This may be the fastest way to randomly read any line of the file.

RandomLineReader.java

import lombok.extern.slf4j.Slf4j;

import java.io.*;
import java.net.URISyntaxException;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

/**
 * Created on 2020/10/27-15:43
 *
 */
@Slf4j
public abstract class RandomLineReader {
    protected File file;
    protected Random random = new Random();

    public RandomLineReader(String fileName) {
        this.file = getFileFromResource(fileName);
    }

    protected File getFileFromResource(String fileName) {
        ClassLoader classLoader = getClass().getClassLoader();
        URL resource = classLoader.getResource(fileName);
        if (resource != null) {
            try {
                return new File(resource.toURI());
            } catch (URISyntaxException e) {
                log.error("", e);
            }
        } else {
            log.error("file not found: {}", fileName);
        }
        return null;
    }

    public String read() {
        return innerRead();
    }

    public void close() {
        log.info("close");
        innerClose();
    }

    protected abstract String innerRead();

    abstract void init();

    protected abstract void innerClose();
  
    /**
     * 通过建立换行索引多次随机读取
     */
    @Slf4j
    public static class LineIndex extends RandomLineReader {
        List<Integer> index = new ArrayList<>();
        RandomAccessFile randomAccessFile;

        public LineIndex(String fileName) {
            super(fileName);
        }

        @Override
        protected String innerRead() {
            int loc = random.nextInt(index.size());
            int from;
            int to;
            if (loc == 0) from = 0;
            else from = index.get(loc - 1);
            to = index.get(loc);
            int size = to - from;  //to - from = line + \n + [\r]
            try {
                randomAccessFile.seek(from);
                byte[] bytes = new byte[size];
                randomAccessFile.read(bytes, 0, size);
                return new String(bytes, StandardCharsets.UTF_8);
            } catch (IOException e) {
                log.info("", e);
            }
            return null;
        }

        @Override
        void init() {
            log.info("init");
            int count = 0;
            try (LineNumberReader reader = new LineNumberReader(new BufferedReader(new FileReader(file)))) {
                String line = reader.readLine();
                while (line != null) {
                    // windows : \r\n
                    // linux: \r
                    log.info("line number {}", reader.getLineNumber());
                    count += line.length() + 1;
                    index.add(count);
                    reader.mark(0);
                    line = reader.readLine();
                }
            } catch (IOException e) {
                log.error("", e);
            }

            try {
                randomAccessFile = new RandomAccessFile(file, "r");
            } catch (FileNotFoundException e) {
                log.error("", e);
            }
        }

        @Override
        protected void innerClose() {
            try {
                randomAccessFile.close();
            } catch (IOException e) {
                log.info("can not close file", e);
            }
        }
    }
}