The proxy pattern is recognized as a pattern for
software designing in the field of computer science. In the most general term, the proxy can be defined as a class which functions as an interface to some
other program or application.
Where is Proxy used?
- A proxy can be used as an interface to anything
such as the following:
- A
network connection
- A
large object present in the memory
- A
file
- Or in other words, we can say that it can be used
for any resource that is quite expensive and it is not affordable to duplicate
it.
- An example of the proxy can be given by a reference counting pointer
object.
- There are situations where it is required to have multiple copies of a
complex object. In such situations proxy pattern comes to play a big role.
- It
is adapted for incorporating the fly weight pattern for reducing the memory
foot print of the application.
- In typical situations, the instance created for a
complex object is only one in count and multiple proxy objects are created.
- All
these proxy objects consist of a reference to an original object that is both
single and complex.
- The operations that are performed in a proxy object are
carried forward to the original object.
- If all the instances created for
the proxy lose their scope, the memory of the complex object is de–allocated
for that particular instance.
- A virtual proxy pattern is used in java.
- A proxy
class can be used to access the remote methods.
About Object Proxy Mechanism
- Firstly, an interface is created
against which the rational functional tester creates the classes using the
proxy patterns.
- An interface may consist of many methods.
- These methods need to
be coded by all the classes which are to implement those particular methods.
- If
a proxy class is running on some other system rather than the original class,
then the proxy class can represent its real image itself over there.
- All the
information regarding the image is obtained from the disk.
- The multiple loading
of the image can be avoided by using the proxy pattern with the code of the image.
- This happens so because the image is accessed in a memory saving manner from
some other system.
- The primary purpose of the proxy object is to act as an
intermediate object between the accessible object and the client.
- The proxy
object then serves the purpose of monitoring the life span of the object that
is accessible.
- Also, if the accessible object is not destroyed, all the calls
are forwarded to it. - The proxy object checks for the availability of the
accessible objects whenever a client makes calls to its accessible properties
for getting some info. - If the object is found to be available, the client’s call
is passed on to that accessible object.
- If the case is opposite i.e., if the
object is unavailable, an error is returned by the proxy object.
- Returning of
an error message by the proxy object is an indication that the destruction of
the object has taken place and this indication is recommended.
- The error
returned is “CO E OBJNOTCONNECTED”.
- The COM or the component object model
returns this error after CoDisconnectObject is called by the server.
- A
transparency is maintained between the client and the proxy object.
- Whenever
client calls an accessible object, a pointer to the interface of that object is
returned to the client.
- In turn when this pointer is used by the client to call
any of the object’s properties or methods, the execution of the code takes
place within proxy object.
- It is important for the rational functional tester
to understand the interface of a given object in order to interact with it.
- Usually, it is easy to interact with objects such as buttons, list boxes etc, however
there are some custom objects in an application for which a proxy needs to be
created.
