base_64coding.java

JAVA邮件系统

import java.lang.Integer;
import java.lang.Math;

public class Base_64Coding implements Encodeing
{
	private static String BaseCode = 
				"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
	static byte  nEncodeTemp , cTempHigh ,cTempLow;
	static byte[]  DecodeTable;
	
	//initial.
	public Base_64Coding(){
		DecodeTable = new byte[256];
		for(int i=0;i<256;i++ )
			DecodeTable[i]=-2;
		//make decode table;
		for( int i=0;i<64;i++ )
		{
			DecodeTable[ BaseCode.charAt (i) ] = (byte)i;
			DecodeTable[ BaseCode.charAt (i) | 0x80 ] = (byte)i;
		}
		DecodeTable[ '=' ] = -1;
		DecodeTable[ '=' | 0x80 ] = -1;
		
	}
	//sometime , before encode , we need calc the number of 
	//hight ascii code in buffer;
	public  int  CalcEncodeLengthForCharBuffer( byte[] sSrc ){
		if( sSrc == null )
			return 1;
		int nLength = sSrc.length;
		return CalcEncodeLength( sSrc , nLength );		
	};
	public  int  CalcEncodeLength( byte[] sSrc , int nLength ){
		return ( nLength/3 + 1 )*4 + 1 + ( nLength/lineCode + 1 )*2 ;
	};
	
	//the buffer should be alloc and free by external module;
	//Now ,it always return true;
	private  int EncodeOneline( byte[] sSrc,byte[] sDes,int nSrcLength 
						,int nOffsetSrc ,int nOffsetDes ){
		if( nSrcLength == 0 || sSrc==null || sDes==null ){
			return 0;
		}
		int nDes = 0;
		char tempc1,tempc2,tempc3;
		// 3 byte => 4 byte ;
		for( int i=0 ; i < nSrcLength ; i = i+3 ){
			//first code;
			tempc1  = (char)( ( (char)sSrc[nOffsetSrc+i] ) & 0x00ff );
			sDes[nOffsetDes+nDes] = (byte)(BaseCode.charAt ( Math.abs(tempc1)>>2 )  );
			
			//second code;
			nEncodeTemp = (byte)(tempc1<<4);
			cTempHigh= (byte)(nEncodeTemp&0x30);
			if( ( i+1 >= nSrcLength ) ){
				sDes[nOffsetDes+nDes+1]	= (byte)(BaseCode.charAt ( Math.abs( cTempHigh) ) );
				sDes[nOffsetDes+nDes+2]	= (byte)'=';
				sDes[nOffsetDes+nDes+3]	= (byte)'=';
				
				return nDes+4;
			}
			else{
				tempc2  = (char)( ( (char)sSrc[nOffsetSrc+i+1] ) & 0x00ff );
				cTempLow = (byte)(tempc2>>4);
				sDes[nOffsetDes+nDes+1]	= (byte)( BaseCode.charAt ( Math.abs( (byte)cTempHigh | cTempLow ) ));
			}
			

			//third code;
			nEncodeTemp = (byte)(tempc2 <<2);
			cTempHigh= (byte)(nEncodeTemp&0x3c);
			if( ( i+2 >= nSrcLength ) ){
				sDes[nOffsetDes+nDes+2]	= (byte)(BaseCode.charAt ( Math.abs(cTempHigh) ));
				sDes[nOffsetDes+nDes+3]	= (byte)('=');
				sDes[nOffsetDes+nDes+4] = 0;
				return nDes+4;
			}
			else{
				tempc3  = (char)( ( (char)sSrc[nOffsetSrc+i+2] ) & 0x00ff );
				cTempLow = (byte)(tempc3>>6);
				sDes[nOffsetDes+nDes+2]	= (byte)(BaseCode.charAt ( Math.abs( (byte)cTempHigh | cTempLow ) ) );
			}
				
