Hi,

try this,

double your_data_double_array = ; // this will holds your double data array

byte byte_array = new byte[your_data_double_array.length]

Double temp_dbl_variable = null;

for(int i=0;i<your_data_double_array.length;i++){

      temp_dbl_variable = new Double(your_data_double_array[i]);

       byte_array[i] = temp_dbl_variable.byteValue();

        temp_dbl_variable = null;

}

use that byte array to write into file, while reading read into a 
byte array and make a object of Byte for each byte value get the 
double value by calling .doubleValue() method on Byte varible

let me know weather it works or not

Thanks,

Ravi