java中IOUtil.readLong_使用io/ioutil进行读写文件
读文件：
package main
import (
"fmt"
"io/ioutil"
)
func main() {
b, err := ioutil.ReadFile("test.log")
if err != nil {
fmt.Print(err)
}
fmt.Println(b)
str := string(b)
fmt.Println(str)
}
写文件：
package main
import (
"io/ioutil"
)
func check(e error) {
if e != nil {
panic(e)
}
}
func main() {
d1 := []byte("hello\ngo\n")
err := ioutil.WriteFile("test.txt", d1,0644)
check(err)
}
使用os进行读写文件
首先要注意的就是两个打开文件的方法：
func Open
func Open(name string) (*File, error)
Open opens the named file for reading. If successful, methods on the returned file can be used for reading; the associated file descriptor has mode O_RDONLY. If there is an error, it will be of type *PathError.
读文件：
fi, err := os.Open(path)
if err != nil {
panic(err)
}
defer fi.Close()
func OpenFile
需要提供文件路径、打开模式、文件权限
func OpenFile(name string, flag int, perm FileMode) (*File, error)
OpenFile is the generalized open call; most users will use Open or Create instead. It opens the named file with specified flag (O_RDONLY etc.) and perm, (0666 etc.) if applicable. If successful, methods on the returned File can be used for I/O. If there is an error, it will be of type *PathError.
读文件：
package main
import (
"log"
"os"
)
func main() {
f, err := os.OpenFile("notes.txt", os.O_RDWR|os.O_CREATE,0755)
if err != nil {
log.Fatal(err)
}
if err := f.Close(); err != nil {
log.Fatal(err)
}
}
读方法
package main
import (
"bufio"
"fmt"
"io"
"io/ioutil"
"os"
)
func check(e error) {
if e != nil {
panic(e)
}
}
func main() {
f, err := os.Open("/tmp/dat")
check(err)
b1 := make([]byte,5)
n1, err := f.Read(b1)
check(err)
fmt.Printf("%d bytes: %s\n", n1, string(b1))
o2, err := f.Seek(6,0)
check(err)
b2 := make([]byte,2)
n2, err := f.Read(b2)
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)
check(err)
fmt.Printf("%d bytes @ %d: %s\n", n3, o3, string(b3))
_, err = f.Seek(0,0)
check(err)
r4 := bufio.NewReader(f)
b4, err := r4.Peek(5)
check(err)
fmt.Printf("5 bytes: %s\n", string(b4))
f.Close()
}
写方法
package main
import (
"bufio"
"fmt"
"io/ioutil"
"os"
)
func check(e error) {
if e != nil {
panic(e)
}
}
func main() {
f, err := os.Create("/tmp/dat2")
check(err)
defer f.Close()
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()
}
几种读取文件方法速度比较
package main
import (
"bufio"
"fmt"
"io"
"io/ioutil"
"os"
"time"
)
func read0(path string) string {
f, err := ioutil.ReadFile(path)
if err != nil {
fmt.Printf("%s\n", err)
panic(err)
}
return string(f)
}
func read1(path string) string {
fi, err := os.Open(path)
if err != nil {
panic(err)
}
defer fi.Close()
chunks := make([]byte,1024,1024)
buf := make([]byte,1024)
for {
n, err := fi.Read(buf)
if err != nil && err != io.EOF {
panic(err)
}
if0 == n {
break
}
chunks = append(chunks, buf[:n]...)
}
return string(chunks)
}
func read2(path string) string {
fi, err := os.Open(path)
if err != nil {
panic(err)
}
defer fi.Close()
r := bufio.NewReader(fi)
chunks := make([]byte,1024,1024)
buf := make([]byte,1024)
for {
n, err := r.Read(buf)
if err != nil && err != io.EOF {
panic(err)
}
if0 == n {
break
}
chunks = append(chunks, buf[:n]...)
}
return string(chunks)
}
func read3(path string) string {
fi, err := os.Open(path)
if err != nil {
panic(err)
}
defer fi.Close()
fd, err := ioutil.ReadAll(fi)
return string(fd)
}
func main() {
file := "test.log"
start := time.Now()
read0(file)
t0 := time.Now()
fmt.Printf("Cost time %v\n", t0.Sub(start))
read1(file)
t1 := time.Now()
fmt.Printf("Cost time %v\n", t1.Sub(t0))
read2(file)
t2 := time.Now()
fmt.Printf("Cost time %v\n", t2.Sub(t1))
read3(file)
t3 := time.Now()
fmt.Printf("Cost time %v\n", t3.Sub(t2))
}
运行结果：
Cost time 4.0105ms
Cost time 11.5043ms
Cost time 7.0042ms
Cost time 2.4983ms
Cost time 4.4925ms
Cost time 11.0053ms
Cost time 5.0082ms
Cost time 2.9992ms
Cost time 3.9866ms
Cost time 15.0085ms
Cost time 7.5054ms
Cost time 2.5035ms
Cost time 4.9989ms
Cost time 14.0112ms
Cost time 7.5045ms
Cost time 3.508ms
Cost time 3.0043ms
Cost time 15.0265ms
Cost time 8.9884ms
Cost time 2.0036ms
总结
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