英文:
Error Parsing Json using Go language
问题
我正在尝试使用GO语言解析JSON并打印数据，然后将其保存在CSV文件中。
使用Println函数可以打印每页所需的10个结果，但无法解析JSON。
以下是我的操作步骤：
-
访问studentresults.com/page=1，显示10个学生的RollNo和Marks，并将其保存在CSV文件中（使用
key.rollno和key.marks）。 -
程序向studentsapimarks.com/api/rollno1,rollno2,rollno3/detail发送请求（将步骤1中获取的所有key.rollno拼接在一起）。
JSON响应如下：[{"name":"James","Percentage":96.5,"Remarks":"VeryGood"}, {"name":"William","Percentage":36.0,"Remarks":"Bad"}, {"name":"Jacob","Percentage":63.0,"Remarks":"Average"}, {"name":"Wilson","Percentage":69.3,"Remarks":"Average"}, {"name":"Kurtson","Percentage":16.9,"Remarks":"VeryBad"}, {"name":"Tom","Percentage":86.3,"Remarks":"Good"}] -
提取Name和Percentage字段，并保存在CSV文件中。
以下是负责打印和保存结果的代码片段：
package main
import (
"encoding/csv"
"fmt"
"net/http"
"os"
"strings"
"encoding/json"
)
type Key struct {
fname string
marks int
rollno int
}
type object struct {
Percentage float64
Name string `json:"name"`
}
func PageRequest(w http.ResponseWriter, r *http.Request) {
// 页面头部
fmt.Fprintf(w, PageHeader, pages, previous, next)
// 保存到CSV文件
csvfile, err := os.OpenFile("marks.csv", os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0666)
if err != nil {
fmt.Println("Error:", err)
return
}
defer csvfile.Close()
writer := csv.NewWriter(csvfile)
defer writer.Flush()
// 定义RollNos
var rollNos []string
// 计算UID的Marks
UID, length := compute(start)
for i := 0; i < length; i++ {
key := UID[i]
// 打印firstname、Marks和Rollno
fmt.Fprintf(w, key.fname, key.marks, key.rollno)
records := [][]string{{key.fname, key.marks, key.rollno}}
for _, record := range records {
err := writer.Write(record)
if err != nil {
fmt.Println("Error:", err)
return
}
}
// 添加所有的key.rollno
rollNos := append(rollNos, key.rollno)
// 发送请求到studentsapimarks.com/api/rollno1,rollno2,rollno3/detail
uri := "https://studentsapimarks.com/api/" + strings.Join(rollNos, ",") + "/detail"
res, err := http.Get(uri)
if err != nil {
log.Fatal(err)
}
defer res.Body.Close()
var s []object
err = json.NewDecoder(res.Body).Decode(&s)
if err != nil {
log.Fatal(err)
}
// 打印Name和Percentage
fmt.Println(s[0].Name)
fmt.Println(s[0].Percentage)
}
// 页面底部
fmt.Fprintf(w, PageFooter, previous, next)
}
func main() {
http.HandleFunc("/", PageRequest)
log.Println("Listening")
log.Fatal(http.ListenAndServe(":8080", nil))
}
`fmt.Fprintf(w, key.fname, key.marks, key.rollno)`可以正常工作，每页显示所有10个结果并保存在CSV文件中。
代码的问题是：
1. 没有将步骤1中获取的所有`key.rollno`追加到`studentsapimarks.com/api/rollno1,rollno2,rollno3/detail`中。
2. 如何将提取的JSON结果`s[0].name`保存到CSV文件中？
<details>
<summary>英文:</summary>
I am trying to Parse Json & Print Data and save in a CSV using GO language .
It is printing the desired 10 result per page with `Println` but couldn't parse JSON .
