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Java 和 JavaScript 之间真正通用的Base64编码

2017-04-15 22:07 423 查看
 

转载自：http://blog.csdn.net/coolmasoft/article/details/2913634

 

在开发Java  Web应用的时候，可能会在服务器端用Java做Base64编码，而在客户端用JavaScript进行解码。这样就要求两边的Base64编码机制保持一致。

使用Base64编码，可能会碰到各种奇怪情况，甚至怀疑编码有bug。但实际上不是这样的。Base64理论上操作的对象不是字符串而是字节数组。它的原理就是把ASCII码的255个字符缩小到用64个来表示。具体就是原来三个字节用四个字节表示，编码后长度有一定的增长。

1) 最好一次编码，避免分段编码，确实要分段编码，每一段字节数应该是3的倍数。

长字节流，如果要边读取边编码，每一段必须是3的倍数，否则就可能在还原的时候出乱。一般人喜欢用2的乘方来定义数组，例如 byte[1024]，因为不是3的倍数，可能还原时出错。正确的例子是：

byte[] bs=new byte[3*100] ....inputStream.read(bs)......encode(bs )....

对于字符串，一般要整个一次编码，以避免分段编码出错。

当然，如果你分段编码，还原的时候也是一段一段地还原，那是没有问题的。

2)确保字符串还原的时候按照原来的编码还原。

因为它操作的是字节数组，所以对于GBK编码的汉字和UTF-8编码汉字，经过 Base64编码后结果是不一样的。例如“我们”这两个字如果是GBK编码，转成Base64后就是ztLDxw== ；如果是UTF-8编码，转成Base64后就是5oiR5Lus。

也就是 “我们” ==》  getBytes("GBK") ==> Base64

所以Java这边用什么编码转换，在JavaScript那边就要用什么编码还原。要保证Java和JavaScript通用，我们采用Unicode的编码（JavaScript转成UTF-8、GBK不方便，所以就采用了其本身的Unicode编码），具体如下：

服务器端：

1）用getBytes("Unicode")转成Unicode字节数组。

2） 编码成Base64字符串

3）传送到客户端

客户端：

1）Base64 解码成字节数组

2）按Unicode还原

代码如下（相关的函数看附件）：

Base64.encode(data,"Unicode"); //java 端编码

decode64(data);   //javascript解码

附一：Java中Base64编码

 

package websharp.util;          

public class Base64 {           

    private static final byte[] encodingTable = {           

            (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E',           

            (byte) 'F', (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J',           

            (byte) 'K', (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O',           

            (byte) 'P', (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T',           

            (byte) 'U', (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y',           

            (byte) 'Z', (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd',           

            (byte) 'e', (byte) 'f', (byte) 'g', (byte) 'h', (byte) 'i',           

            (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n',           

            (byte) 'o', (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's',           

            (byte) 't', (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x',           

            (byte) 'y', (byte) 'z', (byte) '0', (byte) '1', (byte) '2',           

            (byte) '3', (byte) '4', (byte) '5', (byte) '6', (byte) '7',           

            (byte) '8', (byte) '9', (byte) '+', (byte) '/'           

        };           

    private static final byte[] decodingTable;           

    static {           

        decodingTable = new byte[128];           

        for (int i = 0; i < 128; i++) {           

            decodingTable[i] = (byte) -1;           

        }           

        for (int i = 'A'; i <= 'Z'; i++) {           

            decodingTable[i] = (byte) (i - 'A');           

        }           

        for (int i = 'a'; i <= 'z'; i++) {           

            decodingTable[i] = (byte) (i - 'a' + 26);           

        }           

        for (int i = '0'; i <= '9'; i++) {           

            decodingTable[i] = (byte) (i - '0' + 52);           

        }           

        decodingTable['+'] = 62;           

        decodingTable['/'] = 63;           

    }           

    public static byte[] encode(byte[] data,int offset) {           

        byte[] bytes;           

        int realCount=data.length-offset;           

        int modulus = realCount % 3;           

        if (modulus == 0) {           

            bytes = new byte[(4 * realCount) / 3];           

        } else {           

            bytes = new byte[4 * ((realCount / 3) + 1)];           

