Refactoring Legacy Code - true story
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The document discusses refactoring legacy code for a client project. It describes steps taken to refactor code for searching products and handling file attachments. For searching, the speaker extracted parameters from a method with 21 parameters and 200 lines of code into a builder pattern. For attachments, switch statements were replaced with polymorphism, and file processing logic was extracted from a service into separate classes. The refactoring was done incrementally using test-driven development practices learned at coderetreats. Tests were added to verify changes at each step, and over 30 commits were made. The refactoring provided value to customers while improving code quality and maintainability.
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Refactoring Legacy Code - true story
- 1. Refactoring legacy code True story
- 3. Aki Salmi @rinkkasatiainen • Hiking guide • Supervisor • Programmer • Blipper – but no pics today.
- 4. Refactoring legacy code True story
- 5. My goals for the talk • Show how what I have learned at coderetreats have been taken into production use • GOAL 1: Encourage us to practice the craft • Show what I’ve done – Test Driving my design • Show steps rather than finished ‘product’ • GOAL 2: initiate discussions on what I’ve done • Learn • GOAL 3: reflect on my work and decisions and how they actually seem now.
- 6. Tips for listeners • There’s going to be a lot of code • Rather than reading the code, try to smell it. • How clean the code seems to be?
- 7. What I’ve done – what I believe in • Is not either good or bad. • It has bugs (I’ve seen those) • It provides value to the customer every day
- 8. What is valuable (for someone) • Client • clients of the Client • Myself & fellow ambientians • How likely this code is going to change? • How likely the change I make is going to introduce bugs in future additions to this feature
- 9. Key process decisions • TDD as design tool. • Unit tests for changes • Practice TDD in real environment. Try to get feedback • Refactor often • Keep tests clean • ”if it is not important for the test, it is important not to be in the test!” • Note: Builder pattern
- 10. Key process decisions • Use proper tools • GIT, IntelliJ IDEA, VIM • Hamcrest, mockito, various other open-source components
- 11. 4 elements of simple design 1. Passes its tests 2. Minimizes duplication 3. Maximizes clarity 4. Has fewer elements
- 12. Coderetreat • 1 day of coding • Pair programming, 6 different pairing partner • Learn through pairing • Deliberate practice • experiment
- 13. Key takeaways from coderetreats • Baby steps – commit to git often. Rebase to keep git log clean • TDD-as-if-you-meant-it • Avoid conditionals, switches, try/catch • Only 4 lines per method • Avoid naked primitives • Only one assert/behavior per test • Sapir-Whorf hypothesis • Tell – Don’t ask: no getters/setters for objects
- 14. Object calisthenics 1. One level of indentation per method 2. Don’t use the ELSE keyword 3. Wrap all primitives and Strings 4. First class collections 5. One dot per line 6. Don’t abbreviate 7. Keep all entities small 8. No classes with more than two instance variables 9. No getters / setters / properties
- 15. Background of the system
- 16. Domain logic POJO, Spring, Hibernate UI (Grails) Controllers + Views Database
- 17. A live service since 2008 Providing value to Client and end-users every day since
- 18. Case 1: adding a search parameter
- 19. Search for a product The method had 21 parameters and 200LOC
- 20. And there’s more
- 21. ..and more ..you see the pattern.
- 22. What to do add yet another parameter?
- 23. What I did was a brief study • How the methods are used in the service? • Grails-based service (200LOC) uses it • Determine the current responsibilities • Service builds valid parameters, DAO consumes it. • Where the changes could be made? • Both the service & DAO • Is the method likely to change later? • YES
- 24. Step 1
- 25. An integration test, See the builder-pattern If it’s not important for the test, it is important not to be on the test
- 26. I changed the signature
- 27. The first model
- 28. And part of the service
- 29. Key decisions • Factory to hide implementation details • Sometimes Criteria handled Date, sometimes Calendar • Make it first to work, refactor then. • Create a ProductSearchCriteria per type – think about the name of the object • There were no tests before – try to make minimal impact on code.
