Java学习笔记 —— 22文件

文件



文件流



Java IO流类



分类



File实例

import java.io.File;
import java.io.IOException;

public class Demo2 {

public static void main(String[] args) {
// TODO Auto-generated method stub
//打开一个文件
File f = new File("d:\\aa.txt");

System.out.println("文件路径" + f.getAbsolutePath());

System.out.println("剩余空间" + f.getFreeSpace());

//创建文件
File f2 = new File("d:\\fasd.txt");
if ( !f2.exists() ) {
//创建文件
try {
f.createNewFile();
} catch (IOException e) {
// TODO: handle exception
e.printStackTrace();
}
} else {
System.out.println("文件已经存在");
}

//创建文件和文件夹
File f3 = new File("d:\\ff");

if( !f3.isDirectory() ){
try {
f3.mkdir();
} catch (Exception e) {
// TODO: handle exception
}
} else {
System.out.println("文件夹已经存在");
}

//列出一个文件夹下面的所有文件
File f4 = new File("D:\\ff");

if ( f4.isDirectory()) {
File[] lists = f4.listFiles();
for (int i = 0; i < lists.length; i++) {
System.out.println("list" + i + ":" + lists[i].getName());
}
}
}

}

FileInputStream实例

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

public class Demo3 {
public static void main(String[] args) {
File f = new File("D:/aa.txt");
FileInputStream fis = null;
//引文File没有读写能力，所以需要使用InputStream
try {

fis = new FileInputStream(f);

//定义一个字节数组
byte[] bytes = new byte[2048];
int n = 0;

//循环读取
while( (n=fis.read(bytes)) != -1){
//吧字节转换成String
String s = new String(bytes, 0 , n);
System.out.println(s);
}

} catch (Exception e) {
e.printStackTrace();
// TODO: handle exception
} finally {
//关闭文件流必须放这里
try {
fis.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}

FileOutputStream实例

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

public class TestFileOutputStream {

public static void main(String[] args) {
// TODO Auto-generated method stub
File f = new File("d:/aa.txt");

FileOutputStream fos = null;

try {
fos = new FileOutputStream(f);

String s = "把地球甩掉\r\n";
String s2 = "一颗心扑通扑通扑通地乱跳";
//定义字节数组
fos.write(s.getBytes());
fos.write(s2.getBytes());
} catch (Exception e) {
e.printStackTrace();
// TODO: handle exception
} finally {
try {
fos.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}

}

ImageStream

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

public class TestImage {
public static void main(String[] args) {
//先把图片读入到内存 ——》写入某个文件
//因为是二进制文件，因此使用字节流完成。

//输入流

FileInputStream fis = null;

//输出流

FileOutputStream fos = null;

try {
fis = new FileInputStream("D:/3.PNG");
fos = new FileOutputStream("D:/computer.PNG");

byte[]	 buf = new byte[512];
int n = 0;
//循环读取
while ((n = fis.read(buf)) != -1) {
//输出到指定文件。
fos.write(buf);
}
} catch (Exception e) {
// TODO: handle exception
} finally {
try {
fis.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
fos.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}
}

文件字符流

Reader

Writer

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class TestReaderWriter {
public static void main(String[] args) {
//文件中取出字符流对象（输入流）
FileReader fr = null;
//写入文件（输出流）
FileWriter fw = null;

try {
//创建dr对象
fr = new FileReader("D:/test.txt");

int n = 0;
//读入到内存
char c[] = new char[1024];
while ( (n = fr.read(c))!= -1) {
String s = new String(c,0,n);

System.out.println(s);
}

while ( (n = fr.read(c)) != -1) {
fw.write(c, 0 ,n);
}
} catch (Exception e) {
e.printStackTrace();
// TODO: handle exception
} finally {
try {
fr.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}

缓冲字符流

BufferedReader

BufferedWriter

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class TestBufferRW {
public static void main(String[] args) {
BufferedReader br = null;
BufferedWriter bw = null;
try {
//先创建FileReader对象
FileReader fr = new FileReader("D:/test.txt");
br = new BufferedReader(fr);

//先创建FileWriter对象
FileWriter fw = new FileWriter("D:/my.txt");
bw = new BufferedWriter(fw);

//循环读取文件
String s = "";
while ( (s = br.readLine()) != null) {
System.out.println(s);
}
//循环写文件
String s2 = "";
while ( (s2 = br.readLine()) != null) {
bw.write(s2  + "\r\n");
}
} catch (Exception e) {
e.printStackTrace();
// TODO: handle exception
} finally {
try {
br.close();
bw.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}
}
}