comp9321 web application engineeringcs9321/17s1/lectures/lec12/lec-12.pdf · static vs. dynamic web...

COMP9321 Web Application EngineeringSemester 1, 2017

Dr. Amin BeheshtiService Oriented Computing Group, CSE, UNSW Australia

Week 12(Wrap-up)

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http://webapps.cse.unsw.edu.au/webcms2/course/index.php?cid=2457

Assignments

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Assignments

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Assignment 1 – GradeBook

Assignment 2 – GradeBook

Assignment 3 – Due end of Week 12 (Sunday, May 28 2017, 23:59:59)

Final Exam

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Final Exam

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Final Exam

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Final Exam

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Sample Final Exam

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Sample Question:

Why is the stateless nature of HTTP a problem in Web application development? You Must illustrate your answer with an example.

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Sample Question:

Why is the stateless nature of HTTP a problem in Web application development? You Must illustrate your answer with an example.

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Sample Question:

Describe the Model-View-Controller (MVC) architecture pattern in detail. What are the advantages of using MVC over an architecture based solely on JSP pages?

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Sample Question:

Describe the Model-View-Controller (MVC) architecture pattern in detail. What are the advantages of using MVC over an architecture based solely on JSP pages?

Week 1 – 11

Review

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Different Layers in an Application

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Presentation Layer


HTML <form> method attribute

how to send form-data

URL variables (with method="get") , or HTTP post transaction (with method="post").

specifies

as

Method? Get/Post

Static vs. Dynamic Web Page


A static web page is delivered to the user exactly as stored, in contrast to dynamic web pages which are generated by a web application, and on demand!

web page whose construction is controlled by an application server processing server-side scripts.

software framework that provides both facilities to create web applications and a server environment to run them.

is-a

is-a

Java application servers

e.g.

It's core set of API and features are defined by Java EE.

The Web modules include Java Servlets and Java Server Pages.

http://docs.oracle.com/javaee/6/tutorial/doc/

Java Servlets


http://java.sun.com/products/servlet/index.jsphttp://docs.oracle.com/javaee/6/tutorial/doc/bnafd.html

A Lifecycle of a Servlet


The Web container controls the lifecycle of a servlet class:

• initialisation • ServletConfig• ServletContext• …

Attributes and Sharing Attributes


Managing the User State

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A problem in HTTP request/response:• HTTP is a stateless protocol.

• A single request/response;• Nothing is remembered 'between requests' from the same user;

• Web applications need to maintain users + their data.

It is a programmer's responsibility:• The term "session" is used to represent the data associated with one user while

she navigates around a Web application.

• Session is a conversional state between client and server.• Session can consists of multiple request and response between client and server.

• Since HTTP is stateless, the only way to maintain a session is when some unique information about the session (session id) is passed between server and client in every request and response.

Cookies


• Cookies are text files stored on the client computer and they are kept for various information tracking purpose.

• Java Servlets transparently supports HTTP cookies.

• There are three steps involved in identifying returning users:• Server script sends a set of cookies to the browser. e.g. session id• Browser stores this information on local machine for future use.• Next time, browser sends request + those cookies to the server

and server uses that information to identify the user.

JavaServer Pages (JSP) Technology


• JavaServer Pages (JSP) technology allows you to easily create web content that has both static and dynamic components.

• JSP technology makes available all the dynamic capabilities ofJava Servlet technology; but provides a more natural approachto creating static content.

• JSP is similar to PHP, but it uses the Java programminglanguage.

• To deploy and run JavaServer Pages, a compatible web serverwith a servlet container, such as Apache Tomcat, is required.

JSP


JSP Basics


JSP Page

JSP Elements

Template Text (HTML bits…)

ScriptingElements

DirectiveElements

ActionElements

Traditional

Modern EL Scripting${…}

ScriptletExpressionDeclarationComments

PageIncludeTaglib

custom

Standard

<abc:mytag>

<jsp:useBean><jsp:getProperty><jsp:setProperty><jsp:include><jsp:forward><jsp:param>

Extensible Markup Language (XML)


• XML originally designed to meet the challenges of large-scaleelectronic publishing.

• XML separates presentation issues from the actual data.

• XML plays an increasingly important role in the exchange of awide variety of data on the Web and elsewhere.• Needs a communication protocol?• e.g. SOAP stands for Simple Object Access Protocol

• SOAP is based on XML• SOAP is a W3C recommendation• SOAP uses XML Information Set for its message format.

The XML Family


XML: a markup language used to describe information.DOM: a programming interface for accessing and updating documents.DTD and XML Schema: describes the structure and content of XML documents.XSLT: a language for transforming XML documentsXPath: a query language for navigating XML documents.

XPointer: for identifying fragments of a document.XLink: generalises the concept of a hypertext link.XInclude: for merging documents.XQuery: a language for making queries across documents.RDF: a language for describing resources.

Semantic Web


• It is a collection of standard technologies to realize a Web of Data!

RDF, OWL, SPARQL, etc.

Web of Data beyond the Web of Documents!

Machine Readable Human Readable

The amount of information is growing exponentially.

W3C's "Semantic Web Vision“


1. Web information has exact meaning2. Web information can be understood and processed by computers3. Computers can integrate information from the web

Resource Description Framework (RDF)


• RDF is a framework for describing resources on the web.

• Publishing such descriptions on the Web creates the Semantic Web.

