java.util.zip.Deflater.setDictionary() 方法示例

說明

java.util.zip.Deflater.setDictionary(byte[] b, int off, int len) 方法設定用於壓縮的預定義詞典。當可以預先確定歷史緩衝區時，就會使用預定義詞典。以後使用 Inflater.inflate() 解壓縮資料時，可以呼叫 Inflater.getAdler() 以獲取解壓縮所需的詞典的 Adler-32 值。

宣告

以下是 java.util.zip.Deflater.setDictionary(byte[] b, int off, int len) 方法的宣告。

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

引數

• b − 詞典資料位元組。

• off − 資料的開始偏移量。

• len − 資料長度。

示例

以下示例顯示瞭如何使用 java.util.zip.Deflater.setDictionary(byte[] b, int off, int len) 方法。

package com.tutorialspoint;

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

public class DeflaterDemo {
   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());
   }
}

讓我們編譯並執行上述程式，這將生成以下結果 −

Original Message length : 300
Total uncompressed bytes output :40
Compressed Message Checksum :368538129
Compressed Message length : 40
UnCompressed Message Checksum :368538129
UnCompressed Message length : 300