lzw 压缩算法的 编码 和译码 的java实现程序

package com.anywhere;
import java.io.*;

/** 一个lzw 压缩算法的 编码 和译码 的实现程序
* 压缩一个已有文件（sourcefile）到目标文件（targetfile） ，然后读取压缩的码；
* 此程序采用12位压缩码，词典作多可以存储2^12个词条；
* 生成的压缩码 经过解压缩，可以恢复为原先文件；
*对文本文件的压缩率，大约为60%,尚不能支持中文的文件输入：）
* @author Lai Yongxuan     2003.3.12
* @version 1.0
*/
public class lzwCode
{
  /**
  @see Dictionary
  */
   Dictionary dic=new Dictionary();
   /**count1: the bytes of input file,count2:the bytes of output  file
   */
   int count1=0,count2=0;
   /** the max number of the dictionary;
   *this number can be add to the codebuf[] if
   * the file has only odd words to be treated ; 
   */
   /** the input file  : character file or coding file
   */
   BufferedInputStream in;
   /** the output file: character file or coding file
   */
   BufferedOutputStream out;
   final short END=4095;
    
/**the entry of the class,and check the arguments first
 @param args array of string arguments
  -c sourceFile [targetFile] 建立一个压缩文件
  -d sourceFile [targetFile]  解压缩一个文件
 @return No return value
 @exception No ecceptions thrown
*/
  public static void main(String []args)
    {
        if ( args.length<=1 || args.length>4 )
        {
            System.out.println("-c sourceFile [targetFile] [-dic]  建立一个压
缩文件\n");
            System.out.println("-d sourceFile [targetFile] [-dic]  解压缩一个
文件\n");
        }
        else if(! ( args[0].equals(new String("-c") )||args[0].equals(new
String("-d") )  )  )
        {
            System.out.println("-c sourceFile [targetFile]  建立一个压缩文件\
n");
            System.out.println("-d sourceFile [targetFile]  解压缩一个文件\n"
);
        }
        else if(args.length>=2)
        {
          lzwCode a=new lzwCode(args);
          a.run(args);
         
        }
        return ;
    }
   
   
/** the constuctor of the class of "lzwCode "
*@param args array of string arguments input at the main()
*
*
*/
    public lzwCode(String []args)
    {
   
        
        try{
                String f=new String();
                in =new BufferedInputStream(
                  new FileInputStream(
                   new File(args[1])));
                  if(args.length==3 && !args[2].equals(new String("-dic")))
                  {
                    f=args[2];
                  }
                  else
                  {
                    int i=args[1].lastIndexOf(new String(".") );
                    f=args[1].substring(0,i)+((args[0].equals("-c")
)?".lzw":".dlzw");
                  }
                 out=new BufferedOutputStream(
                     new FileOutputStream(
                      new File(f)));
                
         
           
          }//try
          catch(FileNotFoundException e )
              {
                System.err.println(e);
                    return;
              }
 
           catch(IOException e )
            {
                System.err.println(e);
                    return;
            }   

         
    }
/** the entry of the process;
@param Srring args[]: array of string arguments input at the main()
         BufferedInputStream in: the input charstream file
         BufferedOutputStream out:the output code stream file
* @return No return value
*/

public void run(String args[] )
{
   
     if(args[0].equals(new String("-c"))   )
          {
            code(in,out);
            }
            else
            {
            decode(in,out);
            }
  if(args[args.length-1].equals(new String("-dic") ))
       System.out.println(dic.toString ());
   
}

/** input the charstream from a file,and output the code stream to anpther
file
* @param BufferedInputStream in: the input charstream file
         BufferedOutputStream out:the output code stream file
* @return No return value

*
*/
  public void code(BufferedInputStream in,BufferedOutputStream out)
  {
    System.out.println("coding...\n"+ ".......\n");
   
    //a:the buffer byte read from the input file,then to be converted to
String
    //buf: the codestream to store in the code file
    //prefix :the pre_String of the dictory
    // the indexbuf[] is the index of dictionary to be converted in
    // the code file
    //str: the current charecter of the character input Stream
    byte a[]=new byte[1],buf[]=new byte[3];
   
    String prefix="",cur="";
    byte i=0;
    short indexbuf[]=new short[2];
   
    String str=null;
    try{
    short m=0;
    while(  (a[0]=(byte)in.read() )  != -1 )
      {
        cur=new String(a);// be converted
        count1++; // the number of bytes of  input file
        str=prefix;
        str=str.concat(cur);
        m=(short)dic.indexOf(str); 
      
        if( m!=-1)//the prefix is in the dictionary,
        {
            prefix=str;
         }
        else//
        {
           
            if(i==0)//the first indexbuf,store in codebuf[]
            {
               indexbuf[0]=(short)dic.indexOf(prefix);
               i=1;
            }
            else// now have 2 index number,then ouput to the code file
            {
              indexbuf[1]=(short)dic.indexOf(prefix);
              zipOutput(out,indexbuf);
             
              count2+=3;//3 bytes stored to the code file
              i=0;
            }
                
            dic.add(str);
            prefix=cur;
           
