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 exceptione.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InputStreamtry {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StringString 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 blocke.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 stubFile 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 blocke.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 blocke.printStackTrace();}try {fos.close();} catch (IOException e) {// TODO Auto-generated catch blocke.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 blocke.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 blocke.printStackTrace();}}}}