如何在Java中定义Base64编码的字符串的编码

Question

I received an XML file with a PDF Attachment in it encoded as Base64 string. I am trying to generate a PDF file out of it. Following code works well:

String base64encodedPdf =" ....   ";
byte[] imgBytes = javax.xml.bind.DatatypeConverter.parseBase64Binary(base64encodedPdf);
IOUtils.write(imgBytes, new FileOutputStream("C:\\\\test.pdf"));

Problem arises when attachment data is too big to copy to editor directly, thought I can copy it to a text file and read file and convert to String . This is how I do it:

org.apache.commons.io.FileUtils.readFileToString(file, encoding)

I am curious what encoding shall I specify... UTF-8 , UTF-16 and why?

EDIT:

This is the meta-information available to me

<AttachmentType tc="1">Document</AttachmentType>
<MimeType>application/pdf</MimeType>
<TransferEncodingTypeString>Base64</TransferEncodingTypeString>
<TransferEncodingTypeTC tc="4">Base64</TransferEncodingTypeTC>

Answer 1

It depends on what encoding you used when writing into the text file. Java text-related IO classes such as PrintWriter has a constructor that allows you to explicitly define the encoding, eg:

new PrintWriter("foo.txt", "UTF-8");

If you don't do so, it will use the default encoding which might vary depending on platform / JVM setting. You check your platform's default encoding using

Charset.defaultCharset()

But it's a good practice to always explicitly specify your intended encoding when writing to a file