Use memory ing in Java to process large files

When processing large files, frequent read/write operations using normal FileInputStream, FileOutputStream, or RandomAccessFile will lead to slow down the process due to frequent read/write. The following is a comparative experiment.
[Java]
Package test;
 
Import java. io. BufferedInputStream;
Import java. io. FileInputStream;
Import java. io. FileNotFoundException;
Import java. io. IOException;
Import java. io. RandomAccessFile;
Import java. nio. MappedByteBuffer;
Import java. nio. channels. FileChannel;
 
Public class Test {
 

Public static void main (String [] args ){
Try {
FileInputStream FCM = new FileInputStream ("/home/tobacco/test/res.txt ");
Int sum = 0;
Int n;
Long t1 = System. currentTimeMillis ();
Try {
While (n = FCM. read ()> = 0 ){
Sum + = n;
}
} Catch (IOException e ){
// TODO Auto-generated catch block
E. printStackTrace ();
}
Long t = System. currentTimeMillis ()-t1;
System. out. println ("sum:" + sum + "time:" + t );
} Catch (FileNotFoundException e ){
// TODO Auto-generated catch block
E. printStackTrace ();
}

Try {
FileInputStream FCM = new FileInputStream ("/home/tobacco/test/res.txt ");
BufferedInputStream bis = new BufferedInputStream (FCM );
Int sum = 0;
Int n;
Long t1 = System. currentTimeMillis ();
Try {
While (n = bis. read ()> = 0 ){
Sum + = n;
}
} Catch (IOException e ){
// TODO Auto-generated catch block
E. printStackTrace ();
}
Long t = System. currentTimeMillis ()-t1;
System. out. println ("sum:" + sum + "time:" + t );
} Catch (FileNotFoundException e ){
// TODO Auto-generated catch block
E. printStackTrace ();
}

MappedByteBuffer buffer = null;
Try {
Buffer = new RandomAccessFile ("/home/tobacco/test/res.txt", "rw"). getChannel (). map (FileChannel. MapMode. READ_WRITE, 0, 1253244 );
Int sum = 0;
Int n;
Long t1 = System. currentTimeMillis ();
For (int I = 0; I <1253244; I ++ ){
N = 0x000000ff & buffer. get (I );
Sum + = n;
}
Long t = System. currentTimeMillis ()-t1;
System. out. println ("sum:" + sum + "time:" + t );
} Catch (FileNotFoundException e ){
// TODO Auto-generated catch block
E. printStackTrace ();
} Catch (IOException e ){
// TODO Auto-generated catch block
E. printStackTrace ();
}
 
}
 
}

The test file is a 1253244-byte file. Test results:
Sum: 220152087 time: 1464
Sum: 220152087 time: 72
Sum: 220152087 time: 25
The read data is correct. Delete the Data Processing Section.
[Java]
Package test;
 
Import java. io. BufferedInputStream;
Import java. io. FileInputStream;
Import java. io. FileNotFoundException;
Import java. io. IOException;
Import java. io. RandomAccessFile;
Import java. nio. MappedByteBuffer;
Import java. nio. channels. FileChannel;
 
Public class Test {
 

Public static void main (String [] args ){
Try {
FileInputStream FCM = new FileInputStream ("/home/tobacco/test/res.txt ");
Int sum = 0;
Int n;
Long t1 = System. currentTimeMillis ();
Try {
While (n = FCM. read ()> = 0 ){
// Sum + = n;
}
} Catch (IOException e ){
// TODO Auto-generated catch block
E. printStackTrace ();
}
Long t = System. currentTimeMillis ()-t1;
System. out. println ("sum:" + sum + "time:" + t );
} Catch (FileNotFoundException e ){
// TODO Auto-generated catch block
E. printStackTrace ();
}

Try {
FileInputStream FCM = new FileInputStream ("/home/tobacco/test/res.txt ");
BufferedInputStream bis = new BufferedInputStream (FCM );
Int sum = 0;
Int n;
Long t1 = System. currentTimeMillis ();
Try {
While (n = bis. read ()> = 0 ){
// Sum + = n;
}
} Catch (IOException e ){
// TODO Auto-generated catch block
E. printStackTrace ();
}
Long t = System. currentTimeMillis ()-t1;
System. out. println ("sum:" + sum + "time:" + t );
} Catch (FileNotFoundException e ){
// TODO Auto-generated catch block
E. printStackTrace ();
}

MappedByteBuffer buffer = null;
Try {
Buffer = new RandomAccessFile ("/home/tobacco/test/res.txt", "rw"). getChannel (). map (FileChannel. MapMode. READ_WRITE, 0, 1253244 );
Int sum = 0;
Int n;
Long t1 = System. currentTimeMillis ();
For (int I = 0; I <1253244; I ++ ){
// N = 0x000000ff & buffer. get (I );
// Sum + = n;
}
Long t = System. currentTimeMillis ()-t1;
System. out. println ("sum:" + sum + "time:" + t );
} Catch (FileNotFoundException e ){
// TODO Auto-generated catch block
E. printStackTrace ();
} Catch (IOException e ){
// TODO Auto-generated catch block
E. printStackTrace ();
}
 
}
 
}

Test results:
Sum: 0 time: 1458
Sum: 0 time: 67
Sum: 0 time: 8
It can be seen that the speed will be improved by ing some or all files to the memory for read/write operations.
This is because the memory ing file first maps the external files to a contiguous area in the memory and is processed as a byte array. read/write operations are performed directly on the memory, then, the memory area is re-mapped to the external storage file, which saves the time for frequent external storage read/write and greatly reduces the read/write time.
Author: tobacco5648