osgi best practices - amazon s3s3-eu-west-1.amazonaws.com/presentations2012/6_presentation.pdf ·...

OSGi Best Practices

Emily Jiang @IBM

Use OSGi in the correct way...

AGENDA

> Why OSGi?

> What is OSGi?

> How to best use OSGi?

emijiang@uk.ibm.com

> Jars have no modularization characteristics– No “jar scoped” access modifiers.– No means for a jar to declare its

dependencies.– No versioning.

JarJar

PackagePackage

ClassClassClassClass

ClassClass

PackagePackage

ClassClass

PackagePackage

ClassClass

Modularization in Java

Problems with Global Java ClassPath

Java VM

barcode4j

commons

ezmorph

freemarker

httpunit

jakarta

jpos18

jython

lucene

naming

resolver

serializer

servlets

tomcat

velocity

ws-commons

wsdl4j

xerces

xmlgraphics

xmlrpc

xmlapis

geronimo

guiapp

hhfacility

manufact.

marketing

minerva

accounting

assetmaint

catalina

common

content

datafile

ecommerce

entity

googlebase

widget

minilang

product

workeffort

workflow

sunjce_prov.

plugin

ClassNot

FoundException

BeginBeginHereHere

emijiang@uk.ibm.com

Problems with EARs/WARs

Enterprise Applications have isolated classpaths but…

> No Sharing

– Common libraries/frameworks in apps and memory

> Version conflicts

webA.war

WEB-INF/classes/servletA.class

WEB-INF/lib/spring.jar

WEB-INF/lib/commons-logging.jar

WEB-INF/lib/junit.jar…

webA.war

WEB-INF/classes/servletA.class

webB.war

WEB-INF/classes/servletB.class

webB.war

WEB-INF/classes/servletB.class

webC.war

WEB-INF/classes/servletC.class

webC.war

WEB-INF/classes/servletC.class

plankton.v1

plankton.v2

AGENDA

> Why OSGi?

> What is OSGi?

JarJar

What is OSGi?

“The dynamic module system for Java”> Mature 10-year old technology> Governed by OSGi Alliance: http://www.osgi.org> Used inside just about all Java-based middleware

– IBM WebSphere, Oracle WebLogic, Red Hat JBoss, Sun GlassFish, Paremus Service Fabric, Eclipse Platform, Apache Geronimo, (non-exhaustive list)http://www.osgi.org/wiki/uploads/News/2008_09_16_worldwide_market.pdf

Package

ClassClassClassClassClassClass

Package

ClassClassClassClassClassClassPackage

Package

Explicit exports

Explicit dependencies

23.05.12 emijiang@uk.ibm.com 9

OSGi Bundles and Class Loading

OSGi Bundle – A jar containing:Classes and resources.

OSGi Bundle manifest.

What’s in the manifest:Bundle-Version: Multiple versions of

bundles can live concurrently.

Import-Package: What packages from other bundles does this bundle depend upon?

Export-Package: What packages from this bundle are visible and reusable outside of the bundle?

Class LoadingEach bundle has its own loader.

No flat or monolithic classpath.

Class sharing and visibility decided by declarative dependencies, not by class loader hierarchies.

OSGi framework works out the dependencies including versions.

Manifest-Version: 1.0Bundle-ManifestVersion: 2Bundle-Name: MyService bundleBundle-SymbolicName: com.sample.myserviceBundle-Version: 1.0.0Bundle-Activator: com.sample.myservice.ActivatorImport-Package: com.something.i.need;version="1.1.2"Export-Package: com.myservice.api;version="1.0.0"

Bundle

OSGi Bundle

Bundles have a dynamic lifecycle

Can come and go independently

Bundle

• Service• An object associated with a list of classes (usually interfaces) it

provides• Dynamic (can come and go), framed by bundle lifecycle• Services are the primary means of collaboration between bundles.

OSGi Service Registry

AGENDA

> Why OSGi?

> What is OSGi?