This is what I am doing
1. Visitor visits studentresults.com/page=1 RollNo. & Marks for 10 students are displayed and it is also saved in a CSV [`key.rollno` & `key.marks`]
2. Program Makes a request to `studentsapimarks.com/api/rollno1,rollno2,rollno3/detail` (appending all key.rollno that we got in step1)
The Json response would be like
[{"name":"James","Percentage":96.5,"Remarks":"VeryGood"},
{"name":"William","Percentage":36.0,"Remarks":"Bad"},
{"name":"Jacob","Percentage":63.0,"Remarks":"Average"},
{"name":"Wilson","Percentage":69.3,"Remarks":"Average"},
{"name":"Kurtson","Percentage":16.9,"Remarks":"VeryBad"},
{"name":"Tom","Percentage":86.3,"Remarks":"Good"}]
3. Extract Name & Percentage fields & save in a csv
Here is my snippet of the code that is responsible for printing and saving the results
package main
import (
"encoding/csv"
"fmt"
"net/http"
"os"
"strings"
"encoding/json"
)
type Key struct {
fname string
marks int
rollno int
}
type object struct {
Percentage float64
Name string `json:"name"`
}
func PageRequest(w http.ResponseWriter, r *http.Request) {
// Page header
fmt.Fprintf(w, PageHeader, pages, previous, next)
// Save in csv
csvfile, err := os.OpenFile("marks.csv", os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0666)
if err != nil {
fmt.Println("Error:", err)
return
}
defer csvfile.Close()
writer := csv.NewWriter(csvfile)
defer writer.Flush()
// Defining RollNos
var rollNos []string
// Marks for UID
UID, length := compute(start)
for i := 0; i < length; i++ {
key := UID[i]
// Prints firstname, Marks and Rollno
fmt.Fprintf(w, key.fname, key.marks, key.rollno)
records := [][]string{{key.fname, key.marks, key.rollno}}
for _, record := range records {
err := writer.Write(record)
if err != nil {
fmt.Println("Error:", err)
return
}
}
// Append All key.rollno
rollNos := append(rollNos, key.rollno)
// Makes a request to as studentsapimarks.com/api/rollno1,rollno2,rollno3/detail
uri := "https://studentsapimarks.com/api/" + strings.Join(rollNos, ",") + "/detail"
res, err := http.Get(uri)
if err != nil {
log.Fatal(err)
}
defer res.Body.Close()
var s []object
err = json.NewDecoder(res.Body).Decode(&s)
if err != nil {
log.Fatal(err)
}
// Prints Name/ Percentage
fmt.Println(s[0].Name)
fmt.Println(s[0].Percentage)
}
// Page Footer
fmt.Fprintf(w, PageFooter, previous, next)
}
func main() {
http.HandleFunc("/", PageRequest)
log.Println("Listening")
log.Fatal(http.ListenAndServe(":8080", nil))
}
`fmt.Fprintf(w, key.fname, key.marks, key.rollno)` is working fine and displays all 10 results per page and saves in a csv .
Problem with the code is
1. It is not appending all `key.rollno` that we got in step1 as `studentsapimarks.com/api/rollno1,rollno2,rollno3/detail`
2. Also how could i save the JSON extracted `s[0].name` results in a CSV ?
</details>
# 答案1
**得分**: 1
JSON解析失败是因为你试图将一个JSON数组解组成一个结构体。你想要将JSON数组解组成一个切片 - 外部结构体是不必要的：
```go
var s []object
err = json.NewDecoder(res.Body).Decode(&s)
此外，它只能解组导出字段（以大写字母开头的字段），所以要获取名称，你需要更改结构体定义。我猜测百分比也没有传递过来，因为在JSON中它是一个单个的浮点数值，但在你的结构体中你使用了一个浮点数切片。
type object struct {
// "Percentage": 96.4 不是一个切片。
// 另外，如果Go和JSON中的字段名相同，你不需要json标签。
Percentage float64
// 字段必须大写，标签可以保持小写
Name string `json:"name"`
}
然后你可以相应地访问这些字段：
// 打印名称/百分比
fmt.Println(s[0].Name)
fmt.Println(s[0].Percentage)
英文:
The JSON parsing is failing because you're trying to unmarshal a JSON array into a struct. You want to unmarshal a JSON array into a slice - the outer struct is not necessary:
var s []object
err = json.NewDecoder(res.Body).Decode(&s)
Also, it can only unmarshal exported fields (those that start with a capital letter), so to get the name, you'll need to change your struct definition. I'm guessing the percentage isn't coming through either, since in the JSON it's a single float value, but in your struct you're taking a float slice.
type object struct {
// "Percentage": 96.4 is not a slice.
// Also if the field name in Go and JSON are identical, you dont need the json tag.
Percentage float64
// The field must be capitalized, the tag can stay lowercase
Name string `json:"name"`
}
Then you'll access those fields accordingly:
// Prints Name/ Percentage
fmt.Println(s[0].Name)
fmt.Println(s[0].Percentage)
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