Introduction to Java Servlets Rochester Java Users Group January 16th, 2002 Tom Bullinger .

Introduction to Java Servlets

Rochester Java Users GroupJanuary 16th, 2002

Tom Bullinger

www.archwise.com

16Jan02 www.archwise.com Tom Bullinger

Agenda

HTTPWeb ArchitectureAppletsServletsSource / DemoReferences


ArchWise, LLC

A professional services firm specializing in software architecture. We provide

technical architecture solutions that are elegant as well as functional, and are

designed to meet the ongoing needs of the business as well as the marketplace.

We help our clients produce the right solution on time and on budget.

Member WWISA (http://www.wwisa.org)


ArchWise Software Architecture Map

Cover Story

BusinessArchitectur

e

Identity

VisionStatement

Goals Principles• To be the best…

• To provide …

• Our core …

• Partner with…

Architecture of Change

Results

Key Events

Projects

Organization Changes

Learnings

Key Hires

MarketArchitectur

e

TechnicalArchitectur

e

Execution

TestLogicalArch. Design

Code

Release

Market Map User Stories

Logical Architecture

Conceptual Architecture

UMLInterfacesUse Cases

Conceptual

Precise

Abstract

Meticulous

Start with: Business Plan

Start with:Architectureof Change

Start with:Conceptual Architecture

Start with:Logical Architecture

CRM

ERP

Supply Chain

Road Map

STAGES/TASKS

• Press Release

• Press Release

• Product Release

• Product Upgrade

MISSION

Q1 ‘02 Q2 ‘02

Stakeholder Profile

Context

Content Area

Menu

Brand

Tools/Status

BusinessGoals

SystemGoals

Magazine

Cover

Brain Storms

BusinessImage

Sidebars

QuotesHumanInterest

Lead Story


HTTP

Hypertext Transfer Protocol is: The primary protocol for Internet

communication Text based messages through sockets

Although payload may not be text Used to exchange resources

Files, video, audio, forms, graphics, etc. A Client / Server protocol (2-tier architecture)

Client opens a connection to a server Client sends a request message to the server Server sends a response message Server closes the connection

A stateless protocol Request Response


HTTP Request

Initial request line has 3 components: Method name Path to requested Resource HTTP version number

GET /web/index.html HTTP/1.0GET /web/index.html HTTP/1.0


HTTP Response

Initial response line (or status line) has 3 components: HTTP version number Response Status Code Reason Phrase

HTTP/1.0 404 Not FoundHTTP/1.0 404 Not Found

HTTP/1.0 200 OKHTTP/1.0 200 OK

HTTP/1.0 500 Server ErrorHTTP/1.0 500 Server Error


HTTP Headers

Headers are mostly optional, and include supporting information for the request or response messagesConsists of 2 parts: Header name Value

From: [email protected]: Mozilla/3.0Gold

From: [email protected]: Mozilla/3.0Gold

(Request)

Server: Apache/1.2b3-devLast-Modified: Fri, 31 Dec 1999 23:59:59 GMTContent-type: text/htmlContent-length: 47

Server: Apache/1.2b3-devLast-Modified: Fri, 31 Dec 1999 23:59:59 GMTContent-type: text/htmlContent-length: 47

(Response)


HTTP ExampleGET /path/file.html HTTP/1.0From: [email protected]: Mozilla/3.0Gold[blank line]

GET /path/file.html HTTP/1.0From: [email protected]: Mozilla/3.0Gold[blank line]

(Request)

HTTP/1.0 200 OKDate: Fri, 31 Dec 1999 23:59:59 GMTContent-Type: text/htmlContent-Length: 1354

<html> <body> <h1>Use Servlets!</h1> . . </body></html>[blank line]

HTTP/1.0 200 OKDate: Fri, 31 Dec 1999 23:59:59 GMTContent-Type: text/htmlContent-Length: 1354

<html> <body> <h1>Use Servlets!</h1> . . </body></html>[blank line]

(Response)


HTTP Methods

GET Requests a resource from the server Data is URL-encoded and appended to URL

HEAD Like GET, but returns the header only, not

the resource

POST Like GET, but data is URL-encoded in

message body Extra header lines Message body (data)

Typically a script or program invocation Response is typically created dynamically


URL Encoded Data (Key/Value)

HTML form data is usually URL-encoded to package it in a GET or POST submission. In a nutshell, here's how you URL-encode the name-value:

1. Convert all "unsafe" characters in the names and values to

"%xx", where "xx" is the ascii value of the character, in hex.

"Unsafe" characters include =, &, %, +, non-printable

characters, and any others you want to encode

2. Change all spaces to plusses.

3. String the names and values together with = and &

name1=value1&name2=value2&name3=value3name1=value1&name2=value2&name3=value3


Web Browser Architecture

Client(browser)

User

Server(web server) File

s


Typical Interaction:Browser

User

:Server HTML:File

URLGET URL HTTP/1.0 Decode(URL)

Read()HTTP/1.0 200 OK…

Display(HTML)


Problems?

Where is the work done?

Is this scalable?

Is this flexible?

What about dynamic content?


Applets

Extends Browser capabilityImplemented in JavaDownloaded from server to clientInterpreted by Browser (or plug-in)Embedded in static web pages (HTML)Provides rich visual functionalityLimited capability on the local machine Cannot access file system Cannot access non-home IP addresses Cannot access underlying OS


Applet Architecture

Client(browser)

User

Server(web server)File

s

Client(applet)

CustomBackend File

s



User

:Server HTML:File

URLGET URL HTTP/1.0 decode(URL)

:Applet

read(…)

read(…)

HTML

Applet

init()

start()paint()


Applet Limitations

No persistence mechanism

Client-side implementation

Requires custom backend for server-side

Practical limit to size (due to download)

Limited functionality on client(Actually limited by security manager, could

be replaced if desired)

Others?


