best practices for enterprise osgi applications - emily jiang
TRANSCRIPT
© 2010 IBM Corporation
OSGi Application Best Practices
Emily Jiang, [email protected]
WebSphere Application Server OSGi Developer, Apache Aries Committer
© 2011 IBM Corporation
2
AGENDA
> Why OSGi?
> What is OSGi?
> How to best use OSGi?
© 2011 IBM CorporationIBM ConfidentialOctober 18, 2012
33
> Jars have no modularization characteristics– No “jar scoped” access modifiers.– No means for a jar to declare its
dependencies.– No versioning.
JarJar
PackagePackage
ClassClassClassClassClassClass
PackagePackage
ClassClassClassClassClassClass
PackagePackage
ClassClassClassClassClassClass
Modularization in Java
4
Problems with Global Java ClassPath
J a va V M
lo g 4 j
ba rc o de 4 j
a xis
ba t ik
c o m m o ns
de rby
fo p
e zm o rph
fre e m a rke r
httpunit
ja ka rta
jc l
js o n
jdbm
jdo m
je nks
jpo s 1 8
jytho n
lo o ks
luc e ne
m a il
m x4 j
na m ing
je tty
po i
re s o lve r
ro m e
s e ria lize r
s e rv le ts
to m c a t
ve lo c ity
w s -c o m m o ns
xa la n
w s dl4 j
xe rc e s
xm lg ra phic s
xm lrpc
xm la pis
..
g e ro nim o
bs h
bs f
g uia pp
hhfa c ility
m a nufa c t .
m a rke ting
m ine rva
a c c o unting
a s s e tm a int
ba s e
bi
c a ta lina
c o m m o n
o a g is
o rde r
e ba y
c o nte nt
da ta file
e c o m m e rc e
e ntity
g o o g le b a s e
o fbiz
w idg e t
m inila ng
pa rty
po s .
pro duc t
w o rke ffo rt
w o rkflo w
…
s unjc e _pro v.
plug in
js s e
jc e
rt
dns ns
..
…C la s s
N o tF o und
E xc e ptio n
B e g inB e g inHe reHe re
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…webB.war
WEB-INF/classes/servletB.class
WEB-INF/lib/spring.jar
WEB-INF/lib/commons-logging.jar
WEB-INF/lib/junit.jar…webC.war
WEB-INF/classes/servletC.class
WEB-INF/lib/spring.jar
WEB-INF/lib/commons-logging.jar
WEB-INF/lib/junit.jar…
plankton.v1
plankton.v2
AGENDA
> Why OSGi?
> What is OSGi?
> How to best use OSGi?
© 2011 IBM Corporation7
JarJar
77
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
ClassClassClassClassClassClassPackage
ClassClassClassClassClassClass
ClassClassClassClassClassClass
Explicit exports
Explicit dependencies
8 31/10/12
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
9
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.
S
OSGi Service Registry
AGENDA
> Why OSGi?
> What is OSGi?
> How to best use OSGi?
12 31 October 2012
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
...
Import-Package: com.ibm.ws.service.api;version=2.0.0
13 31 October 2012
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
14 31 October 2012
BP2 - Split Package examples
API A
org.hal.api 1.0.0
API B
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
15 31 October 2012
BP2 - Split Package examples
API A
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
16 31 October 2012
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
– 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.
17 31 October 2012
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)
API A
org.hal.a 1.0.0
API Borg.hal.a 1.0.0
Client A
Imports:org.hal.a [1.0, 2.0)
API Borg.hal.a 1.1.0
API A
org.hal.a 1.0.0
Client A
Imports:org.hal.a [1.0, 2.0)
Client B
Imports:org.hal.a [1.1, 2.0)
Implementation B
Imports:org.hal.a [1.1, 1.2)
Implementation A
Imports:org.hal.a [1.0, 1.1)
Figure 4: How a client and implementation are affected differently by a minor API version change
18 31 October 2012
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
API B
Client A
Imports:org.hal.a [1.0, 2.0)
Client B
Imports:org.hal.a [2.0, 3.0)
Implementation B
Imports:org.hal.a [2.0, 2.1)
Implementation A
Imports:org.hal.a [1.0, 1.1)
API A
19 31 October 2012
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
20 31 October 2012
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
21 31 October 2012
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.
s
22 31 October 2012
BP4 & 5 - examples
API
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
23 31 October 2012
BP4 & 5 - examples
API
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
24 31 October 2012
BP6 – Make Bundles Loosely Coupled & Highly Cohesive
'Hairball' effect – one bundle has many package
dependencies
org.hal.log.impl
Implementation
org.hal.log.impl
SomeotherAPI
DBAPI
TransactionsAPI
FileSystemAPI
JPAAPI
API
org.hal.log.api org.hal.fslog.impl
Figure 9. Poorly purposed system where a single bundle provides multiple implementations of the same API
25 31 October 2012
BP6 – Make Bundles Loosely Coupled & Highly Cohesive
Implementation
org.hal.DBlog.implDBAPI
API
org.hal.log.api
Implementation
org.hal.fslog.impl
FileSystemAPI
Implementation
org.hal.DBlog.impl
DBAPI
Implementation
org.hal.DBlog.impl
DBAPI
Figure 10. A well purposed system where each implementation of an API is provided by a separate bundle
26 31 October 2012
Using services can be hard!
@Overridepublic 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) {ls.set((LogService) ctx.getService(ref));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) {ls.set((LogService) ctx.getService(ref));lr.set(ref);}}
27 31 October 2012
BP7 - 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 is a part of the server runtime (compared
to the Spring container which is part of the application.)
dependencies injectedpublishesservice consumes
service
A static assembly and configuration of
components (POJOs)Blueprint bundle
OSGI-INF/blueprint/blueprint.xml
28 31 October 2012
BP7 - 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.
29 31 October 2012
BP7- 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
30 31 October 2012
OSGi Application 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 – Make bundles loosely coupled & highly cohesive– BP7 - Use Blueprint
Summary
31
Quiz – What best practices are used?
BloggingService Blog
PersistenceService
blog-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
blog-persistence
blog-api
32 31 October 2012
Questions?