Whoops!Where did my

architecture go?Approaches to architecture management for

Java and Spring applications

Oliver Gierke

Oliver GierkeSpringSource EngineerSpring Data

ogierke@vmware.comolivergierkewww.olivergierke.de

Background5 years of consulting

Lots of code reviews

Eoin Woods‘ talk on InfoQ

RoadmapArchitecture 101

A Java packages model

Hera

Architecture 101

Know your dependencies

GranularityModules

Layers

Vertical slices

Subsystems

GranularityJava ARchive

Package

Class

Of layersand slices…

Layer 1

Layer 2

Layer 3

Layer 1

Layer 2

Layer 3

Layer 1

Layer 2

Layer 3

Layer 1

Layer 2

Layer 3

Slice A Slice B Slice C

Layer 1

Layer 2

Layer 3

Slice A Slice B Slice C

Layer 1

Layer 2

Layer 3

Slice A Slice B Slice C

LayersWell understood

Known to developers

Less important to business

SlicesHardly understood

New to developers

Key for business req

Layer 1

Layer 2

Layer 3

Slice A Slice B Slice C

"How to implement an architectureinside a codebase?

ArchitectureVS.

Codebase

"How to implement an architectureinside a codebase?

"How to implement an architectureinside a codebase?

"How to enforcean architectureinside a codebase?

Code analysisJDepend

Sonar

Demo

SonargraphFormerly known as SonarJ

Demo

A plain Javabased approach

Layer 1

Layer 2

Layer 3

Slice A Slice B Slice C

….${layer}.${slice}VS.

….${slice}.${layer}

Layers firstLeaks slice internals

Lower layers visible to everyone

"Start with less packages and the least visibility possible…

Layer 1

Layer 2

Layer 3

Slice A Slice B Slice C

Layer 1

Layer 2

Layer 3

Slice A Slice B Slice C

Slices firstStart with package per slice

Expose interfaces and domain types

Keep implementations private

Slices firstEncapsulates business module

Internals understood anyway

Subsystems

BackgroundRisk mgmt. at German public bank

Quite a few other SpringSource clients

Host

Host

SPI SPI SPI

Host

SPI SPI SPI

Plugin Plugin

Host

SPI SPI SPI

Plugin Plugin

Host

SPI SPI SPI

Plugin Plugin

ContextNo OSGi

Spring based

Build-time composition

Don‘t touch the host system

Host

Host

Plugin Plugin

Host

Plugin Plugin

App

"How to make the host aware of the plugins?

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

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

Host

Host

SPI SPI SPI

Host

SPI SPI SPI

Plugin Plugin

Host

SPI SPI SPI

Plugin Plugin

Host

SPI SPI SPI

Plugin Plugin

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

SPI SPI SPI

META-INF/spring/plugin-

context.xml

META-INF/spring/plugin-

context.xml

@Componentpublic class MyComponentImpl implements TransferService {

private List<MyPlugin> plugins;

@Autowired public MyComponentImpl(List<MyPlugin> plugins) { this.plugins = plugins; } …}

public interface MyPlugin {void doSomething();

}

Demo

XML?Back in the days

(XML?)Back in the days

Probably not a big deal anymore

Easy access?

@Componentpublic class MyComponentImpl implements TransferService {

private List<MyPlugin> plugins;

@Autowired public MyComponentImpl(List<MyPlugin> plugins) { this.plugins = plugins; } …}

public interface MyPlugin {void doSomething();

}

@Componentpublic 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?

}}

Hera

"The smallest plugin system ever!

PluginsSelection criterion

Callback method

Let the implementation decide

RegistryEquipped with plugins

Common access patterns

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);…

}

@Componentpublic 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();

}

@Componentpublic 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()); }}

OrderAwarePluginRegistryRespects @Order/Ordered

OAPR.reverse()

Bells‘n‘whistlesFactoryBean

Spring namespace

Lazy-eval

Herahttp://hera.synyx.org

Apache 2.0

Soon to be on GitHub

Spring Integration2

<bean class="….FirstSamplePlugin" /><bean class="….SecondSamplePlugin" />

<int:channel id="input" /><int:channel id="output" />

<int-hera:dynamic-service-activatorinput-channel="input" outputChannel="output" plugin-type= "….MyPlugin" method= "myBusinessMethod"delimiter="payload" invocation-arguments= "payload" />

Demo

Take-awaysKnow your dependencies

On every granularity

Start as strict as possible

Get lenient where necessary

Thanks & creditsEoin Woods - Talk @ InfoQ

ResourcesSpring Data JPA @ GitHub

Sonargraph

Hera