Java复习（5）－I/O

1.字节流操作

字节流操作的输入／输出。这里介绍2个类：

输入：FileInputStream

输出：FileOutputStream

1.1 FileInputStream

读入的文件内容如图：

代码如下：
import java.io.*;

public class FileInput {

public static void main(String[] args){
try{
FileInputStream file = new FileInputStream("/Users/xxm/Documents/soft/helloSpark.txt");
while(file.available() > 0){
System.out.println((char)file.read());
}
file.close();
}
catch(Exception e){
System.out.println("not found file");
}
}
}

运行结果：

H
e
l
l
o

S
p
a
r
k

H
e
l
l
o

H
a
d
o
o
p

H
e
l
l
o

F
l
i
n
k

S
p
a
r
k

i
s

A
w
e
s
o
m
e

1.2 FileOutputStream

实现功能：把上面出现的文件helloSpark.txt中的内容复制到新的文件write.txt里，并加入自己的一些字节。

代码如下：

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileOutput {
public static void main(String[] args){
int i;
try{
FileInputStream aa = new FileInputStream("/Users/xxm/Documents/soft/helloSpark.txt");
FileOutputStream bb = new FileOutputStream("/Users/xxm/Documents/soft/write.txt");
bb.write('h');
bb.write('e');
bb.write('l');
bb.write('l');
bb.write('o');
bb.write('\n');
byte[] writetest ={'w','r','i','t','e',' ','f','r','o','m',' ','m','y',' ','f','i','l','e'};
bb.write(writetest);
bb.write('\n');
i = aa.read();
while(i != -1){
bb.write(i);
i = aa.read();

}
aa.close();
bb.close();
}
catch(IOException e){
System.out.println("do not open this file");
}
}
}

运行结果，在文件中打开write.txt查看内容。



1.3 DataInputStream和DataOutputStream用法

使用的类DataInputStream（Obj）和DataOutputStream（Obj）来读写文件。

import java.io.*;

public class DataOne {
public static void main(String[] args) {

try{
FileOutputStream file1 = new FileOutputStream("/Users/xxm/Documents/soft/do.txt");
DataOutputStream da = new DataOutputStream(file1);
da.writeInt(12);
da.writeDouble(12.12d);
da.writeBoolean(true);
da.writeChars("Java数据流#");
file1.close();

FileInputStream file2 = new FileInputStream("/Users/xxm/Documents/soft/do.txt");
DataInputStream di = new DataInputStream(file2);
System.out.println(di.readInt());
System.out.println(di.readDouble());
System.out.println(di.readBoolean());
char aa;
while((aa = di.readChar()) != '#')
System.out.print(aa);
System.out.println("\n");
file2.close();
}
catch(IOException e){
System.out.println(e);
}

}
}

运行结果

12
12.12
true
Java数据流

1.4 用缓冲流读写

一个个字节读写速度太慢，不能满足要求，可以使用缓冲流来读写。

使用的类BufferedInputStream（Obj）和BufferedOutputStream（Obj）来读写文件。

import java.io.*;

public class DataTwo {
public static void main(String[] args){
FileInputStream fis;
FileOutputStream fos;
BufferedInputStream bis;
BufferedOutputStream bos;

int i;
try{
fis = new FileInputStream("/Users/xxm/Documents/soft/one.txt");
bis = new BufferedInputStream(fis);
fos = new FileOutputStream("/Users/xxm/Documents/soft/two.txt");
bos = new BufferedOutputStream(fos);

i = bis.read();
while(i!=-1){
bos.write(i);
bos.flush();
i = bis.read();
}
fis.close();
fos.close();
bis.close();
bos.close();

}
catch(IOException e){
System.out.println(e);
}
}
}

运行结果：



2.字符流操作

2.1 如何读写字符文件

用FileReader和FileWriter类进行读写字符文件。

2.1.1 FileReader

import java.io.*;

public class ReaderOne {
public static void main(String[] args){
try{
FileReader fr = new FileReader("/Users/xxm/Documents/soft/helloSpark.txt");
char[] c = new char[500];
while(fr.read(c) != -1){
System.out.print(new String(c));
fr.close();
}
}
catch(Exception e){
System.out.println(e);
}
}
}

运行结果：

Hello Spark
Hello Hadoop
Hello Flink
Spark is Awesomejava.io.IOException: Stream closed

这里运行出了问题java.io.IOException: Stream closed。修改了几次，每成功，先放放。有大神看到，可以留言问题在哪里？

2.1.2 通过字符读取文件

import java.io.BufferedReader;
import java.io.FileReader;

public class BufRW {
public static void main(String[] args){
try{
FileReader fr = new FileReader("/Users/xxm/Documents/soft/helloSpark.txt");
BufferedReader br = new BufferedReader(fr);

String a;
while((a = br.readLine()) != null){
System.out.println(a);
}
fr.close();
br.close();
}
catch(Exception e){
System.out.println(e);
}
}
}

运行结果：

Hello Spark
Hello Hadoop
Hello Flink
Spark is Awesome

2.1.2 通过字符读取文件及写入

package com.xxm.javaLange.test;

import java.io.*;

public class BufRW2 {
public static void main(String[] args){
try{
FileInputStream fis = new FileInputStream("/Users/xxm/Documents/soft/two.txt");
InputStreamReader isr = new InputStreamReader(fis);
BufferedReader br = new BufferedReader(isr);
FileOutputStream fos = new FileOutputStream("/Users/xxm/Documents/soft/one.txt");
OutputStreamWriter osw = new OutputStreamWriter(fos);
BufferedWriter bw = new BufferedWriter(osw);
String s;
while((s = br.readLine()) != null){
bw.write(s);
bw.flush();
}
br.close();
bw.close();
}
catch(IOException e){
System.out.println(e);
}
}
}

3.常用I/o处理文件

举个例子：

import java.io.*
;

public class FileDemo {
public static void main(String[] args){
File f2 = new File("/Users/xxm/Documents/soft/one.txt");
//File f2 = new File(f1,"/Users/xxm/Documents/soft/six.txt");
System.out.println(f2);
System.out.println(f2.exists());
System.out.println(f2.isFile());
System.out.println(f2.isDirectory());
System.out.println(f2.canRead());
System.out.println(f2.canWrite());
System.out.println(f2.isHidden());
System.out.println(f2.setReadOnly());
System.out.println(f2.getName());
System.out.println(f2.getParentFile());
System.out.println(f2.getAbsolutePath());
System.out.println(f2.lastModified());
System.out.println(f2.length());
System.out.println(f2.mkdir());

}
}

运行结果：

/Users/xxm/Documents/soft/one.txt
true
true
false
true
true
false
true
one.txt
/Users/xxm/Documents/soft
/Users/xxm/Documents/soft/one.txt
1457870343000
17
false

在使用中FileWriter的调试一直报错。不知是不是参考的书籍有误。所以找来博客中其他人的文章。作为参考

java中的 FileWriter类 和 FileReader类的一些基本用法

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