BP1 - Use Import-Package not Require-Bundle Require-Bundle

– Tightly coupled with a particular bundle with the specified symbolic name and version

– High coupling between bundles

– Import all packages

– Bundle version management

• Import-Package

– Can wire to any bundles exporting the specified package

– Loose coupling between bundles

– Only import the package you need

– Package version management

MANIFEST.MF

Require-Bundle: com.ibm.ws.service;bundle-version=2.0.0

MANIFEST.MF

Require-Bundle: com.ibm.ws.service;bundle-version=2.0.0

MANIFEST.MF

Import-Package: com.ibm.ws.service.api;version=2.0.0

MANIFEST.MF

Import-Package: com.ibm.ws.service.api;version=2.0.0

BP2 - Avoid split packages

• Split package

– A package is exported by two bundles at the same version and the set of classes provided by each bundle differs.

• Why?

– Leads to the use of Require-Bundle, compromising the extent to which systems using the bundles can be extended and maintained.

• How?

– Keep all of the classes from any one package in a single bundle

BP2 - Split Package examples

org.hal.api 1.0.0

Implementation C

org.hal.a 1.0.0

Bundle C has to use 'Require-Bundle' to

ensure that it has classes from both parts of the API

Figure 1. Consumers of split packages need to use the Require-Bundle header

BP2 - Split Package examples

org.hal.api 1.0.0

Implementation C

org.hal.a 1.0.0

Figure 2. A complete package exported from a single bundle maintains high bundle cohesion

BP3 - Version bundles and packages

• What is semantic versioning?

– Uses a major.minor.micro.qualifier numbering scheme

• Major - Packages with versions that have different major parts are not compatible both for providers as well as consumers.

• Minor – API enhancement, e.g. adding methods to an API

• Micro – bug fixing

• Qualifier – identifier such as timestamp

• Example: 1.1.2.20101122am, 1.0.0, 2.0

– Changes in major: a binary incompatible, minor: enhanced API, micro: no API changes

• Why?

– Clients can protect themselves against API changes that might break them.

BP3 - Version bundles and packages examples

Figure 3: A client and an implementation can use either of two equivalently versioned packages

Implementation A

Imports:org.hal.a [1.0, 1.1)

org.hal.a 1.0.0

Client A

org.hal.a 1.1.0

org.hal.a 1.0.0

Client A

Client B

Implementation B

Implementation A

Figure 4: How a client and implementation are affected differently by a minor API version change

BP3 - Version bundles and packages examples

Figure 5. How clients and implementations are similarly affected by a major API version change

org.hal.a 1.0.0

org.hal.a 2.0.0

Client A

Client B

Implementation B

Implementation A

BP4 - Separate API from Implementations

• Why?

– Great flexibility

– Many implementation bundles → enable more services provided

– Reduce package dependencies → reduce circular dependencies

• How?

– Put API classes in one bundle

– Put implementation classes in a separate bundle

BP4 - Separate API and implementation examples

Figure 6. Badly designed provider bundle where the API and implementation classes are in the same bundle

API + Implementation

org.hal.myapi

org.hal.a.impl

Client

org.hal.b.client

Both API and implementation packages

imported by client

BP5 - Share services not implementations

• Use the OSGi service registry to construct instances

• Why?

– Able to obtain an instance of an implementation without knowing which one

– Achieve a loosely coupling of client, API and implementation

• How?

– Register an instance of the API interface in the OSGi service registry

– Register an implementation of the OSGi ServiceFactory interface in the OSGi service registry.

BP4 & 5 - examples

org.hal.myapi

Client

org.hal.b.client

API and implementation packages in different bundles

but still imported by client

Implementation

org.hal.a.impl

Figure 7. Badly designed provider bundles where the API and implementation classes have been separated

BP4 & 5 - examples

org.hal.myapi

Client

org.hal.b.client

Client and implementation in separate bundles, both import API. Client uses implementation through a service

defined by the API.

Implementation

org.hal.a.impl

Figure 8: Well designed provider bundles where the API and implementation classes have been separated

Using services can be hard!

