L19 Application Architecture

Lecture 19
Application Architecture

Agenda
 Layering
 Application Architecture
 Play! implementation
 Introduction to REST

Three Layers
 Presentation Layer for the User Interface
 Domain Layer for the domain logic
 Data Source Layer for the data access
Client
Client
Domain Data Source
– Separation of concern

Presentation Layer
 Consideration
– Separating the Presentation Logic from the Domain
Logic
– Simple vs. Rich user interface
– Should content be editable frequently

User Interfaces
 Clear separation of concerns is important
– Define the Presentation Logic
– Design the domain layer so the presentation can get
the information needed
– Semantics – or the meaning of things is important
– Presentation logic must avoid making assumptions on
the domain – the semantics should be a part of the
domain
• Use Data Transfer Objects to store semantics

Client Types
 Native OS Applications
– Windows, iOS, Android, Linux
 Embedded
– Run inside Web Browsers
– Flash, Java Applets
 Interactive Web Applications
– HTML with JavaScript
 HTML Presentation in Browsers
– Simple HTML

Client Types
 Mobile is not a client type
– It’s just smaller screen
– Which 60% people hold vertically
 People have their phones with them all the time
 Check their phone about110 times per day

Responsive Web Design
 Web pages that automatically adjust to the
screen size
– Should be the default design
 Problems with RWD
– Does not deal with context
– What would a persons be
looking for when using
a mobile phone?
– Excuse to avoid apps, when app might be a better
choice

MOBILE WEB MOBILE APP
Downloaded, runs
Using a mobile
on native hardware
web browser
PROS
Content is indexable
Device independent (almost)
Easier/Faster development & update
Easier to measure
CONS
Connection Dependence
Limited hardware integration
Bandwidth & browser limited UX
PROS
Connection independence
Better hardware integration
Better graphic performance & UX
CONS
Content is not web indexable
Device dependence
More expensive development & update
More complex to measue
Source: moz.com/blog/

Content Delivery
 Native, Embedded and Interactive Web Apps
– Require HTTP API call for dynamic content
– For example SOAP, REST with Json or XML
 HTML Presentation in Browsers
– Server side generated

Content Type
 Static Content such as graphic assets, doesn’t
change frequently
 Editable Content such as text, layout, mashed-up
content, editable by content owners,
frequently
 Dynamic Content stored in database and
manipulated by the domain logic

Content Management Systems
 Content is separated form the Enterprise system
– Managed by CMS software with its own database
– HTTP API calls for dynamic content from the
enterprise system
CLIENT
Web Browser
HTML
JavaScript CMS
Enterprise
Application
HTTP/REST/Json
OPERATOR
Editable
content
Static
content
Dynamic
content
Static
content

Domain Layer
 Where is the domain logic?
– Application Servers
– Lightweight Containers

Application Servers
 Domain Components are deployed on
Application Servers
– Distributed Multi-tiered Applications
– Example:
• Web Servers, EJB Servers

Lightweight Containers
 Assemble components from different projects
into a cohesive application
– Wiring is done with “Inversion of Control” - config
– Provide life-cycle management of objects
– Provide context
Web Browser
(User Interface)
Web Browser
(User Interface)
Web Server
Web Layer
Lightweight Container
Domain
Layer
Data
Source
Layer
Database

Data Source Layer
 How to create the mapping from the domain to
the Data Source Layer
– Gateways with no domain logic
– Records managed with some domain logic
– Data Mappers

Data Source Layer
 Domain Model uses gateway
Domain
Layer
Data
Source
Layer

Object Relational Mapping (ORM)
 Use a mapping layer to map between objects
and tables
– Mapping a data representation from an object model
to a relational data model with a SQL-based schema
 Mapping requires
metadata
– XML
 Authoring and
maintaining
metadata is less work than maintaining SQL

The Big Picture
Client
Web
Data
Domain
Server Source
DB
CMS
REST

The Big Picture in SOA
Client
Web
SERVICE Data
Domain
Server Source
DB
CMS
REST
Web
Data
REST
SERVICE Domain
Server Source
DB
Frameworks Libraries
Shared
Objects

Advice is a dangerous gift
There are no right answers
“Use the advice to prod your thinking, but don’t use it as
a replacement for your thinking”

Three Layers
 Presentation Layer for the User Interface
 Domain Layer for the domain logic
 Data Source Layer for the data access
Presentation
Layer
Domain Data Source
– What patterns to use?

