Modular Web Applications with OSGi

Modular Web Applications
with OSGi
eJUG Seminar Sam Brannen
Linz, Austria Software Consultant
17 September 2009

Speaker Profile
  Software Consultant
  Spring Framework Core Developer
  Previous SpringSource dm Server™ developer: OSGi-
enabled Web deployment models, Tomcat integration,
Test Framework

  Java developer with 10+ years' experience
  Regular speaker at conferences on Spring, dm Server,
Java, OSGi, and testing

  Co-author of Spring in a Nutshell; chief technical
reviewer for Spring Recipes

Copyright 2008-2009 Sam Brannen and SpringSource. Copying, publishing or distributing without express written permission is prohibited.
2

Overview
The Challenge?
Monolithic WAR deployments hinder both
development and runtime modularity and promote
library bloat.

The Solution!
Harness the flexibility of the OSGi Web Container
standard, Spring, Spring-DM, and the SpringSource
dm Server™.

3

Agenda
  Status Quo
  OSGi
  Spring DM
  OSGi Web Container
  SpringSource dm Server™
  Demos
  Q&A

4

Status Quo

5

Standard Java EE WAR
  Java Servlet 2.5
  WAR format
  Static content
  Dynamic content
  WEB-INF
  WEB-INF/classes
  WEB-INF/lib

  All-in-one deployment model
  EAR
  Container shared libraries

6

Introduction to Demos
 Spring MVC 2.5 based "Hello World" web application
 Domain model: HelloMessage
 Service layer: HelloService, HelloServiceImpl
 Presentation layer:
  Controllers: HelloController
  Views: JSP + JSTL

7

DEMO

Standard WAR

8

OSGi

9

It's a module system
  Partition a system into a number of modules –
“bundles”
  Dynamic: bundles can be installed, started, stopped,
uninstalled and updated ... at runtime!
  Strict visibility rules
  Resolution process satisfies dependencies of a
module
  Versioning
  Packages & Services
  Deploy multiple versions of a module
10

It's even service-oriented
  Bundles can publish services… dynamically!

  Service Registry allows other bundles to consume
services

  Services come and go at runtime
  … transparently when using Spring-DM

11

OSGi Bundle
  The fundamental unit of deployment and
modularity in OSGi
  Just a JAR file
  with additional entries in META-INF/MANIFEST.MF
  Common manifest headers:
  Bundle-SymbolicName
  Bundle-Version
  Bundle-Name
  Bundle-ManifestVersion
  Export-Package
  Import-Package

12

Export & Import Packages
Declare package-level visibility and dependencies of
your bundle.

Export-Package: com.xyz.bar
Export-Package: com.xyz.bar;version="1.0.5"
Import-Package: com.xyz.foo
>= 1.0.3; e.g.,
Import-Package: 1.0.3, 1.0.3.GA,
com.xyz.foo;version="1.0.3" 1.0.4, 2.0, etc.
Import-Package:
com.xyz.foo;version="[1.0.3,1.0.3]"
Import-Package:
com.xyz.foo;version="[1.0.3,1.1.0)",
com.xyz.bar;version="[1.0.3,2.0.0)"
13

Publish a Service

ServiceRegistration reg =
bundleContext.registerService(
Bar.class.getName(), myBarService);
...
reg.unregister();

14

Consume a Service
ServiceReference ref =

bundleContext.getServiceReference(
Bar.class.getName());
Bar bar = (Bar)
bundleContext.getService(ref);
...
bundleContext.ungetService(ref);
// bar should no longer be used here

Complex… Potential resource leaks!
15

Implementations & Tools
  OSGi implementations:
  Equinox
  Knopflerfish
  Felix
  IDEs
  Eclipse PDE
  SpringSource Tool Suite

  Build support:
  BND
  Bundlor

16

Spring DM

17

Spring-DM: App. Context
  Configuration files in /META-INF/spring
  Automatically merged
  ..and an ApplicationContext is created
  one per Bundle

  Spring-DM manages the ApplicationContext lifecycle
  OSGi manages the Bundle lifecycle

18

Spring-DM: Service Registry
Contrast with programmatic
<beans ...> API
<osgi:service ref="customerDAO"

interface="dao.CustomerDAO" />

<osgi:reference id="dataSource"

interface="javax.sql.DataSource" />

</beans>

Also supports filters, listeners, collections (lists and sets), etc.

