Java实现将MultipartFile转换为base64编码

在实际项目中，有些场景我们需要将图片文件转换为base64来进行操作，特此记录一下如何转换

方式一：通过JDK自带的Base64

String imageUrl = "要转换的内容或者是图片url";
Base64.getEncoder().encodeToString(imageUrl.getBytes(StandardCharsets.UTF_8))

方式二：直接将如下代码封装到一个工具类即可

public class Base64Util {
          
   
    private static final char last2byte = (char) Integer.parseInt("00000011", 2);
    private static final char last4byte = (char) Integer.parseInt("00001111", 2);
    private static final char last6byte = (char) Integer.parseInt("00111111", 2);
    private static final char lead6byte = (char) Integer.parseInt("11111100", 2);
    private static final char lead4byte = (char) Integer.parseInt("11110000", 2);
    private static final char lead2byte = (char) Integer.parseInt("11000000", 2);
    private static final char[] encodeTable = new char[]{
          
   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, +, /};

    public Base64Util() {
          
   
    }

    /**
     * 把图片转为base64串
     * @param from
     * @return
     */
    public static String encode(byte[] from) {
          
   
        StringBuilder to = new StringBuilder((int) ((double) from.length * 1.34D) + 3);
        int num = 0;
        char currentByte = 0;

        int i;
        for (i = 0; i < from.length; ++i) {
          
   
            for (num %= 8; num < 8; num += 6) {
          
   
                switch (num) {
          
   
                    case 0:
                        currentByte = (char) (from[i] & lead6byte);
                        currentByte = (char) (currentByte >>> 2);
                    case 1:
                    case 3:
                    case 5:
                    default:
                        break;
                    case 2:
                        currentByte = (char) (from[i] & last6byte);
                        break;
                    case 4:
                        currentByte = (char) (from[i] & last4byte);
                        currentByte = (char) (currentByte << 2);
                        if (i + 1 < from.length) {
          
   
                            currentByte = (char) (currentByte | (from[i + 1] & lead2byte) >>> 6);
                        }
                        break;
                    case 6:
                        currentByte = (char) (from[i] & last2byte);
                        currentByte = (char) (currentByte << 4);
                        if (i + 1 < from.length) {
          
   
                            currentByte = (char) (currentByte | (from[i + 1] & lead4byte) >>> 4);
                        }
                }

                to.append(encodeTable[currentByte]);
            }
        }

        if (to.length() % 4 != 0) {
          
   
            for (i = 4 - to.length() % 4; i > 0; --i) {
          
   
                to.append("=");
            }
        }
        return to.toString();
    }
}

调用示例：

参考：https://amore.blog..net/article/details/110135801?spm=1001.2014.3001.5502