Tech Bites

• Jul 14, 2020
• Programming

Rules of Thumb for Software Developers

Fetching Data

• Remember Performance issues go unnoticed during development because the data set is too small - Vlad Mihalcea
• A transaction should fetch only as much data as required by the current executing business logic - Vlad Mihalcea

Optimization

• Premature optimization is the root of all evil - Donald E. Knuth
• Measure performance before and after each attempted optimization. J Bloch
• Programs spend 90 percent of their time in 10 percent of the code.

Design

• The components of design that are most difficult to change after the fact are those specifying interactions between components and with the outside world. Cheif among these design components are APIs, wire-level protocols, and persistent data formats. Bloch
• Strive to write good programs rather than fast ones. J Block

• Jun 20, 2020
• Command Line

Find a File From the Command Line

To find a file from the command line:

find . -type f -iname "*pattern_search_for*"

• Jul 18, 2019
• DevOps

Install Heroku CLI and Setup Heroku Autocomplete

On a Mac command line

brew tap heroku/brew && brew install heroku

Enable heroku autocomplete

heroku autocomplete
printf "$(heroku autocomplete:script bash)" >> ~/.bashrc; source ~/.bashrc

To use autocomplete type: Heroku and Tab,Tab

• Apr 20, 2019
• Git

Git: Pretty Git Graphs

In order to view git history from the command line:

git log

However if you want to view the history in a cleaner format I recommend a custom git log.

Add the following to .gitconfig (typically at ~.gitconfig)

[alias]
    lg = lg1
    lg1 = lg1-specific --all
    lg2 = lg2-specific --all

    lg1-specific = log --graph --abbrev-commit --decorate --format=format:'%C(bold blue)%h%C(reset) - %C(bold green)(%ar)%C(reset) %C(white)%s%C(reset) %C(dim white)- %an%C(reset)%C(auto)%d%C(reset)'
    lg2-specific = log --graph --abbrev-commit --decorate --format=format:'%C(bold blue)%h%C(reset) - %C(bold cyan)%aD%C(reset) %C(bold green)(%ar)%C(reset)%C(auto)%d%C(reset)%n''          %C(white)%s%C(reset) %C(dim white)- %an%C(reset)'

Now from the command line run:

• Jan 01, 0001
• Batch Processing

Spring Batch: Query All the Steps of a Batch Job

In Spring Batch, in order to get the job_execution_id of the last batch job instance for a given batch job name use this query:

select bje.job_execution_id from batch_job_instance bji
join batch_job_execution bje
on bji.job_instance_id = bje.job_instance_id
where bji.job_name = 'jobname'
order by bje.start_time desc
limit 1;

In order to get all the steps for the latest batch job instance for a given batch job name use this query:

select *
from batch_job_execution bje
join batch_job_instance bji
on bje.job_instance_id = bji.job_instance_id
join batch_job_step_execution bse
on bse.job_execution_id = bje.job_execution_id
and bje.job_execution_id = 
(
    select bje.job_execution_id from batch_job_instance bji
    join batch_job_execution bje
    on bji.job_instance_id = bje.job_instance_id
    where bji.job_name = 'jobname'
    order by bje.start_time desc
    limit 1
)
order by bse.start_time;

• Jan 01, 0001
• Java

Java Tip: ComputeIfAbsent

Often we have to loop through a list of items and convert it into a map, with the key being some sort of category and the value being a set of the associated items ie Map<Key, Set<Object>>. The old way of doing this looped through the list and before adding checked if the key was present. Using computeIfAbsent we can clean up this syntax considerably.

Instead of

// Map of item types to items
Map<String, Set<Items>> map = new HashMap<>();

for (Item item: items) {
    if (map.containsKey(item.getType())) {
        map.get(item.getType().add(item));
    } else {
        Set newSet = new HashSet<>();
        newSet.add(item);
        map.put(item.getType(), newSet));
    }
}

Do

// Map of item types to items
Map<String, Set<Items>> map = new HashMap<>();

for (Item item: items) {
    map.computeIfAbsent(item.getType(), v -> new HashSet<>()).
    add(item);
}