19

Spring-DM: Service Registry
  Dynamic services handled automatically
  Instances and collections are proxied
  Method calls are buffered
  Configurable timeouts
  Purely declarative
  Application code is typically decoupled from OSGi
  Spring’s POJO programming model
  Testable, out-of-container

20

Out-of-scope for Spring-DM
  Easy import of bundles and libraries
  Using JPA or Hibernate in OSGi
  Seamless Web support
  Notion of an application

  Enter:
  OSGi Web Container
  SpringSource dm Server

21

OSGi Web Container

22

Web Bundle
  RFC 66: OSGi Web Container specification
  Reference implementation by SpringSource
  Web Bundle = web application in OSGi
  Multiple supported formats
  Standard WAR
  Shared Libraries WAR
  Shared Services WAR
  Context path defined via query parameter or in
manifest:
  Web-ContextPath: /my-web-app

23

OSGi Web Migration Path
  Status quo: everything in a
monolithic WAR

  Goals:
  Libraries: eradicate library bloat
  Services: OSGi Service Registry

  Results: decrease overall
footprint

24

Standard Java EE WAR
 Supported as is
 The WAR file is transformed into an OSGi bundle and
installed into the Servlet Container

 All standard WAR contracts are honored
 Easy on-ramp for web applications in OSGi

25

Shared Libraries WAR
 Eradicate the library bloat of monolithic Java EE WARs
 Declare dependencies via OSGi manifest headers
•  Import-Package & Require-Bundle
•  Import-Library & Import-Bundle Import-Package

 Reduce application deployment footprint
 SpringSource Enterprise Bundle Repository: central
source for OSGi bundles

26

DEMO

Shared Libraries WAR

27

Shared Services WAR
 Share services between bundles and web applications
 Spring-DM simplifies usage of the OSGi Service Registry
  Publish services via <osgi:service … />
  Consume them via <osgi:reference … />

• ServerOsgiBundleXmlWebApplicationContext: use as
contextClass property for ContextLoaderListener and
DispatcherServlet
 Program to interfaces and decouple web artifacts from the
domain model, services, infrastructure, etc.

28

DEMO

Shared Services WAR

29

SpringSource dm Server™

30

dm Server Architecture
 Built on Equinox
 Modular architecture
 Subsystems
 Bundles
 Small footprint
 Modular profiles
 Bundle repository
 Library provisioning
 Serviceability
 FFDC
 Logging
 Tracing
31

Import: Library & Bundle
  Plain OSGi + …
  Import-Library and Import-Bundle
  Library imports  bundle imports
  Bundle imports  package imports
  OSGi runtime semantics remain the same

Import-Library: org.springframework.spring;
version="[2.5.6,3.0)"

Import-Bundle: com.springsource.org.hibernate;
version="[3.2.6.ga,3.2.6.ga]"

32

PAR
  Packaging format for all
modules in an app.
  JAR with Application-*
manifest headers
  Single unit: deploy, refresh,
undeploy
  Application boundaries
  Scoping of types / services
  DataSource does not leak out of
the application
  Hibernate can change domain
objects

33

DEMO

PAR

34

Plan
  Conceptually similar to the PAR format:
  Defines all modules within an application
  Single configuration for deployment, etc.
  Application boundaries
  Scoping of types / services

  Differences:
  Plan = XML file with „.plan“ extension
  Application modules are referenced within XML
  Modules are installed stand-alone in the repository
  Control deployment order of modules
  Share modules between plans
  Configure scoping and atomicity

35

Slices
  Slice = mechanism for extending a host web bundle
  Goes beyond mere code
  Slices can provide code and content to a host
  Slices can use content and services from a host
  Analogous to OSGi fragments, slices attach to a host
web bundle:
  Slice-Host: hello.war.host;version="[1.0,2.0)”
  Slice-ContextPath: /de
  Host interacts with slices via slices tag library
  Slices provide configuration properties to host

36

DEMO

Slices

37

Closing

38

Further Resources
  OSGi:
http://osgi.org
  Spring Framework:
http://springframework.org
  Spring-DM:
http://springframework.org/osgi
  SpringSource dm Server:
http://springframework.org/dmserver
  SpringSource Team Blog:
http://blog.springsource.com
  German Getting Started:
http://www.dpunkt.de/buecher/3231.html

39

Q&A

Sam Brannen

sam [at] sambrannen [dot] com

http://SamBrannen.com

http://twitter.com/sam_brannen

40

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