This document discusses the adapter and proxy patterns. The adapter pattern converts the interface of one class into another interface that clients expect. It allows classes to work together that otherwise could not due to incompatible interfaces. The proxy pattern provides a surrogate or placeholder for another object to control access to it. There are several types of proxies including virtual, cache, protection, remote, synchronization, copy-on-write, smart reference, and firewall proxies. Examples of each pattern are provided.

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
•
•
•
•
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