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Servlet & JSP

Serkan Erdur

&

Levent Özgür

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What is Servlet?

Java application that runs on the server side Answers html requests and produces

dynamic html responses to send them to the

client independent server and platform Java alternative to cgi scripts

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Servlet Work Flow Client sends request to server

1. Server sends the request knowledge to servlet

2. Servlet produces dynamic result and send it to server

3. Server sends the result to client.

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Servlet Work Flow

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Advantages of Servlet

Platform independent because of Java use Persistency and as a result increase in

performance Java background

Not scripting, a real programming language Object oriented programming Uses all advantages of Java

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Temporary & Permanent Servlets

A temporary servlet is started when a request arrives and shut down after the response is generated.

A permanent servlet is loaded when the server is started and lives until the server is shut down. is useful when startup costs are high Provides faster response to client requests

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Using Servlets

Install Java Servlet Development (JSDK).

Servlets can be tested with the utility program servlet runner

Servlet API is a standard extension for the JDK under javax

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Performance Advantages Servlet and Application Server runs in the

same JVM. Runs and remains in memory Can be loaded when request comes or start to run

when server runs Hold session information Can use system advantages in

multiprocessor systems and heterogeneous systems. (clustered servers and workload management)

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Life Cycle of Servlet init

First method to be called Work with the servlet is created

service (doGet, doPost) Run whenever there is any client call

destroy Method that runs before servlet is destroyed

Generally there is one servlet object in the memory that is shared by all clients

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init method

The init method is invoked when the servlet is first started. For permanent servlets, this is when the server is started.

The init method is called only once and is guaranteed to finish before any calls to the service method.

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service method public void service (ServletRequest req,

ServletResponse res) Each request message from the client results

in invoking the service method. More than one instance of the service method

can be invoked at one time to respond to multiple requests.

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destroy method

Called when the servlet in unloaded to clean up any open resources.

Although the server normally waits until all service calls are terminated to invoke destroy, it may not be possible, and your destroy method should make sure that resources are not being used.

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Java Servlet API Consists of java classes that define standard

communication between web client & web server Consists of two packages

javax.servlet javax.servlet.http

javax.servlet packet is general, protocol independent and have classes that supports servlet

javax.servlet.http packet additionally owns private classes of http protocol.

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HttpServlet (javax.servlet.http.HttpServlet)

Special servlet type for http requests Methods:

doGet(): runs when getrequest comes doPost(): runs when postrequest comes

doGet() and doPost() called by service() method

Subclasses overrides these methods and also init() & destroy() methods can be overrided.

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Requests and Responses

Service(), doGet() and doPost() take two parameters. HttpServletRequest:

Enables us to read Request parameters, HttpSession and other info. Comes with request.

HttpServletResponse Enables us to return an answer to the client

Ingeneral, servlet programming is reading requests + writing responses

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Request Protocol

getParameterNames() Returns the parameter names comes with the

request. getParameter(String name)

Returns the value of the parameter comes with the request

getReader() Returns request body as BufferedReader object.

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Response Protocol

Provides data communication channel to Client

Can return contents and errors Can set content header Can redirect url to another url

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Response Protocol

getWriter() produces PrintWriter object Html tags are written in this object

setContentType(String type) Content type of response message(Eg: text/html)

sendRedirect(String URL) Redirect url to another url

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Utility Classes

Two exception classes in the servlet API

javax.servlet.ServletException: servlet should throw this exception to server in event of general failure

javax.servlet.UnavailableException:servlet can report this at any time to server. The servlet may write a log entry so that an administrator can take some action.

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Servlet Examplepublic class MerhabaServlet extends HttpServlet{public void doGet(HttpServletRequest req, HttpServletResponse res) throws

ServletException {

res.setContentType(“text/html”);printWriter out = res.getWriter();out.println(“<title>MERHABA SERVLET</title> <HTML><BODY>”);out.println(“ MERHABA DUNYA “);out.println(“</BODY></HTML>”);

} }

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JavaServer Pages (JSP)

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Goals

JavaServer Pages technology JSP in web applications Basic JSP syntax

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Web Page content

Content of the page that is sent to client: static dynamic

Page design and style can be done by HTML, XSL,..

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Server-side Scripting Server-side Scripting

Page that is composed of dynamic and static parts are prepared in server before sent to client

Code in the server side is run to produce dynamic parts

Example technologies: JavaServer Pages (JSP) Active Server Pages (ASP)

ASP and JSP files are similar in shape to html files

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A Simple JSP

<HTML><HEAD>

<TITLE>JSP</TITLE></HEAD><BODY>

Tarih : <%= new java.util.Date() %></BODY>

</HTML>

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JSP Execution Model

Java Server Page is first converted to servlet and then run

This is page compilation JSP source code parsed Java sevlet code produced Servlet code compiled, loaded and run.

