1. Distributed system examples
Commercial middleware
J2EE Overview
.NET Overview
Web services: where middleware systems meet
Web service from Open Source middleware
11/22/2018
Distributed Systems - Comp 655

2. Distributed Systems - Comp 655
Java EE Overview
The problem Java EE attempts to solve: maximize the use of Java technologies by providing a suite of Java technology specifications that is
Integrated
Suitable for enterprise applications
Widely available
Includes all of the basic middleware capabilities for building distributed systems
11/22/2018
Distributed Systems - Comp 655

3. Enterprise applications require
High throughput
Load balancing
Efficient communications
High availability
Highly reliable communications
Persistent, asynchronous communication option
Distributed transactions
High security
Ability to interoperate with whatever
Structured naming with de-centralized administration
11/22/2018
Distributed Systems - Comp 655

4. Distributed Systems - Comp 655
Trademarks etc
Java, J2EE, J2SE, J2ME, and all Java-based marks are trademarks or registered trademarks of Sun Microsystems, Inc. in the United States and other countries.
Graphics on pages 3, 4, 5 Copyright © Sun Microsystems, Inc. All Rights Reserved.
11/22/2018
Distributed Systems - Comp 655

5. Distributed Systems - Comp 655
The 3 Cs of Java EE
Components
Containers
Connectors
11/22/2018
Distributed Systems - Comp 655

6. Distributed Systems - Comp 655
J2EE Overview
11/22/2018
Distributed Systems - Comp 655

7. Distributed Systems - Comp 655
J2EE Structure
11/22/2018
Distributed Systems - Comp 655

8. Key middleware services
Communication: RMI-IIOP, JMS
Naming: JNDI (part of Java SE)
Persistence: JPA, JDBC, JDO
Transactions: JTA, JTS
Security: (next page)
11/22/2018
Distributed Systems - Comp 655

9. Java SE v1.4 Security Features
JAAS – Java Authentication and Authorization Service
JCE – Java Cryptography Extension
JSSE – Java Secure Socket Extension
Java GSS-API – Kerberos V5 secure communications
Java Certification Path API
11/22/2018
Distributed Systems - Comp 655

10. Java EE for web services
Java Architecture for XML Binding (JAXB)
Java API for RESTful Services (JAX-RS)
Java API for XML-Based Web Services (JAX-WS)
SOAP with Attachments API for Java (SAAJ)
Java API for XML Messaging (JAXM)
Java API for XML Processing (JAXP)
Java API for XML Registries (JAXR)
Java API for XML-Based Remote Procedure Call (JAX-RPC)
Two leading registry standards: ebXML Registry and Repository standard, UDDI (Universal Description, Discovery, and Integration)
SOAP was originally part of JAXM
11/22/2018
Distributed Systems - Comp 655

11. Distributed Systems - Comp 655
Enterprise Java Beans
Session beans
Represent business processes and data about an interaction with a client
Two types:
Stateless
Stateful
Entity beans (FROZEN at EJB 2.5)
Represent persistent data and data integrity rules
Two types of persistence:
Container-managed persistence
Bean-managed persistence
11/22/2018
Distributed Systems - Comp 655

12. Distributed Systems - Comp 655
Invoking an EJB method
EJB Container
Home
Object 3
Request new EJB object 5
Return EJB object reference
Client
EJB
Object 4
Create EJB object 6
Invoke method
JNDI
NS, eg
LDAP
Request home object 1 2
Return home object reference 7
Delegate request to enterprise bean(s)
Enterprise
Bean(s)
11/22/2018
Distributed Systems - Comp 655

13. Distributed Systems - Comp 655
A familiar look to it …
11/22/2018
Distributed Systems - Comp 655

14. Distributed Systems - Comp 655
Message-driven beans
MDB are stateless beans that
Listen for and handle JMS messages
Participate in transactions if necessary
MDB have no
Home interface
Remote interface
Interfaces directly callable by clients (clients just send messages)
An MDB tutorial
An MDB article
11/22/2018
Distributed Systems - Comp 655

