Proxy Design Pattern Tutorial

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Welcome to my Proxy Design Pattern Tutorial! The Proxy design pattern limits access to just the methods you want made accessible in another class.

It can be used for security reasons, because an Object is intensive to create, or is accessed from a remote location. You can think of it as a gate keeper that blocks access to another Object. I demonstrate how the proxy pattern works using some code used in my state design pattern tutorial. You may want to check that tutorial out before proceeding.

State Design Pattern Tutorial:


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35 responses to “Proxy Design Pattern Tutorial”

  1. ForgottenKnight1 Avatar

    "Expensive" not "intensive" :d

  2. Ranjan Sparrow Avatar

    is proxy and dynamic proxy same?

  3. beepIL Avatar

    So wait i dont get it,
    in order to create atm proxy we basically need to create real atm machine (inside the proxy)
    now for that to happen it means the code needs to KNOW real atm class to begin with.
    so if we can create atm proxy instance, we can create real atm machine instance in whatever code we work,
    then we would simply access whatever we want from the real atm and simply ignore the proxy…
    how is this really limiting someone? what forces someone to work only with the proxy? what prevents them from just creating real atm machine instance and using that, so what is exactly limiting this "outside program" from doing just that?

  4. beepIL Avatar

    getCashInMachine returning int
    hmmmm i smell small change thievery going on in this bank

  5. Liam Elliott Avatar

    Could you not do a dynamic cast from GetATMData on the real machine to ATMMachine?

  6. Nitin Khola Avatar

    Hi Derek,
    Can you please explain what is the right way of passing the original obejct to the proxy object? In the video it is not clear . https://snag.gy/biaUoG.jpg . Instead of passing the instance of real object , you are just creating a new object in every call to your proxy methods .

  7. volkan15 Avatar

    If I have two different classes that use the same interface and I want to secure both with my Proxy-Class, do I need in this case two Proxy-Classes or is one enogh for both?

  8. Tanvi Patel Avatar

    Thanks Derek! Amazing tutorials. Thanks for all the efforts 🙂

  9. Prem Tiwari Avatar

    Derek i must say you have explained it in a very clear and crisp manner.
    my sincere thanks …please keep uo good stuff….again many thanks from India 🙂

  10. In Out Avatar

    It is good to follow good coding practice.
    When you define interface name , it should be preceded by letter 'I' that would help to differentiate an interface from a class.

    Anyway , I want to thank you for the knowledge sharing.
    and i clicked on the like button too 🙂

  11. Prasad Avatar

    can u create proxy (ip) changer soft. that can automatically change the proxy "IP"in given time dynamically and also create proxy chains.. 🙂 plz…. at least algorithm i cant think how to create this .

  12. jivan patil Avatar

    why can't we use Abstract class instead of Interface ?

  13. Frickes Avatar

    easiest to understand explanation on the interwebs. 🙂 Thank you!

  14. HCT Avatar

    I love your videos, explained short and clearly!
    Keep this Derek 🙂

  15. StarTiik .D Avatar

    Nice work on those tutorials Derek ! But I have little problem I do not find the whole code from class ATMMachine.java , could you provide it to me? Thanks in advance.

  16. Mo Avatar

    if you use an object of interface type, which is apparantly doing the job of the proxy which is to limit access to methods, what is the use for the proxy object then?
    great video by the way 🙂

  17. Ayoub Falah Avatar

    Hello Derek Banas,

    Thank you first for the great toturial. I have a question about the main idea behind the proxy design pattern. Let M be a set of methods defined in the protected class ATMMachine, and S is a subset of M, with for each element m in S, m should not be accessible outside of the class ATMMachine(S ist the set of secure methods). In this case we can declare the elements of S as private and M S (The set of methods that are accessible outside of the ATMMachine) as public. This implies that the secure methods a not visible outside of the class ATMMachine. Does this approach has any limits that we must use the proxy design pattern. If this is the case, then why?

    Thank you in advance!
    Ayoub

  18. Martijn Millecamp Avatar

    I don't understand this function in the proxy
    public int getCashInMachine() {
    ATMMachine realATMMachine = new ATMMachine();
    return realATMMachine.getCashInMachine();
    }
    This function always return 2000 because every time this function is used it creates an new machine?

