import org.apache.james.mime4j.codec.QuotedPrintableInputStream; //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.QuotedPrintableInputStream; //导入依赖的package包/类
/**
 * Decodes an encoded word encoded with the 'Q' 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 decodeQ(String encodedWord, String charset) {

    /*
     * Replace _ with =20
     */
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < encodedWord.length(); i++) {
        char c = encodedWord.charAt(i);
        if (c == '_') {
            sb.append("=20");
        } else {
            sb.append(c);
        }
    }

    byte[] bytes = sb.toString().getBytes(Charset.forName("US-ASCII"));

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

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

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

        QuotedPrintableInputStream is = new QuotedPrintableInputStream(
                                           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();
}