handler
 mymux := &MyMux1{}
 //基于TCP服务监听8088端口
 ln, err := net.Listen("tcp", ":8089")
 if err != nil {
 fmt.Printf("设置监听端口出错...")
 }
 //调用http.Serve(l net.Listener, handler Handler)方法，启动监听
 err1 := http.Serve(ln, mymux)
 if err1 != nil {
 fmt.Printf("启动监听出错")
 }
}

func (mux *MyMux1) testJson(w http.ResponseWriter, r *http.Request) {
 if r.Method != "GET" {
 http.Error(w, "the method is not allowed", http.StatusMethodNotAllowed)
 }
 jsontest := &JsonTest{}
 jsontest.Test1 = "value1"
 jsontest.Test2 = make([]string, 0)
 jsondata,_ := json.Marshal(jsontest)
 w.Header().Set("Content-Type", "application/json")
 fmt.Fprintf(w, "%s", jsondata)
}

package main
import (
 "fmt"
 "encoding/json"
)
type Test struct {
 A string
 B int
 C string
}
func (t *Test) UnmarshalJSON(data []byte) error {
 type testAlias Test
 test := &testAlias{
 A: "default A",
 B: -2,
 }
 _ = json.Unmarshal(data, test)
 *t = Test(*test)
 return nil
}
var example []byte = []byte(`[{"A": "1", "C": "3"}, {"A": "4", "B": 2}, {"C": "5"}]`)
func main() {
  out := &[]Test{}
  _ = json.Unmarshal(example, &out)
  fmt.Print(out)
}