go编程之常见工具函数

1、时间格式化

　　基于模式的布局进行时间格式化和解析

package main

import "fmt"
import "time"

func main() {
    p := fmt.Println

    t := time.Now()
    p(t.Format(time.RFC3339))

    t1, e := time.Parse(
        time.RFC3339,
        "2012-11-01T22:08:41+00:00")
    p(t1)

    p(t.Format("3:04PM"))
    p(t.Format("Mon Jan _2 15:04:05 2006"))
    p(t.Format("2006-01-02T15:04:05.999999-07:00"))
    form := "3 04 PM"
    t2, e := time.Parse(form, "8 41 PM")
    p(t2)

    fmt.Printf("%d-%02d-%02dT%02d:%02d:%02d-00:00\n",
        t.Year(), t.Month(), t.Day(),
        t.Hour(), t.Minute(), t.Second())

    ansic := "Mon Jan _2 15:04:05 2006"
    _, e = time.Parse(ansic, "8:41PM")
    p(e)
}

　　执行上面代码，将得到以下输出结果

2017-03-23T11:41:52+08:00
2012-11-01 22:08:41 +0000 +0000
11:41AM
Thu Mar 23 11:41:52 2017
2017-03-23T11:41:52.246508+08:00
0000-01-01 20:41:00 +0000 UTC
2017-03-23T11:41:52-00:00
parsing time "8:41PM" as "Mon Jan _2 15:04:05 2006": cannot parse "8:41PM" as "Mon"

2、字符串格式化

package main

import "fmt"
import "os"

type point struct {
    x, y int
}

func main() {
    p := point{1, 2}
    fmt.Printf("%v\n", p)

    fmt.Printf("%+v\n", p)

    fmt.Printf("%#v\n", p)

    fmt.Printf("%T\n", p)

    fmt.Printf("%t\n", true)

    fmt.Printf("%d\n", 123)

    fmt.Printf("%b\n", 14)

    fmt.Printf("%c\n", 33)

    fmt.Printf("%x\n", 456)

    fmt.Printf("%f\n", 78.9)

    fmt.Printf("%e\n", 123400000.0)
    fmt.Printf("%E\n", 123400000.0)

    fmt.Printf("%s\n", "\"string\"")

    fmt.Printf("%q\n", "\"string\"")

    fmt.Printf("%x\n", "hex this")

    fmt.Printf("%p\n", &p)

    fmt.Printf("|%6d|%6d|\n", 12, 345)

    fmt.Printf("|%6.2f|%6.2f|\n", 1.2, 3.45)

    fmt.Printf("|%-6.2f|%-6.2f|\n", 1.2, 3.45)

    fmt.Printf("|%6s|%6s|\n", "foo", "b")

    fmt.Printf("|%-6s|%-6s|\n", "foo", "b")

    s := fmt.Sprintf("a %s", "string")
    fmt.Println(s)

    fmt.Fprintf(os.Stderr, "an %s\n", "error")
}

{1 2}
{x:1 y:2}
main.point{x:1, y:2}
main.point
true
123
1110
!
1c8
78.900000
1.234000e+08
1.234000E+08
"string"
"\"string\""
6865782074686973
0xc042004280
|    12|   345|
|  1.20|  3.45|
|1.20  |3.45  |
|   foo|     b|
|foo   |b     |
a string
an error

3、正则表达式

package main

import "bytes"
import "fmt"
import "regexp"

func main() {

    // This tests whether a pattern matches a string.
    match, _ := regexp.MatchString("p([a-z]+)ch", "peach")
    fmt.Println(match)

    // Above we used a string pattern directly, but for
    // other regexp tasks you'll need to `Compile` an
    // optimized `Regexp` struct.
    r, _ := regexp.Compile("p([a-z]+)ch")

    // Many methods are available on these structs. Here's
    // a match test like we saw earlier.
    fmt.Println(r.MatchString("peach"))

    // This finds the match for the regexp.
    fmt.Println(r.FindString("peach punch"))

    // This also finds the first match but returns the
    // start and end indexes for the match instead of the
    // matching text.
    fmt.Println(r.FindStringIndex("peach punch"))

    // The `Submatch` variants include information about
    // both the whole-pattern matches and the submatches
    // within those matches. For example this will return
    // information for both `p([a-z]+)ch` and `([a-z]+)`.
    fmt.Println(r.FindStringSubmatch("peach punch"))

    // Similarly this will return information about the
    // indexes of matches and submatches.
    fmt.Println(r.FindStringSubmatchIndex("peach punch"))

    // The `All` variants of these functions apply to all
    // matches in the input, not just the first. For
    // example to find all matches for a regexp.
    fmt.Println(r.FindAllString("peach punch pinch", -1))

