Java:How can i get the encoding from inputStream?

Question

I want get the encoding from a stream.

1st method - to use the InputStreamReader.

But it always return OS encode.

InputStreamReader reader = new InputStreamReader(new FileInputStream("aa.rar"));
System.out.println(reader.getEncoding());

output:GBK

2nd method - to use the UniversalDetector.

But it always return null.

    FileInputStream input = new FileInputStream("aa.rar");

    UniversalDetector detector = new UniversalDetector(null);
    byte[] buf = new byte[4096];

    int nread;
    while ((nread = input.read(buf)) > 0 && !detector.isDone()) {
        detector.handleData(buf, 0, nread);
    }

    // (3)
    detector.dataEnd();

    // (4)
    String encoding = detector.getDetectedCharset();

    if (encoding != null) {
        System.out.println("Detected encoding = " + encoding);
    } else {
        System.out.println("No encoding detected.");
    }

    // (5)
    detector.reset();

output:null

How can I get the right? :(

Answer 1

    public String getDecoder(InputStream inputStream) {

    String encoding = null;

    try {
        byte[] buf = new byte[4096];
        UniversalDetector detector = new UniversalDetector(null);
        int nread;

        while ((nread = inputStream.read(buf)) > 0 && !detector.isDone()) {
            detector.handleData(buf, 0, nread);
        }

        detector.dataEnd();
        encoding = detector.getDetectedCharset();
        detector.reset();

        inputStream.close();

    } catch (Exception e) {
    }

    return encoding;
}

Answer 2

Let's resume the situation:

• InputStream delivers bytes
• *Readers deliver chars in some encoding
• new InputStreamReader(inputStream) uses the operating system encoding
• new InputStreamReader(inputStream, "UTF-8") uses the given encoding (here UTF-8)

So one needs to know the encoding before reading. You did everything right using first a charset detecting class.

Reading http://code.google.com/p/juniversalchardet/ it should handle UTF-8 and UTF-16. You might use the editor JEdit to verify the encoding, and see whether there is some problem.