Whoops! Where did my architecture go?

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2 Oliver Gierke Spring Source engineer Project lead Core/JPA/MongoDB ogierke@vmware.com www.olivergierke.de olivergierke

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3 Spring Data Modern Data Access For Enterprise Java NoSQL JPA JDBC Redis Big Data Hadoop HBase MongoDB Neo4j REST exporter Roo Hive Pig Querydsl Repositories 1 free copy per attendee! Gemﬁre Splunk

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

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Roadmap Architecture 101 A plain Java based approach Spring Plugin 5

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The 3 C' of Architecture Constraints Complexity Change 6

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The 2 C' of Architecture 7 Complexity Change

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Architecture 101 8

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Know your dependencies 9

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Granularity Modules Layers Vertical slices Subsystems 10

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Granularity Java ARchive Package Class 11

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Of layers and slices… 12

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Presentation Service Data Access Account Customer Core 13

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14 Layers Well understood Known to developers Less important to business

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Slices Hardly understood New to developers Key for business req 15

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Presentation Service Data Access Account Customer Core 16

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17 "How to implement an architecture inside a codebase?

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Architecture VS. Codebase 18

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19 "How to implement an architecture inside a codebase?

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20 "How to enforce an architecture inside a codebase?

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Code analysis JDepend Sonar 21

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Demo 22

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Sonargraph Formerly known as SonarJ 23

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Demo 24

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A plain Java based approach 25

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26 "How far can we get with plain Java means only?

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Presentation Service Data Access Account Customer Core 27

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28 Packages

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29 …. layer.slice ? …. slice.layer ? … slice ?

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30 …web.core …service.core …repository.core

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31 …core.web …core.service …core.repository

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32 … core … customer … account

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Layers ﬁrst 33 Leaks slice internals Lower layers visible to everyone

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Slices ﬁrst/only Start with package per slice Expose interfaces and domain types Keep implementations private 34

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Slices ﬁrst/only Encapsulates business module Internals understood anyway 35

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36 "Start with less packages and the least visibility possible…

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Presentation Service Data Access Account Customer Core 37

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Presentation Service Data Access Account Customer Core 38

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Subsystems 39

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

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Systems grow big! 41

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Remember the 2 C's? 42

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Complexity & Change 43

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44 "How to localize change?

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45 "Separate frequent from infrequent change!

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46 Granularity Class Package Java ARchive

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Host SPI SPI SPI Plugin Plugin 47

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

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Host Plugin Plugin App 49

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

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

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

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Host SPI SPI SPI Plugin Plugin 53

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classpath*:META-INF/ spring/plugin-context.xml SPI SPI SPI META-INF/ spring/plugin- context.xml META-INF/ spring/plugin- context.xml 54

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@Component public class MyComponentImpl implements TransferService { private List plugins; @Autowired public MyComponentImpl(List plugins) { this.plugins = plugins; } … } public interface MyPlugin { void doSomething(); } 55

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Demo 56

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XML? 57 Back in the days

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(XML?) Back in the days Probably not a big deal anymore 58

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Easy access? 59

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@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? } } 61

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62 Spring Plugin

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63 "The smallest plugin system ever!

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64 Plugins Selection criterion Callback method Let the implementation decide

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Registry Equipped with plugins Common access patterns 65

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public interface Plugin { public boolean supports(T delimiter ); } public interface PluginRegistry, T> { T getPluginFor(S delimiter); T getPluginFor(S delimiter, T default); T getPluginFor(S del, E e) throws E; List getPluginsFor(S delimiter); … } 66

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@Component public class MyComponentImpl implements TransferService { private PluginRegistry plugins; @Autowired public MyComponentImpl(PluginRegistry plugins) { this.plugins = plugins; } } public interface MyPlugin extends Plugin { void doSomething(); } 67

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@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()); } } 68

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

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Bells‘n‘whistles FactoryBean Spring namespace Lazy-eval 70

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Spring Plugin 71

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Spring Integration2 72

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Demo 74

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Take-aways 75 Know your dependencies On every granularity Start as strict as possible Get lenient where necessary

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Thanks & credits Eoin Woods - Talk @ InfoQ Uwe Friedrichsen - Slides @ Slideshare 76

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Resources Spring Data JPA @ GitHub Sonargraph Spring Plugin Whoops sample code 77