Java – how to quickly load large txt files into BigInteger?

I'm importing a large 17 million bit text file. I'm using this Code:

BufferedReader reader = new BufferedReader(new FileReader("test2.txt"));
String line = reader.readLine();
System.out.println("Done");
BigInteger num = new BigInteger(line);
System.out.println("Done Again");

It loads the file almost immediately and prints out "done", but it takes a long time (about an hour) to convert the string to BigInteger. What can I do to speed up and load the numbers quickly?

Solution

As an optimization, because BigInteger is serializable, you can save it as a binary file once and greatly speed up your loading

Loading serialized objects should be faster than parsing a huge string at a time

Use objectoutputstream to save large integers and objectinputstream to read them back