Java/File Input Output/MappedByteBuffer

Map FileChannel to MappedByteBuffer

   <source lang="java">

import java.io.FileInputStream; import java.nio.MappedByteBuffer; import java.nio.channels.FileChannel; public class Main {

 public static void main(String args[]) throws Exception {
   String filename = args[0];
   int start = 10;
   int length = 20;
   FileInputStream fin = new FileInputStream(filename);
   FileChannel finc = fin.getChannel();
   MappedByteBuffer mbb = finc.map(FileChannel.MapMode.READ_ONLY, start, length);
   for (int i = 0; i < length; ++i) {
     System.out.println(mbb.get(i);
   }
   fin.close();
 }

}

 </source>
   
  
 
  

Persisting Changes to a Memory-Mapped ByteBuffer

   <source lang="java">

import java.io.File; import java.io.RandomAccessFile; import java.nio.MappedByteBuffer; import java.nio.channels.FileChannel; public class Main {

 public static void main(String[] argv) throws Exception {
   File file = new File("filename");
   FileChannel channel = new RandomAccessFile(file, "rw").getChannel();
   MappedByteBuffer buf = channel.map(FileChannel.MapMode.READ_WRITE, 0, (int) channel.size());
   buf.put(0, (byte) 0xFF);
   buf.force();
   channel.close();
 }

}

 </source>
   
  
 
  

Read file upside/down with RandomAccessFile

   <source lang="java">

import java.io.RandomAccessFile; import java.nio.MappedByteBuffer; import java.nio.channels.FileChannel; public class Main {

 public static void main(String[] args) throws Exception {
   RandomAccessFile f = new RandomAccessFile("hello.txt", "rw");
   FileChannel fc = f.getChannel();
   MappedByteBuffer mbb = fc.map(FileChannel.MapMode.READ_WRITE, 0, f.length());
   int len = (int) f.length();
   for (int i = 0, j = len - 1; i < j; i++, j--) {
     byte b = mbb.get(i);
     mbb.put(i, mbb.get(j));
     mbb.put(j, b);
   }
   fc.close();
 }

}

 </source>