什么是HTTP Basic Authentication？直接看http://en.wikipedia.org/wiki/Basic_authentication_scheme吧。

    在你访问一个需要HTTP Basic Authentication的URL的时候，如果你没有提供用户名和密码，服务器就会返回401，如果你直接在浏览器中打开，浏览器会提示你输入用户名和密码(google浏览器不会，bug？)。
你可以尝试点击这个url看看效果：http://api.minicloud.com.cn/statuses/friends_timeline.xml

    要在发送请求的时候添加HTTP Basic Authentication认证信息到请求中，有两种方法：

    一是在请求头中添加Authorization：

    Authorization: "Basic 用户名和密码的base64加密字符串"

    二是在url中添加用户名和密码：

    http://userName:password@api.minicloud.com.cn/statuses/friends_timeline.xml  

    //需要Base64见：http://www.webtoolkit.info/javascript-base64.html

    function make_base_auth(user, password) {

      var tok = user + ':' + pass;

      var hash = Base64.encode(tok);

      return "Basic " + hash;

    }   

    var auth = make_basic_auth('QLeelulu','mypassword');

    var url = 'http://example.com';   

    // 原始JavaScript

    xml = new XMLHttpRequest();

    xml.setRequestHeader('Authorization', auth);

    xml.open('GET',url)   

    // ExtJS

    Ext.Ajax.request({

        url : url,

        method : 'GET',

        headers : { Authorization : auth }

    });   

    // jQuery

    $.ajax({

        url : url,

        method : 'GET',

        beforeSend : function(req) {

            req.setRequestHeader('Authorization', auth);

        }

    });  

    <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

    }

    }

    %>   

    =======Java段代码==================  

    //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();

    }

    }