How to detect illegal UTF-8 byte sequences to replace them in java inputstream?

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独厮守ぢ
独厮守ぢ 2021-02-02 15:22

The file in question is not under my control. Most byte sequences are valid UTF-8, it is not ISO-8859-1 (or an other encoding). I want to do my best do extract as much informat

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  • 2021-02-02 15:36

    java.nio.charset.CharsetDecoder does what you need. This class provides charset decoding with user-definable actions on different kinds of errors (see onMalformedInput() and onUnmappableCharacter()).

    CharsetDecoder writes to an OutputStream, which you can pipe into an InputStream using java.io.PipedOutputStream, effectively creating a filtered InputStream.

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  • 2021-02-02 15:43

    The behaviour you want is already the default for InputStreamReader. So there is no need to specify it yourself. This suffices:

    final BufferedInputStream in = new BufferedInputStream(istream);
    final Reader inputReader = new InputStreamReader(in, StandardCharsets.UTF_8);
    
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  • 2021-02-02 15:49

    One way would be to read the first few bytes to check Byte Order Mark (if exists). More information on BOM: http://en.wikipedia.org/wiki/Byte_order_mark In the given url, you will find a table of the BOM bytes. However, one problem is, UTF-8 does not require to use BOM in its' header. There is another way to solve the problem is by pattern recognition (read few bytes-8 bits each time). Anyway, this is the complicated solution..

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