在序列化的過(guò)程中，我們將一個(gè)對(duì)象序列化為字符串的過(guò)程中會(huì)出現(xiàn)亂碼的情形，這中情況，我們可以使用一種Base64編碼的方式，將亂碼的字符串轉(zhuǎn)化為ascii編碼的方式，那么這種編碼是如何實(shí)現(xiàn)的呢?
我們采用的是利用將已有的編碼進(jìn)行長(zhǎng)度擴(kuò)充，Base64是將原來(lái)3個(gè)字節(jié)擴(kuò)充為4個(gè)字節(jié)，我們將3個(gè)字節(jié)拆成4等份，每份都是6個(gè)bit，然后將這個(gè)bit值映射到一個(gè)數(shù)組，數(shù)組如下:

'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O',
'P','Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d',
'e','f','g','h','i','j','k','l','m','n','o','p','q','r','s',
't','u','v','w','x','y','z','0','1','2','3','4','5','6','7',
'8','9','+','/'

編碼后的數(shù)組就是經(jīng)過(guò)Base64編碼的結(jié)果。
正如上面我們看到的，是對(duì)每3個(gè)字節(jié)進(jìn)行編碼，假如字符串的長(zhǎng)度不是3的倍數(shù)，怎么辦，沒關(guān)系，我們根據(jù)字符串的長(zhǎng)度和3的余數(shù)進(jìn)行末尾填充'=’，在編碼的時(shí)候填充\x00,解碼的時(shí)候根據(jù)'='號(hào)的數(shù)目來(lái)進(jìn)行判斷并解碼，Base64編碼的方式就是這樣，下面是我針對(duì)Base64編碼的一個(gè)實(shí)現(xiàn)，代碼如下

public class Base64Realize {
    //進(jìn)行base64映射的字符數(shù)組
    private final static char[] str = {'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',
                                   'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',
                                   '0','1','2','3','4','5','6','7','8','9','+','/'};

    /**
     * 獲取解碼器
     * @return
     */
    public static Base64Realize getDecoder(){
        return new Base64Realize();
    }

    /**
     * 解碼
     * @param code
     * @return
     */
    public String decode(String code){
        //對(duì)字符串的長(zhǎng)度進(jìn)行計(jì)算
        int length = code.length();
        //判斷長(zhǎng)度的合法性
        if(length == 0 || length % 4 != 0)
            return null;
        //獲取字符串末尾的'='號(hào)數(shù)目
        int endEqualNum = 0;
        if(code.endsWith("=="))
            endEqualNum = 2;
        else if(code.endsWith("="))
            endEqualNum = 1;
        //對(duì)末尾的=號(hào)進(jìn)行替換
        code.replace('=','0');
        StringBuilder sb = new StringBuilder(length);
        //解碼
        int blockNum = length / 4;
        String afterDecode = "";
        for(int i = 0;i < blockNum;i++){
            afterDecode = decodeDetail(code.substring(i * 4,i * 4 + 4));
            sb.append(afterDecode);
        }
        //返回字符串
        String result = sb.toString();
        return result.substring(0,result.length() - endEqualNum);
    }

    /**
     * 編碼
     * @param code
     * @return
     */
    public String encode(String code){
        //初始化判斷
        if (code == null || code.equals(""))
            return null;
        //獲取需編碼字符串的長(zhǎng)度
        int length = code.length();
        StringBuilder sb = new StringBuilder(length * 2);
        //轉(zhuǎn)化為char型數(shù)組
        char[] code1 = code.toCharArray();
        //獲取長(zhǎng)度對(duì)3的取余
        int mod = length % 3;
        //獲取長(zhǎng)度對(duì)3的倍數(shù)的
        int div = length / 3;
        //編碼
        for(int i = 0;i < div;i++){
            int temp = i * 3;
            sb.append(encodeDetail(code1[temp],code1[temp + 1],code1[temp + 2]));
        }
        //對(duì)超出的進(jìn)行額外的編碼
        if (mod == 1) {
            String str = encodeDetail(code1[length - 1], '\0', '\0');
            sb.append(str.substring(0,str.length() - 2) + "==");
        }
        if(mod == 2) {
            String str = encodeDetail(code1[length - 2], code1[length - 1], '\0');
            sb.append(str.substring(0,str.length() - 1) + "=");
        }
        return sb.toString();
    }

    /**
     * 編碼的詳細(xì)步驟
     * @param a1
     * @param a2
     * @param a3
     * @return
     */
    private String encodeDetail(char a1,char a2,char a3){
        char[] b = new char[4];
        b[0] = str[((a1 & 0xFC) >> 2)];
        b[1] = str[(a1 & 0x03) << 4 | (a2 & 0xF0) >> 4];
        b[2] = str[(a2 & 0x0F) << 2 | (a3 & 0xC0) >> 6];
        b[3] = str[(a3 & 0x3F)];
        return String.copyValueOf(b);
    }


    /**
     * 解碼的詳細(xì)步驟
     * @param str
     * @return
     */
    private String decodeDetail(String str){
        int len = str.length();
        if(len != 4)
            return null;
        char[] b = new char[3];
        int a1 = getIndex(str.charAt(0));
        int a2 = getIndex(str.charAt(1));
        int a3 = getIndex(str.charAt(2));
        int a4 = getIndex(str.charAt(3));
        b[0] = (char) (a1 << 2 | (a2 & 0x30) >> 4);
        b[1] = (char) ((a2 & 0x0F) << 4 | (a3 & 0x3C) >> 2);
        b[2] = (char) ((a3 & 0x03) << 6 | a4);
        return String.copyValueOf(b);
    }

    /**
     * 獲取字節(jié)的映射位置
     * @param c
     * @return
     */
    private int getIndex(char c){
        for(int i = 0;i < str.length;i++){
            if(str[i] == c)
                return i;
        }
        return -1;
    }

    /**
     * 獲取編碼器
     * @return
     */
    public static Base64Realize getEncoder(){
        return new Base64Realize();
    }
}