    // These `All` variants are available for the other
    // functions we saw above as well.
    fmt.Println(r.FindAllStringSubmatchIndex(
        "peach punch pinch", -1))

    // Providing a non-negative integer as the second
    // argument to these functions will limit the number
    // of matches.
    fmt.Println(r.FindAllString("peach punch pinch", 2))

    // Our examples above had string arguments and used
    // names like `MatchString`. We can also provide
    // `[]byte` arguments and drop `String` from the
    // function name.
    fmt.Println(r.Match([]byte("peach")))

    // When creating constants with regular expressions
    // you can use the `MustCompile` variation of
    // `Compile`. A plain `Compile` won't work for
    // constants because it has 2 return values.
    r = regexp.MustCompile("p([a-z]+)ch")
    fmt.Println(r)

    // The `regexp` package can also be used to replace
    // subsets of strings with other values.
    fmt.Println(r.ReplaceAllString("a peach", "<fruit>"))

    // The `Func` variant allows you to transform matched
    // text with a given function.
    in := []byte("a peach")
    out := r.ReplaceAllFunc(in, bytes.ToUpper)
    fmt.Println(string(out))
}

　　执行上面代码，将得到以下输出结果

true
true
peach
[0 5]
[peach ea]
[0 5 1 3]
[peach punch pinch]
[[0 5 1 3] [6 11 7 9] [12 17 13 15]]
[peach punch]
true
p([a-z]+)ch
a <fruit>
a PEACH

4、Json

package main

import "encoding/json"
import "fmt"
import "os"

// We'll use these two structs to demonstrate encoding and
// decoding of custom types below.
type Response1 struct {
    Page   int
    Fruits []string
}
type Response2 struct {
    Page   int      `json:"page"`
    Fruits []string `json:"fruits"`
}

func main() {

    // First we'll look at encoding basic data types to
    // JSON strings. Here are some examples for atomic
    // values.
    bolB, _ := json.Marshal(true)
    fmt.Println(string(bolB))

    intB, _ := json.Marshal(1)
    fmt.Println(string(intB))

    fltB, _ := json.Marshal(2.34)
    fmt.Println(string(fltB))

    strB, _ := json.Marshal("gopher")
    fmt.Println(string(strB))

    // And here are some for slices and maps, which encode
    // to JSON arrays and objects as you'd expect.
    slcD := []string{"apple", "peach", "pear"}
    slcB, _ := json.Marshal(slcD)
    fmt.Println(string(slcB))

    mapD := map[string]int{"apple": 5, "lettuce": 7}
    mapB, _ := json.Marshal(mapD)
    fmt.Println(string(mapB))

    // The JSON package can automatically encode your
    // custom data types. It will only include exported
    // fields in the encoded output and will by default
    // use those names as the JSON keys.
    res1D := &Response1{
        Page:   1,
        Fruits: []string{"apple", "peach", "pear"}}
    res1B, _ := json.Marshal(res1D)
    fmt.Println(string(res1B))

    // You can use tags on struct field declarations
    // to customize the encoded JSON key names. Check the
    // definition of `Response2` above to see an example
    // of such tags.
    res2D := &Response2{
        Page:   1,
        Fruits: []string{"apple", "peach", "pear"}}
    res2B, _ := json.Marshal(res2D)
    fmt.Println(string(res2B))

    // Now let's look at decoding JSON data into Go
    // values. Here's an example for a generic data
    // structure.
    byt := []byte(`{"num":6.13,"strs":["a","b"]}`)

    // We need to provide a variable where the JSON
    // package can put the decoded data. This
    // `map[string]interface{}` will hold a map of strings
    // to arbitrary data types.
    var dat map[string]interface{}

    // Here's the actual decoding, and a check for
    // associated errors.
    if err := json.Unmarshal(byt, &dat); err != nil {
        panic(err)
    }
    fmt.Println(dat)

    // In order to use the values in the decoded map,
    // we'll need to cast them to their appropriate type.
    // For example here we cast the value in `num` to
    // the expected `float64` type.
    num := dat["num"].(float64)
    fmt.Println(num)

    // Accessing nested data requires a series of
    // casts.
    strs := dat["strs"].([]interface{})
    str1 := strs[0].(string)
    fmt.Println(str1)

    // We can also decode JSON into custom data types.
    // This has the advantages of adding additional
    // type-safety to our programs and eliminating the
    // need for type assertions when accessing the decoded
    // data.
    str := `{"page": 1, "fruits": ["apple", "peach"]}`
    res := Response2{}
    json.Unmarshal([]byte(str), &res)
    fmt.Println(res)
    fmt.Println(res.Fruits[0])