Domain Layer
 Transaction Script
 Domain Model
 Table Module

Domain Layer
 Transaction Script
– Procedural
– Encapsulates the logic of each transaction
– Works well for systems that are transactional in
nature
 Drawbacks
– Does not handle complexity of logic
– Code duplications

Domain Layer
 Domain Model
– Works nicely for any type of domain logic
– Flexibility in creating an object oriented classes that
use abstractions and polymorphism
– Beautiful code
 Drawbacks
– Learning curve – understanding the model
– Requires skills
– Doesn’t map easily to relational database

Domain Layer
 Table Module
– Works well for data driven applications
– Fits well with relational databases
– Requires Record Set functionality
 Drawbacks
– Structured around the database
– Needs tooling support, for example Record Set
– Can become dependent on the environment

Data Source Layer
 Data Source for Transaction Script
– Fits well to use the Gateway patterns
– Row Data Gateway or Table Data Gateway
– Depends on the applications
– If the transactions are dealing with each row per
transactions, then Row Data Gateway works
– If working with tables, Table Data Gateway works

Data Source Layer
 Data Source for Table Module
– Table Module requires good support from Record
Set
– Table Data Gateway fits this well

Data Source Layer
 Data Source for Domain Model
– If the Domain Model is fairly simple, and maps the
database, Active Record works well
– If you want to provide abstraction the gateway
patterns become better choice, Row Data Gateway
and Table Data Gateway
– If things get more complication and there is need to
keep the model independent from the data source,
Data Mapper should be considered

Model View Controller
 For all types MVC architectural patterns applies
 Web Frameworks are usually implemented
using the Front Controller pattern
 Each request has an Action or a Controller
 Views are handle by Template View

The Big Picture
Domain Layer
Presentation
Layer
Service
Layer
Data Source
Domain
DB

QUIZ
We have a relatively simple domain logic that maps nicely to
the data schema, and we have good tools for Record Set
handling. What Domain Layer pattern would make sense?
A) Service Layer
B) Domain Model
C) Transaction Script
D) Table Module
✔

Exercise
 Design Web Application RuNews
– Front page displays RSS news items
– Content read with ImportContentProcess
– User can sign up and login

Overivew
Controller
View
Service Layer
Domain Model
Table Data
Gateway
routes ApplicationConext.xml
users

Signup
 As a user, I want to be able to sign up
Registration
Fields: name, username, password, email
Validtaion:
all fields are required
username must be at least 4 characters
password must be confirmed (typed in twice)

Play setup
43
 Project is created: RuNews
 Structure
controllers
is.ru.honn.news
views

The Database
 Table users
44
CREATE TABLE users
(
id int Identity (1, 1) primary key NOT NULL,
name varchar(128),
username varchar(128) unique,
password varchar(128),
email varchar(128),
)

Application.java
45
package controllers;
import play.*;
import play.mvc.*;
import views.html.*;
public class Application extends Controller
{
public static Result index()
{
return ok(index.render());
}
}

index
 View is views/index.scala.html
 Compiled: views/html/index
46
@main(Html("RuNews")) {
<h2>Registration</h2>
<p>
Here you can sign up: <a class="btn”
href="@routes.SignUp.blank">Sign up</a>
</p>
}

Routing
 conf/routes contains the routing information
47
# Routes
# This file defines all application routes (Higher priority routes first)
# ~~~~
# Home page
GET / controllers.Application.index()
# Sign Up
GET /signup controllers.SignUp.blank()
POST /signup controllers.SignUp.submit()
# Map static resources from the /public folder to the /assets URL path
GET /assets/*file controllers.Assets.at(path="/public", file)

