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<title>Proxy pattern</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Proxy pattern</span></span>

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<p>In <a href="Computer_programming" title="Computer programming">computer programming</a>, the <b>proxy pattern</b> is a <a href="Software_design_pattern" title="Software design pattern">software design pattern</a>. A <i>proxy</i>, in its most general form, is a class functioning as an interface to something else. The proxy could interface to anything: a network connection, a large object in memory, a file, or some other resource that is expensive or impossible to duplicate. In short, a proxy is a wrapper or agent object that is being called by the client to access the real serving object behind the scenes. Use of the proxy can simply be <a href="Forwarding_(object-oriented_programming)" title="Forwarding (object-oriented programming)">forwarding</a> to the real object, or can provide additional logic. In the proxy, extra functionality can be provided, for example caching when operations on the real object are resource intensive, or checking preconditions before operations on the real object are invoked. For the client, usage of a proxy object is similar to using the real object, because both implement the same interface.

</p>

<div class="mw-heading mw-heading2"><h2 id="Overview">Overview</h2></div>

<p>The Proxy

design pattern is one of the twenty-three well-known

<i><a href="Design_Patterns" title="Design Patterns">GoF design patterns</a></i>

that describe how to solve recurring design problems to design flexible and reusable object-oriented software, that is, objects that are easier to implement, change, test, and reuse.

</p>

<div class="mw-heading mw-heading3"><h3 id="What_problems_can_the_Proxy_design_pattern_solve?">What problems can the Proxy design pattern solve?</h3></div>

<p>Source:<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

</p>

<ul><li>The access to an object should be controlled.</li>

<li>Additional functionality should be provided when accessing an object.</li></ul>

<p>When accessing sensitive objects, for example, it should be possible to check that clients have the needed access rights.

</p>

<div class="mw-heading mw-heading3"><h3 id="What_solution_does_the_Proxy_design_pattern_describe?">What solution does the Proxy design pattern describe?</h3></div>

<p>Define a separate <code>Proxy</code> object that

</p>

<ul><li>can be used as a substitute for another object (<code>Subject</code>), and</li>

<li>implements additional functionality to control the access to this subject.</li></ul>

<p>This makes it possible to work through a <code>Proxy</code> object to perform additional functionality when accessing a subject, like checking the access rights of clients accessing a sensitive object.

</p><p>To act as a substitute for a subject, a proxy must implement the <code>Subject</code> interface. Clients can't tell whether they work with a subject or its proxy.

</p><p>See also the UML class and sequence diagram below.

</p>

<div class="mw-heading mw-heading2"><h2 id="Structure">Structure</h2></div>

<div class="mw-heading mw-heading3"><h3 id="UML_class_and_sequence_diagram">UML class and sequence diagram</h3></div>

<p>In the above <a href="Unified_Modeling_Language" title="Unified Modeling Language">UML</a> <a href="Class_diagram" title="Class diagram">class diagram</a>,

the <code>Proxy</code> class implements the <code>Subject</code> interface so that it can act as substitute for <code>Subject</code> objects. It maintains a reference (<code>realSubject</code>)

to the substituted object (<code>RealSubject</code>) so that it can forward requests to it

(<code>realSubject.operation()</code>).

</p><p>The sequence diagram

shows the run-time interactions: The <code>Client</code> object

works through a <code>Proxy</code> object that

controls the access to a <code>RealSubject</code> object.

In this example, the <code>Proxy</code> forwards the request to the <code>RealSubject</code>, which performs the request.

</p>

<div class="mw-heading mw-heading3"><h3 id="Class_diagram">Class diagram</h3></div>

<div class="mw-heading mw-heading2"><h2 id="Possible_usage_scenarios">Possible usage scenarios</h2></div>

<div class="mw-heading mw-heading3"><h3 id="Remote_proxy">Remote proxy</h3></div>

<p>In <a href="Distributed_object_communication" title="Distributed object communication">distributed object communication</a>, a local object represents a remote object (one that belongs to a different address space). The local object is a proxy for the remote object, and method invocation on the local object results in <a href="Remote_method_invocation" class="mw-redirect" title="Remote method invocation">remote method invocation</a> on the remote object. An example would be an <a href="Automated_teller_machine" class="mw-redirect" title="Automated teller machine">ATM</a> implementation, where the ATM might hold proxy objects for bank information that exists in the remote server.

