import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;

public class ReadingUTF8TextFile {

    public static void main(String[] args) throws IOException {
        //StandardCharsets is available since Java 1.7
        //for ealier version use Charset.forName("UTF-8");
        try (BufferedWriter wr = Files.newBufferedWriter(Paths.get("test.txt"), StandardCharsets.UTF_8)) {
            wr.write("Strange cyrillic symbol Ы");
        }
        /* First Way. For big files */
        try (BufferedReader reader = Files.newBufferedReader(Paths.get("test.txt"), StandardCharsets.UTF_8)) {

            String line;
            while ((line = reader.readLine()) != null) {
                System.out.print(line);
            }
        }
        
        System.out.println(); //just separating output
        
        /* Second way. For small files */
        String s = new String(Files.readAllBytes(Paths.get("test.txt")), StandardCharsets.UTF_8);
        System.out.print(s);
    }
}

import java.io.BufferedWriter;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;

public class WritingUTF8TextFile {
    public static void main(String[] args) throws IOException {
        //StandardCharsets is available since Java 1.7
        //for ealier version use Charset.forName("UTF-8");
        try (BufferedWriter wr = Files.newBufferedWriter(Paths.get("test2.txt"), StandardCharsets.UTF_8)) {
            wr.write("Cyrillic symbol Ы");
        }
    }
}

import java.nio.charset.StandardCharsets;
import java.util.Arrays;

public class GetUtf8BytesFromString {

    public static void main(String[] args) {
        String str = "Cyrillic symbol Ы";
        //StandardCharsets is available since Java 1.7
        //for ealier version use Charset.forName("UTF-8");
        byte[] textInUtf8 = str.getBytes(StandardCharsets.UTF_8);

        System.out.println(Arrays.toString(textInUtf8));
    }
}