domain driven web development with webjinn sergei kojarski college of computer & information...

Domain Driven Web Development With WebJinn

Sergei KojarskiCollege of Computer & Information Science

Northeastern University

joint work withDavid H. Lorenz

http://webjinn.org

Outline

Background Overview Problem Solution Conclusion Future work

Web Application

WebApp

WebApp

Client HTTP Server

Browser Resource

• An HTTP gateway to a server–side resource

• HTTP Request/Response model

• Converts between HTTP and Resource terms

BACKGROUNDBACKGROUND

Web Development

Written in two programming languages:

Functionality (e.g., Java, C, Perl)

Presentation (e.g., XML, HTML)


Fille

Insert 2 people: designer and

Theory and Practice

Well-understood Simple

functionality Interactions

patterns


Difficult to create Complicated

implementations No reusable

components

Concept State of the art

Fille

Insert 2 people: designer and

Schema

HTTP ResourceSchema

Functionality

server-side operations

Presentation

HTML response

Control

high-level control-flow

Functionality

Presentation

Control

<%@ page import="java.sql.*" %> <%try{

Class.forName("org.gjt.mm.mysql.Driver").newInstance(); java.sql.Connection conn; conn = DriverManager.getConnection( "jdbc:mysql://localhost/database?user=login&password=pass"); try { Statement st = conn.createStatement(); ResultSet rs = st.executeQuery("select name,email,message from guestbook");%>

<%if (rs.next() {%>

<table width=100% border=0 cellspacing=1 cellpadding=1><%do {%> <tr><td>Visitor: <a href='mailto: <%=rs.getString("emai")%>'> <%=rs.getString("name")%></a></td></tr> <tr><td><%=rs.getString("message")%></td></tr><%} while (rs.next());%></table>

<%} else {%>  Guest book is empty.  <%} } finally {conn.close();} } catch (Exception e) {%> Server error: <%=e.getMessage()%><%}%>

The Problem: Tangling and Scattering

page code example:

name email message

Visitor: <%=rs.getString(“email”)%><%=rs.getString(“name”)%>

<%=rs.getString(“message”)%>

OVERVIEWOVERVIEW

Server error: <%=e.getMessage()%>

 Server error: <%=e.getMessage()%>

Separation of concerns

<%@ page import="java.sql.*" %> <%try{ Class.forName("org.gjt.mm.mysql.Driver").newInstance(); java.sql.Connection conn; conn = DriverManager.getConnection( "jdbc:mysql://localhost/database?user=login&password=pass"); try { PreparedStatement pst = conn.prepareStatement( (“insert into guestbook (name,email,message) values (?,?,?)”); pst.setString(1,request.getParameter(“name”); pst.setString(2,request.getParameter(“email”); pst.setString(3,request.getParameter(“message”); pst.execute(); %>

Message was successfully added

} finally {conn.close();} } catch (Exception e) {%>

<%}%>



<%if (rs.next() {%>

<table width=100% border=0 cellspacing=1 cellpadding=1><%do {%> <tr><td> Visitor: <a href='mailto: <%=rs.getString("emai")%> '> <%=rs.getString("name")%> </a></td></tr> <tr><td> <%=rs.getString("message")%> </td></tr><%} while (rs.next());%></table>

<%} else {%>  Guest book is empty.  <%} } finally {conn.close();} } catch (Exception e) {%>

<%}%>

<form action="doInsert.jsp"><tr><th colspan=2>New Message</th></tr><tr><td>Your Name</td><td><input type=text name="name"></tr><tr><td>E-mail</td><td><input type=text name="email"></tr><tr><td>Message</td><td><textarea name="message"></textarea><tr><td colspan=2><input type=submit value="Add"></td></tr></form>

select.jsp doInsert.jsp

insertForm.jsp

name email message

name email message pst.setString(1,request.getParameter(“name”);

<input type=text name="name">Your Name

pst.setString(1,request.getParameter(“email”); pst.setString(1,request.getParameter(“message”);

E-mailMessage

<input type=text name=“email"><textarea name=“message"></textarea>

?,?,?



Main contribution: schema concern modularization

OVERVIEWOVERVIEW

Fille

Easier step: collpasing intraHarder step: unweaving inter

Outline


Example:Guestbook

PROBLEMPROBLEM

Example: Guestbook

• Typical client-server interaction• Typical components (select, insert)• Typical problems

• intra-crosscutting• inter-crosscutting

PROBLEMPROBLEM

Guestbook Architecture

Browser guestbook database table

SQL queries

select.jsp

doInsert.jsp

insertForm.jsp

HTTP

PROBLEMPROBLEM

Retrieves messagesRetrieves messages

A form for adding a message

A form for adding a message

Posts a new messagePosts a new message

Select records from guestbook table

Print “Content”

Load driver and connect to database

If table is not empty then

Else

Print “No records”

Close database connection

Catch exception

Print “Service not available”

select.jsp



<%if (rs.next() {%>

<table width=100% border=0 cellspacing=1 cellpadding=1><%do {%> <tr><td>Visitor: <a href='mailto: <%=rs.getString("emai")%>'> <%=rs.getString("name")%></a></td></tr> <tr><td><%=rs.getString("message")%></td></tr><%} while (rs.next());%></table>

<%} else {%>  Guest book is empty.  <%} } finally {conn.close();} } catch (Exception e) {%> Server error: <%=e.getMessage()%><%}%>

page code description

name email message



select name, email, message from …name email message

<%=rs.getString(“name”)%>

href=“ <%=rs.getString(“email”)%>

> </a>

<%=rs.getString(“message”)%> </td>

PROBLEMPROBLEM

Construct and execute SQL insert statement

Print “Fail”

