Web Technologies – Server-side

What’s in store… Basic Server concepts HTTP Request, Response and Session Understanding Servlets The deal with JSP s The quest for scriptless JSPs – Taglibs , JSTL Security, Filters and Listeners Understanding the web application descriptor – web.xml The evolution of Web Application Architecture

Basic Server concepts

HTTP Request, Response and Session

Understanding Servlets

The deal with JSP s

The quest for scriptless JSPs – Taglibs , JSTL

Security, Filters and Listeners

Understanding the web application descriptor – web.xml

The evolution of Web Application Architecture

R O L E of a S E R V E R Receives the request, finds the resource, returns the response Of course, there’s 404 ! What are the other status codes? Can be the physical m/c [hardware] or web server app [software] Most of the communication is HTTP based Provides a container within which server code can execute

Receives the request, finds the resource, returns the response

Of course, there’s 404 ! What are the other status codes?

Can be the physical m/c [hardware] or web server app [software]

Most of the communication is HTTP based

Provides a container within which server code can execute

Protocols P R O T O C O L S HTTP is the most commonly used Other supported protocols are FTP, HTTPS, FILE Each of these protocols operate on top of TCP/IP TCP chunks data into blocks and makes sure all of it reaches dest IP underlying protocol to move/route data packets between src & dest

HTTP is the most commonly used

Other supported protocols are FTP, HTTPS, FILE

Each of these protocols operate on top of TCP/IP

TCP chunks data into blocks and makes sure all of it reaches dest

IP underlying protocol to move/route data packets between src & dest

HTTP R E Q U E S T method informs server about the type of request, how the message is formatted GET and POST are most common, but there are others – PUT, HEAD, DELETE, etc Total amount of info through GET is limited Submitted request data is visible with GET. Passwords! Bookmarking of <form> data submission not possible with POST

method informs server about the type of request, how the message is formatted

GET and POST are most common, but there are others – PUT, HEAD, DELETE, etc

Total amount of info through GET is limited

Submitted request data is visible with GET. Passwords!

Bookmarking of <form> data submission not possible with POST

G E T Request Internals Request Line HTTP Method Path to the resource All the request parameters Protocol version for the request Request headers

P O S T Request Internals Request Line HTTP Method Path to the resource Protocol version for the request Request headers Message body – “payload”

Response Internals Protocol version used by server HTTP Response status code Response headers Text version of status code Body content – HTML or other Mime-type

HTTP S E S S I O N The conversational state Both browsers and servers possess NO short/long term memory! HTTP is stateless ! In comes session management – URL rewriting - URL needs to be encoded – response.encodeURL(“…”) Cookie handling

The conversational state

Both browsers and servers possess NO short/long term memory!

HTTP is stateless !

In comes session management –

URL rewriting - URL needs to be encoded – response.encodeURL(“…”)

Cookie handling

S E R V L E T S … Live to service clients Needs to know what and how to find data in request Send back the response to the browser, or elsewhere The servlet container transforms HTTP Request and Response to HTTPRequest and HTTPResponse objects The container relies on web descriptor to determine which servlet to invoke

Live to service clients

Needs to know what and how to find data in request

Send back the response to the browser, or elsewhere

The servlet container transforms HTTP Request and Response to HTTPRequest and HTTPResponse objects

The container relies on web descriptor to determine which servlet to invoke

S E R V L E T L I F E C Y C L E init – only ONCE when servlet gets loaded So when all does the servlet get loaded ? service – every time a particular servlet is invoked HTTPServlet provides the doGet and doPost methods destroy – when the web application is brought down <<interface>> Servlet GenericServlet HTTPServlet YourServletClass

init – only ONCE when servlet gets loaded

So when all does the servlet get loaded ?

service – every time a particular servlet is invoked

HTTPServlet provides the doGet and doPost methods

destroy – when the web application is brought down

S E R V L E T S – Important Methods HTTPRequest – getParameter(String) get/set Attribute(String, Object) getSession(boolean) getCookies()… HTTPResponse – addCookie() addHeader() setStatus() getOutputStream() getWriter()

HTTPRequest –

getParameter(String)

get/set Attribute(String, Object)

getSession(boolean)

getCookies()…

HTTPResponse –

addCookie()

addHeader()

setStatus()

getOutputStream()

getWriter()

J S P – Java Servlet Pages Container converts JSP -> Java source code -> compiles into a Servlet Can directly write Java code in a JSP, but DO NOT! Java code contained within <% javaCodeComesHere; %> Incase of expressions, never end with a semi-colon - <%= expression %> Certain Java objects are available implicitly request, response, out, session, config, application, page, … Taglibs or JSTL are much better options

Container converts JSP -> Java source code -> compiles into a Servlet

Can directly write Java code in a JSP, but DO NOT!

