Java

Decompress Large Text File in Blocks

See more Compression Examples

Decompresses a large text file in blocks, and compares the restored (decompressed) file with the original to make sure it's correct. Java

import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    boolean success = false;

    //  This example requires the Chilkat API to have been previously unlocked.
    //  See Global Unlock Sample for sample code.

    //  First, let's compress a text file.
    //  We'll then decompress in blocks, and compare the decompressed with the original file.

    //  Compress a text file:
    CkCompression compress = new CkCompression();
    compress.put_Algorithm("deflate");

    success = compress.CompressFile("qa_data/hamlet.xml","qa_data/hamlet_compressed.dat");
    if (success == false) {
        System.out.println(compress.lastErrorText());
        return;
        }

    CkFileAccess fac = new CkFileAccess();

    //  Examine the uncompressed and compressed sizes:
    String originalPath = "qa_data/hamlet.xml";
    //  Note: The FileSize method returns a signed 32-bit integer.  If the file is potentially larger than 2GB, call FileSizeStr instead to return
    //  the size of the file as a string, then convert to an integer value.
    System.out.println("uncompressed size: " + fac.FileSize(originalPath));
    System.out.println("compressed size: " + fac.FileSize("qa_data/hamlet_compressed.dat"));

    //  Decompress in blocks..
    CkFileAccess facSrc = new CkFileAccess();
    CkFileAccess facDest = new CkFileAccess();

    facSrc.OpenForRead("qa_data/hamlet_compressed.dat");

    //  If we compress in 32K chunks, find out how many blocks there will be.
    int blockSize = 32768;
    int numBlocks = facSrc.GetNumBlocks(blockSize);

    //  Open an output file for the decompressed data.
    String restoredPath = "qa_output/hamlet_restored.xml";
    success = facDest.OpenForWrite(restoredPath);
    if (success == false) {
        System.out.println(facDest.lastErrorText());
        return;
        }

    String decompressedStr;
    CkByteData compressedBytes = new CkByteData();

    //  Assuming numBlocks > 1
    compress.put_FirstChunk(true);
    compress.put_LastChunk(false);

    int i = 0;
    while (i < numBlocks) {
        success = facSrc.ReadBlock(i,blockSize,compressedBytes);
        decompressedStr = compress.decompressString(compressedBytes);

        facDest.AppendText(decompressedStr,"utf-8");

        i = i+1;

        compress.put_FirstChunk(false);
        if (i == (numBlocks - 1)) {
            compress.put_LastChunk(true);
            }

        }

    facSrc.FileClose();
    facDest.FileClose();

    //  Examine the size of the restored file.
    System.out.println("restored size: " + fac.FileSize(restoredPath));

    //  Compare the contents of the original with the restored.
    boolean bEqualContents = fac.FileContentsEqual(restoredPath,originalPath);
    System.out.println("Contents Equal: " + bEqualContents);
  }
}