        }           

        int dataLength = (data.length - modulus);           

        int a1;           

        int a2;           

        int a3;           

        for (int i = offset, j = 0; i < dataLength; i += 3, j += 4) {           

            a1 = data[i] & 0xff;           

            a2 = data[i + 1] & 0xff;           

            a3 = data[i + 2] & 0xff;           

            bytes[j] = encodingTable[(a1 >>> 2) & 0x3f];           

            bytes[j + 1] = encodingTable[((a1 << 4) | (a2 >>> 4)) & 0x3f];           

            bytes[j + 2] = encodingTable[((a2 << 2) | (a3 >>> 6)) & 0x3f];           

            bytes[j + 3] = encodingTable[a3 & 0x3f];           

        }           

        int b1;           

        int b2;           

        int b3;           

        int d1;           

        int d2;           

        switch (modulus) {           

        case 0: /* nothing left to do */           

            break;           

        case 1:           

            d1 = data[data.length - 1] & 0xff;           

            b1 = (d1 >>> 2) & 0x3f;           

            b2 = (d1 << 4) & 0x3f;           

            bytes[bytes.length - 4] = encodingTable[b1];           

            bytes[bytes.length - 3] = encodingTable[b2];           

            bytes[bytes.length - 2] = (byte) '=';           

            bytes[bytes.length - 1] = (byte) '=';           

            break;           

        case 2:           

            d1 = data[data.length - 2] & 0xff;           

            d2 = data[data.length - 1] & 0xff;           

            b1 = (d1 >>> 2) & 0x3f;           

            b2 = ((d1 << 4) | (d2 >>> 4)) & 0x3f;           

            b3 = (d2 << 2) & 0x3f;           

            bytes[bytes.length - 4] = encodingTable[b1];           

            bytes[bytes.length - 3] = encodingTable[b2];           

            bytes[bytes.length - 2] = encodingTable[b3];           

            bytes[bytes.length - 1] = (byte) '=';           

            break;           

        }           

        return bytes;           

    }           

    public static byte[] decode(byte[] data) {           

        byte[] bytes;           

        byte b1;           

        byte b2;           

        byte b3;           

        byte b4;           

        data = discardNonBase64Bytes(data);           

        if (data[data.length - 2] == '=') {           

            bytes = new byte[(((data.length / 4) - 1) * 3) + 1];           

        } else if (data[data.length - 1] == '=') {           

            bytes = new byte[(((data.length / 4) - 1) * 3) + 2];           

        } else {           

            bytes = new byte[((data.length / 4) * 3)];           

        }           

        for (int i = 0, j = 0; i < (data.length - 4); i += 4, j += 3) {           

            b1 = decodingTable[data[i]];           

            b2 = decodingTable[data[i + 1]];           

            b3 = decodingTable[data[i + 2]];           

            b4 = decodingTable[data[i + 3]];           

            bytes[j] = (byte) ((b1 << 2) | (b2 >> 4));           

            bytes[j + 1] = (byte) ((b2 << 4) | (b3 >> 2));           

            bytes[j + 2] = (byte) ((b3 << 6) | b4);           

        }           

        if (data[data.length - 2] == '=') {           

            b1 = decodingTable[data[data.length - 4]];           

            b2 = decodingTable[data[data.length - 3]];           

            bytes[bytes.length - 1] = (byte) ((b1 << 2) | (b2 >> 4));           

        } else if (data[data.length - 1] == '=') {           

            b1 = decodingTable[data[data.length - 4]];           

            b2 = decodingTable[data[data.length - 3]];           

            b3 = decodingTable[data[data.length - 2]];           

            bytes[bytes.length - 2] = (byte) ((b1 << 2) | (b2 >> 4));           

            bytes[bytes.length - 1] = (byte) ((b2 << 4) | (b3 >> 2));           

        } else {           

            b1 = decodingTable[data[data.length - 4]];           

            b2 = decodingTable[data[data.length - 3]];           

            b3 = decodingTable[data[data.length - 2]];           

            b4 = decodingTable[data[data.length - 1]];           

            bytes[bytes.length - 3] = (byte) ((b1 << 2) | (b2 >> 4));           

            bytes[bytes.length - 2] = (byte) ((b2 << 4) | (b3 >> 2));           

            bytes[bytes.length - 1] = (byte) ((b3 << 6) | b4);           

        }           

        return bytes;           

    }           

    public static byte[] decode(String data) {           

        byte[] bytes;           

        byte b1;           

        byte b2;           

        byte b3;           

        byte b4;           

        data = discardNonBase64Chars(data);           

        if (data.charAt(data.length() - 2) == '=') {           

            bytes = new byte[(((data.length() / 4) - 1) * 3) + 1];           