- 30. Test on localhost. • The context is a bit more complex than I originally thought: • In one case, it was not enough to limit on Date/Calendar • Thus, the original factory-idea would turn into a bit more complicated problem
- 31. Step 2
- 32. Firstly: factory into builder • Build what you need – add items to CompositeSearchCriteria as need arises • Again – do the minimal changes to the grails- service in order to minimize errors
- 33. Second try
- 34. Second try
- 36. Builder maybe too many responsibilities?
- 37. Key decisions • Do the smallest amount that is needed • Builder to support only those methods that are used.
- 38. Step 3
- 39. Minor changes to fix a bug
- 40. Bug # 2
- 41. Minor changes to fix a bug
- 42. Bug # 3
- 43. Sometimes maths just is too much
- 44. Bug # 4
- 45. Minor changes to fix a bug
- 46. Learnings • Fast to refactor • Next time: start from integration test • But one cannot integration test the whole – too many parameters • Minor changes somewhere in the controller code caused it to fail on other places. • Later, a colleague joined me. His first task was to add a new concept to domain. • Also for search
- 47. Case 2: Attachment handling
- 48. Targets • System used to have ~ 20 different attachment types. • Only 5 were needed. • Earlier supported only 1 attachment / type / product. Now should support more.
- 50. Decision to be made • Where to start? • The only (business) knowledge came from the previous changes • I decided to tackle the switch-case structure • It was spread 4 times throughout the code • To ease the change from 20 to 5
- 51. A story of FileType
- 55. FileType
- 56. Step 2 Get rid of switch-case
- 57. From …
- 58. … to
- 59. Or in picture
- 62. … to • Private method, thus no tests for this. • How am I sure this works? • I am not. Now. I was pretty sure. I think. Hope.
- 64. … to
- 65. Step 3 Work with attachment directory/name
- 66. Things not to do • Have a constructor to throw an Exception. • How would I change this now: • Factory to create the directory • Create AttachmentDirectory only if dir exists • ready?
- 70. AttachmentFile(Factory) • Similar concept with AttachmentFile and AttachmentFileFactory • With one difference • AttachmentFile is interface and has two concrete classes PlainAttachmentFile and WebImageAttachmentFile • Use of Template-pattern (which changed a lot later)
- 72. AttachmentFileTemplate starting to get messy
- 74. Step 4 do similar changes to AttachmentService# moveToAttachmentDir
- 75. AttachmentFile
- 76. AttachmentFile • Too many responsibilities. • Would turn up with lot of methods. I needed to do something. • Did try to not to repeat myself (not shown – ask for more info later)
- 77. The first draft
- 78. Step 5 Copying and moving files
- 79. >150 LOC @ AttachmentService
- 80. … to 4*4
- 81. The classes within the process
- 82. Steps • Factory to create an AttachmentFile • Factory creates a AttachmentFileProcess – process to move/copy/clone/delete the AttachmentFile • For specific AttachmentFileType, it does different things • The execute method takes one argument, AttachmentFileAction, which either is move/copy/clone/delete/rename
- 83. Some steps
- 88. FileCopyAction
- 89. FileDeleteAction
- 91. Later steps • Renaming classes, reordering packages • Using template
- 92. One last thing – listen the tests
- 93. The difference:
- 94. And that led to • New class: AttachmentFileName • A domain logic for handling name of the Attachment • I’m working with this. Now.
- 95. Learnings • Slow to refactor • Test-Driven design can work even in brown-field projects • Integration to old system required integration tests • How valuable the changes were to the customer • With my current understanding: • Split the changes to two – deploy both separately.
- 97. Questions?
- 98. Puhelin: +358 50 341 5620 email: aki.salmi@iki.fi / aki.salmi@ambientia.fi Twitter: @rinkkasatiainen Aki Salmi