Java java.util.zip.Deflater.setDictionary()用法及代码示例

描述

这个java.util.zip.Deflater.setDictionary(byte[] b, int off, int len)方法设置用于压缩的预设字典。当可以预先确定历史缓冲区时，使用预设字典。当数据稍后用 Inflater.inflate() 解压缩时，可以调用 Inflater.getAdler() 以获得解压缩所需的字典的 Adler-32 值。

声明

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

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

参数

• b- 字典数据字节。

• off− 数据的起始偏移量。

• len- 数据的长度。

示例

下面的例子展示了 java.util.zip.Deflater.setDictionary(byte[] b, int off, int len) 方法的用法。

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());
   }
}

让我们编译并运行上面的程序，这将产生以下结果 -

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