			//fourth code;
			sDes[nOffsetDes+nDes+3]	= (byte)(BaseCode.charAt ( Math.abs( tempc3&0x3f ) ) );

			nDes +=4;
		}
		return nDes;	
	};
	
	public  int Encode( byte[] sSrc,byte[] sDes,int nSrcLength 
						,int nOffsetSrc ,int nOffsetDes ){
		if( nSrcLength == 0 || sSrc==null || sDes==null ){
			return 0;
		}
		int nDes = 0;
		int nLine =nSrcLength/Encodeing.lineCode;
		int nTail = nSrcLength%Encodeing.lineCode;
		if( nTail!=0 )
			nLine++;
		int nSrcNow = 0;
		for( int i=0;i<nLine;i++ ){
			if( i == nLine -1 )
				nDes += EncodeOneline ( sSrc,sDes,
										nTail,nSrcNow ,nDes);
			else
				nDes += EncodeOneline ( sSrc,sDes,
										Encodeing.lineCode
										,nSrcNow ,nDes );
			sDes[nDes] = 0xd;
			sDes[nDes+1] = 0xa;
			nDes += 2;
			nSrcNow += Encodeing.lineCode;
		}
		return nDes;	
	};

	//the buffer should be alloc and free by external module;
	//Now ,it always return true;
	public  int Decode( byte[] sSrc,byte[] sDes,int nSrcLength 
						,int nOffsetSrc ,int nOffsetDes ){
		if( nSrcLength == 0 || sSrc==null || sDes==null ){
			return 0;
		}
		//convert the decode src code;
		for( int i=0;i<nSrcLength;i++ ){
			sSrc[nOffsetSrc+i] = DecodeTable[ sSrc[nOffsetSrc+i] & 0x7F ];
		}

		// 4 byte => 3 byte ;
		int  nDes=0;
		byte cSrc0,cSrc1,cSrc2,cSrc3;
		for( int i=0 ; i < nSrcLength ; ){
			//first get the code ;
			while( sSrc[nOffsetSrc+i] <= -1 ){
				if( i >= nSrcLength-1 ){
					return nDes;
				}
				i++;
			}
			if( i >= nSrcLength ){
				return nDes;
			}
			cSrc0 = sSrc[nOffsetSrc+i];
			i++;
			if( i>= nSrcLength || sSrc[nOffsetSrc+i] <= -1 ){
				cSrc1 = -1;
			}
			else{
				cSrc1 = sSrc[nOffsetSrc+i];
				i++;
			}
			if( i>= nSrcLength || sSrc[nOffsetSrc+i] <= -1 ){
				cSrc2 = -1;
			}
			else{
				cSrc2 = sSrc[nOffsetSrc+i];
				i++;
			}
			if( i>= nSrcLength || sSrc[nOffsetSrc+i] <= -1 ){
				cSrc3 = -1;
			}
			else{
				cSrc3 = sSrc[nOffsetSrc+i];
				i++;
			}
			//first code;
			cTempHigh = (byte)(cSrc0<<2);
			if( cSrc1 < 0 ){
				sDes[nOffsetDes+nDes] = cTempHigh;
				nDes++;
				continue;
			}
			else{
				cTempLow = (byte)(cSrc1>>4); 
				sDes[nOffsetDes+nDes] = (byte)(cTempHigh|cTempLow);
				nDes++;
			}
			
			//second code;
			cTempHigh = (byte)(cSrc1<<4);
			if( cSrc2 < 0 ){
				sDes[nOffsetDes+nDes]	= cTempHigh ;
				nDes++;
				continue;
			}
			else{
				cTempLow = (byte)(cSrc2>>2);
				sDes[nOffsetDes+nDes]	= (byte)(cTempHigh | cTempLow);
				nDes++;
			}

			//third code;
			cTempHigh= (byte)(cSrc2<<6);
			if( cSrc3 < 0 ){
				continue;
			}
			else{
				sDes[nOffsetDes+nDes]	= (byte)(cTempHigh | cSrc3);
				nDes++;
			}
				
		}

		return nDes;
	};
}