021.3 IO stream - byte stream - FileInputStream reads bytes

Content: file reading method, example of reading method, value of buf in read(buf) method, byte stream buffer object - improving reading speed ///

File reading method: fis.read(), fis.read(buf), see the example for details

Example: file read - read file, display

public class FileInputStreamDemo
{
    public static void main(String[] args)
    {
        // To ensure that the file must exist before reading. Encapsulate the string path into a File object 
        File file = new File("F:"+File.separator+"eclipse_javaCode"+File.separator+"day22"
        +File.separator+"src"+File.separator+"demo"+File.separator+"GetMoney.java");
        if(!file.exists()){
            throw new RuntimeException("文件不存在!");
        }
        
        // Create a file byte read stream object 
        FileInputStream fis = null ;
         try {
            fis = new FileInputStream(file);
             // first read method, single read
 //             int ch = 0;
 //             while(ch!=-1){
 //                 ch = fis.read();
 //                 System.out.println(ch);   // The first method of reading the file, the acsii code is returned successfully, and the failure returns -1
 //             }
             // The second reading method, batch read 
            byte [] buf = new  byte [1024 ];
             int len ​​= 0 ;
             while ((len = fis.read(buf)) != -1 ){
                System.out.println(new String(buf,0,len));
            }
        } catch (IOException e) {
        }
    }
}

 

################################################## ###############
Generally do not directly create a byte buffer of the corresponding size. The
buffer size is generally a multiple of bytes, a multiple of 1024

public static void main(String[] args) throws IOException
{
    File file = new File("F:\\eclipse_javaCode\\day21\\src\\day21\\shangxin.txt");
    System.out.println(file.length());     // Get the number of bytes in the file 
    FileInputStream fis = new FileInputStream(file);
    System.out.println(fis.available());      // Get the number of bytes of the file associated with it
    
    byte [] buf = new  byte [fis.available()];    // Generally, a buffer of the corresponding size will not be created at once, such as high-definition movies, which is troublesome.
    // Generally created is a multiple of 1024 
    fis.read(buf);
    String s = new String(buf);
    System.out.println(s);
    
    fis.close();
}

 

byte stream - copy text

public static void main(String[] args) throws IOException
{
    FileOutputStream fos = new FileOutputStream("xxx_copy.txt");
    FileInputStream fis = new FileInputStream("FileInputStreamDemo.java");
    
    byte[] buf = new byte[1024];
    int len = 0;
    while((len = fis.read(buf))!= -1){
        fos.write(buf,0,len);
        fos.flush();
    }
    
    fis.close();
    fos.close();
}

 

Buffer object of
byte stream #####byte stream copy text - use buffer object to improve efficiency

private static void copyByBuffer() throws IOException
{
    FileInputStream fis = new FileInputStream("aaaa.txt");
    BufferedInputStream bufis = new BufferedInputStream(fis);
    
    FileOutputStream fos = new FileOutputStream("aaaa_copy.txt");
    BufferedOutputStream bufos = new BufferedOutputStream(fos);
    
    byte[] buf = new byte[1024];
    
    int by = 0;
    while((by = bufis.read(buf))!=-1){
        bufos.write(buf,0,by);
        bufos.flush();
    }
    
    fos.close();
    fis.close();

}