Write a computer program to display the value of a byte in hexadecimal (One byte can be represented as two hexadecimal digits), and then apply the program to an array of bytes. Add an extra space after every four bytes to make the output easier to read.

Also, extend the hexadecimal dump program above to also print the character representation of any printable character. For characters that do not have a printable representation (for 7 bits ASCII character in a byte, the ASCII value should be in the range of [32-127]), arrange for the program to print a period.

Please use java.