java.util.zip.Deflater.setDictionary(byte[] b, int off, int len)方法示例

java.util.zip.Deflater.setDictionary(byte[] b, int off, int len)方法设置预设字典进行压缩。 当可以预先确定历史缓冲器时使用预设字典。 当数据随后使用Inflater.inflate()进行解压缩时，可以调用Inflater.getAdler()以获取解压缩所需的字典的Adler-32值。

声明

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

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。

返回值

• N/A

示例

以下示例显示了java.util.zip.Deflater.setDictionary(byte[] b, int off, int len)方法的用法。

package com.zaixian;

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 xuhuhu.com;"
         +"Welcome to xuhuhu.com;"
         +"Welcome to xuhuhu.com;"
         +"Welcome to xuhuhu.com;"
         +"Welcome to xuhuhu.com;"
         +"Welcome to xuhuhu.com;"
         +"Welcome to xuhuhu.com;"
         +"Welcome to xuhuhu.com;"
         +"Welcome to xuhuhu.com;"
         +"Welcome to xuhuhu.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());
   }
}

执行上面示例代码，得到以下结果 -

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