How to read a text file with mixed encodings in Scala or Java?

Question

I am trying to parse a CSV file, ideally using weka.core.converters.CSVLoader. However the file I have is not a valid UTF-8 file. It is mostly a UTF-8 file but some of the f

Answer 1

This is how I managed to do it with java:

    FileInputStream input;
    String result = null;
    try {
        input = new FileInputStream(new File("invalid.txt"));
        CharsetDecoder decoder = Charset.forName("UTF-8").newDecoder();
        decoder.onMalformedInput(CodingErrorAction.IGNORE);
        InputStreamReader reader = new InputStreamReader(input, decoder);
        BufferedReader bufferedReader = new BufferedReader( reader );
        StringBuilder sb = new StringBuilder();
        String line = bufferedReader.readLine();
        while( line != null ) {
            sb.append( line );
            line = bufferedReader.readLine();
        }
        bufferedReader.close();
        result = sb.toString();

    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch( IOException e ) {
        e.printStackTrace();
    }

    System.out.println(result);

The invalid file is created with bytes:

0x68, 0x80, 0x65, 0x6C, 0x6C, 0xC3, 0xB6, 0xFE, 0x20, 0x77, 0xC3, 0xB6, 0x9C, 0x72, 0x6C, 0x64, 0x94

Which is hellö wörld in UTF-8 with 4 invalid bytes mixed in.

With .REPLACE you see the standard unicode replacement character being used:

//"h�ellö� wö�rld�"

With .IGNORE, you see the invalid bytes ignored:

//"hellö wörld"

Without specifying .onMalformedInput, you get

java.nio.charset.MalformedInputException: Input length = 1
    at java.nio.charset.CoderResult.throwException(Unknown Source)
    at sun.nio.cs.StreamDecoder.implRead(Unknown Source)
    at sun.nio.cs.StreamDecoder.read(Unknown Source)
    at java.io.InputStreamReader.read(Unknown Source)
    at java.io.BufferedReader.fill(Unknown Source)
    at java.io.BufferedReader.readLine(Unknown Source)
    at java.io.BufferedReader.readLine(Unknown Source)