@Override

public void serviceChanged(ServiceEvent event)

ServiceReference ref = event.getServiceReference();

if (ls.get() == null && event.getType() == ServiceEvent.REGISTERED) {

ls.set((LogService) ctx.getService(ref));

} else if (ls.get() != null && event.getType() == ServiceEvent.UNREGISTERING &&

ref == lr.get()) {

ref = ctx.getServiceReference(LogService.class.getName());

if (ref != null) {

lr.set(ref);

private BundleContext ctx;

private AtomicReference<LogService> ls = new AtomicReference<LogService>();

private AtomicReference<ServiceReference> lr = new AtomicReference<ServiceReference>();

public void start(BundleContext ctx) throws InvalidSyntaxException

this.ctx = ctx;

ctx.addServiceListener(this, "(objectClass=org.osgi.service.log.LogService)");

ServiceReference ref = ctx.getServiceReference(LogService.class.getName());

if (ref != null) {

lr.set(ref);

BP6 - Use Blueprint

• Specifies a Dependency Injection container, standardizing established Spring conventions

• Configuration and dependencies declared in XML “module blueprint”, which is a standardization of Spring “application context” XML.

– Extended for OSGi: publishes and consumes components as OSGi services• Simplifies unit test outside either Java EE or OSGi r/t.• The Blueprint DI container can be a part of the server runtime

(compared to the Spring container which is part of the application.)

dependencies injected

publishesservice consumes

service

A static assembly and configuration of

components (POJOs)Blueprint bundle

OSGI-INF/blueprint/blueprint.xml

BP6 - Blueprint service-bundle examples

public interface BillingService {void bill(Order o);

Billing

<blueprint> <service ref=”service” interface =

”org.example.bill.BillingService” /> <bean id=”service” scope=”prototype”

class=”org.example.bill.impl.BillingServiceImpl” /></blueprint>

Billing service bundle

-“prototype” scope indicates a new instance is created by the container for each use.-“singleton” scope is the default.

BP6- Blueprint client-bundle examples

public class ShopImpl {

private BillingService billingService;void setBillingService(BillingService srv) {

billingService = srv;}

void process(Order o) {billingService.bill(o);}

e-Commerce

<blueprint> <bean id=”shop” class=”org.example.ecomm.ShopImpl”> <property name=”billingService” ref=”billingService” /> </bean> <reference id=”billingService”

interface=”org.example.bill.BillingService” /></blueprint>

e-Commerce bundle

-injected service reference-service can change over time-can be temporarily absent without the bundle caring-managed by Blueprint container

BP7 – Make Bundles Loosely Coupled & Highly Cohesive

'Hairball' effect – one bundle has many package

dependencies

org.hal.log.impl

Implementation

org.hal.log.impl

SomeotherAPI

TransactionsAPI

FileSystemAPI

JPAAPI

org.hal.log.api org.hal.fslog.impl

Figure 9. Poorly purposed system where a single bundle provides multiple implementations of the same API

BP7 – Make Bundles Loosely Coupled & Highly Cohesive

Implementation

org.hal.DBlog.impl

org.hal.log.api

Implementation

org.hal.fslog.impl

FileSystemAPI

Implementation

org.hal.DBlog.impl

Implementation

org.hal.DBlog.impl

Figure 10. A well purposed system where each implementation of an API is provided by a separate bundle

Summary – OSGi Best Practices

> BP1 - Use Import-Package instead of Require-Bundle

> BP2 - Avoid split packages

> BP3 - Version bundles and packages

> BP4 - Separate API from implementations

> BP5 - Share services not implementations

> BP6 - Use Blueprint

> BP7 - Make bundles loosely coupled & highly cohesive

Quiz – What best practices are used?

BloggingService

BlogPersistence

Serviceblog-servlet

Web application bundle

META-INF/persistence.xml

WEB-INF/

web.xml OSGI-INF/blueprint/blueprint.xml

OSGI-INF/blueprint/blueprint.xml

JNDI EM

blog-persistence

blog-api

Questions?

Additional References

OSGi Best Practiceswww.ibm.com/developerworks/websphere/techjournal/1007_charters/1007_charters.html

Enterprise OSGi YouTube Channel: www.youtube.com/user/EnterpriseOSGi

Contact: emijiang@uk.ibm.com

IBM, the IBM logo, and ibm.com are trademarks or registered trademarks of International Business Machines Corp., registered in many jurisdictions worldwide. Other product and service names might be trademarks of IBM or other companies. A current list of IBM trademarks is available on the Web at “Copyright and trademark information” at www.ibm.com/legal/copytrade.shtml.

Copyright and Trademarks

osgi best practices - amazon s3s3-eu-west-1.amazonaws.com/presentations2012/6_presentation.pdf ·...

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