Java/File Input Output/New IO

Copy a file using NIO

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
  public static void main(String args[]) {
    FileInputStream fIn;
    FileOutputStream fOut;
    FileChannel fIChan, fOChan;
    long fSize;
    MappedByteBuffer mBuf;
    try {
      fIn = new FileInputStream(args[0]);
      fOut = new FileOutputStream(args[1]);
      fIChan = fIn.getChannel();
      fOChan = fOut.getChannel();
      fSize = fIChan.size();
      mBuf = fIChan.map(FileChannel.MapMode.READ_ONLY, 0, fSize);
      fOChan.write(mBuf); // this copies the file
      fIChan.close();
      fIn.close();
      fOChan.close();
      fOut.close();
    } catch (IOException exc) {
      System.out.println(exc);
      System.exit(1);
    } catch (ArrayIndexOutOfBoundsException exc) {
      System.out.println("Usage: Copy from to");
      System.exit(1);
    }
  }
}

FileChannel: map(FileChannel.MapMode mode,long position,long size)

import java.io.FileInputStream;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
  public static void main(String args[]) {
    FileInputStream fileInputStream;
    FileChannel fileChannel;
    long fileSize;
    MappedByteBuffer mBuf;
    try {
      fileInputStream = new FileInputStream("test.txt");
      fileChannel = fileInputStream.getChannel();
      fileSize = fileChannel.size();
      mBuf = fileChannel.map(FileChannel.MapMode.READ_ONLY, 0, fileSize);
      for (int i = 0; i < fileSize; i++)
        System.out.print((char) mBuf.get());
      fileChannel.close();
      fileInputStream.close();
    } catch (IOException exc) {
      System.out.println(exc);
      System.exit(1);
    }
  }
}

Use a mapped file to read a text file

import java.io.FileInputStream;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
  public static void main(String args[]) {
    FileInputStream fileInputStream;
    FileChannel fileChannel;
    long fileSize;
    MappedByteBuffer mBuf;
    try {
      fileInputStream = new FileInputStream("test.txt");
      fileChannel = fileInputStream.getChannel();
      fileSize = fileChannel.size();
      mBuf = fileChannel.map(FileChannel.MapMode.READ_ONLY, 0, fileSize);
      for (int i = 0; i < fileSize; i++)
        System.out.print((char) mBuf.get());
      fileChannel.close();
      fileInputStream.close();
    } catch (IOException exc) {
      System.out.println(exc);
      System.exit(1);
    }
  }
}

Use New Java IO to write string into a file

/*
 * Output:
File stream created successfully.
New buffer:           position = 0  Limit = 1024  capacity = 1024
Buffer after loading: position = 30  Limit = 1024  capacity = 1024
Buffer after flip:    position = 0  Limit = 30  capacity = 1024
Buffer contents written to file.
 */
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.FileNotFoundException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
  public static void main(String[] args) {
    String phrase = new String("www.jexp.ru\n");
    File aFile = new File("test.txt");   
    FileOutputStream outputFile = null;  
    try {
      outputFile = new FileOutputStream(aFile, true);
      System.out.println("File stream created successfully.");
    } catch (FileNotFoundException e) {
      e.printStackTrace(System.err);
    } 
    FileChannel outChannel = outputFile.getChannel();
    
    ByteBuffer buf = ByteBuffer.allocate(1024);
    System.out.println("New buffer:           position = " + buf.position()
                       + "\tLimit = " + buf.limit() + "\tcapacity = "
                       + buf.capacity());
    // Load the data into the buffer
    for (char ch : phrase.toCharArray()) {
      buf.putChar(ch);
    }
    System.out.println("Buffer after loading: position = " + buf.position()
                       + "\tLimit = " + buf.limit() + "\tcapacity = "
                       + buf.capacity());
    buf.flip();
    System.out.println("Buffer after flip:    position = " + buf.position() 
                       + "\tLimit = " + buf.limit() + "\tcapacity = " 
                       + buf.capacity());
    try {
      outChannel.write(buf);
      outputFile.close();
      System.out.println("Buffer contents written to file.");
    } catch (IOException e) {
      e.printStackTrace(System.err);
    }
  }
}

Write A String As Bytes

/*
 * Output:
 */
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
  public static void main(String[] args) {
    String phrase = new String("www.jexp.ru API \n");
    File aFile = new File("test.txt");
    FileOutputStream file = null;
    try {
      file = new FileOutputStream(aFile, true);
    } catch (FileNotFoundException e) {
      e.printStackTrace(System.err);
    }
    FileChannel outChannel = file.getChannel();
    ByteBuffer buf = ByteBuffer.allocate(phrase.length());
    byte[] bytes = phrase.getBytes();
    buf.put(bytes);
    buf.flip();
    try {
      outChannel.write(buf);
      file.close();
    } catch (IOException e) {
      e.printStackTrace(System.err);
    }
  }
}

Write to a file using the new I/O

import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
  public static void main(String args[]) {
    FileOutputStream fileOutputStream;
    FileChannel fileChannel;
    ByteBuffer byteBuffer;
    try {
      fileOutputStream = new FileOutputStream("test.txt");
      fileChannel = fileOutputStream.getChannel();
      byteBuffer = ByteBuffer.allocateDirect(26);
      for (int i = 0; i < 26; i++)
        byteBuffer.put((byte) ("A" + i));
      byteBuffer.rewind();
      fileChannel.write(byteBuffer);
      fileChannel.close();
      fileOutputStream.close();
    } catch (IOException exc) {
      System.out.println(exc);
    }
  }
}

Write to a mapped file

import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
  public static void main(String args[]) {
    RandomAccessFile randomAccessFile;
    FileChannel fileChannel;
    ByteBuffer byteBuffer;
    try {
      randomAccessFile = new RandomAccessFile("test.txt", "rw");
      fileChannel = randomAccessFile.getChannel();
      byteBuffer = fileChannel.map(FileChannel.MapMode.READ_WRITE, 0, 26);
      for (int i = 0; i < 10; i++)
        byteBuffer.put((byte) ("A" + i));
      fileChannel.close();
      randomAccessFile.close();
    } catch (IOException exc) {
      System.out.println(exc);
      System.exit(1);
    }
  }
}