</p>

<div class="mw-heading mw-heading3"><h3 id="Virtual_proxy">Virtual proxy</h3></div>

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</style><div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Lazy_loading" title="Lazy loading">Lazy loading</a></div>

<p>In place of a complex or heavy object, a skeleton representation may be advantageous in some cases. When an underlying image is huge in size, it may be represented using a virtual proxy object, loading the real object on demand.

</p>

<div class="mw-heading mw-heading3"><h3 id="Protection_proxy">Protection proxy</h3></div>

<p>A protection proxy might be used to control access to a resource based on access rights.

</p>

<ul><li><a href="Composite_pattern" title="Composite pattern">Composite pattern</a></li>

<li><a href="Decorator_pattern" title="Decorator pattern">Decorator pattern</a></li>

<li><a href="Lazy_initialization" title="Lazy initialization">Lazy initialization</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite id="CITEREFErich_Gamma,_Richard_Helm,_Ralph_Johnson,_John_Vlissides1994" class="citation book cs1">Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides (1994). <span class="id-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/designpatternsel00gamm/page/207"><i>Design Patterns: Elements of Reusable Object-Oriented Software</i></a></span>. Addison Wesley. pp. <a rel="nofollow" class="external text" href="https://archive.org/details/designpatternsel00gamm/page/207">207ff</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-201-63361-2</bdi>.</cite><span class="cs1-maint citation-comment"><code class="cs1-code">{{cite book}}</code>: CS1 maint: multiple names: authors list (link)</span></span>

</li>

<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://w3sdesign.com/?gr=s07&ugr=proble">"The Proxy design pattern - Problem, Solution, and Applicability"</a>. <i>w3sDesign.com</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2017-08-12</span></span>.</cite></span>

</li>

<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://w3sdesign.com/?gr=s07&ugr=struct">"The Proxy design pattern - Structure and Collaboration"</a>. <i>w3sDesign.com</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2017-08-12</span></span>.</cite></span>

</li>

</ol></div></div>

<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

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<div class="side-box-text plainlist">The Wikibook <i><a href="https://en.wikibooks.org/wiki/Computer_Science_Design_Patterns" class="extiw external" title="wikibooks:Computer Science Design Patterns">Computer Science Design Patterns</a></i> has a page on the topic of: <i><b><a href="https://en.wikibooks.org/wiki/Computer_Science_Design_Patterns/Proxy" class="extiw external" title="wikibooks:Computer Science Design Patterns/Proxy">Proxy implementations in various languages</a></b></i></div></div>

</div>

<div class="side-box-text plainlist">Wikimedia Commons has media related to <span style="font-weight: bold; font-style: italic;"><a href="https://commons.wikimedia.org/wiki/Category:Proxy_pattern" class="extiw external" title="commons:Category:Proxy pattern">Proxy pattern</a></span>.</div></div>

</div>

<ul><li><cite id="CITEREFGeary2002" class="citation web cs1">Geary, David (February 22, 2002). <a rel="nofollow" class="external text" href="https://www.infoworld.com/article/2074068/take-control-with-the-proxy-design-pattern.html">"Take control with the Proxy design pattern"</a>. <i><a href="JavaWorld" class="mw-redirect" title="JavaWorld">JavaWorld</a></i><span class="reference-accessdate">. Retrieved <span class="nowrap">2020-07-20</span></span>.</cite></li>

<li><a rel="nofollow" class="external text" href="https://perfectjpattern.sourceforge.net/dp-proxy.html">PerfectJPattern Open Source Project</a>, Provides componentized implementation of the Proxy Pattern in Java</li>

<li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20120311202925/http://www.netobjectives.com/PatternRepository/index.php?title=AdapterVersusProxyVersusFacadePatternComparison">Adapter vs. Proxy vs. Facade Pattern Comparison</a> at the <a href="Wayback_Machine" title="Wayback Machine">Wayback Machine</a> (archived 2012-03-11)</li>

<li><a rel="nofollow" class="external text" href="https://sourcemaking.com/design_patterns/proxy">Proxy Design Pattern</a></li>

<li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20141019100543/http://patterns.org.pl/proxy.html">Proxy pattern C++ implementation example</a> at the <a href="Wayback_Machine" title="Wayback Machine">Wayback Machine</a> (archived 2014-10-19)</li>

