An Enterprise Service Bus (ESB) addresses integration challenges by providing routing, transformation, and management of messages between disparate systems. Mule is an open-source ESB that uses connectors and transformations to integrate applications and services. Mule flows define the routing of messages between connectors using processing steps like transformers and routers. Mule provides flexibility but also complexity, as it aims to support many integration standards.

1. Introduction to ESBs:
Mule
UC San Diego
CSE 294
November 14, 2008
Barry Demchak

2. Agenda
 What is an ESB?
 Java Business Integration (JBI)
 Mule Architecture
 Mule in the Real World

3. Source Material
 [Ric] Mark Richards, “The Role of the
Enterprise Service Bus”, NFJS, Oct 23,
2006. http://www.infoq.com/presentations/Enterprise-Service-Bus
 [Mul] Mule Architecture Guide.
http://mule.mulesource.org/display/MULE/Architecture+Guide
 September [mule-user archive]

4. Problems Addressed by ESBs
 Integration of existing systems
 Refactorable in real time
 Flexibility to change as requirements change
 Decentralized (service-location transparency)
 Scalable (point solutions to full enterprise)
 Sharing of services across enterprise
 Ability to separate Business Services from
Service Implementations
 Leverages standards

5. Definition(s)
Gartner Group
Giant exercise in Separation of Concerns
[Ric]

6. Definitions (more)
www.datapower.com
[Ric]

7. ESB Features
 Routing
 Message Transformation
 Message Enhancement
 Protocol Transformation
 Service Mapping
 Message Processing
 Process Choreography
 Service Orchestration
 Transaction Management
 Security
[Ric]

8. An ESB Blueprint
General case
Client calls Choreographer Client calls Mediator
vs
[Ric]

9. Java Business Integration (JBI)
 JSR-208 Standard
 Defines service engines (SE – choreographers,
transformers, security, etc) and binding components
(BC – xml, http, etc)
 Concerned with how internal customers (not external
services) interact with service providers
COTS
[Ric]

10. JBI Example
 XSLT – message transformation
 PXE – choreography
 Groovy – scripting
[Ric]

11. JBI Case Study: Service Mix
Service Mix
Binding Components
Service Engines
[Ric]

12. Mule Architecture
[Mule]

13. Mule Flow View
 Channel – a method of connecting between two points (not part
of Mule)
 Connector – a transport provider (e.g., http, jms, soap, smtp,
etc) implementing message receive and message dispatch
 Transformer – converts message structure/format (e.g., http to
xml)
 Router – moves messages amongst UMOs and connectors
[Mule]

14. Mule Connector View
http://myapp.com pop3://user@userland.comhttp→xml xml→pop3
myUMO (xml→xml)
[Mule]

15. Mule Transports
 AS400 DQ
 EJB
 E-mail
 File
 FTP
 HTTP
 IMAP
 JDBC
 JMS
 Multicast
 POP3
 Quartz
RMI
 Servlet
 SMTP
 SOAP
 SSL
 Stream
 TCP
 UDP
 VFS
 VM
 WSDL
 XMPP

16. UMO Execution
 Requires a component resolver (e.g., Spring
or Pico) for
 Instantiation of UMOs
 Configuration of UMOs
 Event processing
 Asynchronous
 Synchronous
 Request-Response
[Mule]

17. Mule Programming Model
Application logic
Application glue
Mule glue
[Mule]

18. Mule Routers
[Mule]

19. Selective Consumer (inbound)
 Applies one or more filters to incoming payload, then
branch based on filter
<inbound-router>
<catch-all-strategy
className="org.mule.routing.ForwardingCatchAllStrategy">
<endpoint address="jms://topic:error.topic"/>
</catch-all-strategy>
<router
className="org.mule.routing.inbound.SelectiveConsumer">
<filter expression="msg/header/resultcode = 'success'"
className="org.mule.routing.filters.xml.JXPathFilter"/>
</router>
</inbound-router>

20. Filtering Outbound (outbound)
<outbound-router>
<catch-all-strategy
className="org.mule.routing.ForwardingCatchAllStrategy">
<endpoint="jms://error.queue"/>
</catch-all-strategy>
<router className="org.mule.routing.outbound.FilteringOutboundRouter">
<endpoint address="smtp://ross@muleumo.org"/>
<filter expectedType="java.lang.Exception"
className="org.mule.routing.filters.PayloadTypeFilter"/>
</router>
<router className="org.mule.routing.outbound.FilteringOutboundRouter">
<endpoint address="jms://string.queue"/>
<filter className="org.mule.routing.filters.logic.AndFilter">
<left-filter expectedType="java.lang.String"
className="org.mule.routing.filters.PayloadTypeFilter"/>
<right-filter pattern="the quick brown (.*)"
className="org.mule.routing.filters.RegExFilter"/>
</filter>
</router>
</outbound-router>

21. Nested Router
 Allows synchronous callouts that can be intercepted and routed
<mule-descriptor name="InvokerComponent"
implementation="org.mule.foo.Invoker">
<inbound-router>
<endpoint address="jms://Invoker.in"/>
</inbound-router>
<nested-router>
<binding interface="org.mule.foo.HelloInterface">
<endpoint
address="axis:http://192.168.2.14:81/services/HelloWebComponent?
method=helloMethod" remoteSync="true"/>
</binding>
</nested-router>
<outbound-router>
<router
className="org.mule.routing.outbound.OutboundPassThroughRouter">
<endpoint address="jms://Invoker.out"/>
</router>
</outbound-router>
</mule-descriptor>

22. Dog Days with Mule
 September [mule-user archive]
 How to get a hold of Endpoint object from the
component? {mule}
 Failed to throw UserDefined Exception {jaxws}
 Failed to invoke lifecycle “start” using CXF in
JBOSS {cxf}
 Problem in loading xsd files {mule}
 Problems with RemoteDispatcher {mule}
 Inject MuleClient Singleton with Spring {mule}
 Mule transaction support {mule}

23. ESB Features
 Routing
 Message Transformation
 Message Enhancement
 Protocol Transformation
 Service Mapping
 Message Processing
 Process Choreography
 Service Orchestration
 Transaction Management
 Security
X
X
√
√
√
√
√

24. Take Away Messages
 Mule’s generality results in great flexibility, but at the
cost of great complexity for users
 Mule is the focal point of ambiguity and difficulties
with many standards-based packages
 Mule delivers (to a degree) on:
 Integration, flexibility, decentralized operation,
scalability
 Mule doesn’t deliver (so much) on:
 Runtime refactoring, conceptualization