如何解码可引用的字符（从引用到char）？

问题描述

我有一个包含的文字。以下是这样一个文本的示例（来自）：

I have a text with quoted-printables. Here is an example of such a text (from a wikipedia article):

我正在寻找一个Java类，它将编码形式解码为字符，例如 = 20 空间。

I am looking for a Java class, which decode the encoded form to chars, e.g., =20 to a space.

更新：感谢精英绅士，我知道我需要使用QuotedPrintableCodec：

UPDATE: Thanks to The Elite Gentleman, I know that I need to use QuotedPrintableCodec:

import org.apache.commons.codec.DecoderException;
import org.apache.commons.codec.net.QuotedPrintableCodec;
import org.junit.Test;

public class QuotedPrintableCodecTest {
private static final String TXT =  "If you believe that truth=3Dbeauty, then surely=20=mathematics is the most beautiful branch of philosophy.";

    @Test
    public void processSimpleText() throws DecoderException
    {
        QuotedPrintableCodec.decodeQuotedPrintable( TXT.getBytes() );
    }
}

然而，我继续收到以下异常：

However I keep getting the following exception:

org.apache.commons.codec.DecoderException: Invalid URL encoding: not a valid digit (radix 16): 109
    at org.apache.commons.codec.net.Utils.digit16(Utils.java:44)
    at org.apache.commons.codec.net.QuotedPrintableCodec.decodeQuotedPrintable(QuotedPrintableCodec.java:186)

我做错了什么？

更新2：我有发现，并了解：

UPDATE 2: I have found this question @ SO and learn about MimeUtility:

import javax.mail.MessagingException;
import javax.mail.internet.MimeUtility;

public class QuotedPrintableCodecTest {
    private static final String TXT =  "If you believe that truth=3Dbeauty, then surely=20= mathematics is the most beautiful branch of philosophy.";

    @Test
    public void processSimpleText() throws MessagingException, IOException
    {
        InputStream is = new ByteArrayInputStream(TXT.getBytes());

            BufferedReader br = new BufferedReader ( new InputStreamReader(  MimeUtility.decode(is, "quoted-printable") ));
            StringWriter writer = new StringWriter();

            String line;
            while( (line = br.readLine() ) != null )
            {
                writer.append(line);
            }
            System.out.println("INPUT:  "  + TXT);
            System.out.println("OUTPUT: " +  writer.toString() );
    }
    }

然而输出仍然不完美， ='：

However the output still is not perfect, it contains '=' :

INPUT:  If you believe that truth=3Dbeauty, then surely=20= mathematics is the most beautiful branch of philosophy.
OUTPUT: If you believe that truth=beauty, then surely = mathematics is the most beautiful branch of philosophy.

现在我做错了什么？

推荐答案

类是RFC 1521引用可打印部分的实现。

Apache Commons Codec QuotedPrintableCodec class does is the implementation of the RFC 1521 Quoted-Printable section.

更新，您可引用的可打印字符串错误，维基百科的示例使用软线路断开。

Update, Your quoted-printable string is wrong, as the example on Wikipedia uses Soft-line breaks.

换行符：

Rule #5 (Soft Line Breaks): The Quoted-Printable encoding REQUIRES
      that encoded lines be no more than 76 characters long. If longer
      lines are to be encoded with the Quoted-Printable encoding, 'soft'
      line breaks must be used. An equal sign as the last character on a
      encoded line indicates such a non-significant ('soft') line break
      in the encoded text. Thus if the "raw" form of the line is a
      single unencoded line that says:

          Now's the time for all folk to come to the aid of
          their country.

      This can be represented, in the Quoted-Printable encoding, as

          Now's the time =
          for all folk to come=
           to the aid of their country.

      This provides a mechanism with which long lines are encoded in
      such a way as to be restored by the user agent.  The 76 character
      limit does not count the trailing CRLF, but counts all other
      characters, including any equal signs.

所以你的文字应该如下：

So your text should be made as follows:

private static final String CRLF = "\r\n";
private static final String S = "If you believe that truth=3Dbeauty, then surely=20=" + CRLF + "mathematics is the most beautiful branch of philosophy.";

Javadoc明确指出：

The Javadoc clearly states:

还有一个对于Apache QuotedPrintableCodec，因为它不支持软线路断开。

And there is a bug logged for Apache QuotedPrintableCodec as it doesn't support the soft-line breaks.

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