Wrap icu4j charset detection

build.gradle

// ...

dependencies {
  // https://mvnrepository.com/artifact/com.ibm.icu/icu4j
  implementation 'com.ibm.icu:icu4j:73.2'
}

CharsetUtils.java

package your.name;

import com.ibm.icu.text.CharsetDetector;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;

public class CharsetUtils {
    public static Charset detectFileCharset(File file) throws IOException {
        CharsetDetector charsetDetector = new CharsetDetector();
        try (var inputStream = Files.newInputStream(Path.of(file.getAbsolutePath()))) {
            var inputStreamIgnoringRestart = new InputStream() {

                @Override
                public int read() throws IOException {
                    return inputStream.read();
                }

                @Override
                public void mark(int readLimit) {
                    // ignore
                }

                @Override
                public void reset() {
                    // ignore
                }
            };
            charsetDetector.setText(inputStreamIgnoringRestart);

        }
        return Charset.forName(charsetDetector.detect().getName());
    }
}

LICENSE

This is free and unencumbered software released into the public domain.
Unlicense: https://choosealicense.com/licenses/unlicense

The dependency icu4j is under the Unicode License.
https://www.unicode.org/faq/unicode_license.html