go语言学习总结

package main

import (
	"bytes"
	"errors"
	"fmt"
	"io/ioutil"
	"net/http"
	"strconv"
	"strings"
)

六、文件读写删除操作

package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"strings"
)
func FileExist(filename string) bool {
	_, err := os.Stat(filename)
	if os.IsNotExist(err) {
		return false
	}
	fmt.Println(err)
	return err == nil || os.IsExist(err)
}

func ReadFileByLine(filename string) []string {
	if !FileExist(filename) {
		return []string{}
	}
	f, err := os.Open(filename)
	fmt.Println(err)
	defer f.Close()
	rd := bufio.NewReader(f)
	result := []string{}
	for {
		line, err := rd.ReadString('\n')
		if err == nil || io.EOF == err {
			line = strings.TrimSpace(line)
			if len(line) > 0 {
				result = append(result, line)
			}
		}
		if io.EOF == err {
			break
		}
		fmt.Println(err)
	}
	return result
}

func WriteFileByLine(filename string, data []string) {
	f, err := os.Create(filename)
	fmt.Println(err)
	defer f.Close()
	wt := bufio.NewWriter(f)
	for i := range data {
		_, err := wt.WriteString(data[i])
		if io.EOF == err {
			break
		}
		fmt.Println(err)
	}
	wt.Flush()
}

func DeleteFile(filename string) {
	if FileExist(filename) {
		err := os.Remove(filename)
		fmt.Println(err)
	}
}

package main

import (
	"errors"
	"fmt"
	"os/exec"
	"runtime"
	"strings"
)

func runInLinux(cmd string) string {
	fmt.Println("Running Linux Cmd:" + cmd)
	result, err := exec.Command("/bin/sh", "-c", cmd).Output()
	if err != nil {
		fmt.Println(err.Error())
	}
	return strings.TrimSpace(string(result))
}

func runInWindows(cmd string) string {
	fmt.Println("Running Win Cmd:" + cmd)
	result, err := exec.Command("cmd", "/c", cmd).Output()
	if err != nil {
		fmt.Println(err.Error())
	}
	return strings.TrimSpace(string(result))
}

func RunCommand(cmd string) string {
	if runtime.GOOS == "windows" {
		return runInWindows(cmd)
	} else {
		return runInLinux(cmd)
	}
}

func RunLinuxCommand(cmd string) string {
	if runtime.GOOS == "windows" {
		return ""
	} else {
		return runInLinux(cmd)
	}
}

func runInLinuxWithErr(cmd string) (string, error) {
	fmt.Println("Running Linux Cmd:" + cmd)
	result, err := exec.Command("/bin/sh", "-c", cmd).Output()
	if err != nil {
		fmt.Println(err.Error())
	}
	return strings.TrimSpace(string(result)), err
}

func runInWindowsWithErr(cmd string) (string, error) {
	fmt.Println("Running Win Cmd:" + cmd)
	result, err := exec.Command("cmd", "/c", cmd).Output()
	if err != nil {
		fmt.Println(err.Error())
	}
	return strings.TrimSpace(string(result)), err
}

func RunCommandWithErr(cmd string) (string, error) {
	if runtime.GOOS == "windows" {
		return runInWindowsWithErr(cmd)
	} else {
		return runInLinuxWithErr(cmd)
	}
}

func RunLinuxCommandWithErr(cmd string) (string, error) {
	if runtime.GOOS == "windows" {
		return "", errors.New("could not run in windows OS")

	} else {
		return runInLinuxWithErr(cmd)
	}
}

八、异常处理

Golang 有2个内置的函数 panic() 和 recover()，用以报告和捕获运行时发生的程序错误，与 error 不同，panic-recover 一般用在函数内部。一定要注意不要滥用 panic-recover，可能会导致性能问题，我一般只在未知输入和不可靠请求时使用。

golang 的错误处理流程：当一个函数在执行过程中出现了异常或遇到 panic()，正常语句就会立即终止，然后执行 defer 语句，再报告异常信息，最后退出 goroutine。如果在 defer 中使用了 recover() 函数,则会捕获错误信息，使该错误信息终止报告。

