3. Where Coupling Exists, Concerns Arise
• Tight coupling is easy
• Loose coupling can be difficult
• Tight coupling causes issues in the long run
• Loose coupling pays off in the long run
• Integrations are usually tightly coupled
• Integrations should be loosely coupled
• Integrations are commonly addressed using commands
• Integrations should be addressed using events
Friday, July 15, 2011
4. What is Coupling?
“... the degree to which each program module relies
on each one of the other modules”
(Wikipedia.com)
• Given two lines of code, A and B, they are coupled when B
must change behavior only because A changed
4
Friday, July 15, 2011
5. Characteristics Tight Coupling
• Components are highly dependent upon one another
• Components are directly linked
• Changes in one component cause a ripple effect
• Less reusability
• More difficult to maintain
• Does not handle unforeseen change well
• Examples
– Clients designed to interact only with specific systems
– Use of proprietary APIs or commands for interaction
– Components designed to work specifically with other
components
5
Friday, July 15, 2011
6. Characteristics of Loose Coupling
• Components have little or no knowledge of one another
• Components are not directly linked to one another
• Changes in one component do not affect other components
• Increased reusability
• Easier to maintain
• More easily handles unforeseen changes
• Examples
– Dependence upon interfaces instead of concrete classes
– Use of DI encourages looser coupling
– A design using a level of indirection
6
Friday, July 15, 2011
7. Tight Coupling is Easy
• App design with tight coupling is more widely understood
• App development with tight coupling requires less time
• Debugging a tightly coupled app is easier
• Benefits of tight coupling are seen immediately
• Tightly coupled prototypes commonly live on
7
Friday, July 15, 2011
8. Loose Coupling is Difficult
• App design with loose coupling is not widely understood
• App development with loosely coupling requires more
thought and more time
• Debugging loosely coupled apps is different
• Benefits of loose coupling are only seen over time
8
Friday, July 15, 2011
9. Integrations and Coupling
• But it’s easy to write a point-to-point, one-off piece of code
for integration!
• Too many disadvantages
– Difficult to maintain
– No reusability
– Every integration is unique
– Bites you over time
9
Friday, July 15, 2011
10. Integrations and Coupling
• But designing integrations to be loosely coupled requires
too much work!
• With the right knowledge and preparation, it doesn’t need
to be this way
10
Friday, July 15, 2011
11. Commands vs. Events
• Commands are not natural
– Verify credit card
• Commands are too specific
• Events are natural
– Order received
• Events are more broad
• Events are what happen in the real world
11
Friday, July 15, 2011
13. Spring Integration
• Provides both concurrency and messaging
– Message Endpoints
• Connections between services
– Channel Adapters
• Adapter between application and message broker
– Messaging Gateways
• Provides uni-directional or bi-directional messaging
– Service Activators
• Invokes a services based on an incoming message
– Routers
• Determines where to dispatch a message
– Splitters and Aggregators
• Breaks up a message and reassembles it after processing
13
Friday, July 15, 2011
14. Spring Integration
• Supports
– AMQP
– Email
– File system
– Gemfire
– JMS
– JMX
– MongoDB
– Redis
– Spring Batch
– Testing
– Web Services
14
Friday, July 15, 2011
