Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Three Principles To Bring Your Legacy Code Into...
Search
Roland Weisleder
December 11, 2023
Programming
0
240
Three Principles To Bring Your Legacy Code Into the Future
Roland Weisleder
December 11, 2023
Tweet
Share
More Decks by Roland Weisleder
See All by Roland Weisleder
Architecture as Code in Practice
rweisleder
0
8
Unit Test Your Java Architecture With ArchUnit
rweisleder
0
490
Immer wieder die gleichen Fehler? Nicht mit ArchUnit!
rweisleder
0
290
Alles einsteigen! Einen eigenen Release Train mit Maven umsetzen
rweisleder
0
310
7 Tipps für eine verständliche Git-Historie
rweisleder
0
150
Other Decks in Programming
See All in Programming
技術的負債の正体を知って向き合う / Facing Technical Debt
irof
0
170
Things You Thought You Didn’t Need To Care About That Have a Big Impact On Your Job
hollycummins
0
230
The Past, Present, and Future of Enterprise Java
ivargrimstad
0
120
NixOS + Kubernetesで構築する自宅サーバーのすべて
ichi_h3
0
850
他言語経験者が Golangci-lint を最初のコーディングメンターにした話 / How Golangci-lint Became My First Coding Mentor: A Story from a Polyglot Programmer
uma31
0
150
アメ車でサンノゼを走ってきたよ!
s_shimotori
0
220
Railsだからできる 例外業務に禍根を残さない 設定設計パターン
ei_ei_eiichi
0
900
理論と実務のギャップを超える
eycjur
0
140
Introducing ReActionView: A new ActionView-Compatible ERB Engine @ Kaigi on Rails 2025, Tokyo, Japan
marcoroth
3
1k
バッチ処理を「状態の記録」から「事実の記録」へ
panda728
PRO
0
160
Software Architecture
hschwentner
6
2.3k
『毎日の移動』を支えるGoバックエンド内製開発
yutautsugi
2
250
Featured
See All Featured
Navigating Team Friction
lara
190
15k
Why You Should Never Use an ORM
jnunemaker
PRO
59
9.6k
Design and Strategy: How to Deal with People Who Don’t "Get" Design
morganepeng
132
19k
The Art of Programming - Codeland 2020
erikaheidi
56
14k
Let's Do A Bunch of Simple Stuff to Make Websites Faster
chriscoyier
508
140k
Art, The Web, and Tiny UX
lynnandtonic
303
21k
Java REST API Framework Comparison - PWX 2021
mraible
34
8.9k
Facilitating Awesome Meetings
lara
56
6.6k
Visualizing Your Data: Incorporating Mongo into Loggly Infrastructure
mongodb
48
9.7k
I Don’t Have Time: Getting Over the Fear to Launch Your Podcast
jcasabona
33
2.5k
[RailsConf 2023 Opening Keynote] The Magic of Rails
eileencodes
31
9.7k
Code Reviewing Like a Champion
maltzj
526
40k
Transcript
@Ro_Wei Roland Weisleder
[email protected]
Three Principles To Bring Your Legacy
Code Into the Future
About Me Independent Software Developer & Consultant Bringing Legacy Java
Systems Into the Future Spring Boot Trainer @ workshops.de Lecturer @ HTW Berlin in/roland-weisleder @rweisleder @Ro_Wei
[email protected]
What is Legacy Code?* • Still in production use •
Relies on outdated technologies • Has insufficient test coverage • Lacks adequate documentation • Expert knowledge unavailable *According to ChatGPT
Big Bang Rewrite? Too time-consuming
What to improve? What you work on anyway
Rewrite or Refactor? Rewrite only with test coverage
Old bugs need to be added to the rewritten system.
Source: https://martinfowler.com/bliki/StranglerFigApplication.html
How to increase test coverage? Add tests for current behavior
How to understand the current behavior?
Where to start?
Source: https://www.commitstrip.com/en/2016/03/03/its-not-working/
Analyze Stack Trace or Thread Dump Source: https://www.jetbrains.com/help/idea/analyzing-external-stacktraces.html
Call Hierarchy
Source: https://twitter.com/codewisdom/status/1154436195126009858
Understand Code
Scratch Refactoring • Learn through refactoring • Make experiments •
Revert everything
Source: https://www.morling.dev/blog/the-code-review-pyramid/
Document Code
Our code is self-documenting.
• What about the input format? • What about malformed
input? • What about null? • What about thrown exceptions?
• What about the return value? * don’t use double
for money…
Suddenly a wild Java update appears
Unit tests are our documentation.
Who has read the tests of their favorite language /
framework / library to understand how to use it?
None
None
not only Don‘t Repeat Yourself but also Documentation Reflects Implementation
Source: https://twitter.com/sweblogtweets/status/1249698475249467393
Test Code
What should I test? The documented behavior.
Use Descriptive Test Names
Concise Implementation Keep relevant stuff together, hide irrelevant stuff
I want to test private methods Private methods are independent
units in disguise. Extract, document and test.
I have to mock everything So the method does nothing
useful? Keep it simple, delete the method.
The code contains hard-to-mock dependencies Current Time Database External Systems
Declare dependencies as parameters vs vs
Declare dependencies as parameters vs
Separate Domain and Infrastructure to simplify testing
Clean Architecture
Code Coverage • Find untested code • Find dead code
Still doing Scratch Refactoring? Revert everything, except the tests. Congratulations!
Time for TDD.
Inverted TDD
Source: https://twitter.com/kentbeck/status/250733358307500032
Improve Code
Source: https://www.morling.dev/blog/the-code-review-pyramid/
Focus on clean APIs
Define Interfaces Input Process Output
Invalid objects …
… vs valid objects
What about null?
Primitive Obsession vs
Source: https://twitter.com/codewisdom/status/1154436195126009858
None
https://www.youtube.com/watch?v=OGZ1JkC-cQc
Key Takeaways Separate Domain and Infrastructure Documentation Reflects Implementation Input
Process Output
Bringing Legacy Code Into the Future Slides: speakerdeck.com/rweisleder Gilded Rose
Kata: github.com/emilybache/GildedRose-Refactoring-Kata Need help with your Legacy Code? Contact me!
[email protected]
in/roland-weisleder @rweisleder @Ro_Wei