<li><a rel="nofollow" class="external text" href="https://wiki.c2.com/?ProxyPattern">Proxy pattern description from the Portland Pattern Repository</a></li></ul>

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</style><div id="Software_design_patterns225" style="font-size:114%;margin:0 4em"><a href="Software_design_pattern" title="Software design pattern">Software design patterns</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Design_Patterns" title="Design Patterns">Gang of Four<br>patterns</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Creational_pattern" title="Creational pattern">Creational</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Abstract_factory_pattern" title="Abstract factory pattern">Abstract factory</a></li>

<li><a href="Builder_pattern" title="Builder pattern">Builder</a></li>

<li><a href="Factory_method_pattern" title="Factory method pattern">Factory method</a></li>

<li><a href="Prototype_pattern" title="Prototype pattern">Prototype</a></li>

<li><a href="Singleton_pattern" title="Singleton pattern">Singleton</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Structural_pattern" title="Structural pattern">Structural</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Adapter_pattern" title="Adapter pattern">Adapter</a></li>

<li><a href="Bridge_pattern" title="Bridge pattern">Bridge</a></li>

<li><a href="Composite_pattern" title="Composite pattern">Composite</a></li>

<li><a href="Decorator_pattern" title="Decorator pattern">Decorator</a></li>

<li><a href="Facade_pattern" title="Facade pattern">Facade</a></li>

<li><a href="Flyweight_pattern" title="Flyweight pattern">Flyweight</a></li>

</ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Behavioral_pattern" title="Behavioral pattern">Behavioral</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Chain-of-responsibility_pattern" title="Chain-of-responsibility pattern">Chain of responsibility</a></li>

<li><a href="Command_pattern" title="Command pattern">Command</a></li>

<li><a href="Interpreter_pattern" title="Interpreter pattern">Interpreter</a></li>

<li><a href="Iterator_pattern" title="Iterator pattern">Iterator</a></li>

<li><a href="Mediator_pattern" title="Mediator pattern">Mediator</a></li>

<li><a href="Memento_pattern" title="Memento pattern">Memento</a></li>

<li><a href="Observer_pattern" title="Observer pattern">Observer</a></li>

<li><a href="State_pattern" title="State pattern">State</a></li>

<li><a href="Strategy_pattern" title="Strategy pattern">Strategy</a></li>

<li><a href="Template_method_pattern" title="Template method pattern">Template method</a></li>

<li><a href="Visitor_pattern" title="Visitor pattern">Visitor</a></li></ul>

</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Concurrency_pattern" title="Concurrency pattern">Concurrency<br>patterns</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Active_object" title="Active object">Active object</a></li>

<li><a href="Balking_pattern" title="Balking pattern">Balking</a></li>

<li><a href="Binding_properties_pattern" title="Binding properties pattern">Binding properties</a></li>

<li><a href="Double-checked_locking" title="Double-checked locking">Double-checked locking</a></li>

<li><a href="Asynchronous_method_invocation" title="Asynchronous method invocation">Event-based asynchronous</a></li>

<li><a href="Guarded_suspension" title="Guarded suspension">Guarded suspension</a></li>

<li><a href="Monitor_(synchronization)" title="Monitor (synchronization)">Monitor</a></li>

<li><a href="Proactor_pattern" title="Proactor pattern">Proactor</a></li>

<li><a href="Reactor_pattern" title="Reactor pattern">Reactor</a></li>

<li><a href="Readers%E2%80%93writer_lock" title="Readers–writer lock">Read–write lock</a></li>

<li><a href="Scheduler_pattern" class="mw-redirect" title="Scheduler pattern">Scheduler</a></li>

<li><a href="Scheduled-task_pattern" title="Scheduled-task pattern">Scheduled-task pattern</a></li>

<li><a href="Semaphore_(programming)" title="Semaphore (programming)">Semaphore</a></li>

<li><a href="Thread_pool" title="Thread pool">Thread pool</a></li>

<li><a href="Thread-local_storage" title="Thread-local storage">Thread-local storage</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Architectural_pattern" title="Architectural pattern">Architectural<br>patterns</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Front_controller" title="Front controller">Front controller</a></li>

<li><a href="Interceptor_pattern" title="Interceptor pattern">Interceptor</a></li>

<li><a href="Specification_pattern" title="Specification pattern">Specification</a></li>