Servlets

Implemented in JavaExtends the request / response capability of the serverHandles client HTTP requestsNo user interface componentCompatible with many serversServer / container manages lifecycleMay be reentrant


Lineage of a Servlet

Servlet

Generic Servlet

HttpServlet

Custom Servlet

(Interface)

(Abstract base class)

(Default implementation)

(user-supplied behavior)


Methods of interest

doGet - implements HTTP GET requests

doPost - implements HTTP POST requests

doPut - implements HTTP PUT requests

doDelete - for HTTP DELETE requests

init and destroy - manage resources that are held for the life of the servlet

getServletInfo - provides information about the servlet


Other Methods

service - Server entry point, dispatches

to doXXX methods

doTrace - implements HTTP TRACE

requests

doOptions - implements HTTP OPTIONS

requests


Servlet Data interface

Two interfaces are utilized in the client / servlet relationship: ServletRequest - encapsulates

communication from the client to the server ServletResponse - encapsulates

communication from the servlet back to the client

Instances provided by the frameworkServletRequest

HttpServletRequest

ServletResponse

HttpServletResponse


A Simple Servletpublic class SimpleServlet extends HttpServlet{ public void doGet (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { PrintWriter out; String title = "Simple Servlet Output";

// set content type and other response header fields first response.setContentType("text/html");

// then write the data of the response out = response.getWriter();

out.println("<HTML><HEAD><TITLE>"); out.println(title); out.println("</TITLE></HEAD><BODY>"); out.println("<H1>" + title + "</H1>"); out.println("<P>This is output from SimpleServlet."); out.println("</BODY></HTML>"); out.close(); }}


Servlet Architecture

Client(browser)

User

Server(web server) File

s

ServletFiles



User

:Server :Servlet

URLGET URL HTTP/1.0 decode(URL)

HTTP/1.0 200 OK…

Display(HTML)

service(rq, rs)

rq:Request rs:Response

doGet(rq, rs)

write(…)

Behaviorgoes here


Handling requests from the Client

HttpServletRequest Encapsulates the data provided by the client Provides several methods for accessing the data:

getParameter(String name) - returns the value of the specified parameter

getParameterValues(String name) - returns an array of strings of parameter values

getParameterNames( ) - returns an enumeration of names

getQueryString( ) - provide raw data from a GET request getReader( ) - for reading raw text data from the request getInputStream( ) - for reading raw binary data from the

request


Responding to Clients

HttpServletResponse Encapsulates the data provided to the client Provides several methods for setting the

data: setContentType(String type) - sets the header

value for content type

getWriter( ) - provides a Writer for adding data to the response

getOutputStream( ) - for writing raw binary data to the response


doGet and doPost Pattern

Read input data from the Request objectGet the output writer from the Response objectSetup the header dataPerform the necessary processing Database access Calculations Input/Output

Write the HTML to the response object


Source Template public void doGet/doPost (HttpServletRequest request, HttpServletResponse response) …{ // set content-type header before accessing the Writer response.setContentType("text/html"); // get the writer PrintWriter out = response.getWriter();

// extract data from the request String name = request.getParameter(“FirstName");

// perform required processing … // write the output to the writer (in HTML) … // cleanup out.close();}


Lifecycle of a servlet

The container: Creates and initializes the Servlet Handles zero or more servic calls from clients Destroys the Servlet and garbage collects it

Servlets persist between service calls Memory footprint is reduced Dynamic resources are held open

database handles Socket connections

Lifecycle overhead is eliminated Each client gets a thread


When should you use a servlet?

For dynamic web content Allows easy connection to database for

persistence mechanism

For stateful protocols Servlet session maintains state

For server performance Servlets are loaded once, reentrant

thereafter

For embedded web servers Web-enabled appliances


Advantages of Servlets

Portability - “write once, serve anywhere” Unlike applets, only need to be tested on the server No complex GUI

Power Full power of Java is available

JDBC RMI J2EE CORBA Bridge EJB JTS JMS JNDI

Support for third-party tools


More Advantages

Efficiency Once loaded, remains loaded Multiple concurrent requests handled by

threads Maintains state across invocations (if

appropriate)

Safety Java type-safety Java memory management Java exception handling Java security manager


More Advantages

Elegance Clean, object-oriented, modular code Base classes provide routine functionality

Programming by difference

Integration As a server extension, leverages server

capability File paths Logging Authorization MIME type mapping

Session tracking Overlays state on HTTP protocol


More Advantages

Extensible Built-in support for HTTP Servlets Others can be created Can create HTML Can work with XML / XSLT


Deploying Servlets

In HTML Specify servlet URL in ACTION tag

Specify servlet URL in HREF tag

Specify servlet URL directly


Servlet Containers

Tomcat Standalone HTTP / servlet container HTTP server extension / servlet container

J2EE Servlet container EJB container JMS JNDI JTA JAXP JDBC Etc.


Demo / Examples

Let’s look at some running Servlets


References

Java Servlet Programming - Jason Hunter with

William Crawford Copyright 2001, 1998 O’Reilly & Associates

The Internet Big Picture - Russ Haynal http://navigators.com/internet_architecture.html

http://www.jmarshall.com/easy/http/

http://java.sun.com/docs/books/tutorial/

servlets/

Introduction to Java Servlets Rochester Java Users Group January 16th, 2002 Tom Bullinger .

Documents

Transcript of Introduction to Java Servlets Rochester Java Users Group January 16th, 2002 Tom Bullinger .