        }//else
         
    
      }//while
     
    //  System.out.println("i="+i);
      if(i==(byte)1) //this is the case that the
               //input file has only odd index number to store
      {
        indexbuf[1]=END;//put a special index number
                        //(the max number of the dictionary) END to the
code file
        zipOutput(out,indexbuf);
        count2+=3;
           
      }
     
      dic.add(str);
      in.close ();
      out.close ();
   
     
      System.out.println("zip rate:"+(float)count2*100/count1+"% ");
     }catch(IOException e )
            {
                System.err.println(e);
                    return;
            }
       catch(OutDictionaryException e)
       {    
               System.err.println(e);
                  return;
        }
           

  }
/** input the code stream from a file,and output the char stream to anpther
file
* @param BufferedInputStream in: the input code   file
         BufferedOutputStream out:the output charstream  stream file
* @return No return value
* @exception No return Exception
*
*
*/ public void decode(BufferedInputStream in,BufferedOutputStream out)
  {
    System.out.println("decoding...\n"+".......\n");
   
    short precode=0,curcode=0;
    String prefix=null;
    short i=0;
    short bufcode[]=new short[2];//2 code read from the code file
    boolean more=true;//indicate the end of the file or some error while
input the file
   
   
   
  //    DataOutputStream out2=new DataOutputStream(out);   
    try{
   
    more=zipInput(in,bufcode);//first input 2 code
    if(more)
    {
     curcode=bufcode[0];
  // out2.writeChars(dic.getString(curcode));
     stringOut(out,dic.getString(curcode) );
    
    
    }
    else
     System.out.println("error in the beginning...");

     while(more)
      {
         precode=curcode;
   
       
         if(i==0)
         {
          curcode=bufcode[1];
          i=1; 
         }
        else
        {
            more=zipInput(in,bufcode);
     
            curcode=bufcode[0];
            if(bufcode[1]==END)
               {
              
                stringOut(out,dic.getString (bufcode[0] ));
                    break;
                }      
             i=0;
        }
               
   
         if(curcode<dic.length())//if the prefix string can be found in the
dictory
         {
        //  out2.writeChars(dic.getString(curcode));
            stringOut(out,dic.getString(curcode) );
            prefix=dic.getString(precode);
                   
            prefix+=(dic.getString(curcode)).substring(0,1);
            dic.add(prefix);
               
        }
        else
        {
            prefix=dic.getString(precode);
            prefix+=prefix.substring(0,1);
        //  out2.writeChars(prefix);
            stringOut(out,prefix );
            dic.add(prefix);
       
           
        }//else
      }//while
    
   
      in.close ();
      out.close ();
 
    }catch( OutDictionaryException e )
            {
               System.err.println(e);
                    return;
               }    
  catch(IOException e)
    {
        System.err.println(e);
                    return;
    }           
   
  } 

/** output the index number of the dictionary  to the code stream;
 ecah index is converted to 12 bit ;and output 2 short numbers at a
 time
* @param  BufferedOutputStream out:the output charstream  stream file
          short index[]:the 2 short array to be converted to code form
* @return No return value
* @exception No return Exception
*
*
*/
  private void zipOutput(BufferedOutputStream out,short index[])
  {
    try{
   
   
    byte buf[]=new byte[3];
 
    buf[1]=(byte)(index[0]<<4);
   
    buf[0]=(byte)(index[0]>>4);
    
    buf[2]=(byte)index[1];
    buf[1]+=(byte)(index[1]>>8);
   
    out.write(buf,0,3);
 
    //out put the decoding
//  System.out.println(index[0]+"\t"+index[1]+"\t"); 
 
 /*     short codebuf[]=new short[2];
       
    //codebuf[0]=(short)(buf[0]<<4);
    codebuf[0]=toRight(buf[0],4);
    codebuf[0]+=(short)(toRight(buf[1],0)>>4);
   
    //codebuf[1]=(short)buf[2];
      codebuf[1]=toRight(buf[2],0);
    //codebuf[1]=(byte)(buf[1]<<4);
    byte temp=(byte)(toRight(buf[1],4));
   
    codebuf[1]+=toRight(temp,4);
  
  
   // codebuf[1]+=(short)(buf[1]<<4);
   
    System.out.println("\t"+codebuf[0]+"\t"+codebuf[1]);
    */     
     }catch( IOException e )
       {
            System.err.println(e);
                    return;
       }    
   