        } else if (data.charAt(data.length() - 1) == '=') {           

            bytes = new byte[(((data.length() / 4) - 1) * 3) + 2];           

        } else {           

            bytes = new byte[((data.length() / 4) * 3)];           

        }           

        for (int i = 0, j = 0; i < (data.length() - 4); i += 4, j += 3) {           

            b1 = decodingTable[data.charAt(i)];           

            b2 = decodingTable[data.charAt(i + 1)];           

            b3 = decodingTable[data.charAt(i + 2)];           

            b4 = decodingTable[data.charAt(i + 3)];           

            bytes[j] = (byte) ((b1 << 2) | (b2 >> 4));           

            bytes[j + 1] = (byte) ((b2 << 4) | (b3 >> 2));           

            bytes[j + 2] = (byte) ((b3 << 6) | b4);           

        }           

        if (data.charAt(data.length() - 2) == '=') {           

            b1 = decodingTable[data.charAt(data.length() - 4)];           

            b2 = decodingTable[data.charAt(data.length() - 3)];           

            bytes[bytes.length - 1] = (byte) ((b1 << 2) | (b2 >> 4));           

        } else if (data.charAt(data.length() - 1) == '=') {           

            b1 = decodingTable[data.charAt(data.length() - 4)];           

            b2 = decodingTable[data.charAt(data.length() - 3)];           

            b3 = decodingTable[data.charAt(data.length() - 2)];           

            bytes[bytes.length - 2] = (byte) ((b1 << 2) | (b2 >> 4));           

            bytes[bytes.length - 1] = (byte) ((b2 << 4) | (b3 >> 2));           

        } else {           

            b1 = decodingTable[data.charAt(data.length() - 4)];           

            b2 = decodingTable[data.charAt(data.length() - 3)];           

            b3 = decodingTable[data.charAt(data.length() - 2)];           

            b4 = decodingTable[data.charAt(data.length() - 1)];           

            bytes[bytes.length - 3] = (byte) ((b1 << 2) | (b2 >> 4));           

            bytes[bytes.length - 2] = (byte) ((b2 << 4) | (b3 >> 2));           

            bytes[bytes.length - 1] = (byte) ((b3 << 6) | b4);           

        }           

        for(int i=0;i<bytes.length;i++) System.out.println(","+bytes[i]);           

        return bytes;           

    }           

    private static byte[] discardNonBase64Bytes(byte[] data) {           

        byte[] temp = new byte[data.length];           

        int bytesCopied = 0;           

        for (int i = 0; i < data.length; i++) {           

            if (isValidBase64Byte(data[i])) {           

                temp[bytesCopied++] = data[i];           

            }           

        }           

        byte[] newData = new byte[bytesCopied];           

        System.arraycopy(temp, 0, newData, 0, bytesCopied);           

        return newData;           

    }           

    private static String discardNonBase64Chars(String data) {           

        StringBuffer sb = new StringBuffer();           

        int length = data.length();           

        for (int i = 0; i < length; i++) {           

            if (isValidBase64Byte((byte) (data.charAt(i)))) {           

                sb.append(data.charAt(i));           

            }           

        }           

        return sb.toString();           

    }           

    private static boolean isValidBase64Byte(byte b) {           

        if (b == '=') {           

            return true;           

        } else if ((b < 0) || (b >= 128)) {           

            return false;           

        } else if (decodingTable[b] == -1) {           

            return false;           

        }           

        return true;           

    }           

    public static String  encode(String data,String charset)throws Exception           

    {           

        // byte[] result =  (data.getBytes("Unicode"));           

         if(data==null || data.length()==0) return data;           

         int offset=0;           

         // getBytes("unicode")转完后会在前头加上两字节”FE“           

         byte[] result=encode (data.getBytes(charset),offset);           

         StringBuffer sb=new StringBuffer(result.length);           

         for (int i=0;i<result.length;i++)   sb.append((char)result[i]);           

         return sb.toString();           

    }           

    public static String  decode(String data,String charset)throws Exception           

    {           

        if(data==null || data.length()==0) return data;            

        return new String(Base64.decode(data),charset);           

    }           

    public static void main(String[] args) throws Exception {           

        String data = "我们";           

        String data1=encode(data,"Unicode");           

        String data2=decode(data1,"Unicode");           

        System.out.println(data);           

        System.out.println(data1);           

        System.out.println(data2);           

    }           

}

 

附二：JavaScript中Base64编码

 

