Whoops! Where did my architecture go?

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

Oliver Gierke

Spring DataCore/JPA/MongoDB

ogierke@vmware.comwww.olivergierke.deolivergierke

BackgroundFew years of consulting

Lots of code reviewsEoin Woods‘ talk on InfoQ

RoadmapArchitecture 101

A Java packages modelHera

Architecture 101

Know your dependencies

GranularityModulesLayers

Vertical slicesSubsystems

GranularityJava ARchive

PackageClass

Of layersand slices…

Layer 1

Layer 2

Layer 3

Slice A Slice B Slice C

LayersWell understood

Known to developersLess important to business

SlicesHardly understoodNew to developers

Key for business req

Layer 1

Layer 2

Layer 3

"How to implement an architectureinside a codebase?

ArchitectureVS.

Codebase

"How to implement an architectureinside a codebase?

"How to enforcean architectureinside a codebase?

Code analysisJDepend

SonargraphFormerly known as SonarJ

A plain Javabased approach

Layer 1

Layer 2

Layer 3

….${layer}.${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

Layer 1

Layer 2

Layer 3

Slices firstStart with package per slice

Expose interfaces and domain typesKeep implementations private

Slices firstEncapsulates business moduleInternals understood anyway

Subsystems

BackgroundRisk mgmt. at German public bank

Quite a few other SpringSource clients

"The smallest plugin systemever!

SPI SPI SPI

Plugin Plugin

ContextNo OSGi

Spring basedBuild-time composition

Don‘t touch the host system

Plugin Plugin

"How to make the host aware of the plugins?

"How to dynami-cally collect Spring beans of a given type?

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

SPI SPI SPI

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();

XML?Back in the days

(XML?)Back in the days

Probably not a big deal anymore

Easy access?

private List<MyPlugin> plugins;

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

public interface MyPlugin {void doSomething();

// 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?

PluginsSelection criterionCallback 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 exception) throws E;

List<T> getPluginsFor(S delimiter);…

private PluginRegistry<MyPlugin, String> plugins;

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

public interface MyPlugin extends Plugin<String> {void doSomething();

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 namespaceLazy-eval

Herahttp://hera.synyx.org

Apache 2.0Soon to be on GitHub

Spring Integration2

<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" />

Take-awaysKnow your dependencies

On every granularityStart as strict as possible

Get lenient where necessary

Thanks & creditsEoin Woods - Talk @ InfoQ

ResourcesSourcecode @ GitHub

Sonargraph

Whoops! Where did my architecture go?

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