Several approaches to processing events (part 1 - synchronous processing)

Let's consider the following problem that we have to solve:

We have a file with numbers (each line has one number).
Our goal is to process every number and count its prime factors.
We need to write the result along with the processed number in a separate file.
In case of any exception during processing we need to write the exception to a file together with the number that was processed by the time it occurred.
Apart from that we also need to write the summary of the time that we spent on processing.

The class that counts prime factors looks as following:

The simplest but not the optimal way to solve this would be to process each line synchronously. It could look like that:

We're reading lines from numbers.txt file and then we're processing each line in a for loop. At the end we're writing everything to three files.

The Reader and Writer classes are quite simple:

They're using Guava and Apache Commons dependencies that have following declaration:

We can check the results in a following test:

On a machine with Core2 Duo 2.53GHz it takes ~73 seconds to process 10 000 numbers.

The whole project can be found at github.

In next posts we'll take a look at other approaches to solve this problem.