  19. Bhargav Jhaveri Avatar

    ATMMachine class is public and the methods which are defined in the interface are also public. So how does it prevent an attacker from using ATMMachine instead of the proxy?

  20. Praveen Reddy Avatar

    Is Data abstraction and proxy design pattern same? why because data abstraction also limits the functionality of a class to an interface object. then what is the main difference?

  21. Jeremie Shaker Avatar

    Hey Derek! Within your ATMProxy class, why do you instantiate a new ATMMachine on every method call? Wouldn't it be more efficient to have it as an instance variable and just access it within each method?

  22. Anand Sridharan Avatar

    Derek Thank you for this service you have provided by giving detailed implementations for these design patterns. Need some help with this one pattern. The realATMMAchine that is created in the TestATMMAchine is not used inside the ATMProxy? Instead ATMProxy uses its own newly generated copy. How do I reconsile this?

  23. João Neves Avatar

    Thank you! It's an amazing tutorial!

  24. Manuel José García Rodríguez Avatar

    In wich way could I protect one class with a proxy, if that class could be instantiated directy?

  25. Brax1982 Avatar

    Automatic Teller Machine Machine

  26. Raul Zuniga Avatar

    You are aware that not all the code is available?  ATMMachine class has only the new stuff and not any of the stuff from the State Design pattern. And several classes are missing once I fix ATMMachine class. These tutorials are supposed to be self-contained, yes?  Besides, that it was a great tutorial. Especially, being able to restrict access to methods of ATMMachine by implementing an GetATMData interface. Pretty elegant.

  27. Nick Askew Avatar

    I'm getting into these design patterns way too late. I hope my ramblings make some sense.

    If the purpose of the proxy is, in this case, for security then clearly it should not be possible for the same client to create an instance of  ATMMachine. Now if ATMMachine implements the interface GetATMData surely that is enough, you don't add anything with the proxy class.

    I suppose a more useful real world implementation would be a web service that uses authorisation and implements the methods ATMMachine and another web service that does not require authorisation that implements GetATMData. However this being the case I'd also not quite see the purpose of the proxy pattern in this case.

    I suppose actually what this example would benefit from would be if it combined one of the builder patterns. Perhaps a Factory would be used to prevent clients creating instances of the ATMMachine. The Factory could then use some kind of authorisation (being a .Net guy myself that should the straightforward and I'm sure Java has something similar) and allow certain clients to create ATMMachine while everyone can create GetATMData. However even then this would not be a proxy.

  28. Stefan Fritzon Avatar

    In the proxy class methods you use new() comando. Dosen't this just give you an new reference to an new object on an machine. in other words you always get start value of the machine?

  29. yangliu3456 Avatar

    Hi Derek, I could not understand why "realATMMachine" cannot access the "secret" variables either. Thanks.

  30. Anirudh Upadhyayula Avatar

    Hi Derek I hope this is not a bad question to ask. I was wondering what is the point of making the realAtMachine when you have already created methods to get information from the ATMMachine class within the proxy. It can work without the realAtMachine right?

  31. Corey Cotton Avatar

    Hi Derek— I understand the desire for simplicity. I was expected that proxy would have a composition relationship with the actual ATMMachine and the proxy would only expose the two methods. What are your thoughts?

  32. Tomislav Tenodi Avatar

    The problem with giving so simple examples is that no one actually sees the benefit of using Proxy. 

  33. Aniket Pednekar Avatar

    Hey, the ATMProxy class constructs a new ATMMachine and returns its field values. How does this help if you need the values of fields from the realATMMachine?

  34. Nikolai Kalashnikov Avatar

    I have a Maven multi-module project with three layers: (3) The Main class that depends upon (2) The middle layer which depends on (1) The API layer (utilities, etc).

    Normally, the middle layer cannot access the Main class (because you can't have circular dependencies)… In order to get around this, I had the Main class implement an interface declared in the first api layer.

    Would this be an example of a Proxy ? Or another design pattern ? Or did I just hack it together and it's not even a design pattern at all ? Thanks!

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