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最近研究了jsp中作HTTP認證的問題，它的工作方式如下︰ 
 
1、server發送一個要求認證代碼401和一個頭信息WWW-authenticate，激發browser彈出一個認證窗口 
 
2、server取得browser送來的認證頭"Authorization",它是加密的了，要用Base64方法解密，取得明文的用戶名和密碼 
 
3、檢查用戶名和密碼，根據結果傳送不同的頁面 
 
 
以下是jsp的片斷，你也可以把它做成include文件。和Base64的加解密的class源碼。 
如有興趣可與我聯系︰unixboy@yeah.net 
 
<jsp:useBean id="base64" scope="page" class="Base64"/> 
<% 
if(request.getHeader("Authorization")==null){ 
   response.setStatus(401); 
   response.setHeader("WWW-authenticate", "Basic realm=\"unixboy.com\""); 
}else{ 
   String encoded=(request.getHeader("Authorization")); 
   String tmp=encoded.substring(6); 
   String up=Base64.decode(tmp); 
   String user=""; 
   String password=""; 
   if(up!=null){ 
        user=up.substring(0,up.indexOf(":")); 
    password=up.substring(up.indexOf(":")+1); 
   } 
   if(user.equals("unixboy")&&password.equals("123456")){ 
        //認證成功 
   }else{ 
        //認證失敗 
   } 
} 
%> 
 
 
//消息加解密class 
public class Base64 
{ 
        /** decode a Base 64 encoded String. 
          * <h4>String to byte conversion</h4> 
          * This method uses a naive String to byte interpretation, it simply gets each 
          * char of the String and calls it a byte. 
          * Since we should be dealing with Base64 encoded Strings that is a reasonable 
          * assumption. 
          * <h4>End of data</h4> 
          * We don't try to stop the converion when we find the "=" end of data padding char. 
          * We simply add zero bytes to the unencode buffer. 
        */ 
        public static String decode(String encoded) 
        { 
                StringBuffer sb=new StringBuffer(); 
                int maxturns; 
                //work out how long to loop for. 
                if(encoded.length()%3==0) 
                maxturns=encoded.length(); 
                else 
                maxturns=encoded.length()+(3-(encoded.length()%3)); 
                //tells us whether to include the char in the unencode 
                boolean skip; 
                //the unencode buffer 
                byte[] unenc=new byte[4]; 
                byte b; 
                for(int i=0,j=0; i<maxturns; i++) 
                { 
                        skip=false; 
                        //get the byte to convert or 0 
                        if(i<encoded.length()) 
                        b=(byte)encoded.charAt(i); 
                        else 
                        b=0; 
                        //test and convert first capital letters, lowercase, digits then '+' and '/' 
                        if(b>=65 && b<91) 
                        unenc[j]=(byte)(b-65); 
                        else if(b>=97 && b<123) 
                        unenc[j]=(byte)(b-71); 
                        else if(b>=48 && b<58) 
                        unenc[j]=(byte)(b+4); 
                        else if(b=='+') 
                        unenc[j]=62; 
                        else if(b=='/') 
                        unenc[j]=63; 
                        //if we find "=" then data has finished, we're not really dealing with this now 
                        else if(b=='=') 
                        unenc[j]=0; 
                        else 
                        { 
                                char c=(char)b; 
                                if(c=='\n' || c=='\r' || c==' ' || c=='\t') 
                                skip=true; 
                                else 
                                //could throw an exception here? it's input we don't understand. 
                                ; 
                        } 
                        //once the array has boiled convert the bytes back into chars 
                        if(!skip && ++j==4) 
                        { 
                                //shift the 6 bit bytes into a single 4 octet word 
                                int res=(unenc[0] << 18)+(unenc[1] << 12)+(unenc[2] << 6)+unenc[3]; 
                                byte c; 
                                int k=16; 
                                //shift each octet down to read it as char and add to StringBuffer 
                                while(k>=0) 
                                { 
                                        c=(byte)(res >> k); 
                                        if ( c > 0 ) 
                                        sb.append((char)c); 
                                        k-=8; 
                                } 
                                //reset j and the unencode buffer 
                                j=0; 
                                unenc[0]=0;unenc[1]=0;unenc[2]=0;unenc[3]=0; 
                        } 
                } 
                return sb.toString(); 
        } 
         
        /** encode plaintext data to a base 64 string 
          * @param plain the text to convert. If plain is longer than 76 characters this method 
          *             returns null (see RFC2045). 
          * @return the encoded text (or null if string was longer than 76 chars). 
        */ 
        public static String encode(String plain) 
        { 
                if(plain.length()>76) 
                return null; 
                int maxturns; 
                StringBuffer sb=new StringBuffer(); 
                //the encode buffer 
                byte[] enc=new byte[3]; 
                boolean end=false; 
                for(int i=0,j=0; !end; i++) 
                { 
                        char _ch=plain.charAt(i); 
                        if(i==plain.length()-1) 
                        end=true; 
                        enc[j++]=(byte)plain.charAt(i); 
                        if(j==3 || end) 
                        { 
                                int res; 
                                //this is a bit inefficient at the end point 
                                //worth it for the small decrease in code size? 
                                res=(enc[0] << 16)+(enc[1] << 8)+enc[2]; 
                                int b; 
                                int lowestbit=18-(j*6); 
                                for(int toshift=18; toshift>=lowestbit; toshift-=6) 
                                { 
                                        b=res >>> toshift; 
                                        b&=63; 
                                        if(b>=0 && b<26) 
                                        sb.append((char)(b+65)); 
                                        if(b>=26 && b<52) 
                                        sb.append((char)(b+71)); 
                                        if(b>=52 && b<62) 
                                        sb.append((char)(b-4)); 
                                        if(b==62) 
                                        sb.append('+'); 
                                        if(b==63) 
                                        sb.append('/'); 
                                        if(sb.length()%76==0) 
                                        sb.append('\n'); 
                                } 
                                //now set the end chars to be pad character if there 
                                //was less than integral input (ie: less than 24 bits) 
                                if(end) 
                                { 
                                        if(j==1) 
                                        sb.append("=="); 
                                        if(j==2) 
                                        sb.append('='); 
                                } 
                                enc[0]=0; enc[1]=0; enc[2]=0; 
                                j=0; 
                        } 
                } 
                return sb.toString(); 
        } 
}

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