最近研究了jsp中作HTTP认证的问题，它的工作方式如下：

　　1、server发送一个要求认证代码401和一个头信息WWW-authenticate，激发browser弹出一个认证窗口

　　2、server取得browser送来的认证头"Authorization",它是加密的了，要用Base64方法解密，取得明文的用户名和密码

　　3、检查用户名和密码，根据结果传送不同的页面

　　
　　以下是jsp的片断，你也可以把它做成include文件。和Base64的加解密的class源码。
　　如有兴趣可与我联系：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")){
　　        //认证成功
　　   }else{
　　        //认证失败
　　   }
　　}
　　%>

　　
　　//消息加解密class
　　public class Base64
　　{
　　        /** decode a Base 64 encoded String.
　　          *<p><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.</p>
　　          *<p>Since we should be dealing with Base64 encoded Strings that is a reasonable
　　          * assumption.</p>
　　          *<p><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.</p>
　　        */
　　        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=='' '' || c=='' '' || c=='' '' || c=='' '')
　　                                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('' '');
　　                                }
　　                                //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();
　　        }
　　}