RuNews Example
 User
48
public class User
{
protected int id;
protected String name;
protected String username;
protected String password;
protected String email;
public User()
{
}
public User(int id, String name, String username, String password,
String email)
{
this.id = id;
this.name = name;
this.username = username;

RuNews Example
 UserService is a Service Layer interface
 UserServiceData contains the implementation
49
public interface UserService
{
public int signup(User user);
public User login(String username, String password);
public void setUserDataGateway(UserDataGateway userDataGateway);
}

Adding Domain and Data Layers
 Implementation of Service
Layer, Domain and Data
Source Layers added
– Added as is
– Should be in model
50

 ApplicationContext.xml added to conf
– Drop data.xml
51
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="userService" class="is.ru.honn.news.service.UserServiceData">
<property name="userDataGateway" ref="userDataGateway"/>
</bean>
<bean id="userDataGateway" class="is.ru.honn.news.data.UserData">
<property name="dataSource" ref="dataSource"/>
</bean>
<bean id="dataSource"
class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName" value="net.sourceforge.jtds.jdbc.Driver"/>
<property name="url" value="jdbc:jtds:sqlserver://hrnem.ru.is:1433"/>

 Table Data Gateway injected into service
52
public class UserServiceData implements UserService
{
RuDataAccessFactory factory;
UserDataGateway userDataGateway;
public UserServiceData()
{
}
public void setUserDataGateway(UserDataGateway UserDataGateway)
{
this.userDataGateway = UserDataGateway;
}

RuNews Example
 Signup is a Controller
53
import views.html.signup.*;
import is.ru.honn.news.domain.UserRegistration;
public class SignUp extends Controller
{
final static Form<UserRegistration> signupForm
= Form.form(UserRegistration.class);
public static Result blank()
{
return ok(form.render(signupForm));
}

RuNews Example
 Signup is a Controller
54
public static Result submit()
{
Form<UserRegistration> filledForm = signupForm.bindFromRequest();
...
if (filledForm.hasErrors()) {
return badRequest(form.render(filledForm));
}
else {
User created = filledForm.get();
ApplicationContext ctx = new FileSystemXmlApplicationContext
("/conf/ApplicationContext.xml");
UserDataGateway userDataGateway =
(UserDataGateway)ctx.getBean("userDataGateway");
userDataGateway.addUser((User)created);
return ok(summary.render(created));
}
}
}

RuNews Example
 form.scala.html is the view
55
@(signupForm: Form[is.ru.honn.news.domain.UserRegistration])
@import helper._
@import helper.twitterBootstrap._
@title = {
Sign Up
}
@main(title, nav = "signup") {
@helper.form(action = routes.SignUp.submit) {
<fieldset>
<legend>Account informations</legend>
@inputText(
signupForm("name"),
'_label -> "Name",
'_help -> "Please enter your name.",
'_error -> signupForm.globalError
)

RuNews Example
 form.scala.html is the view
56
@inputText(
signupForm("username"),
'_label -> "Username",
'_help -> "Please choose a valid username.",
'_error -> signupForm.globalError
)
@inputText(
signupForm("email"), '_label -> "Email",
'_help -> "Enter a valid email address."
)
@inputPassword(
signupForm("password"),
'_label -> "Password",
'_help -> "A password must be at least 6 characters. "
)...
</fieldset>

RuNews Example
 forms.scala.html is the view
57
<fieldset>
@checkbox(
signupForm("accept"),
'_label -> None, '_text -> "You agree the Terms and conditions",
'_showConstraints -> false
)
</fieldset>
<div class="actions">
<input type="submit" class="btn primary" value="Sign Up">
<a href="@routes.Application.index" class="btn">Cancel</a>
</div>
}
}

RuNews Example
 summary.scala.html displayes the user
58
@(user: is.ru.honn.news.domain.User)
@main(Html("Account created!"), nav = "signup") {
<h2>Your account:</h2>
<p>Name: @user.getName()</p>
<p>Username: @user.getUsername()</p>
<p>Email: @user.getEmail()</p>
}

L19 Application Architecture

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