package main
import (
 "log"
 "strconv"
)
//捕获因未知输入导致的程序异常
func catch(nums ...int) int {
 defer func() {
  if r := recover(); r != nil {
   log.Println("[E]", r)
  }
 }()
 return nums[1] * nums[2] * nums[3] //index out of range
}
//主动抛出 panic，不推荐使用，可能会导致性能问题
func toFloat64(num string) (float64, error) {
 defer func() {
  if r := recover(); r != nil {
   log.Println("[W]", r)
  }
 }()
 if num == "" {
  panic("param is null") //主动抛出 panic
 }
 return strconv.ParseFloat(num, 10)
}
func main() {
 catch(2, 8)
 toFloat64("")
}

go语言有异常的返回会有两个返回参数包括值跟error，判断error是否为nil进行相应处理就可以最好不要panic

九、defer(延迟语句)

defer语句会在函数返回前，从后到前的依次执行defer

package main

import (
	"fmt"
)

func main() {
	fmt.Println("start================")
	fmt.Println("t5返回值", t5())
	fmt.Println("end================")
}
func t1() {
	fmt.Println("t1")
}
func t2() {
	fmt.Println("t2")
}
func t3() {
	fmt.Println("t3")
}
func t4() {
	fmt.Println("t4")
}
func t5() int {
	defer t1()
	defer t2()
	defer t3()
	defer t4()
	return 1
}

程序输出:
start================
t4
t3
t2
t1
t5返回值 1
end================

十、数据库操作

package main

import (
	"database/sql"
	"errors"
	"fmt"
	"sync"

	_ "github.com/mattn/go-sqlite3"
)

var db *sql.DB
var dbLock sync.Mutex

func main() {
	//查询调用RunQuery或者RunQueryWithErr
	//?为占位符对应相应参数
	rows := RunQuery("select age from table where id = ? and name = ?", 1, "abc")
	//也可以使用struct构建对象,获取数据库字段时需要用sql.Null...否则取空值会报错
	var age sql.NullInt64
	var ages []Int64

	//如果有多条返回值用for循环遍历,如果确定只有一条可以用if,这里只有一条所以用if,也可以将if改为for
	if rows.Next() {
		err := rows.Scan(&age)
		if err != nil {
			//........
		}
		//sql.NullInt64中有两个方法Int64和Valid,Valid用来判断值是否为空返回值为true、false
		//Int64为实际值,sql.NullInt64对象如果为空Int64值为0
		if age.Valid {
			//对获取到的age做操作
			fmt.Println(age.Int64)
		}
	}
	//sqlite3中使用完rows之后一定要调用close释放锁,否则继续调用数据库语句会报数据库被锁的异常
	rows.Close()
	//sqlite3中查询和增删改不能同时进行,也会报数据库被锁的异常
	//需要在查询之后统一进行增删改操作,增删改调用ExecSQL或ExecSqlWithErr
}

func OpenDB() {
	var err error
	//foo.db为数据库名字
	db, err = sql.Open("sqlite3", "./foo.db?_txlock=exclusive")
	fmt.Println(err)
	_, err = db.Exec("PRAGMA synchronous = OFF;")
	fmt.Println(err)
}

func CloseDB() {
	if db != nil {
		err := db.Close()
		db = nil
		fmt.Println(err)
	}
}

func ExecSQL(query string, args ...interface{}) sql.Result {
	dbLock.Lock()
	defer dbLock.Unlock()
	if db == nil {
		OpenDB()
	}
	if query == "" {
		panic("Empty sql input")
	}
	fmt.Println("Running Exec:")
	fmt.Println(query)
	fmt.Println(args...)
	res, err := db.Exec(query, args...)
	fmt.Println(err)
	return res
}

func RunQuery(query string, args ...interface{}) *sql.Rows {
	dbLock.Lock()
	defer dbLock.Unlock()
	if db == nil {
		OpenDB()
	}
	if query == "" {
		panic("Empty sql input")
	}
	fmt.Println("Running Query:")
	fmt.Println(query)
	fmt.Println(args...)
	res, err := db.Query(query, args...)
	fmt.Println(err)
	return res
}
//多条语句的事物操作
func ExecTransaction(querys []string, args [][]string) {
	dbLock.Lock()
	defer dbLock.Unlock()
	if db == nil {
		OpenDB()
	}
	tx, err := db.Begin()
	fmt.Println(err)
	fmt.Println("Running Trans:")
	for index, query := range querys {
		if query == "" {
			panic("Empty sql input")
		}
		oldArgs := args[index]
		newArgs := make([]interface{}, len(oldArgs))
		for i, v := range oldArgs {
			newArgs[i] = interface{}(v)
		}
		fmt.Println(query)
		fmt.Println(newArgs...)
		_, err := tx.Exec(query, newArgs...)
		fmt.Println(err)
	}
	err = tx.Commit()
	fmt.Println(err)
}

