Google资深工程师深度讲解Go语言-错误处理和资源管理(七)
【摘要】
一.defer调用:实现资源管理
确保调用在函数结束时发生参数在defer语句时计算defer列表为后进先出
何时使用defer调用
Open/CloseLock/UnlockPrintHeader/PrintFooter
package main import "fmt" func tryDefer(){ defer fmt.Pr...
一.defer调用:实现资源管理
- 确保调用在函数结束时发生
- 参数在defer语句时计算
- defer列表为后进先出
何时使用defer调用
- Open/Close
- Lock/Unlock
- PrintHeader/PrintFooter
-
package main
-
-
import "fmt"
-
-
func tryDefer(){
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defer fmt.Println(1)
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defer fmt.Println(2)//defer 相当于栈:先进后出
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fmt.Println(3)
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//结果:3 2 1
-
}
-
func main() {
-
tryDefer()
-
}
-
package main
-
-
import (
-
"../../functional/fib"
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"bufio"
-
"fmt"
-
"os"
-
)
-
-
func tryDefer() {
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defer fmt.Println(1)
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defer fmt.Println(2) //defer 相当于栈:先进后出
-
fmt.Println(3)
-
//结果:3 2 1
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//return
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panic("error occurred")
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fmt.Println(4)
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//3
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//2
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//1
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//panic: error occurred
-
}
-
//参数在defer语句时计算
-
func tryDefer2() {
-
for i := 0; i < 100; i++ {
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defer fmt.Println(i) //
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if i == 10 {
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panic("print too many")
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}
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}
-
}
-
-
func writeFile(filename string) {
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file, err := os.Create(filename)
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if err != nil {
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panic(err)
-
}
-
defer file.Close()
-
-
writer := bufio.NewWriter(file)
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defer writer.Flush()
-
-
f := fib.Fibonacci()
-
for i := 0; i < 10; i++ {
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fmt.Fprintln(writer, f())
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}
-
}
-
-
func main() {
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//tryDefer()
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tryDefer2()
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writeFile("fib.txt")
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}
二.错误处理理念
-
func writeFile(filename string) {
-
//file, err := os.Create(filename)
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file, err := os.OpenFile(filename, os.O_EXCL|os.O_CREATE, 0666) //O_EXCL 如果文件存在的话打开不了
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// panic: open fib.txt: file exists
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err = errors.New("this is a custum error")
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if err != nil {
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//fmt.Println("Error:",err.Error())
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if pathError, ok := err.(*os.PathError); !ok {
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panic(err)
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} else {
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fmt.Printf("%s ,%s ,%s\n ", pathError.Op, pathError.Path, pathError.Err)
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}
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return
-
}
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defer file.Close()
-
-
writer := bufio.NewWriter(file)
-
defer writer.Flush()
-
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f := fib.Fibonacci()
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for i := 0; i < 10; i++ {
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fmt.Fprintln(writer, f())
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}
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}
三.服务器统一出错处理
web.go
-
package main
-
-
import (
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"./filelisting"
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"log"
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"net/http"
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"os"
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)
-
-
type appHandler func(writer http.ResponseWriter, request *http.Request) error
-
-
//错误包装
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func errWrapper(handler appHandler) func(http.ResponseWriter, *http.Request) {
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return func(writer http.ResponseWriter, request *http.Request) {
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err := handler(writer, request)
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if err != nil {
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log.Printf("Error handing request:%s",err.Error()) //2020/08/29 17:17:36 Error handing request:open fib2.txt: permission denied
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code := http.StatusOK
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switch {
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case os.IsNotExist(err):
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//http.Error(writer, http.StatusText(http.StatusNotFound), http.StatusNotFound)
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code = http.StatusNotFound
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case os.IsPermission(err):
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code = http.StatusForbidden
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default:
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code = http.StatusInternalServerError
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}
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http.Error(writer, http.StatusText(code), code)
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}
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}
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}
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func main() {
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http.HandleFunc("/list/", errWrapper(filelisting.HandleFileList))
-
-
err := http.ListenAndServe(":8081", nil)
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if err != nil {
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panic(err)
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}
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}
handler.go
-
package filelisting
-
-
import (
-
"io/ioutil"
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"net/http"
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"os"
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)
-
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func HandleFileList(writer http.ResponseWriter, request *http.Request) error {
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path := request.URL.Path[len("/list/"):]
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file, err := os.Open(path)
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if err != nil {
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//panic(err)
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/*http.Error(writer,
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err.Error(),
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http.StatusInternalServerError)
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return*/
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return err
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}
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defer file.Close()
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all, err := ioutil.ReadAll(file)
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if err != nil {
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//panic(err)
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return err
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}
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writer.Write(all)
-
return nil
-
}
四.panic和recover
panin功能作用
- 停止当前函数执行
- 一直向上返回,执行每一层的defer
- 如果没有遇见recover,程序退出
recover功能作用
- 仅在defer调用中使用
- 获取panic的值
- 如果无法处理,可重新panic
-
package main
-
-
import (
-
"fmt"
-
)
-
-
func tryRecover() {
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defer func() {
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r := recover()
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if err, ok := r.(error); ok {
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fmt.Println("Error occurred:", err)
-
} else {
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fmt.Println(r)
-
}
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}()
-
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//panic(errors.New("this is an error")) //Error occurred: this is an error,下面不执行,panic停止当前函数执行
-
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b := 0
-
a := 5 / b
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fmt.Println(a) //Error occurred: runtime error: integer divide by zero
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}
-
func main() {
-
tryRecover()
-
}
五.服务器统一出错处理
- 意料之中的:使用error,如文件打不开
- 意料之外的:使用panic,如数组越界
文章来源: blog.csdn.net，作者：lxw1844912514，版权归原作者所有，如需转载，请联系作者。
原文链接：blog.csdn.net/lxw1844912514/article/details/108291996
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