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
9
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
エンジニアインターン「Treasure」とHonoの2年、そして未来へ / Our Journey with Hono Two Years at Treasure and Beyond
carta_engineering
0
400
CSC509 Lecture 06
javiergs
PRO
0
260
Catch Up: Go Style Guide Update
andpad
0
240
品質ワークショップをやってみた
nealle
0
590
Developer Joy - The New Paradigm
hollycummins
1
330
CSC509 Lecture 08
javiergs
PRO
0
230
登壇は dynamic! な営みである / speech is dynamic
da1chi
0
350
20251016_Rails News ~Rails 8.1の足音を聴く~
morimorihoge
2
660
When Dependencies Fail: Building Antifragile Applications in a Fragile World
selcukusta
0
110
CSC305 Lecture 09
javiergs
PRO
0
300
bootcamp2025_バックエンド研修_WebAPIサーバ作成.pdf
geniee_inc
0
120
What Spring Developers Should Know About Jakarta EE
ivargrimstad
0
380
Featured
See All Featured
GraphQLの誤解/rethinking-graphql
sonatard
73
11k
Building Applications with DynamoDB
mza
96
6.7k
Why Our Code Smells
bkeepers
PRO
340
57k
Making Projects Easy
brettharned
120
6.4k
CoffeeScript is Beautiful & I Never Want to Write Plain JavaScript Again
sstephenson
162
15k
Balancing Empowerment & Direction
lara
5
700
jQuery: Nuts, Bolts and Bling
dougneiner
65
7.9k
Learning to Love Humans: Emotional Interface Design
aarron
274
41k
Principles of Awesome APIs and How to Build Them.
keavy
127
17k
Easily Structure & Communicate Ideas using Wireframe
afnizarnur
194
16k
How to Think Like a Performance Engineer
csswizardry
27
2.1k
Fantastic passwords and where to find them - at NoRuKo
philnash
52
3.5k
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