func OpenDBWithErr() error {
	var err error
	db, err = sql.Open("sqlite3", "./pjm.db?_txlock=exclusive")
	if err != nil {
		return err
	}
	_, err = db.Exec("PRAGMA synchronous = OFF;")
	return err
}

func CloseDBWithErr() error {
	if db != nil {
		err := db.Close()
		db = nil
		return err
	}
	return nil
}

func ExecSQLWithErr(query string, args ...interface{}) (sql.Result, error) {
	dbLock.Lock()
	defer dbLock.Unlock()
	if db == nil {
		err := OpenDBWithErr()
		if err != nil {
			return nil, err
		}
	}
	if query == "" {
		return nil, errors.New("Empty sql input")
	}
	fmt.Println("Running Exec With Err:")
	fmt.Println(query)
	fmt.Println(args...)
	return db.Exec(query, args...)
}

func RunQueryWithErr(query string, args ...interface{}) (*sql.Rows, error) {
	dbLock.Lock()
	defer dbLock.Unlock()
	if db == nil {
		err := OpenDBWithErr()
		if err != nil {
			return nil, err
		}
	}
	if query == "" {
		return nil, errors.New("Empty sql input")
	}
	fmt.Println("Running Query With Err:")
	fmt.Println(query)
	fmt.Println(args...)
	return db.Query(query, args...)
}

func ExecTransactionWithErr(querys []string, args [][]string) error {
	dbLock.Lock()
	defer dbLock.Unlock()
	if db == nil {
		err := OpenDBWithErr()
		if err != nil {
			return err
		}
	}
	tx, err := db.Begin()
	if err != nil {
		return err
	}
	fmt.Println("Running Trans With Err:")
	for index, query := range querys {
		if query == "" {
			return errors.New("Empty sql input")
		}
		oldArgs := args[index]
		newArgs := make([]interface{}, len(oldArgs))
		for i, v := range oldArgs {
			newArgs[i] = interface{}(v)
		}
		fmt.Println(query)
		fmt.Println(newArgs...)
		_, err := tx.Exec(query, newArgs...)
		if err != nil {
			return err
		}
	}
	return tx.Commit()
}

十一、go语言web编程

package main

import (
	"fmt"
	"html/template"
	"log"
	"net/http"
	"strings"
)

func sayhelloName(w http.ResponseWriter, r *http.Request) {
	r.ParseForm() //解析url传递的参数，对于POST则解析响应包的主体（request body）
	//注意:如果没有调用ParseForm方法，下面无法获取表单的数据
	fmt.Println(r.Form) //这些信息是输出到服务器端的打印信息
	fmt.Println("path", r.URL.Path)
	fmt.Println("scheme", r.URL.Scheme)
	fmt.Println(r.Form["url_long"])
	for k, v := range r.Form {
		fmt.Println("key:", k)
		fmt.Println("val:", strings.Join(v, ""))
	}
	fmt.Fprintf(w, "Hello astaxie!") //这个写入到w的是输出到客户端的
}

func login(w http.ResponseWriter, r *http.Request) {
	fmt.Println("method:", r.Method) //获取请求的方法
	//Handler里面是不会自动解析form的，必须显式的调用r.ParseForm()后，才能对这个表单数据进行操作
	r.ParseForm()
	if r.Method == "GET" {
		t, _ := template.ParseFiles("login.html")
		t.Execute(w, nil)
	} else {
		//请求的是登陆数据，那么执行登陆的逻辑判断
		fmt.Println("username:", r.Form["username"])
		fmt.Println("password:", r.Form["password"])
		//获取username的值需要[0]
		if r.Form["username"][0] == "abc" {
			//如果username为abc跳转到user.html页面打印abc=====
			t, _ := template.ParseFiles("./user.html")
			//t.Execute第二个参数可以传各种类型的数据到页面
			t.Execute(w, "abc=====")
		} else if r.Form["username"][0] == "efg" {
			t, _ := template.ParseFiles("./userMap.html")
			result := map[string]string{}
			result["key"] = "value"
			//返回map
			t.Execute(w, result)
		} else {
			t, _ := template.ParseFiles("./userMaps.html")
			result := []map[string]string{}
			m1 := map[string]string{}
			m2 := map[string]string{}
			m3 := map[string]string{}
			m1["a1"] = "111"
			m1["a2"] = "222"
			m1["a3"] = "333"
			m1["a4"] = "444"
			m2["a1"] = "555"
			m2["a2"] = "666"
			m2["a3"] = "777"
			m2["a4"] = "888"
			m3["a1"] = "999"
			m3["a2"] = "123"
			m3["a3"] = "456"
			m3["a4"] = "789"
			result = append(result, m1, m2, m3)
			//返回多个map
			t.Execute(w, result)
		}
	}
}

