場景

前端使用Vue，驗證碼圖片的src屬性來自于后臺SpringBoot接口。

后臺驗證碼接口生成驗證碼圖片并將其使用Base64進行編碼。

前端就可以直接使用

data:image/png;base64,

后面加上編碼后的代碼就可以進行顯示圖片。那么后臺就需要有個對圖片文件進行Base64編碼的工具類。

注：

博客：
https://blog.csdn.net/badao_liumang_qizhi
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實現

Base64是網絡上最常見的用于傳輸8Bit字節碼的編碼方式之一，Base64就是一種基于64個可打印字符來表示二進制數據的方法。

什么是“可打印字符”呢？為什么要用它來傳輸8Bit字節碼呢？在回答這兩個問題之前我們有必要來思考一下什么情況下需要使用到Base64？Base64一般用于在HTTP協議下傳輸二進制數據，由于HTTP協議是文本協議，所以在HTTP協議下傳輸二進制數據需要將二進制數據轉換為字符數據。然而直接轉換是不行的。因為網絡傳輸只能傳輸可打印字符。什么是可打印字符？在ASCII碼中規定，0~31、127這33個字符屬于控制字符，32~126這95個字符屬于可打印字符，也就是說網絡傳輸只能傳輸這95個字符，不在這個范圍內的字符無法傳輸。那么該怎么才能傳輸其他字符呢？其中一種方式就是使用Base64。