15. If you remember one thing
Enterprise beans are
Single-threaded
Ignorant of security
Ignorant of transactions
Ignorant of networking
The container handles all that
Containers tend to be pricey
11/22/2018
Distributed Systems - Comp 655

16. Leading EJB containers
Oracle/BEA Weblogic
IBM Websphere
JBoss (open source)
GlassFish (open source)
Geronimo (open source)
11/22/2018
Distributed Systems - Comp 655

17. Deployment descriptors
Deferred binding for many of the things the bean developer need not worry about, including
Access control
Transaction requirements
Persistence parameters
Type of bean
Classes used for home and remote interfaces
11/22/2018
Distributed Systems - Comp 655

18. Deployment descriptor example
<?xml version="1.0" encoding="ISO "?>
<!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Enterprise
JavaBeans 2.0//EN" "
<ejb-jar>
<description>Deployment descriptor for the samplemdb JOnAS example</description>
<display-name>samplemdb example</display-name>
<enterprise-beans>
<message-driven>
<description>Describe here the message driven bean Mdb</description>
<display-name>Message Driven Bean Mdb</display-name>
<ejb-name>Mdb</ejb-name>
<ejb-class>samplemdb.MdbBean</ejb-class>
<transaction-type>Container</transaction-type>
<acknowledge-mode>Auto-acknowledge</acknowledge-mode>
<message-driven-destination>
<destination-type>javax.jms.Topic</destination-type>
<subscription-durability>NonDurable</subscription-durability>
</message-driven-destination>
</message-driven>
</enterprise-beans>
<assembly-descriptor>
<container-transaction>
<method>
<method-name>*</method-name>
</method>
<trans-attribute>Required</trans-attribute>
</container-transaction>
</assembly-descriptor>
</ejb-jar>
11/22/2018
Distributed Systems - Comp 655

19. Distributed Systems - Comp 655
Java EE 5
Replaces the well-established “J2EE” with a similar but less-pronounceable name 
Emphasis: make enterprise development easier
EJB 3
Web services
Persistence
Dependency injection
Summary of changes
11/22/2018
Distributed Systems - Comp 655

20. Distributed Systems - Comp 655
EJB 3
Developer does not have to implement EJB interfaces
EJB interface implementations inferred from annotations (for
In many cases, explicit deployment descriptors are not needed
In many cases, deployment information can be inferred from annotations (for
Enterprise beans frozen at version 2.5, replaced by Java Persistence API (JPA), based on Hibernate
11/22/2018
Distributed Systems - Comp 655

21. Distributed Systems - Comp 655
EJB 3, continued
In many cases, explicit JNDI lookups are not necessary
In many cases, system can infer the required lookup from annotations (for
11/22/2018
Distributed Systems - Comp 655

22. Distributed Systems - Comp 655
EJB roles
Source: Mastering Enterprise JavaBeans, Second Edition, by Ed Roman, Scott Ambler, and Tyler Jewell
11/22/2018
Distributed Systems - Comp 655

23. Web sites (3 of thousands)
Sun’s J2EE site:
Mastering EJB 3.0 (downloadable)
EJB design patterns (downloadable)
J2EE Architect’s Handbook (downloadable)
11/22/2018
Distributed Systems - Comp 655

24. Dissent: Spring framework
Java EE should be easier to use
It's best to program to interfaces, rather than classes. Spring reduces the complexity cost of using interfaces to zero.
JavaBeans offer a great way of configuring applications.
OO design is more important than any implementation technology, such as Java EE.
Checked exceptions are overused in Java. A framework shouldn't force you to catch exceptions you're unlikely to be able to recover from.
Testability is essential, and a framework such as Spring should help make your code easier to test.
Our philosophy is summarized in Expert One-on-One J2EE Design and Development by Rod Johnson.
11/22/2018
Distributed Systems - Comp 655

