gaspersic/java-design-patterns
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

Update README.md

Browse Source
This commit is contained in:
Ilkka Seppälä
2020-09-01 20:06:47 +03:00
parent b9b6777d15
commit 25cca3547d
3 changed files with 105 additions and 70 deletions
Download Patch File Download Diff File Expand all files Collapse all files

60
proxy/README.md
View File

@ -10,16 +10,20 @@ tags:
---
## Also known as
Surrogate
## Intent
Provide a surrogate or placeholder for another object to control
access to it.
Provide a surrogate or placeholder for another object to control access to it.
## Explanation
Real world example
> Imagine a tower where the local wizards go to study their spells. The ivory tower can only be accessed through a proxy which ensures that only the first three wizards can enter. Here the proxy represents the functionality of the tower and adds access control to it.
> Imagine a tower where the local wizards go to study their spells. The ivory tower can only be
> accessed through a proxy which ensures that only the first three wizards can enter. Here the proxy
> represents the functionality of the tower and adds access control to it.
In plain words
@ -27,11 +31,17 @@ In plain words
Wikipedia says
> A proxy, in its most general form, is a class functioning as an interface to something else. 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 forwarding 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.
> A proxy, in its most general form, is a class functioning as an interface to something else.
> 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 forwarding 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.
**Programmatic Example**
Taking our wizard tower example from above. Firstly we have the wizard tower interface and the ivory tower class
Taking our wizard tower example from above. Firstly we have the `WizardTower` interface and the
`IvoryTower` class.
```java
public interface WizardTower {
@ -50,7 +60,7 @@ public class IvoryTower implements WizardTower {
}
```
Then a simple wizard class
Then a simple `Wizard` class.
```java
public class Wizard {
@ -68,7 +78,7 @@ public class Wizard {
}
```
Then we have the proxy to add access control to wizard tower
Then we have the `WizardTowerProxy` to add access control to `WizardTower`.
```java
public class WizardTowerProxy implements WizardTower {
@ -97,28 +107,41 @@ public class WizardTowerProxy implements WizardTower {
}
```
And here is tower entering scenario
And here is the tower entering scenario.
```java
var proxy = new WizardTowerProxy(new IvoryTower());
proxy.enter(new Wizard("Red wizard")); // Red wizard enters the tower.
proxy.enter(new Wizard("White wizard")); // White wizard enters the tower.
proxy.enter(new Wizard("Black wizard")); // Black wizard enters the tower.
proxy.enter(new Wizard("Green wizard")); // Green wizard is not allowed to enter!
proxy.enter(new Wizard("Brown wizard")); // Brown wizard is not allowed to enter!
proxy.enter(new Wizard("Red wizard"));
proxy.enter(new Wizard("White wizard"));
proxy.enter(new Wizard("Black wizard"));
proxy.enter(new Wizard("Green wizard"));
proxy.enter(new Wizard("Brown wizard"));
```
Program output:
```
Red wizard enters the tower.
White wizard enters the tower.
Black wizard enters the tower.
Green wizard is not allowed to enter!
Brown wizard is not allowed to enter!
```
## Class diagram
![alt text](./etc/proxy.urm.png "Proxy pattern class diagram")
## Applicability
Proxy is applicable whenever there is a need for a more
versatile or sophisticated reference to an object than a simple pointer. Here
are several common situations in which the Proxy pattern is applicable
Proxy is applicable whenever there is a need for a more versatile or sophisticated reference to an
object than a simple pointer. Here are several common situations in which the Proxy pattern is
applicable.
* Remote proxy provides a local representative for an object in a different address space.
* Virtual proxy creates expensive objects on demand.
* Protection proxy controls access to the original object. Protection proxies are useful when objects should have different access rights.
* Protection proxy controls access to the original object. Protection proxies are useful when
objects should have different access rights.
## Typical Use Case
@ -136,7 +159,8 @@ are several common situations in which the Proxy pattern is applicable
* [java.lang.reflect.Proxy](http://docs.oracle.com/javase/8/docs/api/java/lang/reflect/Proxy.html)
* [Apache Commons Proxy](https://commons.apache.org/proper/commons-proxy/)
* Mocking frameworks Mockito, Powermock, EasyMock
* Mocking frameworks [Mockito](https://site.mockito.org/),
[Powermock](https://powermock.github.io/), [EasyMock](https://easymock.org/)
## Related patterns