新建Base64.java

/*** Base64工具類*/ public final class Base64 {static private final int???? BASELENGTH?????????? = 128;static private final int???? LOOKUPLENGTH???????? = 64;static private final int???? TWENTYFOURBITGROUP?? = 24;static private final int???? EIGHTBIT???????????? = 8;static private final int???? SIXTEENBIT?????????? = 16;static private final int???? FOURBYTE???????????? = 4;static private final int???? SIGN???????????????? = -128;static private final char??? PAD????????????????? = '=';static final private byte[]? base64Alphabet?????? = new byte[BASELENGTH];static final private char[]? lookUpBase64Alphabet = new char[LOOKUPLENGTH];static{for (int i = 0; i < BASELENGTH; ++i){base64Alphabet[i] = -1;}for (int i = 'Z'; i >= 'A'; i--){base64Alphabet[i] = (byte) (i - 'A');}for (int i = 'z'; i >= 'a'; i--){base64Alphabet[i] = (byte) (i - 'a' + 26);}for (int i = '9'; i >= '0'; i--){base64Alphabet[i] = (byte) (i - '0' + 52);}base64Alphabet['+'] = 62;base64Alphabet['/'] = 63;for (int i = 0; i <= 25; i++){lookUpBase64Alphabet[i] = (char) ('A' + i);}for (int i = 26, j = 0; i <= 51; i++, j++){lookUpBase64Alphabet[i] = (char) ('a' + j);}for (int i = 52, j = 0; i <= 61; i++, j++){lookUpBase64Alphabet[i] = (char) ('0' + j);}lookUpBase64Alphabet[62] = (char) '+';lookUpBase64Alphabet[63] = (char) '/';}private static boolean isWhiteSpace(char octect){return (octect == 0x20 || octect == 0xd || octect == 0xa || octect == 0x9);}private static boolean isPad(char octect){return (octect == PAD);}private static boolean isData(char octect){return (octect < BASELENGTH && base64Alphabet[octect] != -1);}/*** Encodes hex octects into Base64** @param binaryData Array containing binaryData* @return Encoded Base64 array*/public static String encode(byte[] binaryData){if (binaryData == null){return null;}int lengthDataBits = binaryData.length * EIGHTBIT;if (lengthDataBits == 0){return "";}int fewerThan24bits = lengthDataBits % TWENTYFOURBITGROUP;int numberTriplets = lengthDataBits / TWENTYFOURBITGROUP;int numberQuartet = fewerThan24bits != 0 ? numberTriplets + 1 : numberTriplets;char encodedData[] = null;encodedData = new char[numberQuartet * 4];byte k = 0, l = 0, b1 = 0, b2 = 0, b3 = 0;int encodedIndex = 0;int dataIndex = 0;for (int i = 0; i < numberTriplets; i++){b1 = binaryData[dataIndex++];b2 = binaryData[dataIndex++];b3 = binaryData[dataIndex++];l = (byte) (b2 & 0x0f);k = (byte) (b1 & 0x03);byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2) : (byte) ((b1) >> 2 ^ 0xc0);byte val2 = ((b2 & SIGN) == 0) ? (byte) (b2 >> 4) : (byte) ((b2) >> 4 ^ 0xf0);byte val3 = ((b3 & SIGN) == 0) ? (byte) (b3 >> 6) : (byte) ((b3) >> 6 ^ 0xfc);encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];encodedData[encodedIndex++] = lookUpBase64Alphabet[val2 | (k << 4)];encodedData[encodedIndex++] = lookUpBase64Alphabet[(l << 2) | val3];encodedData[encodedIndex++] = lookUpBase64Alphabet[b3 & 0x3f];}// form integral number of 6-bit groupsif (fewerThan24bits == EIGHTBIT){b1 = binaryData[dataIndex];k = (byte) (b1 & 0x03);byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2) : (byte) ((b1) >> 2 ^ 0xc0);encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];encodedData[encodedIndex++] = lookUpBase64Alphabet[k << 4];encodedData[encodedIndex++] = PAD;encodedData[encodedIndex++] = PAD;}else if (fewerThan24bits == SIXTEENBIT){b1 = binaryData[dataIndex];b2 = binaryData[dataIndex + 1];l = (byte) (b2 & 0x0f);k = (byte) (b1 & 0x03);byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2) : (byte) ((b1) >> 2 ^ 0xc0);byte val2 = ((b2 & SIGN) == 0) ? (byte) (b2 >> 4) : (byte) ((b2) >> 4 ^ 0xf0);encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];encodedData[encodedIndex++] = lookUpBase64Alphabet[val2 | (k << 4)];encodedData[encodedIndex++] = lookUpBase64Alphabet[l << 2];encodedData[encodedIndex++] = PAD;}return new String(encodedData);}/*** Decodes Base64 data into octects** @param encoded string containing Base64 data* @return Array containind decoded data.*/public static byte[] decode(String encoded){if (encoded == null){return null;}char[] base64Data = encoded.toCharArray();// remove white spacesint len = removeWhiteSpace(base64Data);if (len % FOURBYTE != 0){return null;// should be divisible by four}int numberQuadruple = (len / FOURBYTE);if (numberQuadruple == 0){return new byte[0];}byte decodedData[] = null;byte b1 = 0, b2 = 0, b3 = 0, b4 = 0;char d1 = 0, d2 = 0, d3 = 0, d4 = 0;int i = 0;int encodedIndex = 0;int dataIndex = 0;decodedData = new byte[(numberQuadruple) * 3];for (; i < numberQuadruple - 1; i++){if (!isData((d1 = base64Data[dataIndex++])) || !isData((d2 = base64Data[dataIndex++]))|| !isData((d3 = base64Data[dataIndex++])) || !isData((d4 = base64Data[dataIndex++]))){return null;} // if found "no data" just return nullb1 = base64Alphabet[d1];b2 = base64Alphabet[d2];b3 = base64Alphabet[d3];b4 = base64Alphabet[d4];decodedData[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);decodedData[encodedIndex++] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));decodedData[encodedIndex++] = (byte) (b3 << 6 | b4);}if (!isData((d1 = base64Data[dataIndex++])) || !isData((d2 = base64Data[dataIndex++]))){return null;// if found "no data" just return null}b1 = base64Alphabet[d1];b2 = base64Alphabet[d2];d3 = base64Data[dataIndex++];d4 = base64Data[dataIndex++];if (!isData((d3)) || !isData((d4))){// Check if they are PAD charactersif (isPad(d3) && isPad(d4)){if ((b2 & 0xf) != 0)// last 4 bits should be zero{return null;}byte[] tmp = new byte[i * 3 + 1];System.arraycopy(decodedData, 0, tmp, 0, i * 3);tmp[encodedIndex] = (byte) (b1 << 2 | b2 >> 4);return tmp;}else if (!isPad(d3) && isPad(d4)){b3 = base64Alphabet[d3];if ((b3 & 0x3) != 0)// last 2 bits should be zero{return null;}byte[] tmp = new byte[i * 3 + 2];System.arraycopy(decodedData, 0, tmp, 0, i * 3);tmp[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);tmp[encodedIndex] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));return tmp;}else{return null;}}else{ // No PAD e.g 3cQlb3 = base64Alphabet[d3];b4 = base64Alphabet[d4];decodedData[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);decodedData[encodedIndex++] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));decodedData[encodedIndex++] = (byte) (b3 << 6 | b4);}return decodedData;}/*** remove WhiteSpace from MIME containing encoded Base64 data.** @param data the byte array of base64 data (with WS)* @return the new length*/private static int removeWhiteSpace(char[] data){if (data == null){return 0;}// count characters that's not whitespaceint newSize = 0;int len = data.length;for (int i = 0; i < len; i++){if (!isWhiteSpace(data[i])){data[newSize++] = data[i];}}return newSize;} }

示例代碼

在生成圖片后使用Base64進行編碼

??????? // 生成圖片int w = 111, h = 36;ByteArrayOutputStream stream = new ByteArrayOutputStream();VerifyCodeUtils.outputImage(w, h, stream, verifyCode);try{AjaxResult ajax = AjaxResult.success();ajax.put("uuid", uuid);ajax.put("img", Base64.encode(stream.toByteArray()));return ajax;}

其中前三行是生成圖片的stream,然后調用Base64的encode編碼方法并將編碼后的數據返回給前端。

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總結

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