How to convert a time to UTC before marshaling as JSON in Go?

huangapple
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英文:

How to convert a time to UTC before marshaling as JSON in Go?

问题

我正在尝试定义一个Time结构体，该结构体实现了Marshaler接口，以便在将其编组为JSON时，以YYYY-mm-ddTHH:MM:SSZ的格式表示，即将时间转换为UTC并四舍五入到最近的秒。我尝试了以下程序：

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  6. 	"log"
  7. 	"time"
  8. )
  10. type Time struct {
  11. 	time.Time
  12. }
  14. func (t *Time) MarshalJSON() ([]byte, error) {
  15. 	return []byte(t.Time.UTC().Round(time.Second).Format(time.RFC3339)), nil
  16. }
  18. func main() {
  19. 	tm := time.Now()
  20. 	// tm := time.Now().UTC().Round(time.Second)
  22. 	tmJSON, err := json.Marshal(tm)
  23. 	if err != nil {
  24. 		log.Fatalf("marshal time: %v", err)
  25. 	}
  27. 	fmt.Println(string(tmJSON))
  28. }

然而，当我运行这个程序时，它打印出：

  1. > go run main.go
  2. "2022-12-07T16:32:51.494597-08:00"

相比之下，如果我将time.Now().UTC().Round(time.Second)作为要编组的输入（即在上面的代码片段中使用被注释掉的那一行），我会得到期望的输出：

  1. > go run main.go
  2. "2022-12-08T00:41:10Z"

我的问题是：为什么我不能在MarshalJSON方法本身中执行UTC转换和四舍五入到最近的秒？

英文:

I'm trying to define a Time struct which implements the Marshaler interface such that, when it is marshaled to JSON, it is represented in the format YYYY-mm-ddTHH:MM:SSZ, that is, the time is converted to UTC and rounded to the nearest second. I've tried the following program:

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  6. 	"log"
  7. 	"time"
  8. )
  10. type Time struct {
  11. 	time.Time
  12. }
  14. func (t *Time) MarshalJSON() ([]byte, error) {
  15. 	return []byte(t.Time.UTC().Round(time.Second).Format(time.RFC3339)), nil
  16. }
  18. func main() {
  19. 	tm := time.Now()
  20. 	// tm := time.Now().UTC().Round(time.Second)
  22. 	tmJSON, err := json.Marshal(tm)
  23. 	if err != nil {
  24. 		log.Fatalf("marshal time: %v", err)
  25. 	}
  27. 	fmt.Println(string(tmJSON))
  28. }

When I run this, however, it prints

  1. > go run main.go
  2. "2022-12-07T16:32:51.494597-08:00"

If, by contrast, I pass in time.Now().UTC().Round(time.Second) as the input to be marshaled (i.e., use the commented-out line in the snippet above), I get the desired output:

  1. > go run main.go
  2. "2022-12-08T00:41:10Z"

My question is: why can't I perform the conversion to UTC and rounding to the nearest second in the MarshalJSON method itself?

答案1

得分: 1

你想做什么？

我尝试运行你的MarshalJSON函数，结果符合预期。

以下是我尝试做的事情：

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  6. 	"log"
  7. 	"time"
  8. )
  10. type Time struct {
  11. 	time.Time
  12. }
  14. func (t *Time) MarshalJSON() ([]byte, error) {
  15. 	return []byte(t.Time.UTC().Round(time.Second).Format(time.RFC3339)), nil
  16. }
  18. func main() {
  19. 	// tm := time.Now().UTC()
  20. 	tm := time.Now().UTC().Round(time.Second)
  22. 	tmJSON, err := json.Marshal(tm)
  23. 	if err != nil {
  24. 		log.Fatalf("marshal time: %v", err)
  25. 	}
  27. 	fmt.Println(string(tmJSON))
  29. 	marshal_time := Time{time.Now().UTC()}
  30. 	byt_arr, _ := marshal_time.MarshalJSON()
  31. 	fmt.Println(string(byt_arr))
  32. }

我得到了以下输出：

  1. "2022-12-08T04:41:59Z"
  2. 2022-12-08T04:41:59Z

第一行是你之前的输出，第二行是你的MarshalJSON函数的输出。

英文:

what are you trying to do?

