Servlets & JSPs - Sharad Ballepu sharadballepu@sharmanj.com www.sharmanj.com

Agenda

Introduction Servlet ArchitectureServlet lifecycleRequest and ResponseBeing a Web ContainerSession managementOverview of JSPJSP ElementsQ & A

Servlets & JSPs

Request-response model. requestresponseHTTP

HTMLHTTP Request

ClientServerIntroduction request-response model

HTTP Request HTTP Response Key elements of a request stream:

HTTP method (action to be performed).

The page to access (a URL).

Form parameters.

Key elements of a response stream:

A status code (for whether the request was successful).

Content-type (text, picture, html, etc).

The content ( the actual content).

Introduction what is a request and response

Where does Servlet come into the picture?Web ServerApplicationHelper ApplicationWeb Server machineI can serve only static HTML pagesNot a problem. I can handle dynamic requests.The Helper Application is nothing but a SERVLETIntroduction What is a Servlet

What is a Web Container?GET...Web ServerServletWeb ContainerGET...GET...requestClientServlet Architecture -Web Container

How does the Container handle a request?Web ContainerServletThreadService()doGet()

. requestresponseresponseWeb ServerHttp requestClientServlet Architecture Web Container

What is the role of Web Container ?

Communication Support

Lifecycle Management

Multi-threading support

Security

JSP Support

The CONTAINERS1S3S4S2JSP1The container can contain multiple Servlets & JSPs within itServlet Architecture Web Container

How does the Container know which Servlet the client has requested for?

A Servlet can have 3 names

Client known URL name

Deployer known secret internal name

Actual file name

LoginServ com.Login

LoginServ /Logon .. ..

Web.xml

Servlet Architecture Deployment Descriptor

The Servlet lifecycle is simple, there is only one main state Initialized.InitializedDoes not existconstructor()init()destroy()Service()Servlet Lifecycle

GenericServletHttpServletYour Servlet Servlet

InterfaceAbstract classAbstract classConcrete classIf not overridden, implements init() method from the Servlet interface,If not overridden, implements service()method.We implement the HTTP methods here.Servlet Lifecycle - Hierarchy

Servlet Lifecycle 3 big moments

When is it calledWhat its forDo you override itinit()The container calls the init() before the servlet can service any client requests.To initialize your servlet before handling any client requests.

Possiblyservice()When a new request for that servlet comes in.To determine which HTTP method should be called. No. Very unlikelydoGet() or doPost()The service() method invokes it based on the HTTP method from the request.To handle the business logic. Always

The Container runs multiple threads to process multiple requests to a single servlet.ServletThread AThread BContainerClient AClient BresponseresponserequestrequestServlet Lifecycle Thread handling

The HTTP request method determines whether doGet() or doPost() runs.Request and Response GET v/s POST

GET (doGet()) POST (doPost())HTTP Request The request contains only the request line and HTTP header.Along with request line and header it also contains HTTP body.Parameter passingThe form elements are passed to the server by appending at the end of the URL.The form elements are passed in the body of the HTTP request.Size The parameter data is limited (the limit depends on the container)Can send huge amount of data to the server.IdempotencyGET is IdempotentPOST is not idempotentUsageGenerally used to fetch some information from the host.Generally used to process the sent data.

RequestCan the Servlet Serve the request?Send resourceYesDoes the Servlet knowWho can serve?Error pageSend RedirectRequest DispatcherNoYesNoRequest and Response The response

Servlet 2Servlet 1Servlet 3JSP 1Servlet ContextServlet ConfigServlet ConfigServlet ConfigServlet ConfigBeing a Web Container Servlet Config and Context

What are init parameters?Difference between Servlet Context and Config Init parameters

Being a Web Container init parameters

Context Init ParametersServlet Init Parameters ScopeScope is Web ContainerSpecific to Servlet or JSPServlet codegetServletContext()getServletConfig()Deployment DescriptorWithin the element but not within a specific elementWithin the element for each specific servlet

What exactly, is an attribute?Difference between Attributes and parameters

Being a Web Container - Attributes

AttributesParametersTypesContextRequestSessionContextRequestServlet InitMethod to setsetAttribute(String, Object)We cannot set Init parameters. Return typeObjectStringMethod to getgetAttribute(String)getInitParameter (String)

How sessions work?ID# 42dark1432ID# 42darkale#4212request, darknewsetAttribute(dark)response, ID# 42request, ale, ID# 42HttpSessionHttpSessionContainerClient AClient AContainerSession Management Session Tracking

HTTP/1.1 200 OKSet-Cookie: JSESSIONID=0ABSContent-Type: text/htmlServer: Apache-Coyote/1.1

POST / login.do HTTP/1.1

Cookie: JSESSIONID=0ABSAccept: text/html

Heres your cookie with session ID insideOK, heres the cookie with my requestHTTP ResponseHTTP RequestHttpSession session = request.getSession();Client AClient AContainerContainerSession Tracking Cookies

URL ;jsessionid=1234567HTTP/1.1 200 OKContent-Type: text/htmlServer: Apache-Coyote/1.1

< a href = http:// www.sharmanj.com/Metavante;jsessionid=0AAB> click me

GET /Metavante;jsessionid=0AAB

HTTP / 1.1Host: www.sharmanj.comAccept: text/html

ContainerContainerClient AClient AHTTP ResponseHTTP RequestSession Tracking URL Rewriting

public void doGet(request, response){ PrintWriter out = response.getWriter(); String name = request.getParameter(name);out.println();out.println("Hello + name);out.println(); }

Hello

Servlets : HTML within Java business logicJSPs : Java within HTML Presentation logicJSP Overview - Servlets v/s JSPs

In the end, a JSP is just a Servlet.

0010 00011100 10010001 0011Import javax.servlet.HttpServlet.*JSPServletMyJsp.jspMyJsp_jsp.javaMyJsp_jsp.classMyJsp_jsp ServletwritesIs translated toCompiles toIs loaded andInitialized asJSP Overview - What is a JSP

Scriptlets

Expressions

Declarations

DirectivesPages - include - taglib -

= out.println(i);= out.println(d.getName());JSP Elements

Where does the JSP code land in the Servlet?

Hello! Welcome

import javax.servlet.HttpServlet.*import foo.*;public class MyJsp_jsp extends HttpServlet{ int count = 0; public void display() { out.println(Hello);} public void _jspService(req, res) { int i = 0; out.println(\r); out.println(Hello! Welcome); } } JSP Elements JSP to Servlet

Q & A