25. Spring’s positive goals
Spring should be a pleasure to use
Your application code should not depend on Spring APIs
Spring should not compete with good existing solutions, but should foster integration.
(For example, JDO, Toplink, and Hibernate are great O/R mapping solutions. We don't need to develop another one.)
11/22/2018
Distributed Systems - Comp 655

26. Distributed Systems - Comp 655
Coming soon: Java EE 6
Defined by JSR 316
Adds
JAX-RS (JSR 311)
Web Beans (JSR 299)
Java Authentication SPI for containers (JSR 196)
Removes
EJB Container-managed persistence
JAX-RPC
And other changes
Approved over a variety of concerns and objections
11/22/2018
Distributed Systems - Comp 655

27. Distributed Systems - Comp 655
.NET Overview
The problem .NET tries to solve: maximize the sale of server-side licenses by providing a suite of Windows technologies that is
Integrated
Suitable for enterprise applications
Includes all of the basic capabilities for building distributed systems
Of course, Microsoft’s strategy for selling lots of server-side licenses includes other initiatives like Visual Studio.NET and the security turnaround
11/22/2018
Distributed Systems - Comp 655

28. Distributed Systems - Comp 655
.NET concepts
What does it mean for an application to be “written in XML” ?
11/22/2018
Distributed Systems - Comp 655

29. Distributed Systems - Comp 655
.NET block picture
11/22/2018
Distributed Systems - Comp 655

30. .NET programming languages
11/22/2018
Distributed Systems - Comp 655

31. Key middleware services (.NET)
Communication: SOAP, http, ORPC
Naming: URI, DNS, COM+ Catalog, Windows Registry
Persistence: ADO, OLE-DB
Transactions: MTS
Security: SSL, Kerberos, NTLM
ORPC is DCE RPC with COM-specific enhancements
Older technologies (registry, ntlm) will probably continue to be important behind firewalls for some time
11/22/2018
Distributed Systems - Comp 655

32. Distributed Systems - Comp 655
RPC in .NET
11/22/2018
Distributed Systems - Comp 655

33. RPC with SOAP Extension in .NET
Intercepting inbound requests and outbound responses should look familiar to Summer 03 people …
11/22/2018
Distributed Systems - Comp 655

34. Distributed Systems - Comp 655
J2EE vs .NET
Microsoft says:
.NET is faster
You write less code and easier code with .NET
Sun says:
.NET is a closed system
.NET is immature
.NET lacks community
java.sun.com/features/2002/07/rimapatel.html
(NOTE: this is getting old) (Java in grade school?)
11/22/2018
Distributed Systems - Comp 655

35. Distributed Systems - Comp 655
J2EE vs .Net continued
IBM says
Only 26% of mid-market companies have Windows only
.Net locks you into Windows
Microsoft competes with its partners
Our WebSphere-based J2EE platform is cheaper than a comparable server-side .Net platform
Read all about it
Of course, Microsoft might dispute IBM’s idea of what constitutes a “comparable” .Net platform
11/22/2018
Distributed Systems - Comp 655

36. Distributed Systems - Comp 655
Web Services
Where middleware systems meet
The idea: allow clients to find and interact with services over the web without regard to how the clients or services are built
How do you do that? With standards …
This is a MAJOR industry bandwagon, as you probably know
Recall from week 1 the importance of standards for open systems
REST (Representational State Transfer) is a class of interaction techniques that is well supported by the web already. REST advocates claim that the web already has everything you need for commerce. Web service advocates respond that with REST you are always building services from scratch, and it’s too hard to set up programmatic interaction.
11/22/2018
Distributed Systems - Comp 655

37. Distributed Systems - Comp 655
SOAP overview
Protocols include HTTP, SMTP, TCP, MSMQ, …
What’s the difference between RPC and request/
response?
11/22/2018
Distributed Systems - Comp 655

