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Tuesday, February 05, 2013

Howto compress and uncompress a Java byte array using JDK Deflater/Inflater

If you ever came across the requirement to store binary data somewhere (e.g. filesystem or database) it might be handy to compress those data.
Besides the common ZIP algorithm Java offers the Deflater and Inflater classes that uses the ZLIB compression library. ZLIB is part of the PNG standard and not protected by any patents.
Here is a small code snippet which shows an utility class that offers two methods to compress and extract a Java byte array.

 package de.qu.compression.demo;  
   
 import java.io.ByteArrayOutputStream;  
 import java.io.File;  
 import java.io.FileInputStream;  
 import java.io.FileOutputStream;  
 import java.io.IOException;  
 import java.io.InputStream;  
 import java.util.List;  
 import java.util.Map;  
 import java.util.zip.DataFormatException;  
 import java.util.zip.Deflater;  
 import java.util.zip.Inflater;  
   
 public class CompressionUtils {  
  private static final Logger LOG = Logger.getLogger(CompressionUtils.class);  
    
    
  public static byte[] compress(byte[] data) throws IOException {  
   Deflater deflater = new Deflater();  
   deflater.setInput(data);  
   
   ByteArrayOutputStream outputStream = new ByteArrayOutputStream(data.length);   
       
   deflater.finish();  
   byte[] buffer = new byte[1024];   
   while (!deflater.finished()) {  
    int count = deflater.deflate(buffer); // returns the generated code... index  
    outputStream.write(buffer, 0, count);   
   }  
   outputStream.close();  
   byte[] output = outputStream.toByteArray();  
   
   deflater.end();

   LOG.debug("Original: " + data.length / 1024 + " Kb");  
   LOG.debug("Compressed: " + output.length / 1024 + " Kb");  
   return output;  
  }  
   
  public static byte[] decompress(byte[] data) throws IOException, DataFormatException {  
   Inflater inflater = new Inflater();   
   inflater.setInput(data);  
   
   ByteArrayOutputStream outputStream = new ByteArrayOutputStream(data.length);  
   byte[] buffer = new byte[1024];  
   while (!inflater.finished()) {  
    int count = inflater.inflate(buffer);  
    outputStream.write(buffer, 0, count);  
   }  
   outputStream.close();  
   byte[] output = outputStream.toByteArray();  
   
   inflater.end();
   
   LOG.debug("Original: " + data.length);  
   LOG.debug("Uncompressed: " + output.length);  
   return output;  
  }  
 }  
   

It is also possible to receive better compression results by calling the method setLevel of the Deflater class and specify the constant Deflater.BEST_COMPRESSION.