java.util.Scanner to read files with different character encoding

There is a library called juniversalchardet, which can help you at guessing the right encoding. It was updated recently and is currently located on GitHub:

https://github.com/albfernandez/juniversalchardet

However, there is no fail-safe tool to detect encodings, as there are many things unknown:

1. Is this file text at all or some PNG?
2. Is it stored in a (1,...,k,...,n)-bit encoding?
3. Which k-bit encoding was used?

Some guesswork can be done by counting the amount of control characters that are not commonly used. When a file contains many control symbols, it is likely that you've chosen the wrong encoding. (Then try the next one.)

Juniversalchardet tries multiple and also more successful ways to determine encodings (even chinese ones). It also provides convenient ways to open a reader from a file with the correct encoding already selected:

(Snippet taken from https://github.com/albfernandez/juniversalchardet#creating-a-reader-with-correct-encoding and adapted)

import org.mozilla.universalchardet.ReaderFactory;
import java.io.File;
import java.io.IOException;
import java.io.Reader;

public class TestCreateReaderFromFile {

    public static void main (String[] args) throws IOException {
        if (args.length != 1) {
            System.err.println("Usage: java TestCreateReaderFromFile FILENAME");
            System.exit(1);
        }

        Reader reader = null;
        try {
            File file = new File(args[0]);
            reader = ReaderFactory.createBufferedReader(file);

            String line;
            while((line=reader.readLine())!=null){
                System.out.println(line); //Print each line to console
            }
        }
        finally {
            if (reader != null) {
                reader.close();
            }
        }

    }

}

Edit: Added ScannerFactory

/*
(C) Copyright 2016-2017 Alberto Fernández <infjaf@gmail.com>
Adapted by Fritz Windisch 2018-11-15
The contents of this file are subject to the Mozilla Public License Version
1.1 (the "License"); you may not use this file except in compliance with
the License. You may obtain a copy of the License at
http://www.mozilla.org/MPL/
Software distributed under the License is distributed on an "AS IS" basis,
WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
for the specific language governing rights and limitations under the
License.
Alternatively, the contents of this file may be used under the terms of
either the GNU General Public License Version 2 or later (the "GPL"), or
the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
in which case the provisions of the GPL or the LGPL are applicable instead
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the provisions above, a recipient may use your version of this file under
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*/

import java.io.BufferedInputStream;
import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Objects;
import java.util.Scanner;
import org.mozilla.universalchardet.UniversalDetector;
import org.mozilla.universalchardet.UnicodeBOMInputStream;

/**
 * Create a scanner from a file with correct encoding
 */
public final class ScannerFactory {

    private ScannerFactory() {
        throw new AssertionError("No instances allowed");
    }
    /**
     * Create a scanner from a file with correct encoding
     * @param file The file to read from
     * @param defaultCharset defaultCharset to use if can't be determined
     * @return Scanner for the file with the correct encoding
     * @throws java.io.IOException if some I/O error ocurrs
     */

    public static Scanner createScanner(File file, Charset defaultCharset) throws IOException {
        Charset cs = Objects.requireNonNull(defaultCharset, "defaultCharset must be not null");
        String detectedEncoding = UniversalDetector.detectCharset(file);
        if (detectedEncoding != null) {
            cs = Charset.forName(detectedEncoding);
        }
        if (!cs.toString().contains("UTF")) {
            return new Scanner(file, cs.name());
        }
        Path path = file.toPath();
        return new Scanner(new UnicodeBOMInputStream(new BufferedInputStream(Files.newInputStream(path))), cs.name());
    }
    /**
     * Create a scanner from a file with correct encoding. If charset cannot be determined,
     * it uses the system default charset.
     * @param file The file to read from
     * @return Scanner for the file with the correct encoding
     * @throws java.io.IOException if some I/O error ocurrs
     */
    public static Scanner createScanner(File file) throws IOException {
        return createScanner(file, Charset.defaultCharset());
    }
}

Your approach will not give you the right encoding.

 FileInputStream fis = new FileInputStream(my_file);
 BufferedReader br = new BufferedReader(new InputStreamReader(fis));
 InputStreamReader isr = new InputStreamReader(fis);
 isr.getEncoding();

This will return the encoding being used by this InputStream (read javadoc) and not that of the charcters written in the file (my_file in your case). And if the encoding is wrong Scanner won't be able to read the file properly.

In fact, do correct me if i am wrong, there is no way to get encoding used for a particular file with 100% accuracy. There are few projects which have a better success rate at guessing the encoding but not 100% accuracy. On the other hand if you know the encoding used then you can read the file using,

Scanner scanner = new Scanner(my_file, "charset");
scanner.nextLine();

Also, find out the correct charset name used in java for ANSI. It's either US-ASCII or Cp1251.

Whichever path you go, be on lookout for any IOException which might point you in the right direction.

To make Scanner available to work with different encoding, you have to provide correct one to the scanner's constructor.

To define file encoding it is better to use external lib (e.g https://github.com/albfernandez/juniversalchardet). But if you definitely know possible encodings, you can check it manually according to Wikipedia

public static void main(String... args) throws IOException {
    List<String> lines = readLinesFromFile(new File("d:/utf8.txt"));
}

public static List<String> readLinesFromFile(File file) throws IOException {
    try (Scanner scan = new Scanner(file, getCharsetName(file))) {
        List<String> lines = new LinkedList<>();

        while (scan.hasNext())
            lines.add(scan.nextLine());

        return lines;
    }
}

private static String getCharsetName(File file) throws IOException {
    try (InputStream in = new FileInputStream(file)) {
        if (in.read() == 0xEF && in.read() == 0xBB && in.read() == 0xBF)
            return StandardCharsets.UTF_8.name();
        return StandardCharsets.US_ASCII.name();
    }
}