<li><a href="Publish%E2%80%93subscribe_pattern" title="Publish–subscribe pattern">Publish–subscribe</a></li>

<li><a href="Naked_objects" title="Naked objects">Naked objects</a></li>

<li><a href="Service_locator_pattern" title="Service locator pattern">Service locator</a></li>

<li><a href="Active_record_pattern" title="Active record pattern">Active record</a></li>

<li><a href="Identity_map_pattern" title="Identity map pattern">Identity map</a></li>

<li><a href="Data_access_object" title="Data access object">Data access object</a></li>

<li><a href="Data_transfer_object" title="Data transfer object">Data transfer object</a></li>

<li><a href="Inversion_of_control" title="Inversion of control">Inversion of control</a></li>

<li><a href="JSP_model_2_architecture" title="JSP model 2 architecture">Model 2</a></li>

<li><a href="Broker_pattern" title="Broker pattern">Broker</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Other<br>patterns</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Blackboard_design_pattern" class="mw-redirect" title="Blackboard design pattern">Blackboard</a></li>

<li><a href="Business_delegate_pattern" title="Business delegate pattern">Business delegate</a></li>

<li><a href="Composite_entity_pattern" title="Composite entity pattern">Composite entity</a></li>

<li><a href="Dependency_injection" title="Dependency injection">Dependency injection</a></li>

<li><a href="Guard_(computer_science)" title="Guard (computer science)">Guard clause</a></li>

<li><a href="Intercepting_filter_pattern" title="Intercepting filter pattern">Intercepting filter</a></li>

<li><a href="Lazy_loading" title="Lazy loading">Lazy loading</a></li>

<li><a href="Mock_object" title="Mock object">Mock object</a></li>

<li><a href="Null_object_pattern" title="Null object pattern">Null object</a></li>

<li><a href="Object_pool_pattern" title="Object pool pattern">Object pool</a></li>

<li><a href="Servant_(design_pattern)" title="Servant (design pattern)">Servant</a></li>

<li><a href="Type_Tunnel_pattern" class="mw-redirect" title="Type Tunnel pattern">Type tunnel</a></li>

<li><a href="Method_chaining" title="Method chaining">Method chaining</a></li>

<li><a href="Delegation_pattern" title="Delegation pattern">Delegation</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Books</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><i><a href="Design_Patterns" title="Design Patterns">Design Patterns</a></i></li>

<li><i><a href="Enterprise_Integration_Patterns" title="Enterprise Integration Patterns">Enterprise Integration Patterns</a></i></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">People</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Christopher_Alexander" title="Christopher Alexander">Christopher Alexander</a></li>

<li><a href="Erich_Gamma" title="Erich Gamma">Erich Gamma</a></li>

<li><a href="Ralph_Johnson_(computer_scientist)" title="Ralph Johnson (computer scientist)">Ralph Johnson</a></li>

<li><a href="John_Vlissides" title="John Vlissides">John Vlissides</a></li>

<li><a href="Grady_Booch" title="Grady Booch">Grady Booch</a></li>

<li><a href="Ward_Cunningham" title="Ward Cunningham">Ward Cunningham</a></li>

<li><a href="Martin_Fowler_(software_engineer)" title="Martin Fowler (software engineer)">Martin Fowler</a></li>

<li><a href="Robert_C._Martin" title="Robert C. Martin">Robert Martin</a></li>

<li><a href="Jim_Coplien" title="Jim Coplien">Jim Coplien</a></li>

<li><a href="Douglas_C._Schmidt" title="Douglas C. Schmidt">Douglas Schmidt</a></li>

<li><a href="Linda_Rising" title="Linda Rising">Linda Rising</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Communities</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="The_Hillside_Group" title="The Hillside Group">The Hillside Group</a></li>

<li><a href="Portland_Pattern_Repository" title="Portland Pattern Repository">Portland Pattern Repository</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">See also</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Anti-pattern" title="Anti-pattern">Anti-pattern</a></li>

<li><a href="Architectural_pattern" title="Architectural pattern">Architectural pattern</a></li></ul>

</div></td></tr></tbody></table></div></div><div><div class="zim-footer">

This article is issued from <a class="external text" title="Last edited on 2025-04-19" href="https://en.wikipedia.org/wiki/?title=Proxy_pattern&oldid=1286408814">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

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