Commons Proxy -
Apache Commons Proxy ™
Last Published: 07 April 2014
Version: 2.0-SNAPSHOT
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Commons Proxy: Dynamic Proxies Made Easy
The
Proxy
design pattern (
GoF
) allows you to provide “a surrogate or placeholder for another object to control access to it”. Proxies can be used in many ways, some of which are:
Deferred Initialization
- the proxy acts as a “stand-in” for the actual implementation allowing it to be instantiated only when absolutely necessary.
Security
- the proxy object can verify that the user actually has the permission to execute the method (a la EJB).
Logging
- the proxy can log evey method invocation, providing valuable debugging information.
Performance Monitoring
- the proxy can log each method invocation to a performance monitor allowing system administrators to see what parts of the system are potentially bogged down.
Commons Proxy
supports dynamic proxy generation using proxy factories, object providers, invokers, and interceptors.
Proxy Factories
ProxyFactory
encapsulates all necessary proxying logic away from your code. Switching proxying techniques/technologies is as simple as using a different proxy factory implementation class.
Commons Proxy
provides several proxy factory implementation modules:
commons-proxy2-jdk
commons-proxy2-cglib
commons-proxy2-javassist
commons-proxy2-asm4
Additionally, the core library provides a proxy factory
implementation
that delegates to instances discoverable using the Java
ServiceLoader
mechanism (including those provided by the listed modules).
Proxy factories allow you to create three different types of proxy objects:
Delegator Proxy
- delegates each method invocation to an object provided by an
ObjectProvider
Interceptor Proxy
- allows an
Interceptor
to intercept each method invocation as it makes its way to the target of the invocation.
Invoker Proxy
- uses an
Invoker
to handle all method invocations.
Object Providers
Object providers
provide the objects which will be the “target” of a proxy. There are two types of object providers:
Core Object Providers
A core object provider provides a core implementation object.
Commons Proxy
supports many different implementations including:
Constant
- Always returns a specific object
Bean
- Instantiates an object of a specified class each time
Cloning
- Reflectively calls the public
clone()
method on a
Cloneable
object
Decorating Object Providers
A decorating object provider decorates the object returned by another provider.
Commons Proxy
provides a few implementations including:
Singleton
- Calls a nested provider at most once, returning that original value on all subsequent invocations
Invokers
An
Invoker
handles all method invocations using a single method.
Commons Proxy
provides a few invoker implementations:
Null
- Always returns a
null
(useful for the “Null Object” pattern)
Duck Typing
- Supports so-called “duck typing” by adapting a class to an interface it does not implement.
Invocation Handler Adapter
- Adapts an implementation of the JDK
InvocationHandler
interface as a
Commons Proxy
Invoker
Interceptors
Commons Proxy
allows you to “intercept” a method invocation using an
Interceptor
. Interceptors provide
rudimentary
aspect-oriented programming (AOP) support, allowing you to alter the parameters/results of a method invocation without actually changing the implementation of the method itself.
Commons Proxy
provides a few interceptor implementations including:
ObjectProvider
- returns the value from an
ObjectProvider
Throwing
- throws an exception
Switch
- provides a fluent API to configure the handling of invoked methods
Serialization
The proxies created by the provided proxy factories are
Serializable
in most cases. For more complex cases
Commons Proxy
provides basic support for the “serialization proxy” pattern. See
org.apache.commons.proxy.serialization
for details.
Stubbing
The
StubBuilder
class allows you to create a proxy with customized behavior specified by a typesafe DSL. The
AnnotationBuilder
variant provides a simple way to create Java annotation instances at runtime.
Releases
The latest version is v1.0
(requires Java 1.4 or later)
. -
Download now!
For previous releases, see the
Apache archive
Support
The
Commons mailing lists
act as the main support forum. The
user
list is suitable for most library usage queries. The
dev
list is intended for the development discussion. Please remember that the lists are shared between all Commons components, so prefix your email subject with
[proxy]
Issues may be reported via
ASF JIRA
. Please read the instructions carefully to submit a useful bug report or enhancement request.
Copyright © 2005-2014
The Apache Software Foundation
Apache Commons, Apache Commons Proxy, Apache, the Apache feather logo, and the Apache Commons project logos are trademarks of The Apache Software Foundation.
All other marks mentioned may be trademarks or registered trademarks of their respective owners.