java.util.zip.Inflater.setDictionary() Method Example



Description

The java.util.zip.Inflater.setDictionary(byte[] b, int off, int len) method sets the preset dictionary to the given array of bytes. Should be called when inflate() returns 0 and needsDictionary() returns true indicating that a preset dictionary is required. The method getAdler() can be used to get the Adler-32 value of the dictionary needed.

Declaration

Following is the declaration for java.util.zip.Inflater.setDictionary(byte[] b, int off, int len) method.

public void setDictionary(byte[] b, int off, int len)

Parameters

  • b − the dictionary data bytes.

  • off − the start offset of the data.

  • len − the length of the data.

Example

The following example shows the usage of java.util.zip.Inflater.setDictionary(byte[] b, int off, int len) method.

package com.tutorialspoint;

import java.io.UnsupportedEncodingException;
import java.util.zip.DataFormatException;
import java.util.zip.Deflater;
import java.util.zip.Inflater;

public class InflaterDemo {
   public static void main(String[] args) 
      throws DataFormatException, UnsupportedEncodingException {
      String message = "Welcome to TutorialsPoint.com;"
         +"Welcome to TutorialsPoint.com;"
         +"Welcome to TutorialsPoint.com;"
         +"Welcome to TutorialsPoint.com;"
         +"Welcome to TutorialsPoint.com;"
         +"Welcome to TutorialsPoint.com;"
         +"Welcome to TutorialsPoint.com;"
         +"Welcome to TutorialsPoint.com;"
         +"Welcome to TutorialsPoint.com;"
         +"Welcome to TutorialsPoint.com;";
      String dictionary = "Welcome";
 
      System.out.println("Original Message length : " + message.length());
      byte[] input = message.getBytes("UTF-8");

      // Compress the bytes
      byte[] output = new byte[1024];
      Deflater deflater = new Deflater();
      deflater.setDictionary(dictionary.getBytes("UTF-8"),0, dictionary.length());
      deflater.setInput(input);
   
      deflater.finish();
      int compressedDataLength = deflater.deflate(output,0 , output.length, Deflater.NO_FLUSH);
      System.out.println("Total uncompressed bytes output :" + deflater.getTotalOut());
      System.out.println("Compressed Message Checksum :" + deflater.getAdler());     
      deflater.finished();

      System.out.println("Compressed Message length : " + compressedDataLength);

      // Decompress the bytes
      Inflater inflater = new Inflater();
      inflater.setInput(output, 0, compressedDataLength);
      byte[] result = new byte[1024];
      int resultLength = inflater.inflate(result);
      if(inflater.needsDictionary()){
    
         inflater.setDictionary(dictionary.getBytes("UTF-8"),0, dictionary.length());
 
         resultLength = inflater.inflate(result);
      }
      inflater.finished();

      // Decode the bytes into a String
      message = new String(result, 0, resultLength, "UTF-8");
      System.out.println("UnCompressed Message Checksum :" + inflater.getAdler());  
      System.out.println("UnCompressed Message length : " + message.length());
   }
}

Let us compile and run the above program, this will produce the following result −

Original Message length : 300
Total uncompressed bytes output :42
Compressed Message Checksum :368538129
Compressed Message length : 42
UnCompressed Message Checksum :368538129
UnCompressed Message length : 300
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javazip_inflater.htm
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