I just wrote this code to give you an idea for how to do conversion manually (In fact this logic can be used in any language).
you may have to change the code as per you requirements: ...
Done some changes for unsigned char and j++
#include<stdio.h>
#include<ctype.h>
int main ( ){
char *bigHexa = "412073696d706c6520737472696e6720412073696d706c6520737";
unsigned char decimalOfHexa = [100]; // change
int i = 0, j = 0;
while(true) {
decimalOfHexa[j] = getDecimal(bigHexa[i], bigHexa[i+1])
if(bigHexa[i+2] == '\0') break;
i = i + 2;
j++; // change
}
}
In java I have least experience so no idea about built in functions.
Marked 
