J2ME经验总结之Base64

Base64内容传送编码被设计用来把任意序列的8位字节描述为一种不易被人直接识别的形式。（The Base64 Content-Transfer-Encoding is designed to represent arbitrary sequences of octets in a form that need not be humanly readable.）

Base64 是网络上最常见的用于传输8Bit字节代码的编码方式之一，在发送电子邮件时，服务器认证的用户名和密码需要用Base64编码，附件也需要用 Base64编码……

下面是以前扒来的MD5算法的JAVA版本，J2ME可以放心使用。

package hlib;



import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.io.OutputStream;

import java.util.Vector;



public class HBase64 {



    private static final char[] legalChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"

            .toCharArray();



    private static Vector nodes = new Vector();



    /**

     * Split string into multiple strings

     * 

     * @param original

     *            Original string

     * @param separator

     *            Separator string in original string

     * @return Splitted string array

     */

    public static String[] split(String original, String separator) {

        nodes.removeAllElements();

        // Parse nodes into vector

        int index = original.indexOf(separator);

        while (index >= 0) {

            nodes.addElement(original.substring(0, index));

            original = original.substring(index + separator.length());

            index = original.indexOf(separator);

        }

        // Get the last node

        nodes.addElement(original);



        // Create splitted string array

        String[] result = new String[nodes.size()];

        if (nodes.size() > 0) {

            for (int loop = 0; loop < nodes.size(); loop++)

                result[loop] = (String) nodes.elementAt(loop);

        }

        return result;

    }



    /*

     * Replace all instances of a String in a String. @param s String to alter.

     * @param f String to look for. @param r String to replace it with, or null

     * to just remove it.

     */

    public static String replace(String s, String f, String r) {

        if (s == null)

            return s;

        if (f == null)

            return s;

        if (r == null)

            r = "";



        int index01 = s.indexOf(f);

        while (index01 != -1) {

            s = s.substring(0, index01) + r + s.substring(index01 + f.length());

            index01 += r.length();

            index01 = s.indexOf(f, index01);

        }

        return s;

    }



    /**

     * Method removes HTML tags from given string.

     * 

     * @param text

     *            Input parameter containing HTML tags (eg. <b>cat</b>)

     * @return String without HTML tags (eg. cat)

     */

    public static String removeHtml(String text) {

        try {

            int idx = text.indexOf("<");

            if (idx == -1)

                return text;



            String plainText = "";

            String htmlText = text;

            int htmlStartIndex = htmlText.indexOf("<", 0);

            if (htmlStartIndex == -1) {

                return text;

            }

            while (htmlStartIndex >= 0) {

                plainText += htmlText.substring(0, htmlStartIndex);

                int htmlEndIndex = htmlText.indexOf(">", htmlStartIndex);

                htmlText = htmlText.substring(htmlEndIndex + 1);

                htmlStartIndex = htmlText.indexOf("<", 0);

            }

            plainText = plainText.trim();

            return plainText;

        } catch (Exception e) {

            System.err.println("Error while removing HTML: " + e.toString());

            return text;

        }

    }



    /** Base64 encode the given data */

    public static String encode(byte[] data) {

        int start = 0;

        int len = data.length;

        StringBuffer buf = new StringBuffer(data.length * 3 / 2);



        int end = len - 3;

        int i = start;

        int n = 0;



        while (i <= end) {

            int d = ((((int) data) & 0x0ff) << 16)
 | ((((int) data[i + 1]) & 0x0ff) << 8)
 | (((int) data[i + 2]) & 0x0ff);
 
 buf.append(legalChars[(d >> 18) & 63]);
 buf.append(legalChars[(d >> 12) & 63]);
 buf.append(legalChars[(d >> 6) & 63]);
 buf.append(legalChars[d & 63]);
 
 i += 3;
 
 if (n++ >= 14) {
 n = 0;
 buf.append(" ");
 }
 }
 
 if (i == start + len - 2) {
 int d = ((((int) data) & 0x0ff) << 16)
 | ((((int) data[i + 1]) & 255) << 8);
 
 buf.append(legalChars[(d >> 18) & 63]);
 buf.append(legalChars[(d >> 12) & 63]);
 buf.append(legalChars[(d >> 6) & 63]);
 buf.append("=");
 } else if (i == start + len - 1) {
 int d = (((int) data) & 0x0ff) << 16;
 
 buf.append(legalChars[(d >> 18) & 63]);
 buf.append(legalChars[(d >> 12) & 63]);
 buf.append("==");
 }
 
 return buf.toString();
 }
 
 private static int decode(char c) {
 if (c >= 'A' && c <= 'Z')
 return ((int) c) - 65;
 else if (c >= 'a' && c <= 'z')
 return ((int) c) - 97 + 26;
 else if (c >= '0' && c <= '9')
 return ((int) c) - 48 + 26 + 26;
 else
 switch (c) {
 case '+':
 return 62;
 case '/':
 return 63;
 case '=':
 return 0;
 default:
 throw new RuntimeException("unexpected code: " + c);
 }
 }
 
 /**
 * Decodes the given Base64 encoded String to a new byte array. The byte
 * array holding the decoded data is returned.
 */
 
 public static byte[] decode(String s) {
 
 ByteArrayOutputStream bos = new ByteArrayOutputStream();
 try {
 decode(s, bos);
 } catch (IOException e) {
 throw new RuntimeException();
 }
 byte[] decodedBytes = bos.toByteArray();
 try {
 bos.close();
 bos = null;
 } catch (IOException ex) {
 System.err.println("Error while decoding BASE64: " + ex.toString());
 }
 return decodedBytes;
 }
 
 private static void decode(String s, OutputStream os) throws IOException {
 int i = 0;
 
 int len = s.length();
 
 while (true) {
 while (i < len && s.charAt(i) <= ' ')
 i++;
 
 if (i == len)
 break;
 
 int tri = (decode(s.charAt(i)) << 18)
 + (decode(s.charAt(i + 1)) << 12)
 + (decode(s.charAt(i + 2)) << 6)
 + (decode(s.charAt(i + 3)));
 
 os.write((tri >> 16) & 255);
 if (s.charAt(i + 2) == '=')
 break;
 os.write((tri >> 8) & 255);
 if (s.charAt(i + 3) == '=')
 break;
 os.write(tri & 255);
 
 i += 4;
 }
 }
 }