Talk that introduces useful techniques to bring agility into a legacy codebase. Covers code smells, design smells, architectural smells, and deployment smells. Examples are representative of typical Java legacy projects. Includes refactoring screencasts. Presented at GIDS.Java 2015 in Bangalore, India.

1. Infusing Agility
into the Java Legacy
Aman King, Lead Consultant

2. About Me
thoughtworker, developer,
lead, coach, trainer, oss,
speaker, author, thinker.
java, ruby, javascript, web,
cloud. agile, xp, scrum, cd.
www.amanking.com

3. www.thoughtworks.com
ambitious missions
need disruptive thinking

4. JAVA_LEGACY -> { AGILITY }

5. dictionary.com/browse/agility

6. Java Legacy
Java Code that is now Legacy Code

7. Legacy Code
Robert C Martin

8. Legacy Code
The phrase strikes disgust…
Murky swamp of tangled
undergrowth with leeches beneath
and stinging flies above…
Not enough to try to prevent the
rot – you have to be able to reverse
it.
Robert C Martin

9. vimeo.com/9981123

10. vimeo.com/9981123

11. Infusing Agility into Java Legacy
– is it possible?

12. Infusing Agility into Java Legacy
– is it possible?

20. Mild Violence
Mild Language
Blood and Gore
Proceed?

22. Extract Method
Extract Variable
Rename

50. Team Health Enemy Health

73. AND WE’RE BACK…

74. Mission Learnings

75. Mission Learnings
Not easy.
But improvement is possible.

76. Mission Learnings
Try one approach.
Doesn’t feel right? Revert, try another
approach.

77. Mission Learnings
Rely on your weapons and toolkit…

78. Mission Learnings
Do not forget strategy!
1. Identify change points
2. Find test points
3. Break dependencies
4. Write tests
5. Make changes and refactor

79. But there is more…
Cod e Smells
Des ign
Smells
Arch itectu re
Smells
Dep lo
y-
ment
Smells

80. • Long methods
• Long class
• Temporal coupling
• Fields as temporary variables
• Out parameters
• Setters
• many more…
Cod e Smells
Des ign
Smells

81. Cod e Smells
Des ign
Smells

82. • Incorrect responsibility-split across layers
• Confusing or inconsistent module structure
• Missing Dependency Injection
• Abused Dependency Injection
• No componentization
• Over-componentization
• Big-bang rewrites: long-lived either-or
• Mixed tech stack
Des ign
Smells
Arch itectu re
Smells

83. Incorrect responsibility-split
across layers
Des ign
Smells
Arch itectu re
Smells

85. Abused Dependency Injection
Des ign
Smells
Arch itectu re
Smells

86. A B C D
Spring IoC

88. A B C D
Spring IoC
E

93. A B C D
Spring IoC
E

94. A B C D
Spring IoC
E Is E really “cross-cutting” or
is it just too easy to inject?
High
coupling

95. A B C D
Spring IoC
E Solution?

96. A B C D
Spring IoC
E
D' E'

97. • Branching based on release / feature / team
• Dependencies not version controlled
• Database changes not version controlled
• Deployment scripts not version controlled
• Shared non-isolated environments
• Infrastructure access highly restricted
Arc h itec tu re
Smells
Deployment
Smells

98. http://martinfowler.com/bliki/FeatureBranch.html
Scary Merge!
Branching based on
release / feature / team
Arc h itec tu re
Smells
Deployment
Smells

99. http://martinfowler.com/bliki/FeatureToggle.html
http://paulhammant.com/blog/branch_by_abstraction.html

100. Arc h itec tu re
Smells
Deployment
Smells
Versioned Change Tracking

104. “Systems that gradually degrade
are systems that can gradually
improve.”
Cod e Smells
Des ign
Smells
Arch itectu re
Smells
Dep lo
y-
ment
Smells
Robert C Martin