• RDF uses Web identifiers (URIs) to identify resources.

• Web documents• concepts from the real world (e.g. people, organisations, topics, things)

e.g.

• URIs (Uniform Resource Identifiers) are very important, providing both the core of the framework itself and the link between RDF and the Web.

Web Ontology Language (OWL)


• Ontology is about the exact description of things (web information) and their relationships.

• OWL was designed to provide a common way to process the content of web information

• OWL and RDF are much of the same thing, but OWL is a stronger language with greater machine interpretability than RDF.

• OWL provides additional vocabulary along with a formal semantics• OWL making it easier for machines to automatically process and integrate

information available on the Web.

• OWL has three sublanguages• OWL Lite• OWL DL• OWL Full

• OWL is complex:• OWL is a large set of additional terms

http://www.w3.org/TR/owl-features/

Rules


• There is a long history of rule languages and rule-based systems

• eg: logic programming (Prolog), production rules

• Lots of small and large rule systems • E.g. from mail filters to expert systems

• Why rules on the Semantic Web?• There are conditions that ontologies (ie, OWL) cannot express• a well known example is Horn rules: (P1 ∧ P2 ∧ …) → C

http://www.w3.org/TR/rif-overview/

A new requirement: exchange of rules


• Applications may want to exchange their rules:• e.g. negotiate eBusiness contracts across platforms• e.g. describe privacy requirements and policies

• Rule Interchange Format (RIF):• Goals:

• expresses the rules a bit like a rule language• can be used to exchange rules among engines

• Challenges:• Rule based systems can be very different

• different rule semantics• A universal exchange format is not feasible

http://www.w3.org/TR/rif-overview/

Linking Open Data (LOD)


- Goal: “expose” open datasets in RDF

- Set RDF links among the data items from different datasets

- Set up query endpoints

- Result: billions of triples and millions of links…

- The important point here is that :• the data becomes available to the World via a unified format

(ie, RDF).• the various datasets are interlinked together• e.g. DBpedia project

Query RDF Data (SPARQL)


• SPARQL Protocol And RDF Query Language, is an RDF query language.

• This specification defines the syntax and semantics of the SPARQL query language for RDF.

• SPARQL can be used to express queries across diverse data sources.

• SPARQL contains capabilities for querying required and optional graph patterns

• The results of SPARQL queries can be results sets or RDF graphs.

http://www.justanswer.com/

Data Persistence


• When you work with a relational database in a Java application, the Java code issues SQL statements to the database via the JDBC API.

• The Java Database Connectivity (JDBC) API provides universal data access from the Java programming language.

• Using the JDBC API, you can access virtually any data source, from relational databases to spreadsheets and flat files.

• The JDBC API is comprised of two packages:• java.sql• javax.sql (Hibernate, pp.5-29)

Accessing DB from an Application


PreparedStatement object


• A more realistic case is that the same kind of SQL statement is processed over and over (rather than a static SQL statement).

• In PreparedStatement, a place holder (?) will be bound to an incoming value before execution (no recompilation).

Data Access Objects (DAO)


Object-Relational Impedance Mismatch Problems


Object-Relational Impedance Mismatch Problems


https://docs.oracle.com/cd/E16162_01/user.1112/e17455/img/mismatch.gif

What is NoSQL?


• Stands for No-SQL or Not Only SQL??

• Class of non-relational data storage systems• E.g. BigTable, Dynamo, PNUTS/Sherpa, ..

• Usually do not require a fixed table schema nor do they use the concept of joins• Distributed data storage systems

• All NoSQL offerings relax one or more of the ACID properties (will talk about the CAP theorem)

Chapter 19: Distributed Databases

CAP Theorem


Three properties of a system• Consistency (all copies have same value)• Availability (system can run even if parts have

failed) Via replication.• Partitions (network can break into two or more

parts, each with active systems that can’t talk to other parts)

• Brewer’s CAP “Theorem”: You can have at most two of these three properties for any system.

• Very large systems will partition at some point.

Design Patterns


A pattern is a proven solution to a problem in a context.

Each pattern expresses a relation between a certain context, a problem, and a solution.

A design pattern represents a solutions to problems that arise when developing a software.

Design pattern are granular and applied at different levels such as:FrameworksSubsystemsSub-subsystems

Categories include:

Design Architectural Analysis Creational Structural Behavioral

J2EE Design Patterns


General Guideline for Servlet/JSP/JavaBeans


Securing your Web Application: Threats!


Session Management…


Transport Layer Security (e.g. HTTPS)


Performance


Performance Metrics


• Response Time• Throughput• Availability• Reliability• Resource Utilization

Scalability


Operational Laws


• Utilization Law• Little’s Law• Forced Flow Law

Architectural Considerations - Network


General Techniques for Improving Performance and Scalability


1. Caching/Replication2. Parallelism3. Redundancy4. Asynchrony5. Resource Pooling

Improving Performance using HTTP features


Improving Database Access


COMP9322 !!

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…from building a web site (cs9321) to building web services (cs9322) ...

context: “global/distributed/complex” business applications

• Goals:• understand the concept of services and business processes• articulate the motivation behind web service-based technologies• apply the knowledge in practical situations

COMP9322 course aims:• provide students with a deep understanding of SOA, service-orientation

paradigm, business processes and Web services as an implementation technology.

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Good Luck!

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