CODEWITHSUNDEEP
filereplacejava-8byte
user5113188
user5113188

Reputation:

Optimizing Replacing Bytes of Some File in Java 8

I have this method in Java and I want to improve it. The method is used to replace some part (at the beginning, in the middle or at the end) of some File with the new bytes (the selected part can be replaced by less or more bytes). The selection is done, by position(start) and quantity.

I can't to use external libraries (guava, or some other).

Here my old code:

public static void replaceBytesFile(RandomAccessFile rafTarget,
    byte[] replacers, int start, int quantity) {
  //replaces exact amount of bytes of a file starting at a specified position
  RandomAccessFile rafTemp = null;

  //Ini Select a Random NonExistent File
  File userDirectory = new File(System.getProperty("user.dir"));
  File temporalFile;
  boolean existsTemporalFile = false;
  String temporalFilename = "";
  while (!existsTemporalFile) {
    temporalFilename = "File_" + Double.toString(100000 * Math.random()) + ".tmp";
    temporalFilename = userDirectory + MethodGen.FS + temporalFilename;
    temporalFile = new File(temporalFilename);
    if (!temporalFile.exists()) {
      existsTemporalFile = true;
    }
  }
  //End Select a Random NonExistent File
  try {
    rafTemp = new RandomAccessFile(temporalFilename, "rw");
    int workBufferSize = 65536;
    //Ini Copy first (Start - 1) MethodBytes
    int step = workBufferSize;
    int countPosition = 0;
    while (countPosition < start) {
      rafTarget.seek(countPosition);
      rafTemp.seek(countPosition);
      if ((start - countPosition) < step) {
        step = start - countPosition;
      }
      byte[] WorkBuffer = new byte[step];
      rafTarget.read(WorkBuffer);
      rafTemp.write(WorkBuffer);
      countPosition += step;
    }
    //End Copy first (start - 1) MethodBytes
    rafTemp.write(replacers);
    rafTarget.seek(start + quantity);
    int end = (int) rafTarget.length();
    //Ini Copy last MethodBytes
    step = workBufferSize;
    countPosition = start + quantity;
    while (countPosition < end) {
      rafTarget.seek(countPosition);
      rafTemp.seek(countPosition - quantity + replacers.length);
      if ((end - countPosition) <= step) {
        step = end - countPosition;
      }
      byte[] WorkBuffer = new byte[step];
      rafTarget.read(WorkBuffer);
      rafTemp.write(WorkBuffer);
      countPosition += step;
    }
    //End Copy last MethodBytes

    rafTarget.setLength(0);
    step = workBufferSize;
    countPosition = 0;
    end = (int) rafTemp.length();
    //Ini Copy all MethodBytes to original
    while (countPosition < end) {
      rafTemp.seek(countPosition);
      rafTarget.seek(countPosition);
      if ((end - countPosition) <= step) {
        step = end - countPosition;
      }
      byte[] WorkBuffer = new byte[step];

      rafTemp.read(WorkBuffer);
      rafTarget.write(WorkBuffer);
      countPosition += step;
    }
    //End Copy all MethodBytes to original
    rafTemp.close();
    temporalFile = new File(temporalFilename);
    temporalFile.delete();
  } catch (IOException ioe) {
    System.out.println(ioe.toString());
  } finally {
    try {
      if (rafTemp != null) {
        rafTemp.close();
      }
    } catch (IOException e) {
    }
  }
}

I'm copying manually in from original file to temporal file where the changes are performed, later ,

My code is working, but I want to know some best alternative in Java 8 (preferred).

Now How is test?

  public static void main(String[] args) {
    String originalFilename = "OriginalTraveling.txt";
    String copiedFilename = "TravelingToBeChanged.txt";

    Path copiedPath = Paths.get(copiedFilename);
    Path originalPath = new File(originalFilename).toPath();
    System.out.println("filename:" + originalFilename);

    String contet = "I want to travel to my Country.";
    try {
      RandomAccessFile raf = new RandomAccessFile(originalFilename, "rw");
      putBytesFile(raf, contet.getBytes(), 0);
      Files.copy(originalPath, copiedPath, StandardCopyOption.REPLACE_EXISTING);
    }
    catch (IOException e) {
      System.out.println("Exception caught " + e.toString());
    }


    try {
      RandomAccessFile raf = new RandomAccessFile(copiedFilename, "rw");
      String toBeChanged = "my Country.";
      String toBeInserted = "India, China, Europe, Latin America, Australia.";
      int position = contet.indexOf(toBeChanged);
      replaceBytesFile(raf, toBeInserted.getBytes(), position, toBeChanged.length());
    }
    catch (IOException e) {
      System.out.println("Exception caught " + e.toString());
    }

    try {
      RandomAccessFile raf = new RandomAccessFile(copiedFilename, "rw");
      String replacedContent = new String(getBytesFile(raf, 0, (int) raf.length()));
      String toBeChanged = "Latin America";
      String toBeInserted = "Colombia";
      int position = replacedContent.indexOf(toBeChanged);
      replaceBytesFile(raf, toBeInserted.getBytes(), position, toBeChanged.length());
    } catch (IOException e) {
      System.out.println("Exception caught " + e.toString());
    }
  }

