Presentation & Business Tier Design Patterns Pearce

Definitions Pattern = reusable design Pattern Catalog = catalog of design patterns –Horizontal –Vertical Architectural pattern = Macro pattern = a composite pattern

Four Tier Architecture

Issues Migrating Business Logic from Presentation to Business Tier Providing B2B Business Tier

The Model-View-Controller Macro Pattern

MVC Variations Service to Worker View-Dispatcher

Service to Worker

Business Tier (Model) Patterns Entities Beans Value Objects Data Access Objects DAO Factories etc.

Entities An entity is an object that represents a persistent business entity such as an account or a customer. Entities must persist between the sessions or transactions that use them. Entities are stored in files or databases Entities are beans –Simple or EJB.

Java Beans A Java bean is an object that conforms to the Java Bean Component Model. –getters & setters for attributes –notifies listeners of attribute changes –serializable –etc.

Example: A Person Entity public class Person extends Entity { private String first; private String last; private Address address; private Phone phone; public Phone getPhone() { return phone; } public void setPhone(Phone p) { phone = p; } // etc. }

Value Objects A value object holds the attributes of one or more entities in public fields. Pass value objects, not entities, between layers. This reduces network traffic. Value objects can update and create entities. Entities can create value objects.

public class PersonVO extends ValueObject { public String first; public String last; public int addressOid; public String street; public String apartment; public String city; public String state ; public String zip; public int phoneOid; public String phone; public void update(Person per) {... } public Person makePerson() {... } } Example: Person VO

Address Book Entities

Data Access Objects (DAOs) A DAO represents a data source. DAOs are created by DAO factories.DAO factories DAOs hide the complexities of connecting with the underlying data source.

Example: Person DAO public interface PersonDAO { public int insert(PersonVO pvo) throws DAOException; public boolean delete(String name) throws DAOException; public PersonVO find(String name) throws DAOException; public boolean update(PersonVO pvo) throws DAOException; }

DAOs & Factories

Presentation Tier Patterns (Controller and View) View View Helper Front Controller

Single access point for all forms. May verify & validate request May analyzes request May assemble business data needed by view (Service-to-Worker) Selects and dispatches to view

View Helper Acts as intermediary between view and business tier Performs view-specific tasks

View Generates HTML response View may assemble the data it needs (Dispatcher-View) Needed data may be assembled by controller (Service-to-Worker) Provides utilities for generating HTML

Dispatcher-View Pattern

Every Servlet has 3 AMaps