输入输出流的应用

Posted 2022-07-19 zhai1997

1、文件复制

用FileInputStream和FileOutPutStream实现文件的复制，此方法不能复制文件夹。

package pers.zhh.copy;

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

public class CopyDemo 
    public static void main(String[] args) throws IOException 
        FileInputStream fi = new FileInputStream("M:\\\\数据库.zip");
        FileOutputStream fo = new FileOutputStream("M:\\\\数据库1.zip");
        int num = 0;
        long startTime = System.currentTimeMillis();
        while ((num = fi.read()) != -1) 
            fo.write(num);

        
        fo.close();
        fi.close();
        long endTime = System.currentTimeMillis();
        System.out.println("执行此程序用了" + (endTime - startTime) + "毫秒。");
    

（2）缓冲数组：

package pers.zzz.copy;

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

public class CopyDemo1 
    public static void main(String[] args) throws IOException 
        FileInputStream fi = new FileInputStream("M:\\\\网页设计.zip");
        FileOutputStream fo = new FileOutputStream("M:\\\\网页设计3.zip");
        byte[] buf = new byte[1024];
        int len = 0;
        long startTime = System.currentTimeMillis();
        while ((len = fi.read(buf)) != -1) 
            fo.write(buf, 0, len); // 将数组中的指定长度的数据写入到输出流中。
        
        fo.close();
        fi.close();
        long endTime = System.currentTimeMillis();
        System.out.println("执行此程序用了" + (endTime - startTime) + "毫秒。");
    

在第一个方法中，一次只能读取一个数据字节，复制只有几M的数据花了7s时间，效率极低。而第二种采用缓冲数组的方式，复制接近1G的文件只花费了4s的时间，效率大大提升。

2、IO流的异常处理

package pers.zzz.copy;

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

public class CopyDemo1 
    public static void main(String[] args) 
        FileOutputStream fo = null;
        FileInputStream fi = null;
        long startTime = System.currentTimeMillis();
        try 
            fi = new FileInputStream("M:\\\\网页设1计.zip");
            fo = new FileOutputStream("M:\\\\网页设计11.zip");

            byte[] buf = new byte[1024];
            int len = 0;

            while ((len = fi.read(buf)) != -1) 
                fo.write(buf, 0, len); // 将数组中的指定长度的数据写入到输出流中。
            
         catch (IOException e) 
            System.out.println(e.toString());
         finally 
            if (fo != null) 
                try 
                    fo.close();
                 catch (IOException e) 
                    System.out.println(e.toString());
                    throw new RuntimeException();
                
            
            if (fi != null) 
                try 
                    fi.close();
                 catch (IOException e) 
                    System.out.println(e.toString());
                    throw new RuntimeException();

                

            

        
        long endTime = System.currentTimeMillis();

        System.out.println("执行此程序用了" + (endTime - startTime) + "毫秒。");