1. Adapter & Proxy Pattern
Philip zhong Feb, 2014

2. Agenda
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Pattern Taxonomy
What’s Adapter?
Adapter Motivation
When To Use Adapter?
Adaptor Examples
What’s Proxy?
Proxy Motivation
When To Use Proxy?
Proxy Types
Proxy Example

3. Pattern Taxonomy
 Structural Patterns
Adapters, Bridges, Facades, and Proxies are
variations on a single theme:
They reduce the coupling between two or more classes.
They introduce an abstract class to enable future
extensions.
They encapsulate complex structures.

4. What’s Adapter
Convert the Interface of a class into
Target
another interface clients expect. Client uses.
Defines the domain-specific interface that
• Adapter
 Also Known As Wrapper
•

Adapts the interface Adaptee to the Target interface.

Adaptee
Defines an existing interface that needs adapting.

Client
Collaborates with objects conforming to the Target interface.

6. Adapter Motivation
• Sometimes a toolkit or class library can
not be used because its interface is
incompatible with the interface required by
an application
• We can not change the library interface,
since we may not have its source code
• Even if we did have the source code, we
probably should not change the library for
each domain-specific application

7. Adapter Example
• Media Player
Client
Uses
VlcPlay er
+ playVlc()
+ playMp4()
MediaPlay er
Implements
Implements
Implements
AudioPlay er
+ play()
Uses
MediaAdapt er
+ play()
Uses
Adv anceMediaPlay er
Implements
Mp4Play er
+ playVlc()
+ playMp4()

8. Adapter Examples
OracleSt ore
MessageSt at em ent s
Message
Dat abasePersist enceAdapt er
+ long messageId
+ String message
+ Timestamp timestamp
+ String client
I Dat abasePersist ence Implements
Uses
Implements
MessagePersist ence
I MessagePersist ence
Uses
Client
Abst ract Dat abaseSt ore
Uses
Implements
MysqlSt ore

9. What’s Proxy
• Provide a surrogate or placeholder for
 Proxy
another object to that lets the proxy it.
Maintains a referencecontrol access toaccess
• the real subject. Surrogate
Also Known As
 Subject Interface
Defines the common interface for RealSubject and
proxy so that a Proxy can be used anywhere a
RealSubject is expected.
 RealSubject
Defines the real object that proxy represents.

10. Proxy Motivation
• There are situations in which a client does
not or can not reference an object directly,
but wants to still interact with the object.
• The proxy object has the same interface as
the target object.
• The proxy holds a reference to the target
object and can forward requests to the target
as required (delegation!).
• In effect, the proxy object has the authority
the act on behalf of the client to interact with
the target object.

11. Proxy Types
• Virtual Proxy :Allows the creation of a memory intensive object on
•
demand. The object will not be created until it is really needed.
Cache Proxy :Provides temporary storage of the results of expensive
target operations so that multiple clients can share the results.
• Protection (Access) Proxy: Provides different clients with
different levels of access to a target object, we can through
java dynamic proxy API to do.
• Remote Proxy :Provides a reference to an object located in a different
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•
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address space on the same or different machine. e.g.: RMI & CORBA
Synchronization Proxy :Provides multiple accesses to a target
object.
Copy-On-Write Proxy :Defers copying (cloning) a target object until
required by client actions. Really a form of virtual proxy.
Smart Reference Proxy :Provides additional actions whenever a
target object is referenced such as counting the number of references to the
object.
Firewall Proxy :Protects targets from bad clients (or vice versa).

12. Virtual Proxy Example
RealI m age
Implements
I m age
Delegates
Uses
Implements
Client
Pr ox y I m age

13. Cache Proxy Example
Cust om er Dao
Implements
Delegates
I Cust om er Dao
Implements
Cust om er CachedPr ox y
+ Uses
Google Cache

14. Dynamic Proxy Example

15. Dynamic Proxy Example

16. Remote Proxy Example
• Java RMI(Remote Method Invocation)

17. Synchronization Proxy Example
Table
Implements
I Table
Delegates
Implements
Row Lock TablePr ox y

18. Q & A