  }
 
/** convert the  code stream to the file in the original way;
* each time deel with 3 bytes,and return  2 index number
* @param  BufferedOutputStream in :the input code  stream file
          short index[]:the 2 short array buffer of index of dictionary
* @return return loolean value:if not the end of file and the converted
code
          is right ,return true;else ,return false
* @exception No return Exception
*
*
*/
  private  boolean  zipInput(BufferedInputStream in,short codebuf[])
  {
    byte buf[]=new byte[3],temp;
    //int intbuf[]=new int[3],temp;
    short le=(short)dic.length();
    try{       
  
    if(in.read(buf,0,3)!=3)
     {
         System.out.println("the end of the file!");
         return false;
      }
    //codebuf[0]=(short)(buf[0]<<4);
    codebuf[0]=toRight(buf[0],4);
    codebuf[0]+=(short)(toRight(buf[1],0)>>4);
   
    //codebuf[1]=(short)buf[2];
    codebuf[1]=toRight(buf[2],0);
    //codebuf[1]=(byte)(buf[1]<<4);
    temp=(byte)(toRight(buf[1],4));
    codebuf[1]+=toRight(temp,4);
  //  System.out.println(codebuf[0]+"\t"+codebuf[1]);
      
       
    if(codebuf[0]<-1 ||codebuf[1]<-1)
      {
        System.out.println("erroring while getting the code
:"+codebuf[0]+"\t"+codebuf[1]);
        System.out.println(dic);
        return false;
      }
    //System.out.println(codebuf[0]+"\t"+codebuf[1]);  
 }
  catch(IOException e )
        {
             System.err.println(e);
                  return false;
        }
  return true;
 }
 
 /**converte a byte number,to the short form;and
  * shift a byte n bits to the right;and reglect whether
  *&the byte is positive or negective
  *@param byte:the byte you want to shift
  *            int :the bits you shift to the right
  *@return int :the result of the shifted
 */ private short toRight(byte buf,int n)
 {
    short s=0;
    for(short i=7;i>=0;i--)
    {
        if( ( (1L<<i)&buf )!=0 )
          s+=(short)(1L<<(i+n));
    }
    return s;
 }

 /**output the String to a file,but in a form of "byte" way;
 * in order to be ecactly as the oririnal file ,i deel with
*  the file in bytes form
*@param BufferedOutputStream out:the output file
*       String str:the buf of String to be output
*/ private  void stringOut(BufferedOutputStream out,String str)
   {
      byte a[]=str.getBytes();
      try{
      out.write(a,0,str.length());
    }
    catch(IOException e )
        {
             System.err.println(e);
                 
        }
       
  }
} 
 

//Dictionary.java 

package com.anywhere;
import java.util.*;
/**the Exception to indicate that the dictionary is too large
*/
 class OutDictionaryException extends Exception
      {
        public  String toString()
            {
                return (super.toString ()+"out of the dictionary size!!");
            }
      }
/**
 a dictonry that  contains at most 2^12 words,and should be inited
 at the beginning; it can be looked up,can be added and return the size
@author :Lai Yongxuan  2002.3.10
@version :1.0
*/
public class Dictionary
{
    /** the container of the dictionary,use ArrayList
    *@see java.util.ArrayList
    */
    ArrayList ar=new ArrayList();
   
    /**the constuctor of the class,and put the 128 ASCII to the dictionary 
    */
    public Dictionary()
    {
      // byte i[]=new byte[1];
       char c[]=new char[1];
       for( c[0]=0;c[0]<128;c[0]++)
       {
        
         ar.add(new String(c));
        
       }
    }
    /**return the index number of the word in the dictionary
    */
    public int indexOf(String a)
    {
        return ar.indexOf(a);
    }
    /**add a string to the dictionary
    @param String :the word to be added
    @return NO returned value
    @Exception OutDictionaryException is thrown if the dictionary is too
        large ,it only can contain 4096(2^12) words at most
    */
    public void add (String a) throws OutDictionaryException
    {
      
       if( length()<4096)
           ar.add(a);
       else
       {
        
          throw(new OutDictionaryException());
       
       }
   }
    /** the size  of the dictionary
    */
    public int length()
    {
   
       return (short)ar.size();
    }

    public String toString()
    {
        Integer le=new Integer(length() );
   
        String str="size of the dictionary: "+le.toString ()+"\n";
        for(int i=0;i<length();i++)
          str+=new String(i+": "+(String)ar.get(i)+"\t");
       return str;
    }
    /** return the word by the index pointor
    */
    public String getString(short i)
    {
        return (String)ar.get(i);
    }
    /** only to test the dictionary
    */
    public static void main(String []args )
    {
        Dictionary a=new Dictionary();
    /* try{
       
        for(int i=128;i<6000;i++)
        {
            a.add(new String("i am a student") );
        }
     
      }
      catch(Exception e)
      { 
      
        System.err.println (e.toString());
       
        }*/
       System.out.println(a);
    }
}