38. Distributed Systems - Comp 655
SOAP intermediaries
11/22/2018
Distributed Systems - Comp 655

39. Distributed Systems - Comp 655
SOAP is (v1.2)
SOAP is a lightweight protocol intended for exchanging structured information in a decentralized, distributed environment. SOAP uses XML technologies to define an extensible messaging framework, which provides a message construct that can be exchanged over a variety of underlying protocols. The framework has been designed to be independent of any particular programming model and other implementation specific semantics.
msdn.microsoft.com/library/default.asp?
url=/library/en-us/dnsoap/html/understandsoap.asp
11/22/2018
Distributed Systems - Comp 655

40. SOAP message structure
<soap:Envelope
xmlns:soap="
<soap:Header> <!-- optional -->
<!-- header blocks go here... -->
</soap:Header>
<soap:Body>
<!-- payload or Fault element goes here... -->
</soap:Body>
</soap:Envelope>
11/22/2018
Distributed Systems - Comp 655

41. Distributed Systems - Comp 655
SOAP message example
<soap:Envelope
xmlns:soap="
<soap:Body>
<x:TransferFunds xmlns:x="urn:examples-org:banking">
<from> </from>
<to> </to>
<amount>100.00</amount>
</x:TransferFunds>
</soap:Body>
</soap:Envelope>
11/22/2018
Distributed Systems - Comp 655

42. SOAP response message example
<soap:Envelope
xmlns:soap="
<soap:Body>
<x:TransferFundsResponse
xmlns:x="urn:examples-org:banking">
<balances>
<account>
<id> </id>
<balance>33.45</balance>
</account>
<id> </id>
<balance>932.73</balance>
</balances>
</x:TransferFundsResponse>
</soap:Body>
</soap:Envelope>
11/22/2018
Distributed Systems - Comp 655

43. SOAP error message example
<soap:Envelope
xmlns:soap="
<soap:Body>
<soap:Fault>
<faultcode>soap:Server</faultcode>
<faultstring>Insufficient funds</faultstring>
<detail>
<x:TransferError xmlns:x="urn:examples-org:banking">
<sourceAccount> </sourceAccount>
<transferAmount>100.00</transferAmount>
<currentBalance>89.23</currentBalance>
</x:TransferError>
</detail>
</x:TransferFunds>
</soap:Body>
</soap:Envelope>
11/22/2018
Distributed Systems - Comp 655

44. SOAP extensibility example
<soap:Envelope
xmlns:soap="
<soap:Header>
<!-- security credentials -->
<s:credentials xmlns:s="urn:examples-org:security">
<username>dave</username>
<password>evad</password>
</s:credentials>
</soap:Header>
<soap:Body>
<x:TransferFunds xmlns:x="urn:examples-org:banking">
<from> </from>
<to> </to>
<amount>100.00</amount>
</x:TransferFunds>
</soap:Body>
</soap:Envelope>
11/22/2018
Distributed Systems - Comp 655

45. Distributed Systems - Comp 655
Must-understand
<soap:Envelope
xmlns:soap="
<soap:Header>
<!-- security credentials -->
<s:credentials xmlns:s="urn:examples-org:security"
soap:mustUnderstand="1"
>
<username>dave</username>
<password>evad</password>
</s:credentials>
</soap:Header>
...
11/22/2018
Distributed Systems - Comp 655

46. Distributed Systems - Comp 655
SOAP in HTTP
11/22/2018
Distributed Systems - Comp 655

47. Distributed Systems - Comp 655
SOAP in context
SOAP is an extensible way to encode requests and responses in XML
WSDL (Web Services Description Language) is a way to describe the requests and responses a web service uses
UDDI (Universal Description, Discovery and Integration) is a way of locating web services
11/22/2018
Distributed Systems - Comp 655

48. Distributed Systems - Comp 655
WSDL
WSDL is an XML format for describing network services as a set of endpoints operating on messages containing either document-oriented or procedure-oriented information.
Protocol bindings described: SOAP 1.1, HTTP GET/POST, MIME
11/22/2018
Distributed Systems - Comp 655

49. Distributed Systems - Comp 655
UDDI
UDDI enables a business to
describe its business and its services
discover other businesses that offer desired services
integrate with these other businesses.
11/22/2018
Distributed Systems - Comp 655

