Design Patterns - Proxy & Composite

Explains foundations of proxy and composite patterns.

Transcript

1. Design Patterns Proxy & Composite @sarat, architect Experion Technologies
2. composite pattern
3. is a structural pattern
4. Structural design patterns ease the design by identifying a simple way to realize relationships between entities
5. Compose objects into tree structures to represent part-whole hierarchies. ! describes that a group of objects are to be treated in the same way as a single instance of an object
6. Leaf (primitive element) • represents leaf objects in the composition. • A leaf has no children. • defines behavior for primitive objects in the composition
7. Composite • defines behavior for components having children. • stores child components. • implements child-related operations in the Component interface.
8. Client ! • manipulates objects in the composition through the Component interface.
10. /** "Component" */ interface Graphic { //Prints the graphic. public void print(); }
11. class CompositeGraphic implements Graphic { //Collection of child graphics. private List<Graphic> childGraphics = new ArrayList<Graphic>();
12. class CompositeGraphic implements Graphic { //Collection of child graphics. private List<Graphic> childGraphics = new ArrayList<Graphic>(); ! //Prints the graphic. public void print() { for (Graphic graphic : childGraphics) { graphic.print(); } }
13. class CompositeGraphic implements Graphic { //Collection of child graphics. private List<Graphic> childGraphics = new ArrayList<Graphic>(); ! //Prints the graphic. public void print() { for (Graphic graphic : childGraphics) { graphic.print(); } } ! //Adds the graphic to the composition. public void add(Graphic graphic) { childGraphics.add(graphic); } //Removes the graphic from the composition. public void remove(Graphic graphic) { childGraphics.remove(graphic); } }
14. /** "Leaf" */ class Ellipse implements Graphic { //Prints the graphic. public void print() { System.out.println("Ellipse"); } }
15. /** Client */ public class Program { public static void main(String[] args) { //Initialize four ellipses Ellipse ellipse1 = new Ellipse(); Ellipse ellipse2 = new Ellipse(); Ellipse ellipse3 = new Ellipse(); Ellipse ellipse4 = new Ellipse();
16. /** Client */ public class Program { public static void main(String[] args) { //Initialize four ellipses Ellipse ellipse1 = new Ellipse(); Ellipse ellipse2 = new Ellipse(); Ellipse ellipse3 = new Ellipse(); Ellipse ellipse4 = new Ellipse(); ! //Initialize three composite graphics CompositeGraphic graphic = new CompositeGraphic(); CompositeGraphic graphic1 = new CompositeGraphic(); CompositeGraphic graphic2 = new CompositeGraphic();
17. /** Client */ public class Program { public static void main(String[] args) { //Initialize four ellipses Ellipse ellipse1 = new Ellipse(); Ellipse ellipse2 = new Ellipse(); Ellipse ellipse3 = new Ellipse(); Ellipse ellipse4 = new Ellipse(); ! //Initialize three composite graphics CompositeGraphic graphic = new CompositeGraphic(); CompositeGraphic graphic1 = new CompositeGraphic(); CompositeGraphic graphic2 = new CompositeGraphic(); ! //Composes the graphics graphic1.add(ellipse1); graphic1.add(ellipse2); graphic1.add(ellipse3); graphic2.add(ellipse4);
18. /** Client */ public class Program { public static void main(String[] args) { //Initialize four ellipses … ! //Initialize three composite graphics … ! //Composes the graphics graphic1.add(ellipse1); graphic1.add(ellipse2); graphic1.add(ellipse3); graphic2.add(ellipse4); graphic.add(graphic1); graphic.add(graphic2); ! graphic.add(graphic1); graphic.add(graphic2);
19. /** Client */ public class Program { public static void main(String[] args) { //Initialize four ellipses … ! //Initialize three composite graphics … ! //Composes the graphics … … ! … ! //Prints the complete graphic (4 times "Ellipse"). graphic.print(); }
20. Questions?
21. What’s proxy pattern?
22. it makes the clients of a component communicate with a representative rather than to the component Itself.
23. enables enhanced efficiency, easier access and protection from unauthorized access.
24. examples?
25. a network proxy
26. large object in memory
27. reference counting pointer objects
28. Context • A client needs access to the services of another component • Direct access is technically possible, but may not be the best approach
29. Problem • Often it’s inappropriate to access the component directly • Direct and unrestricted access can be insecure and inefficient
30. Key considerations
31. run-time efficient
32. cost effective
33. safe for both client and component
34. transparent interfaces
35. should be similar to component’s interface
36. aware of performance penalties
37. solution
38. communicate to representative — proxy
39. proxy performs pre & post processing (e.g access control)
40. structure
41. uses proxy to fulfill it’s task Client
42. a common interface for proxy and original AbstractOriginal
43. provides interface of the original to clients proxy
44. ensures safe, efficient and correct access to the original proxy
45. collaborates with original proxy
46. implements a particular service Original
48. dynamics
50. implementation considerations
51. migrate all client responsibilities to proxy
52. remove all direct relationship with client and original
53. variants
54. To shield network addresses and inter-process communication protocols from clients Remote Proxy
55. Access authorization e.g network authorization to use Internet Protection Proxy
56. Multiple local components can share results from a remote proxy e.g. Cache server Cache Proxy
57. Provide synchronized access to services in a multi-access or multi- threaded environment Synchronization Proxy
58. Prevents accidental deletion of components or collects usage statistics e.g. reference counting objects Counting Proxy
59. Protects local clients from outside world Firewall proxy
60. benefits
61. enhanced efficiency and lower cost e.g. cache proxy
62. decouple clients from real objects
63. separate housekeeping from functionality
64. liabilities
65. less efficiency due to indirection
66. overkill using sophisticated strategies ! e.g. caching server in a dynamic environment
67. Questions?