func main() {
	http.HandleFunc("/", sayhelloName)       //设置访问的路由
	http.HandleFunc("/login", login)         //设置访问的路由
	err := http.ListenAndServe(":9090", nil) //设置监听的端口
	if err != nil {
		log.Fatal("ListenAndServe: ", err)
	}
}

<html>
<head>
<title></title>
</head>
<body>
<form action="/login" method="post">
    用户名:<input type="text" name="username">
    密码:<input type="password" name="password">
    <input type="submit" value="登陆">
</form>
</body>
</html>

<html>
<head>
<title></title>
</head>
<body>
从后台获取的值为: {{.}}
</body>
</html>

<html>
<head>
<title></title>
</head>
<body>
从后台获取的值为: {{.key}}
</body>
</html>

<html>
<head>
<title></title>
</head>
<body>
{{range $index,$re :=.}}
{{$re.a1}}</br>
{{$re.a2}}</br>
{{$re.a3}}</br>
{{$re.a4}}</br>
{{end}}
</body>
</html>

//分页方法，根据传递过来的页数，每页数，总数，返回分页的内容 7个页数 前 1，2，3，4，5 后 的格式返回,小于5页返回具体页数
func Paginator(page, prepage int, nums int64) map[string]interface{} {

	var firstpage int //前一页地址
	var lastpage int  //后一页地址
	//根据nums总数，和prepage每页数量 生成分页总数
	totalpages := int(math.Ceil(float64(nums) / float64(prepage))) //page总数
	if page > totalpages {
		page = totalpages
	}
	if page <= 0 {
		page = 1
	}
	var pages []int
	switch {
	case page >= totalpages-5 && totalpages > 5: //最后5页
		start := totalpages - 5 + 1
		firstpage = page - 1
		lastpage = int(math.Min(float64(totalpages), float64(page+1)))
		pages = make([]int, 5)
		for i, _ := range pages {
			pages[i] = start + i
		}
	case page >= 3 && totalpages > 5:
		start := page - 3 + 1
		pages = make([]int, 5)
		firstpage = page - 3
		for i, _ := range pages {
			pages[i] = start + i
		}
		firstpage = page - 1
		lastpage = page + 1
	default:
		pages = make([]int, int(math.Min(5, float64(totalpages))))
		for i, _ := range pages {
			pages[i] = i + 1
		}
		firstpage = int(math.Max(float64(1), float64(page-1)))
		lastpage = page + 1
		//fmt.Println(pages)
	}
	paginatorMap := make(map[string]interface{})
	paginatorMap["pages"] = pages
	paginatorMap["totalpages"] = totalpages
	paginatorMap["firstpage"] = firstpage
	paginatorMap["lastpage"] = lastpage
	paginatorMap["currpage"] = page
	return paginatorMap
}

  <div class="am-cf">
  共{{.totals}}条记录 共记{{.paginator.totalpages}} 页 当前页  {{.paginator.currpage}}
  <div class="am-fr">
    <ul class="am-pagination">
    <li class=""><a href="/clubadmin/topics/{{.paginator.firstpage}}">«</a></li> 
    {{range $index,$page := .paginator.pages}}
      <li  {{if eq $.paginator.currpage $page }}class="am-active"{{end}}><a href="/clubadmin/topics/{{$page}}">{{$page}}</a></li>  
    {{end}}
      <li><a href="/clubadmin/topics/{{.paginator.lastpage}}">»</a></li>
    </ul>
  </div>
</div>