<html>          

<head>           

<title>base64 Encoding/Decoding</title>           

</head>           

<script type="text/javascript"><!--           

var keyStr = "ABCDEFGHIJKLMNOP" +           

             "QRSTUVWXYZabcdef" +           

             "ghijklmnopqrstuv" +           

             "wxyz0123456789+/" +           

             "=";

function encode64(input) {          

   input = unicodetoBytes(input);           

   var output = "";           

   var chr1, chr2, chr3 = "";           

   var enc1, enc2, enc3, enc4 = "";           

   var i = 0;

   do {          

      chr1 = input[i++];           

      chr2 = input[i++];           

      chr3 = input[i++];

      enc1 = chr1 >> 2;          

      enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);           

      enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);           

      enc4 = chr3 & 63;

      if (isNaN(chr2)) {          

         enc3 = enc4 = 64;           

      } else if (isNaN(chr3)) {           

         enc4 = 64;           

      }

      output = output +           

         keyStr.charAt(enc1) +            

         keyStr.charAt(enc2) +            

         keyStr.charAt(enc3) +            

         keyStr.charAt(enc4);           

      chr1 = chr2 = chr3 = "";           

      enc1 = enc2 = enc3 = enc4 = "";           

   } while (i < input.length);

   return output;          

}

function decode64(input) {          

   var output = "";           

   var chr1, chr2, chr3 = "";           

   var enc1, enc2, enc3, enc4 = "";           

   var i = 0;

   // remove all characters that are not A-Z, a-z, 0-9, +, /, or =          

   var base64test = /[^A-Za-z0-9/+///=]/g;           

   if (base64test.exec(input)) {           

      alert("There were invalid base64 characters in the input text./n" +           

            "Valid base64 characters are A-Z, a-z, 0-9, '+', '/', and '='/n" +           

            "Expect errors in decoding.");           

   }           

   input = input.replace(/[^A-Za-z0-9/+///=]/g, "");           

    output=new Array();           

   do {           

      enc1 = keyStr.indexOf(input.charAt(i++));           

      enc2 = keyStr.indexOf(input.charAt(i++));           

      enc3 = keyStr.indexOf(input.charAt(i++));           

      enc4 = keyStr.indexOf(input.charAt(i++));

      chr1 = (enc1 << 2) | (enc2 >> 4);          

      chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);           

      chr3 = ((enc3 & 3) << 6) | enc4;

      output.push(chr1);          

      if (enc3 != 64) {           

         output.push(chr2);           

      }           

      if (enc4 != 64) {           

         output.push(chr3);           

      }

      chr1 = chr2 = chr3 = "";          

      enc1 = enc2 = enc3 = enc4 = "";

   } while (i < input.length);          

   return bytesToUnicode(output);           

}

  function unicodetoBytes(s)          

   {           

      var result=new Array();           

      if(s==null || s=="") return result;           

      result.push(255); // add "FE" to head            

      result.push(254);           

      for(var i=0;i<s.length;i++)           

      {           

        var c=s.charCodeAt(i).toString(16);           

        if(c.length==1) i="000"+c;           

        else if(c.length==2) c="00"+c;           

        else if(c.length==3) c="0"+c;           

        var var1=parseInt( c.substring(2),16);           

        var var2=parseInt( c.substring(0,2),16);           

        result.push( var1);           

        result.push(var2) ;           

      }           

      return result;           

   }

   function bytesToUnicode(bs)          

   {           

     var result="";           

      var offset=0;           

      if(bs.length>=2 && bs[0]==255 && bs[1]==254) offset=2;  // delete "FE"           

      for(var i=offset;i<bs.length;i+=2)           

      {           

            var code=bs[i]+(bs[i+1]<<8);           

            result+=String.fromCharCode(code);           

      }           

      return result;           

   }           

//-->           

</script>           

<body>           

<form name="base64Form">           

   Type in the message you want to encode in base64, or paste<br>           

   base64 encoded text into the text field, select Encode or Decode, <br>           

   and click the button!<br>

   <textarea name="theText" cols="40" rows="6"></textarea><br>

   <input type="button" name="encode" value="Encode to base64"          

      onClick="document.base64Form.theText.value=encode64(document.base64Form.theText.value);">           

   <input type="button" name="decode" value="Decode from base64"            

      onClick="document.base64Form.theText.value=decode64(document.base64Form.theText.value);">           

</form>           

</body>           

</html>

 
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