50. Distributed Systems - Comp 655
Dissent: REST
REST's proponents: the Web’s scalability and growth result directly from a few key design principles:
Application state and functionality are divided into resources
Every resource is uniquely addressable using a universal syntax for use in hypermedia links
All resources share a uniform interface for the transfer of state between client and resource:
Constrained set of well-defined operations
Constrained set of content types, optionally supporting code-on-demand
A protocol that is:
Client/Server
Stateless
Cacheable
Layered
11/22/2018
Distributed Systems - Comp 655

51. Distributed Systems - Comp 655
REST resources
The previous slide came from Wikipedia’s article
JAX-RS
Roy Fielding’s dissertation started the “movement”
Del.icio.us is a well-known (almost) example
Joe Gregorio on REST and WS-*
RESTful Web Services book
11/22/2018
Distributed Systems - Comp 655

52. Web service from open source
Two authors from HP
Chris Peltz
Claire Rogers
Goal: set up a weather-forecast web service on a laptop, using all Open Source infrastructure
11/22/2018
Distributed Systems - Comp 655

53. Distributed Systems - Comp 655
Decisions, decisions …
Linux distribution
DBMS
Programming language
Java runtime
Java IDE
Web container
Web service container
Build environment
Testing
11/22/2018
Distributed Systems - Comp 655

54. Distributed Systems - Comp 655
Linux distribution
RedHat – closes the gap between Windows and Unix, good for Linux novices
SuSE – good for existing Windows users
Debian – used by well-seasoned Linux developers [selected]
They also liked GNOME
11/22/2018
Distributed Systems - Comp 655

55. Distributed Systems - Comp 655
Open source database
PostgreSQL – robust, full-featured
MySQL – maximize Web application performance, but no stored procedures or triggers [selected]
It took several tries to get MySQL installed, but it worked well once it was set up.
11/22/2018
Distributed Systems - Comp 655

56. Distributed Systems - Comp 655
Java SDK
J2SE SDK from Sun
Blackdown JDK
BEA’s JRockit [selected, primarily for performance reasons]
They liked the “M x N” threading model
11/22/2018
Distributed Systems - Comp 655

57. Another industry benchmark
TPC is best known for TPC-C, which pioneered the $/tpmC approach
11/22/2018
Distributed Systems - Comp 655

58. Distributed Systems - Comp 655
Java IDE
vi or emacs
NetBeans (based on Swing, considered more platform-independent)
Eclipse (based on SWT, considered faster and more attractive on-screen) [selected]
They liked Eclipse’s plug-ins
HP is developing several plug-ins
11/22/2018
Distributed Systems - Comp 655

59. Distributed Systems - Comp 655
Web container
Resin
Jboss
Jetty
Tomcat [selected, for performance, stability, and because it’s the default web container for Apache Axis]
They were able to start and stop Tomcat from Eclipse, with the help of a plug-in
11/22/2018
Distributed Systems - Comp 655

60. Web services container
They concluded that Apache Axis is currently the only “robust” open source web services platform.
They recommend writing your own WSDL for complex services, but for simple ones, Axis’ Java2WSDL is OK.
11/22/2018
Distributed Systems - Comp 655

61. Distributed Systems - Comp 655
More on Apache Axis
Some manual coding was needed to adapt their server-side code to the web service environment (example: had to make the Forecast class a Bean so it could be serialized)
The hardest part was figuring out what had to change.
One commenter on the ServerSide web site complained that they should have said more about the Axis serialization/deserialization classes, which he found very confusing.
11/22/2018
Distributed Systems - Comp 655

62. Distributed Systems - Comp 655
Build and test
Ant for building.
WSDL2Java from Axis generates a client proxy class from the WSDL. Handy for testing.
Axis tcpmon for monitoring SOAP traffic.
Web service testing tools
JUnit
Grinder
Anteater
PushToTest TestMaker [selected]
TestMaker scripts are written in Jython
11/22/2018
Distributed Systems - Comp 655