Java code contained within <% javaCodeComesHere; %>

Incase of expressions, never end with a semi-colon - <%= expression %>

Certain Java objects are available implicitly

request, response, out, session, config, application, page, …

Taglibs or JSTL are much better options

J S P Structure Non-implicit Java classes can be imported using directive <%@ page import=“org.abc.xyz.*” %> “ ,” can be used to separate multiple imports Scriptlet - <% … %> Directive - <%@ … %> Expression - <%= … %> Comments - <%-- … --%> Declaration - <%! … %>

Non-implicit Java classes can be imported using directive

<%@ page import=“org.abc.xyz.*” %>

“ ,” can be used to separate multiple imports

Scriptlet - <% … %>

Directive - <%@ … %>

Expression - <%= … %>

Comments - <%-- … --%>

Declaration - <%! … %>

J S P Lifecycle Container first checks amongst the directives Creates an HttpServlet sub-class In Tomcat, org.apache.jasper.runtime.HttpJspBase , extended Imports are resolved A package declaration – org.apache.jsp.[folderStructure] – is added Builds the service() method - _jspService() The servlet class – JspName_jsp.java – is created

Container first checks amongst the directives

Creates an HttpServlet sub-class

In Tomcat, org.apache.jasper.runtime.HttpJspBase , extended

Imports are resolved

A package declaration – org.apache.jsp.[folderStructure] – is added

Builds the service() method - _jspService()

The servlet class – JspName_jsp.java – is created

J S P - I M P L I C I T Objects JspWriter – out HttpServletRequest – request HttpServletResponse – response HttpSession – session ServletContext – application ServletConfig – config JspException – exception PageContext – pageContext Object -- page

JspWriter – out

HttpServletRequest – request

HttpServletResponse – response

HttpSession – session

ServletContext – application

ServletConfig – config

JspException – exception

PageContext – pageContext

Object -- page

Scriptless J S P - Taglibs & JSTL Taglibs are powerful – but non-standardised! Multiple vendors – different Taglibs – chaos! Operations requiring scripting – iteration, accessing scoped objects, etc JSTL encapsulates core functionalities related to – Iteration & conditionals [ Core ] XML [ XML ] – useful in case of XML content Database access [ Database ] Internationalised formatting [ Internationalization ] Utility functions [ Functions ]

Taglibs are powerful – but non-standardised!

Multiple vendors – different Taglibs – chaos!

Operations requiring scripting – iteration, accessing scoped objects, etc

JSTL encapsulates core functionalities related to –

Iteration & conditionals [ Core ]

XML [ XML ] – useful in case of XML content

Database access [ Database ]

Internationalised formatting [ Internationalization ]

Utility functions [ Functions ]

Inside J S T L Core library – iterations, scope access, conditionals <%@ taglib prefix=&quot;c&quot; uri=&quot;http://java.sun.com/jsp/jstl/core&quot; %> <c:set scope=“”>, <c:remove> - set/remove variables in defined ‘scope’ <c:forEach var=“” items=“” begin=“” end=“” varStatus=“”> - Iteration <c:if test=“”> - conditional if <c:choose> - condition if-else <c:when test=“”></c:when> <c:otherwise></c:otherwise> </c:choose> <c:import> - including another JSP file, no buffering

Core library – iterations, scope access, conditionals

<%@ taglib prefix=&quot;c&quot; uri=&quot;http://java.sun.com/jsp/jstl/core&quot; %>

<c:set scope=“”>, <c:remove> - set/remove variables in defined ‘scope’

<c:forEach var=“” items=“” begin=“” end=“” varStatus=“”> - Iteration

<c:if test=“”> - conditional if

<c:choose> - condition if-else <c:when test=“”></c:when> <c:otherwise></c:otherwise> </c:choose>

<c:import> - including another JSP file, no buffering

Inside J S T L … Expression Language [EL] library – powerful set of functions <%@ taglib prefix=&quot;fn&quot; uri=&quot;http://java.sun.com/jsp/jstl/functions&quot; %> <fn:length>, <fn:toUpperCase>, <fn:toLowerCase>, <fn:substring>, <fn:substringBefore>, <fn:substringAfter>… <%-- truncate name to 30 chars and display it in uppercase --%> ${fn:toUpperCase(fn:substring(name, 0, 30))} <%-- Display the name if it contains the search string --%> <c:if test=&quot;${fn:containsIgnoreCase(name, searchString)}&quot;> Found name: ${name} </c:if>