Print “Message added”

doInsert.jsp

<%@ page import="java.sql.*" %> <%try{ Class.forName("org.gjt.mm.mysql.Driver").newInstance(); java.sql.Connection conn; conn = DriverManager.getConnection( "jdbc:mysql://localhost/database?user=login&password=pass"); try { PreparedStatement pst = conn.prepareStatement( (“insert into guestbook (name, email, message) values (?,?,?)”); pst.setString(1,request.getParameter(“name”); pst.setString(2,request.getParameter(“email”); pst.setString(3,request.getParameter(“message”); pst.execute(); %>


} finally {conn.close();} } catch (Exception e) {%> Server error: <%=e.getMessage()%><%}%>

Load driver and connect to database

Close connection

Catch exception


name email messagepst.setString(1,request.getParameter(“name”);pst.setString(1,request.getParameter(“email”);

pst.setString(1,request.getParameter(“message”);

?,?,?

PROBLEMPROBLEM

insertForm.jsp

Return an HTML formthat the visitor can fill in order to add a new message into the guestbook.

<form action="doInsert.jsp"><table> <tr><th colspan=2>New Message</th></tr> <tr> <td>Your Name</td> <td><input type=text name="name"> </tr> <tr> <td>E-mail</td> <td><input type=text name="email"> </tr> <tr> <td>Message</td> <td><textarea name="message"></textarea> </tr><tr><td colspan=2><input type=submit value="Add"></td></tr></table></form>


<input type=text name="name">

Your Name

E-mail

Message

<input type=text name=“email">

<textarea name=“message"></textarea>

PROBLEMPROBLEM

Intra- versus inter-crosscutting

Intra Tangling Dynamic pages Page scoped OOP solution

Inter Scattering Dynamic and static Crosscuts pages AOP solution

All scheme expressions relate to

the same instance

insertForm.jsp

select.jsp doInsert.jspIllustration


<%@ page import="java.sql.*" %>

<%try{


<%if (rs.next() {%>


<%} else {%>

 Guest book is empty. 

<%}

} finally {conn.close();}

} catch (Exception e) {%>


<%}%>


Class.forName("org.gjt.mm.mysql.Driver").newInstance(); java.sql.Connection conn; conn = DriverManager.getConnection( "jdbc:mysql://localhost/database?user=login&password=pass"); try { PreparedStatement pst = conn.prepareStatement( (“insert into guestbook (name,email,message) values (?,?,?)”); pst.setString(1,request.getParameter(“name”); pst.setString(2,request.getParameter(“email”); pst.setString(3,request.getParameter(“message”); pst.execute(); %>


} finally {conn.close();} } catch (Exception e) {%>

 Server error: <%=e.getMessage()%>

<%}%>

TanglingTangling

ScatteringScattering

Dynamic pagesDynamic pages

Dynamic and staticDynamic and static

Page scopedPage scoped

Crosscuts pagesCrosscuts pages

OOP solutionOOP solution

AOP solutionAOP solution

PROBLEMPROBLEM

High development cost

High maintenance cost

Loss of reuse opportunities

Increases dependency between developer groups, error-prone, etc.

Natural language

Correct?

Consequence of inter-crosscutting

PROBLEMPROBLEM





Loss of reuse opportunitiesLoss of reuse opportunities

Changes to the schema trigger complex code updates

Cost of schema changes out-weights reuse benefits

Outline






Unweaving inter-crosscutting



<%if (rs.next() {%>


<%} else {%>


<%} } finally {conn.close();} } catch (Exception e) {%>


<%}%>


name email message

name email message pst.setString(1,request.getParameter(“name”);

<input type=text name="name">Your Name

pst.setString(1,request.getParameter(“email”); pst.setString(1,request.getParameter(“message”);

E-mailMessage

<input type=text name=“email"><textarea name=“message"></textarea>

?,?,?



Schema-related expressions are clustered by operationselect.jsp doInsert.jsp

insertForm.jsp

Constructing SQL select statement

Constructing SQL insert statement

Rendering guest book messages as HTML table

Rendering HTML form for inserting a message

XP1

XP2

XP4

1. Substitute clusters with schema-shy extension points1. Substitute clusters with schema-shy extension points

To unweave inter-crosscutting we…

2. Specify schema-related code in a separate module2. Specify schema-related code in a separate module







<%if (rs.next() {%>


<%} else {%>


<%} } finally {conn.close();} } catch (Exception e) {%>


<%}%>


XP1

XP2

XP3

XP4

Abstract application SchemaWeaver

XP33. Employ weaver to produce executable code 3. Employ weaver to produce executable code

XP ModelXP Model

SOLUTIONSOLUTION

DDD model

SOLUTIONSOLUTION

DDD = MVC + XPWhat about having one model that solves both problems?

Solution space

SOLUTIONSOLUTION

Problem Model Framework

Intra-crosscutting

MVC Apache Struts

Inter-crosscutting

XP WebJinn/XP

Intra- and Inter-

crosscuttingDDD WebJinn

WebJinn Architecture

Resource

ModelController

View

request

response

Java classes

JSP pages

Controller servlet

Schema

SOLUTIONSOLUTION

Benefits of WebJinn

Decreased dependency between developer groups

Adaptability to schema changes High code reusability

SOLUTIONSOLUTION

Dynamicpage

DDDevolution

Conclusion

CONCLUSIONCONCLUSION

Intra-crosscutting

Inter-crosscutting

Staticpage

CG

I scripts

MVC

XP

Future Work

AOP Model AOP Web Development

More Information www.webjinn.org

Questions

Coffee?

Related Models & Frameworks

Apache Struts Java Server Facets The MVC Model JSP PHP ASP

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