I tried running your MarshalJSON function and it works as expected

here is what I tried to do:

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  6. 	"log"
  7. 	"time"
  8. )
  10. type Time struct {
  11. 	time.Time
  12. }
  14. func (t *Time) MarshalJSON() ([]byte, error) {
  15. 	return []byte(t.Time.UTC().Round(time.Second).Format(time.RFC3339)), nil
  16. }
  18. func main() {
  19. 	// tm := time.Now().UTC()
  20. 	tm := time.Now().UTC().Round(time.Second)
  22. 	tmJSON, err := json.Marshal(tm)
  23. 	if err != nil {
  24. 		log.Fatalf("marshal time: %v", err)
  25. 	}
  27. 	fmt.Println(string(tmJSON))
  29. 	marshal_time := Time{time.Now().UTC()}
  30. 	byt_arr, _ := marshal_time.MarshalJSON()
  31. 	fmt.Println(string(byt_arr))
  32. }

and i got the following output:

  1. "2022-12-08T04:41:59Z"
  2. 2022-12-08T04:41:59Z

The first line is your previous output and the second output is of your MarshalJSON function.

答案2

得分: 0

你可以使用AppendFormat将时间字符串转换为缓冲区。

此外，在你的问题中，你没有初始化用于编组的Time结构。

以下是一个可能的解决方案：

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"errors"
  6. 	"fmt"
  7. 	"log"
  8. 	"time"
  9. )
  11. type Time struct {
  12. 	time.Time
  13. }
  15. func (t *Time) MarshalJSON() ([]byte, error) {
  16. 	if y := t.Year(); y < 0 || y >= 10000 {
  17. 		return nil, errors.New("Time.MarshalJSON: year outside of range [0,9999]")
  18. 	}
  20. 	b := make([]byte, 0, len(time.RFC3339)+2)
  21. 	b = append(b, '"')
  22. 	b = t.UTC().Round(time.Second).AppendFormat(b, time.RFC3339)
  23. 	b = append(b, '"')
  24. 	return b, nil
  25. }
  27. func main() {
  28. 	now := time.Now()
  29. 	mt := &Time{now}
  30. 	bytArr, err := json.Marshal(mt)
  31. 	if err != nil {
  32. 		log.Fatalf("marshal time: %v", err)
  33. 	}
  35. 	fmt.Println(string(bytArr))
  36. }

希望对你有帮助！

英文:

You can use AppendFormat to convert your time string into buffer.

Also in your question you are not initialising your Time struct for Marshalling.

Here is a probable solution

  1. package main
  3. import (
  4. 	&quot;encoding/json&quot;
  5. 	&quot;errors&quot;
  6. 	&quot;fmt&quot;
  7. 	&quot;log&quot;
  8. 	&quot;time&quot;
  9. )
  11. type Time struct {
  12. 	time.Time
  13. }
  15. func (t *Time) MarshalJSON() ([]byte, error) {
  16. 	if y := t.Year(); y &lt; 0 || y &gt;= 10000 {
  17. 		return nil, errors.New(&quot;Time.MarshalJSON: year outside of range [0,9999]&quot;)
  18. 	}
  20. 	b := make([]byte, 0, len(time.RFC3339)+2)
  21. 	b = append(b, &#39;&quot;&#39;)
  22. 	b = t.UTC().Round(time.Second).AppendFormat(b, time.RFC3339)
  23. 	b = append(b, &#39;&quot;&#39;)
  24. 	return b, nil
  25. }
  27. func main() {
  28. 	now := time.Now()
  29. 	mt := &amp;Time{now}
  30. 	bytArr, err := json.Marshal(mt)
  31. 	if err != nil {
  32. 		log.Fatalf(&quot;marshal time: %v&quot;, err)
  33. 	}
  35. 	fmt.Println(string(bytArr))
  36. }

huangapple
  • 本文由 发表于 2022年12月8日 08:42:19
  • 转载请务必保留本文链接：https://go.coder-hub.com/74724346.html
  • encoding-json-go
  • go
  • json
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