Embed Size (px)
DESCRIPTION
Proxy Pattern. What’s a Proxy?. A remote proxy acts as a local representative of a remote object Remote Object: instantiated in a different JVM heap (a different address space) The proxy looks like the remote object, but isn’t - PowerPoint PPT Presentation
Citation preview
Proxy PatternProxy Pattern
What’s a Proxy?What’s a Proxy?
• A remote proxy acts as a local representative of a remote object
• Remote Object: instantiated in a different JVM heap (a different address space)
• The proxy looks like the remote object, but isn’t
• The proxy takes method calls and handles all the details of network communication to the remote object
• A remote proxy acts as a local representative of a remote object
• Remote Object: instantiated in a different JVM heap (a different address space)
• The proxy looks like the remote object, but isn’t
• The proxy takes method calls and handles all the details of network communication to the remote object
What’s a Proxy?What’s a Proxy?
ClientCode
Proxy
Local Heap Remote Heap
RemoteObject
RMIRMI• Luckily, we don’t have to write the code to
handle network communications• RMI: Remote Method Invocation
• Java provides packages that we can easily use to make our current code ready for network communication with very few changes
• The book provides a very detailed guide to this process
• Luckily, we don’t have to write the code to handle network communications
• RMI: Remote Method Invocation
• Java provides packages that we can easily use to make our current code ready for network communication with very few changes
• The book provides a very detailed guide to this process
RMIRMI
ClientObject
Client helper
Local Heap Remote Heap
ServiceObjectService
helper
Proxy, pretends to be the actual service.Packs requests and handles network communications
Unpacks requests from client helper; calls requests on the Service Object
RMIRMI
ClientObject
Client helper
Local Heap Remote Heap
ServiceObjectService
helper
doBigJob()
RMIRMI
ClientObject
Client helper
Local Heap Remote Heap
ServiceObjectService
helper
doBigJob()
Client helper packages up the info about the method call (Serializable) & ships it over the network
“client wants to call a method”
RMIRMI
ClientObject
Client helper
Local Heap Remote Heap
ServiceObjectService
helper
Service helper packs the result and handles network communications
result
RMIRMI
ClientObject
Client helper
Local Heap Remote Heap
ServiceObjectService
helper
Client helper unpacks the result and passes it back to the Client Object
packaged result
RMIRMI
ClientObject
Client helper
Local Heap Remote Heap
ServiceObjectService
helper
The Client Object doesn’t know it isn’t talking to the Service Object in its own heap!
result
RMIRMI
ClientObject
Client helper
Local Heap Remote Heap
ServiceObjectService
helper
Newer versions of Java don’t require an explicit skeleton object, but something is still taking care of the skeleton behavior.
RMI STUBRMI
SKELETON
Making a Remote ServiceMaking a Remote Service1. Make a remote Interface
Defines the methods that can be called remotelyStub and Service Object will implement it
2. Make a Remote ImplementationThis is the class that does the “real work”
3. Rmic to generate stubs & skeletons (Server)Rmic comes with the Java SDKImplementation_stub.classImplementation_Skel.class
4. Start the registry (Server): rmiregistry 5. Start the remote service (server)
Needs to be in a separate thread from the rmiregistry
1. Make a remote InterfaceDefines the methods that can be called remotelyStub and Service Object will implement it
2. Make a Remote ImplementationThis is the class that does the “real work”
3. Rmic to generate stubs & skeletons (Server)Rmic comes with the Java SDKImplementation_stub.classImplementation_Skel.class
4. Start the registry (Server): rmiregistry 5. Start the remote service (server)
Needs to be in a separate thread from the rmiregistry
Back to the PatternBack to the PatternDEFINITION:
The Proxy Pattern provides a surrogate or placeholder for another object to control access to it.
DEFINITION:
The Proxy Pattern provides a surrogate or placeholder for another object to control access to it.
Class diagramClass diagram
<<interface>>Subject
request()
RealSubject
request()
Proxy
request()
subject
