Java中IO流解析及代码实例详解

package com.io.stream;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.IOException;

public class TestFileInputStream {

     //定义一个流对象

     private static FileInputStream fis;

     public static void main(String[] args) {

         try {

             //1、 创建流对象.参数可以是一个File类、String字符串表示的文件路径

             fis = new FileInputStream( "E:\\aaa.txt" ); //在e盘下有一个aaa.txt的文件夹，内容为（abcdefg）

             //2、使用流的方法对文件进行读

             while ( true ) {

                 int read = fis.read(); //注意这里返回的是int类型，代表是字符的ASCII值

                 if (read==- 1 ) { //读到最后会返回-1，退出条件

                     break ;

                 }

                 System.out.println(read);

             }

         } catch (FileNotFoundException e) { //异常细粒化，不同异常可以选择不同的处理方式

             e.printStackTrace();

         } catch (IOException e) {

             e.printStackTrace();

         } finally {

             try {

                 //3、关闭流

                 fis.close();

             } catch (IOException e) {

                 e.printStackTrace();

             }

         }

     }

}

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.util.Arrays;

public class TestFileInputStream2 {

     private static FileInputStream fis;

     public static void main(String[] args) {

         try {

             fis = new FileInputStream( "IO流\\aaa.txt" );

             //准备一个byte数组

             byte [] b= new byte [ 3 ];

             int readNum = 0 ;

             while ( true ) {

                 //先进行读操作。

                 readNum=fis.read(b);

                 //判断

                 if (readNum == - 1 ) {

                     break ;

                 }

                 //将字符数组转为String,后面两个参数为起始位置，和长度

                 String str = new String(b, 0 , readNum);

                 System.out.println(str);

             }

             /*输出

                 abc

                 def

                 g

             */

         } catch (FileNotFoundException e) {

             e.printStackTrace();

         } catch (IOException e) {

             e.printStackTrace();

         } finally {

             try {

                 //关闭流

                 fis.close();

             } catch (IOException e) {

                 e.printStackTrace();

             }

         }

     }

}

public class TestFileInputStream3 {

     public static void main(String[] args) throws IOException {

         FileInputStream fis = new FileInputStream( "IO流\\aaa.txt" );

         byte [] bytes = new byte [fis.available()]; //创建一个和文件字符数量一样大的byte数组，文件不能太大。

         fis.read(bytes);

         System.out.println( new String(bytes)); //b转为字符串，输出abcdefg

     }

}

package com.io.stream.output;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.IOException;

/**

  * @Author cyh

  * @Date 2021/8/7 17:21

  */

public class Test1 {

     private static FileOutputStream fos;

     public static void main(String[] args) {

         try {

             //新建一个输出流，参数是输出的路径，最后的为文件名。

             fos = new FileOutputStream( "IO流\\bbb.txt" );

             //新建一个byte数组，里面对应的是abcd的ascii值

             byte [] bytes = { 97 , 98 , 99 , 100 , 101 , 127 }; //注意byte的范围是-128~127

             //输出流调用write方法写入byte数组，以文件形式保存到上面的路径

             fos.write(bytes);

             //写完之后，一定要刷新

             fos.flush();

         } catch (IOException e) {

             e.printStackTrace();

         } finally {

             try {

                 fos.close();

             } catch (IOException e) {

                 e.printStackTrace();

             }

         }

     }

}

//新建一个输出流，参数是输出的路径，最后的为文件名。增加true表示开启追加写

fos = new FileOutputStream( "IO流\\bbb.txt" , true );

package com.io.stream.copy;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.IOException;

/**

  * @Author cyh

  * @Date 2021/8/7 17:53

  */

public class TestCopy {

     private static FileInputStream fis;

     private static FileOutputStream fos;

     public static void main(String[] args) {

         try {

             //创建一个输入流

             fis = new FileInputStream( "D:\\edgeDownload\\VSCodeUserSetup-x64-1.55.0.exe" );

             //创建一个输出流

             fos = new FileOutputStream( "C:\\Users\\PC\\Desktop\\copy\\b\\VSCodeUserSetup-x64-1.55.0.exe" );

             //核心，一边读、一边写

             byte [] bytes = new byte [ 1024 * 1024 ]; //1MB,一次最多拷贝1MB

             int readNum= 0 ;

             while ((readNum=fis.read(bytes))!=- 1 ){

                 fos.write(bytes, 0 ,readNum); //将bytes全部写入

             }

             //刷新

             fos.flush();

         } catch (FileNotFoundException e) {

             e.printStackTrace();

         } catch (IOException e) {

             e.printStackTrace();

         } finally {

             //资源要分开释放，不然一个出错会导致另一个无法释放

             try {

                 fis.close();

             } catch (IOException e) {

                 e.printStackTrace();

             }

             try {

                 fos.close();

             } catch (IOException e) {

                 e.printStackTrace();

             }

         }

     }

}