BufferedInputStream

import java.io.IOException;
import java.io.InputStream;

public class BufferedInputStream extends InputStream {
    private InputStream inputStream;
    private byte[] buffer = new byte[5];
    private int start;
    private int count;

    public BufferedInputStream(InputStream inputStream) {
        this.inputStream = inputStream;
    }

    @Override
    public int read() throws IOException {
        if (start == count) {
            count = inputStream.read(buffer);
            start = 0;
        }

        if (count == -1) {
            return -1;
        }
        int value = buffer[start];
        start++;
        return value;
    }

    @Override
    public int read(byte[] b) throws IOException {
        return super.read(b);
    }

    @Override
    public int read(byte[] b, int off, int len) throws IOException {
        if (b.length < len){
            throw new IndexOutOfBoundsException();
        } else if (len == 0){
            return 0;
        }

        int n = 0;
        while(true) {
            if (buffer.length < len - n) {
                count = inputStream.read(buffer, off + n, buffer.length - n);
            } else {
                count = inputStream.read(buffer, off + n, len);
            }

            if (count == -1) {
                return -1;
            }

            System.arraycopy(buffer, off + n, b, n, count);
        }
        
    }

    @Override
    public void close() throws IOException {
        buffer = null;
        inputStream.close();
    }
}

BufferedInputStream2

package com.petrovskiy.Streams;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

public class BufferedInputStream extends InputStream {
    private static final int DEFAULT_BUFFER_SIZE = 5;

    private InputStream inputStream;
    private byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
    private int index;
    private int count;

    public BufferedInputStream(InputStream inputStream) {
        this.inputStream = inputStream;
    }

    @Override
    public int read() throws IOException {
        if (index == count) {
            count = inputStream.read(buffer);
            index = 0;
        }

        if (count == -1) {
            return -1;
        }

        int value = buffer[index];
        index++;
        return value;
    }

    @Override
    public int read(byte[] b) throws IOException {
        int value;
        int indexB = 0;
        while ((value = read()) != -1) {
            if (indexB >= b.length){
                return indexB;
            }
            b[indexB] = (byte) value;
            indexB++;
        }

        return indexB;
    }

    @Override
    public int read(byte[] b, int off, int len) throws IOException {
        if (b.length < len){
            throw new IndexOutOfBoundsException("Length parameter is higher than array length!");
        } else if (len == 0){
            return 0;
        }

        int index = 0;
        while(count != -1) {
            if (buffer.length < len - index) {
                count = inputStream.read(buffer, off + index, buffer.length - index);
            } else {
                count = inputStream.read(buffer, off + index, len);
            }

            System.arraycopy(buffer, index, b, index, count);
        }
        return -1;
    }

    @Override
    public void close() throws IOException {
        buffer = null;
        inputStream.close();
    }
}

class Test{
    public static void main(String[] args) throws IOException {
        InputStream inputStream = new BufferedInputStream(new FileInputStream("1.txt"));
        byte[] res = new byte[7];
        System.out.println(inputStream.read(res));
        for (byte re : res) {
            System.out.println((char)re);
        }
    }
}

Test

import java.io.FileInputStream;
import java.io.IOException;

public class Test {
    public static void main(String[] args) throws IOException {
        BufferedInputStream bufferedInputStream = new BufferedInputStream(new FileInputStream("1.txt"));
        byte[] b = new byte[10];
        bufferedInputStream.read(b,0,6);
        for (byte b1 : b) {
            System.out.println(b1);
        }
    }
}