Expression Language [EL] library – powerful set of functions

<%@ taglib prefix=&quot;fn&quot; uri=&quot;http://java.sun.com/jsp/jstl/functions&quot; %>

<fn:length>, <fn:toUpperCase>, <fn:toLowerCase>, <fn:substring>, <fn:substringBefore>, <fn:substringAfter>…

<%-- truncate name to 30 chars and display it in uppercase --%> ${fn:toUpperCase(fn:substring(name, 0, 30))}

<%-- Display the name if it contains the search string --%> <c:if test=&quot;${fn:containsIgnoreCase(name, searchString)}&quot;> Found name: ${name} </c:if>

Inside J S T L Core library – iterations, scope access, conditionals <%@ taglib prefix=&quot;c&quot; uri=&quot;http://java.sun.com/jsp/jstl/core&quot; %> <c:set scope=“”>, <c:remove> - set/remove variables in defined ‘scope’ <c:forEach var=“” items=“” begin=“” end=“” varStatus=“”> - Iteration <c:if test=“”> - conditional if <c:choose> - condition if-else <c:when test=“”></c:when> <c:otherwise></c:otherwise> </c:choose> <c:import> - including another JSP file, no buffering

Core library – iterations, scope access, conditionals

<%@ taglib prefix=&quot;c&quot; uri=&quot;http://java.sun.com/jsp/jstl/core&quot; %>

<c:set scope=“”>, <c:remove> - set/remove variables in defined ‘scope’

<c:forEach var=“” items=“” begin=“” end=“” varStatus=“”> - Iteration

<c:if test=“”> - conditional if

<c:choose> - condition if-else <c:when test=“”></c:when> <c:otherwise></c:otherwise> </c:choose>

<c:import> - including another JSP file, no buffering

The WEB D E S C R I P T O R More famously known as the web.xml Defines almost all aspects of the deployed behaviour of the application Context of web application – the logical root folder of deployed resources <welcome-file-list> - The list of lookup files when context root is accessed <servlet-mapping> - maps URL patterns to servlets <servlet> - maps servlet names to servlet classes <init-parameter> - Servlet specific initialisation parameter <context-param> - Application context parameters

More famously known as the web.xml

Defines almost all aspects of the deployed behaviour of the application

Context of web application – the logical root folder of deployed resources

<welcome-file-list> - The list of lookup files when context root is accessed

<servlet-mapping> - maps URL patterns to servlets

<servlet> - maps servlet names to servlet classes

<init-parameter> - Servlet specific initialisation parameter

<context-param> - Application context parameters

The Evolution of Web Application Architecture Started with the servlets being the centre of the world Then came JSP, but soon all the Java scriptlets ruined it! Separation of Concerns! In came MVC [M]odel - Simple POJOs represent datasets [V]iew – JSPs without any or rare usage of Java scriptlets [C]ontroller – The servlets determined the flow of control Greater configurability and modularity led to MVC2 – Struts2, Spring, etc

Started with the servlets being the centre of the world

Then came JSP, but soon all the Java scriptlets ruined it!

Separation of Concerns!

In came MVC

[M]odel - Simple POJOs represent datasets

[V]iew – JSPs without any or rare usage of Java scriptlets

[C]ontroller – The servlets determined the flow of control

Greater configurability and modularity led to MVC2 – Struts2, Spring, etc

Some more Advanced Concepts Listeners – listen to any change events , provide hooks Typically have created and destroyed kind of methods ServletContextListener HttpSessionListener Filters – like a light-weight servlet that doesn’t create its own content Plugs into the request or response handling mechanism Mapped to a particular URL pattern If URL is mapped to servlet – filter will get executed before servlet Typical use – generating user access statistics

Listeners – listen to any change events , provide hooks

Typically have created and destroyed kind of methods

ServletContextListener

HttpSessionListener

Filters – like a light-weight servlet that doesn’t create its own content

Plugs into the request or response handling mechanism

Mapped to a particular URL pattern

If URL is mapped to servlet – filter will get executed before servlet

Typical use – generating user access statistics

R E F E R E N C E S Head First Servlets And JSP JSTL Presentation – Sang Shin, Sun Microsystems Java Boutique Wikipedia

Head First Servlets And JSP

JSTL Presentation – Sang Shin, Sun Microsystems

Java Boutique

Wikipedia