字符流应用：复制图像copyPic()、使用缓冲区技术复制copyFileBuffer()、复制文本文件copyFile()、带行号的文件复制copyLNFile()、

/*
FileReader,FileWriter
BufferedReader,BufferedWriter(4个字符流对象)

InputStream,OutputStream
BufferedReader,BufferedWriter(4个字节流对象);

操作图片数据，就需要用到字节流了
*/

import java.io.*;
class FileStream 
{
    public static void main(String[] args)throws IOException
    {
        readfile3();
    }
    
    public static void readfile3()throws IOException
    {
        FileInputStream fis =new FileInputStream("fos.txt");

        byte [] buf =new byte[fis.available()];//定义一个刚刚好的缓冲区就不需要循环了
        fis.read(buf);
        sop(new String(buf));
        fis.close();
    }

    public static void readfile2()throws IOException
    {
        FileInputStream fis =new FileInputStream("fos.txt");
        byte [] buf =new byte[1024];
        int len=0;
        while((len=fis.read(buf))!=-1)
        {
            String s =new String(buf,0,len);
                /*
                  public String(byte[] bytes,int offset,int length)
                  通过使用平台的默认字符集解码指定的 byte 子数组，构造一个新的 String。
                  新 String 的长度是字符集的函数，因此可能不等于该子数组的长度。 
                */
            sop(s);
        }
        fis.close();
    }

    public static void readFile()throws IOException
    {
        FileInputStream fis =new FileInputStream("fos.txt");
        int ch =0;
        while((ch=fis.read())!=-1)
        {
            sop((char)ch);
        }
        fis.close();
    }
    
    public static void writefile()throws IOException
    {
        FileOutputStream fos =new FileOutputStream("fos.txt");
        
        fos.write("whoisjena".getBytes());
        fos.close();
    }

    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}

 

正式开工:

public static void copyPic()
    {
        FileInputStream fis =null;
        FileOutputStream fos =null;

        try
        {
            fis =new FileInputStream("拷贝图片.png");
            fos =new FileOutputStream("拷贝图片copy.png");

            byte[] buf =new byte[1024];
            int len =0;
            while((len=fis.read(buf))!=-1)
            {
                fos.write(buf,0,len);
            }
        }
        catch (IOException e)
        {
            throw new RuntimeException("图片读写失败");
        }

        finally
        {
            try
            {
                if (fis!=null)
                {
                    fis.close();
                }
            }
            catch (IOException e)
            {
                throw new RuntimeException("图片读取失败");
            }
            try
            {
                if (fos!=null)
                {
                    fos.close();
                }
            }
            catch (IOException e)
            {
                throw new RuntimeException("图片写入失败");
            }
        }
    }

 

当然为了提高效率，可以使用缓冲区技术：

//使用缓冲区的文件复制
    public static void copyFileBuffer()
    {
        BufferedInputStream bufis =null;
        BufferedOutputStream bufos =null;
        try
        {
            bufis =    new BufferedInputStream(new FileInputStream("book.pdf"));
            bufos = new BufferedOutputStream(new FileOutputStream("bookcopyb.pdf"));
            byte[] buf =new byte[1024];
            int len=0;
            while((len=bufis.read(buf))!=-1)
            {
                bufos.write(buf,0,len);
            }
        }
        catch (IOException e)
        {
            throw new RuntimeException("文件读写失败");
        }
        finally
        {
            try
            {
                if (bufis!=null)
                {
                    bufis.close();
                }
            }
            catch (IOException e)
            {
                throw new RuntimeException("读失败");
            }

            try
            {
                if (bufos!=null)
                {
                    bufos.close();
                }
            }
            catch (IOException e)
            {
                throw new RuntimeException("写失败");
            }

        }
    }

 效果还是比较明显的：使用缓冲区后时间约为之前的1/3:

public static void main(String[] args)
    {
        long start =System.currentTimeMillis();
        copyPicBuffer();
        long end =System.currentTimeMillis();
        sop(end-start);
    }

 

public static void copyLNFile()throws IOException
    {
        //BufferedReader bufr =null;
        FileReader fr =null;//定义fr便于异常处理时关闭流
        LineNumberReader lnr =null;
        BufferedWriter bufw =null;
        
        lnr =new LineNumberReader(fr =new FileReader("Test.java"));
        bufw =new BufferedWriter(new FileWriter("Testcopy.java"));
        String line=null;
        while((line=lnr.readLine())!=null)
        {
            
            //System.out.println(lnr.getLineNumber());//在控制台是可以正常显示行号的
            bufw.write(lnr.getLineNumber()+" "+line);//write语句要放在一起，如果分开到了文件中由于编码问题会导致行号变为了符号
            //bufw.write(line);
            bufw.newLine();
            bufw.flush();
        }
    }