    // In the examples above we always used bytes and
    // strings as intermediates between the data and
    // JSON representation on standard out. We can also
    // stream JSON encodings directly to `os.Writer`s like
    // `os.Stdout` or even HTTP response bodies.
    enc := json.NewEncoder(os.Stdout)
    d := map[string]int{"apple": 5, "lettuce": 7}
    enc.Encode(d)
}

　　执行上面代码，将得到以下输出结果

true
1
2.34
"gopher"
["apple","peach","pear"]
{"apple":5,"lettuce":7}
{"Page":1,"Fruits":["apple","peach","pear"]}
{"page":1,"fruits":["apple","peach","pear"]}
map[num:6.13 strs:[a b]]
6.13
a
{1 [apple peach]}
apple
{"apple":5,"lettuce":7}

5、数字解析

package main

// The built-in package `strconv` provides the number
// parsing.
import "strconv"
import "fmt"

func main() {

    // With `ParseFloat`, this `64` tells how many bits of
    // precision to parse.
    f, _ := strconv.ParseFloat("1.234", 64)
    fmt.Println(f)

    // For `ParseInt`, the `0` means infer the base from
    // the string. `64` requires that the result fit in 64
    // bits.
    i, _ := strconv.ParseInt("123", 0, 64)
    fmt.Println(i)

    // `ParseInt` will recognize hex-formatted numbers.
    d, _ := strconv.ParseInt("0x1c8", 0, 64)
    fmt.Println(d)

    // A `ParseUint` is also available.
    u, _ := strconv.ParseUint("789", 0, 64)
    fmt.Println(u)

    // `Atoi` is a convenience function for basic base-10
    // `int` parsing.
    k, _ := strconv.Atoi("135")
    fmt.Println(k)

    // Parse functions return an error on bad input.
    _, e := strconv.Atoi("wat")
    fmt.Println(e)
}

　　执行上面代码，将得到以下输出结果

1.234
123
456
789
135
strconv.ParseInt: parsing "wat": invalid syntax

6、Url解析

package main

import "fmt"
import "net"
import "net/url"

func main() {

    s := "postgres://user:pass@host.com:5432/path?k=v#f"

    u, err := url.Parse(s)
    if err != nil {
        panic(err)
    }

    fmt.Println(u.Scheme)

    fmt.Println(u.User)
    fmt.Println(u.User.Username())
    p, _ := u.User.Password()
    fmt.Println(p)

    fmt.Println(u.Host)
    host, port, _ := net.SplitHostPort(u.Host)
    fmt.Println(host)
    fmt.Println(port)

    fmt.Println(u.Path)
    fmt.Println(u.Fragment)

    fmt.Println(u.RawQuery)
    m, _ := url.ParseQuery(u.RawQuery)
    fmt.Println(m)
    fmt.Println(m["k"][0])
}

　　执行上面代码，将得到以下输出结果

postgres
user:pass
user
pass
host.com:5432
host.com
5432
/path
f
k=v
map[k:[v]]
v

7、SHA1哈希

package main

// Go implements several hash functions in various
// `crypto/*` packages.
import "crypto/sha1"
import "fmt"

func main() {
    s := "sha1 this string"//原始字符串

    h := sha1.New()//加密对象

    h.Write([]byte(s))//将原始字符串转换成字节切片传给加密对象

    bs := h.Sum(nil)//哈希结果追加和片段  可以不需要

    fmt.Println(s)//打印原始字符串
    fmt.Printf("%x\n", bs)//输出哈希结果
}

　　执行上面代码，将得到以下输出结果

sha1 this string
cf23df2207d99a74fbe169e3eba035e633b65d94

8、Base64编码

　　Go提供对base64编码/解码的内置支持。导入带有b64名称的encoding/base64软件包，而不是默认的base64。它会节省我们一些空间。编码器需要一个[]byte，所以将字符串转换为该类型。

import b64 "encoding/base64"
import "fmt"

func main() {
    data := "abc123!?$*&()'-=@~"

    sEnc := b64.StdEncoding.EncodeToString([]byte(data))
    fmt.Println(sEnc)


    sDec, _ := b64.StdEncoding.DecodeString(sEnc)
    fmt.Println(string(sDec))
    fmt.Println()

    uEnc := b64.URLEncoding.EncodeToString([]byte(data))
    fmt.Println(uEnc)
    uDec, _ := b64.URLEncoding.DecodeString(uEnc)
    fmt.Println(string(uDec))
}

　　执行上面代码，将得到以下输出结果

YWJjMTIzIT8kKiYoKSctPUB+
abc123!?$*&()'-=@~

YWJjMTIzIT8kKiYoKSctPUB-
abc123!?$*&()'-=@~

9、文件读写

　　读取和写入文件是许多Go程序所需的基本任务。

1、读取文件

package main

import (
    "bufio"
    "fmt"
    "io"
    "io/ioutil"
    "os"
)
//检查error状态 如果包含错误信息  则使用panic中断
func check(e error) {
    if e != nil {
        panic(e)
    }
}

func main() {

    dat, err := ioutil.ReadFile("/tmp/dat")//直接读取文件内容到内存
    check(err)
    fmt.Print(string(dat))