Method to put Bytes!

  public static void putBytesFile(RandomAccessFile RAFTarget, byte[] content, int position) {
    int size = content.length;
    try {
      long oldPosition = RAFTarget.getFilePointer();
      if (!((position < 0) || !(size > 0))) {
        RAFTarget.seek(position);
        RAFTarget.write(content);
        RAFTarget.seek(oldPosition);
      }
    } catch (java.io.IOException e) {
      System.out.println(e.toString());
    }
  }

Method Get Files!

  public static byte[] getBytesFile(RandomAccessFile RAFSource, int position, int quantity) {
    byte[] content = null;
    try {
      long oldPosition = RAFSource.getFilePointer();
      if ((position < 0) || !(quantity > 0)) {
        return (content);
      } else {
        if (RAFSource.length() < (position + quantity)) {
          quantity = (int) RAFSource.length() - position;
        }
        RAFSource.seek(position);
        content = new byte[quantity];
        RAFSource.read(content);
        RAFSource.seek(oldPosition);
      }
    } catch (java.io.IOException e) {
      System.out.println(e.toString());
    }
    return content;
  }

Content of OriginalTraveling.txt 

I want to travel to my Country.

Content of TravelingToBeChanged.txt

I want to travel to India, China, Europe, Latin America, Australia.

Finally the Content of TravelingToBeChanged.txt

I want to travel to India, China, Europe, Colombia, Australia.

If it can be noticed, they are NOT changed by the same number of bytes.

Do you know some alternative to replace contents of File?

Upvotes: 1

Views: 524

Answers (1)

Holger
Holger

Reputation: 298409

Even for ancient code, this looks unnecessary complicated.

E.g. instead of 

//Ini Select a Random NonExistent File
File userDirectory = new File(System.getProperty("user.dir"));
File temporalFile;
boolean existsTemporalFile = false;
String temporalFilename = "";
while (!existsTemporalFile) {
  temporalFilename = "File_" + Double.toString(100000 * Math.random()) + ".tmp";
  temporalFilename = userDirectory + MethodGen.FS + temporalFilename;
  temporalFile = new File(temporalFilename);
  if (!temporalFile.exists()) {
    existsTemporalFile = true;
  }
}

just use

File temporalFile = File.createTempFile("File_", ".tmp", userDirectory);

See createTempFile

Further, instead of

int step = workBufferSize;
int countPosition = 0;
while (countPosition < start) {
  rafTarget.seek(countPosition);
  rafTemp.seek(countPosition);
  if ((start - countPosition) < step) {
    step = start - countPosition;
  }
  byte[] WorkBuffer = new byte[step];
  rafTarget.read(WorkBuffer);
  rafTemp.write(WorkBuffer);
  countPosition += step;
}

Use

for(int step=workBufferSize, countPosition=0; countPosition < start; countPosition += step){
  rafTarget.seek(countPosition);
  rafTemp.seek(countPosition);
  if ((start - countPosition) < step) {
    step = start - countPosition;
  }
  byte[] WorkBuffer = new byte[step];
  rafTarget.read(WorkBuffer);
  rafTemp.write(WorkBuffer);
}

As you clearly have an initial statement, a condition and an increment operation, in other words, a typical for loop. The same applies to the other two while loops.

However, with newer APIs, things are much simpler anyway:

// consider using long for position and Path for the file, unless
// the RandomAccessFile is really needed for other purposes
public static void replaceBytesFile(RandomAccessFile rafTarget,
    byte[] replacers, int start, int quantity) throws IOException {

    // no need to force a particular directory for the temp file
    Path tmp = Files.createTempFile("File_", ".tmp");
    // use import static java.nio.file.StandardOpenOption.*;
    // try( ... ) closes automatically, perfect for a temp file with DELETE_ON_CLOSE
    try(FileChannel tmpCh = FileChannel.open(tmp, READ, WRITE, DELETE_ON_CLOSE)) {
        // closing the target channel would also close rafTarget RandomAccessFile
        FileChannel target = rafTarget.getChannel();
        // just keep the data before start position, only copy remainder
        long retainStart = start + (long)quantity, toCopy = target.size() - retainStart;
        target.transferTo(retainStart, toCopy, tmpCh);
        // write the replacement
        target.write(ByteBuffer.wrap(replacers), start);
        // copy back the remainder, to the new position
        tmpCh.position(0);
        target.transferFrom(tmpCh, start + (long)replacers.length, toCopy);
        // adapt the length if necessary
        target.truncate(start + toCopy + replacers.length);
    }
}

Upvotes: 3

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