Whoops! Where did my architecture go?

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

Oliver Gierke

© 2011 SpringOne 2GX 2011. All rights reserved. Do not distribute without permission.

Oliver Gierke

Spring Data
Core/JPA/MongoDB

ogierke@vmware.com
www.olivergierke.de
olivergierke


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


Roadmap
Architecture 101
A Java packages model
Hera


Architecture 101


Know your
dependencies


Granularity
Modules
Layers
Vertical slices
Subsystems


Granularity
Java ARchive
Package
Class


Of layers
and slices…


Slice A Slice B Slice C

Layer 1

Layer 2

Layer 3


Layers
Well understood
Known to developers
Less important to business


Slices
Hardly understood
New to developers
Key for business req


" How to implement
an architecture
inside a codebase?


Architecture
VS.
Codebase


" How to enforce
an architecture
inside a codebase?


Code analysis
JDepend
Sonar


Demo


Sonargraph
Formerly known as SonarJ


A plain Java
based approach


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


Layers ﬁrst
Leaks slice internals
Lower layers visible to everyone


" Start with less
packages and the
least visibility
possible…


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


Slices ﬁrst
Encapsulates business module
Internals understood anyway


Subsystems


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


" The smallest
plugin system
ever!


Host

SPI SPI SPI

Plugin Plugin


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


App

Plugin Plugin

Host


" 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


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

SPI SPI SPI

META-INF/spring/ META-INF/spring/
plugin-context.xml plugin-context.xml


@Component
public 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?


@Component

// 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?
}
}


Plugins
Selection criterion
Callback method
Let the implementation decide


Registry
Equipped 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);
…
}


@Component

private PluginRegistry<MyPlugin, String> plugins;

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

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


@Component
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());
}
}


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


Bells‘n‘whistles
FactoryBean
Spring namespace
Lazy-eval


Hera


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


Spring
Integration 2


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


Thanks & credits
Eoin Woods - Talk @ InfoQ


Resources
Sourcecode @ GitHub
Sonargraph


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