    //使用os.Open打开文件 以获取文件的更多操作
    f, err := os.Open("/tmp/dat")
    check(err)

    b1 := make([]byte, 5)
    n1, err := f.Read(b1)//读取5个字节
    check(err)
    fmt.Printf("%d bytes: %s\n", n1, string(b1))

    o2, err := f.Seek(6, 0)//定位到文件开头6个字符后
    check(err)
    b2 := make([]byte, 2)
    n2, err := f.Read(b2)//读取2个字节
    check(err)
    fmt.Printf("%d bytes @ %d: %s\n", n2, o2, string(b2))

    o3, err := f.Seek(6, 0)
    check(err)
    b3 := make([]byte, 2)
    n3, err := io.ReadAtLeast(f, b3, 2)//使用io对象读取
    check(err)
    fmt.Printf("%d bytes @ %d: %s\n", n3, o3, string(b3))

    _, err = f.Seek(0, 0)//定位到文件开始位置
    check(err)

    r4 := bufio.NewReader(f)//bufio先读取到缓存
    b4, err := r4.Peek(5)//然后从缓存中拿字节  比较高效
    check(err)
    fmt.Printf("5 bytes: %s\n", string(b4))

    f.Close()
}

　　执行上面代码，将得到以下输出结果

abcdfawef!@
cawfe
awefawef

awefaf
5 bytes: abcdf
2 bytes @ 6: we
2 bytes @ 6: we
5 bytes: abcdf

2、文件写入

package main

import (
    "bufio"
    "fmt"
    "io/ioutil"
    "os"
)

func check(e error) {
    if e != nil {
        panic(e)
    }
}

func main() {
    d1 := []byte("hello\ngo\n")
    err := ioutil.WriteFile("dat1.txt", d1, 0644)
    check(err)

    f, err := os.Create("dat2.txt")
    check(err)

    defer f.Close()//延迟关闭文件操作(f超出作用域)

    d2 := []byte{115, 111, 109, 101, 10}
    n2, err := f.Write(d2)
    check(err)
    fmt.Printf("wrote %d bytes\n", n2)

    n3, err := f.WriteString("writes\n")
    fmt.Printf("wrote %d bytes\n", n3)

    f.Sync()

    w := bufio.NewWriter(f)
    n4, err := w.WriteString("buffered\n")
    fmt.Printf("wrote %d bytes\n", n4)

    w.Flush()
}

10、行过滤器

package main

import (
    "bufio"//读写
    "fmt"//格式化输出
    "os"//操作系统
    "strings"//字符串
)

func main() {
    scanner := bufio.NewScanner(os.Stdin)//扫描标准输入

    for scanner.Scan() {
        ucl := strings.ToUpper(scanner.Text())//标
        fmt.Println(ucl)
    }

    if err := scanner.Err(); err != nil {//发送错误  退出
        fmt.Fprintln(os.Stderr, "error:", err)
        os.Exit(1)
    }
}

11、环境变量

　　通过os包获取和设置环境变量

package main

import "os"
import "strings"
import "fmt"

func main() {

    // To set a key/value pair, use `os.Setenv`. To get a
    // value for a key, use `os.Getenv`. This will return
    // an empty string if the key isn't present in the
    // environment.
    os.Setenv("FOO", "1")
    fmt.Println("FOO:", os.Getenv("FOO"))
    fmt.Println("BAR:", os.Getenv("BAR"))

    // Use `os.Environ` to list all key/value pairs in the
    // environment. This returns a slice of strings in the
    // form `KEY=value`. You can `strings.Split` them to
    // get the key and value. Here we print all the keys.
    fmt.Println()
    for _, e := range os.Environ() {
        pair := strings.Split(e, "=")
        fmt.Println(pair[0])
    }
}

12、信号

　　信号通知通过在通道上发送os.Signal值来工作。

package main

import "fmt"
import "os"
import "os/signal"
import "syscall"

func main() {

    sigs := make(chan os.Signal, 1)//信号通道
    done := make(chan bool, 1)

    signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)

    go func() {
        sig := <-sigs//等待信号
        fmt.Println()
        fmt.Println(sig)
        done <- true//发送给done通道
    }()

    fmt.Println("awaiting signal")
    <-done//收到匿名函数发送的true值后  退出程序
    fmt.Println("exiting")
}

　　执行上面代码，将得到以下输出结果

awaiting signal
[Ctl+C]
interrupt
exiting