This document discusses approaches to managing architecture in Java and Spring applications. It recommends starting with a strict packages model organized by slices and layers, then using tools like Sonar to analyze dependencies and enforce architecture. It also introduces Hera, a small plugin system that allows selecting plugins based on criteria and callbacks. Hera provides a registry and common access patterns to integrate plugins dynamically.

1. Whoops!
Where did my
architecture go?
Approaches to architecture management for
Java and Spring applications
Oliver Gierke

2. Oliver Gierke
SpringSource Engineer
Spring Data
ogierke@vmware.com
olivergierke
www.olivergierke.de

3. Background
5 years of consulting
Lots of code reviews
Eoin Woods‘ talk on InfoQ

4. Roadmap
Architecture 101
A Java packages model
Hera

5. Architecture 101

6. Know your
dependencies

7. Granularity
Modules
Layers
Vertical slices
Subsystems

8. Granularity
Java ARchive
Package
Class

9. Of layers
and slices…

12. Layer 1
Layer 2
Layer 3

13. Layer 1
Layer 2
Layer 3

14. Layer 1
Layer 2
Layer 3

15. Slice A Slice B Slice C
Layer 1
Layer 2
Layer 3

16. Slice A Slice B Slice C
Layer 1
Layer 2
Layer 3

17. Slice A Slice B Slice C
Layer 1
Layer 2
Layer 3

18. Layers
Well understood
Known to developers
Less important to business

19. Slices
Hardly understood
New to developers
Key for business req

20. Slice A Slice B Slice C
Layer 1
Layer 2
Layer 3

21. " How to implement
an architecture
inside a codebase?

22. Architecture
VS.
Codebase

23. " How to implement
an architecture
inside a codebase?

24. " How to implement
an architecture
inside a codebase?

25. " How to enforce
an architecture
inside a codebase?

26. Code analysis
JDepend
Sonar

27. Demo

28. Sonargraph
Formerly known as SonarJ

29. Demo

30. A plain Java
based approach

31. Slice A Slice B Slice C
Layer 1
Layer 2
Layer 3

32. ….${layer}.${slice}
VS.
….${slice}.${layer}

33. Layers first
Leaks slice internals
Lower layers visible to everyone

34. " Start with less
packages and the
least visibility
possible…

35. Slice A Slice B Slice C
Layer 1
Layer 2
Layer 3

36. Slice A Slice B Slice C
Layer 1
Layer 2
Layer 3

37. Slices first
Start with package per slice
Expose interfaces and domain types
Keep implementations private

38. Slices first
Encapsulates business module
Internals understood anyway

39. Subsystems

40. Background
Risk mgmt. at German public bank
Quite a few other SpringSource clients

41. Host

42. Host
SPI SPI SPI

43. Host
SPI SPI SPI
Plugin Plugin

44. Host
SPI SPI SPI
Plugin Plugin

45. Host
SPI SPI SPI
Plugin Plugin

46. Context
No OSGi
Spring based
Build-time composition
Don‘t touch the host system

47. Host

48. Plugin Plugin
Host

49. App
Plugin Plugin
Host

50. " How to make the
host aware of the
plugins?

51. " How to dynamically
collect Spring beans
of a given type?

52. classpath*:META-INF/
spring/plugin-context.xml

53. Host

54. Host
SPI SPI SPI

55. Host
SPI SPI SPI
Plugin Plugin

56. Host
SPI SPI SPI
Plugin Plugin

57. Host
SPI SPI SPI
Plugin Plugin

58. classpath*:META-INF/
spring/plugin-context.xml
SPI SPI SPI
META-INF/ META-INF/
spring/plugin- spring/plugin-
context.xml context.xml

59. @Component
public class MyComponentImpl implements TransferService {
private List<MyPlugin> plugins;
@Autowired
public MyComponentImpl(List<MyPlugin> plugins) {
this.plugins = plugins;
}
…
}
public interface MyPlugin {
void doSomething();
}

60. Demo

61. XML?
Back in the days

62. (XML?)
Back in the days
Probably not a big deal anymore

63. Easy access?

64. @Component
public class MyComponentImpl implements TransferService {
private List<MyPlugin> plugins;
@Autowired
public MyComponentImpl(List<MyPlugin> plugins) {
this.plugins = plugins;
}
…
}
public interface MyPlugin {
void doSomething();
}

65. @Component
public class MyComponentImpl implements TransferService {
// Constructor omitted
public Result myMethod(SomeParameter parameter) {
// Select the first one to match to invoke?
// Select multiple ones to invoke?
// Select and fallback to one if none found?
// Select and throw an exception if none found?
}
}

66. Hera

67. " The smallest plugin
system ever!

68. Plugins
Selection criterion
Callback method
Let the implementation decide

69. Registry
Equipped with plugins
Common access patterns

70. public interface Plugin<T> {
public boolean supports(T delimiter );
}
public interface PluginRegistry<S extends Plugin<T>, T> {
T getPluginFor(S delimiter);
T getPluginFor(S delimiter, T default);
<E extends Exception> T getPluginFor(S del, E e) throws E;
List<T> getPluginsFor(S delimiter);
…
}

71. @Component
public class MyComponentImpl implements TransferService {
private PluginRegistry<MyPlugin, String> plugins;
@Autowired
public MyComponentImpl(
PluginRegistry<MyPlugin, String> plugins) {
this.plugins = plugins;
}
}
public interface MyPlugin extends Plugin<String> {
void doSomething();
}

72. @Component
public class MyComponentImpl implements TransferService {
private final MyPlugin defaultPlugin = new
MyDefaultPlugin();
public Result myMethod(String parameter) {
// Select the first one to match to invoke?
… = plugins.getPluginFor(parameter);
// Select multiple ones to invoke?
… = plugins.getPluginsFor(parameter);
// Select and fallback to one if none found?
… = plugins.getPluginFor(parameter, defaultPlugin);
// Select and throw an exception if none found?
… = plugins.getPluginsFor(parameter, new
RuntimeException());
}
}

73. OrderAware
PluginRegistry
Respects @Order/Ordered
OAPR.reverse()

74. Bells‘n‘whistles
FactoryBean
Spring namespace
Lazy-eval

75. Hera
http://hera.synyx.org
Apache 2.0
Soon to be on GitHub

76. Spring Integration2

77. <bean class="….FirstSamplePlugin" />
<bean class="….SecondSamplePlugin" />
<int:channel id="input" />
<int:channel id="output" />
<int-hera:dynamic-service-activator
input-channel="input"
outputChannel="output"
plugin-type= "….MyPlugin"
method= "myBusinessMethod"
delimiter="payload"
invocation-arguments= "payload" />

78. Demo

79. Take-aways
Know your dependencies
On every granularity
Start as strict as possible
Get lenient where necessary

80. Thanks & credits
Eoin Woods - Talk @ InfoQ

81. Resources
Spring Data JPA @ GitHub
Sonargraph
Hera