import org.apache.james.mime4j.codec.Base64InputStream; //导入依赖的package包/类
InputStream getDecodingInputStream(final InputStream rawInputStream, @Nullable String encoding) {
    if (MimeUtil.ENC_BASE64.equals(encoding)) {
        return new Base64InputStream(rawInputStream) {
            @Override
            public void close() throws IOException {
                super.close();
                rawInputStream.close();
            }
        };
    }
    if (MimeUtil.ENC_QUOTED_PRINTABLE.equals(encoding)) {
        return new QuotedPrintableInputStream(rawInputStream) {
            @Override
            public void close() throws IOException {
                super.close();
                rawInputStream.close();
            }
        };
    }

    return rawInputStream;
}
 

import org.apache.james.mime4j.codec.Base64InputStream; //导入依赖的package包/类
/**
 * Decodes a string containing base64 encoded data.
 *
 * @param s the string to decode.
 * @param monitor
 * @return the decoded bytes.
 */
private static byte[] decodeBase64(String s, DecodeMonitor monitor) {
    ByteArrayOutputStream baos = new ByteArrayOutputStream();

    try {
        byte[] bytes = s.getBytes("US-ASCII");

        Base64InputStream is = new Base64InputStream(
                                    new ByteArrayInputStream(bytes), monitor);

        int b = 0;
        while ((b = is.read()) != -1) {
            baos.write(b);
        }
    } catch (IOException e) {
        // This should never happen!
        throw new IllegalStateException(e);
    }

    return baos.toByteArray();
}
 

import org.apache.james.mime4j.codec.Base64InputStream; //导入依赖的package包/类
private MimeBodyPart binaryBodyPart() throws IOException,
        MessagingException {
    String encodedTestString = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
            + "abcdefghijklmnopqrstuvwxyz0123456789+/";

    BinaryTempFileBody tempFileBody = new BinaryTempFileBody();

    InputStream in = new Base64InputStream(new ByteArrayInputStream(
            encodedTestString.getBytes("UTF-8")));

    OutputStream out = tempFileBody.getOutputStream();
    try {
        IOUtils.copy(in, out);
    } finally {
        out.close();
    }

    MimeBodyPart bodyPart = new MimeBodyPart(tempFileBody,
            "application/octet-stream");
    bodyPart.setEncoding(MimeUtil.ENC_BASE64);

    return bodyPart;
}
 

import org.apache.james.mime4j.codec.Base64InputStream; //导入依赖的package包/类
/**
 * Decodes an encoded word encoded with the 'B' encoding (described in
 * RFC 2047) found in a header field body.
 *
 * @param encodedWord the encoded word to decode.
 * @param charset the Java charset to use.
 * @return the decoded string.
 */
private static String decodeB(String encodedWord, String charset) {
    byte[] bytes = encodedWord.getBytes(Charset.forName("US-ASCII"));

    Base64InputStream is = new Base64InputStream(new ByteArrayInputStream(bytes));
    try {
        return CharsetSupport.readToString(is, charset);
    } catch (IOException e) {
        return null;
    }
}