Java Base64→文字列相互変換、Base64→ファイル、ストリーム相互変換

1、変換クラス

import org.apache.commons.codec.binary.Base64;

import java.io.*;
import java.nio.file;
import java.nio.file.Paths;
import java.nio.file;

public class Base64Object {
    /**
     * convert stream to base64 string
     * @param in
     * @return
     */
    public static String streamToBase64(InputStream in) {
        byte[] data = null;
        // Read an array of image bytes
        try {
            ByteArrayOutputStream swapStream = new ByteArrayOutputStream();
            byte[] buff = new byte[100];
            int rc;
            while ((rc = in.read(buff, 0, 100)) > 0) {
                swapStream.write(buff, 0, rc);
            }
            data = swapStream.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (in ! = null) { try {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return new String(Base64.encodeBase64(data));
    }
    /**
     * convert file to base64 string
     * @param path
     * @return
     */
    public static String fileToBase64(String path) {
        String base64 = null;
        InputStream in = null;
        try {
            File file = new File(path);
            in = new FileInputStream(file);
            byte[] bytes = new byte[(int)file.length()];
            in.read(bytes);
            base64 = java.util.Base64.getEncoder().encodeToString(bytes);
// base64 = Base64.getEncoder().encodeToString(bytes);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (in ! = null) { try {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return base64;
    }

    /**
     * base64 to file
     * @param base64
     * @param filePath
     */
    public static void base64ToFile(String base64, String filePath) {
        try {
            Files.write(Paths.get(filePath), java.util.Base64.getDecoder().decode(base64), StandardOpenOption.CREATE);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    /**
     * Convert String's to base64 code
     */
    public static String stringToBase64(String ss) {
        byte[] bytes = ss.getBytes();
        String encode = Base64Util.encode(bytes);
        return encode;
    }

    /**
     * Convert the base64 String code to a normally displayed string
     */
    public static String base64ToString(String base64) throws Exception {
        String result;
        try {
            byte[] decode = Base64Util.decode(base64);
            result = new String(decode);
        }catch (Exception e){
            throw new Exception(base64+": Format error! ");
        }
        return result;
    }
}

2. 基本クラス

public final class Base64Util {
    private static final int BASELENGTH = 128;
    private static final int LOOKUPLENGTH = 64;
    private static final int TWENTYFOURBITGROUP = 24;
    private static final int EIGHTBIT = 8;
    private static final int SIXTEENBIT = 16;
    private static final int FOURBYTE = 4;
    private static final int SIGN = -128;
    private static char PAD = '=';
    private static byte[] base64Alphabet = new byte[BASELENGTH];
    private static char[] lookUpBase64Alphabet = new char[LOOKUPLENGTH];
    static {
        for (int i = 0; i < BASELENGTH; ++i) {
            base64Alphabet[i] = -1;
        }

    }
    /**
     Convert a 64-bit byte array to a String
     */
    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 groups
        if (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);
    }
    /**
     * Convert the Base64 bit encoding to a byte array
     */
    public static byte[] decode(String encoded) {
        if (encoded == null) {
            return null;
        }
        char[] base64Data = encoded.toCharArray();
        // remove white spaces
        int 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 d

これは私も文書変換をまとめるのに相当します、オリジナルリンクです。 https://www.jb51.net/article/109046.htm