First run of a JSP

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JSP Elements

Directives Declarations Scriptlets Expressions Comments

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Directives JSP directives are messages to the JSP

Engine Syntax:

<%@ directive {attribute=“value”}* %> JSP 1.0 directives :

page, include, taglib

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Page Directive

Properties that are specific to that page <%@ page attr_list %> Attr_list: Ex:

language=“scripting language” “java”

import=“package list”"java.util.*"

session=“true/false”

buffer=“none|sizekb”

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Page Directive

Attr_list (continue):

errorPage=“error jsppage_url”

isErrorPage=“true|false”

contentType=“Type|Type;charSet=CHARSET”

Eg: contentType=“text/html;charSet=ISO-8859-9”

autoFlush=“true/false”

extends=“className”

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Include ve Taglib Directive’leri include directive

To make additions to include jsp file from another file

<%@ include file=“relativeURLspec” %> Ex: <%@ include file="copyright.html"%>

taglib directive To define jsp tag library <%@ taglib uri=“tagLibraryURI” prefix=“tagPrefix”

%> Seen with JSP 1.0

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Declerations

<%! Decleration %> includes java code Variables and methods defined Code that is written in tag is included in

servlet class as class members (outside the methods) So that parameters will take te same value in all

instances of the servlet

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Declerations

Eg:

<%!private int i =0;private void arttır(){

i++;}

%>

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Scriptlets

<% java code %> Enables us to use java code Written in service method in which java code

will be implemented Run with every request coming to server Scriptlets are combined with the same

ordering of their order in jsp file

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Scriptlets

Eg:<%if

(Calendar.getInstance().get(Calendar.AM_PM)==

Calendar.AM)

{%>

Good Morning

<%}else

{%>

Good Afternoon

<%}%>

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Expressions

<%= expression %> Expression is the java code in which, its result

is converted to String object The result is sent to output stream to be

shown in browser Usually for running and showing results of the

methods of Java beans which is defined in JSP or defined in decleration.

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Expressions ClassCastException is throwed if the result of

expression can not be converted to String object

Ex:<%= i %>

All Java primitive types (int,short,long..) can be converted to String automatically. Classses should have toString method for conversion.

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Comments

Two types of comments used in JSP1. Output comment: comment is in browser

<!-- comments ... -->

2. Fully secret comment: Comment is not in browser<%-- comment text --%>

Comments can be constructed dynamicly by adding expressions in it

<!--comment text <%=expression %> comment text -->

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Implicit Objects

Implicit Objects: Objects that can be used in scripts and

expressions without defining them before. request: javax.servlet.HttpServletRequest

request object that is the reason for the servlet to run response: javax.servlet.HttpServletResponse

Response for the request session: javax.servlet.http.HttpSession

Session object for the client

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Implicit Objects

out: javax.servlet.jsp.JspWriter Output stream writer

pageContext : javax.servlet.jsp.PageContext By getPage, getSession, getException methods , it

enables us to reach JSP objects page : java.lang.Object

Instance of the class which is composed of the page that answers the request

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A JSP

<html><title>Tarih Ekranı</title><body><!--D I R E C T I V E S --><%@page language ="java"%><%@page import ="java.util.*"%><%@page contentType ="TEXT/HTML"%><!--S C R I P T L E T S--><H3><%if (Calendar.getInstance().get(Calendar.AM_PM)==Calendar.AM){%>Bu sabah nasılsınız,<%}else {%>Bu öğlen nasılsınız,<%}%>WebSphere 3.5 Kullanıcısı ?</H3><HR><!--A C C E S S I N G I M P L I C I T O B J E C T S --><%out.println("İşte <b>Tarih Gösteren JSP</b>");%>

tarih.jsp source code

<!--D E C L A R A T I O N S --><%!private int calledCount =0;private String getDate(GregorianCalendar gcalendar){StringBuffer dateStr =new StringBuffer();dateStr.append(gcalendar.get(Calendar.DATE));dateStr.append("/");dateStr.append(gcalendar.get(Calendar.MONTH)+1);dateStr.append("/");dateStr.append(gcalendar.get(Calendar.YEAR));return (dateStr.toString());}private int incrementCounter(){return (++calledCount);}%><H1>Bugünün Tarihi:<%=getDate(new GregorianCalendar())%></H1><H1>Bu sayfa:<%=incrementCounter()%> kere yüklenmiştir</H1></body></html>

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Actions

Standard Actions:

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

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jsp:useBean <jsp:useBean id=“name” scope=“page|request|session|

application” beanDetails >Scripts and tags that are used for initialisation of bean

</jsp:useBean> beanDetails is one of the following:

class=“className” class=“className” type=“typeName” beanName=“beanName” type=typeName” type=“typeName” ;optional. Tha same value as class by default

id : name to use bean object Scope: scope of the referance for bean. Default: page

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jsp:useBean

Scope: Page:

Object reference cleared after Servlet.service() method was run

New object created for every client request Request

Object still survives when HttpRequest object is used although request passes to another page.

New object created for every client request

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jsp:useBean Session

Object is connected to HttpSession New object created for every client request and object

survives during session time Application

Longest time Connected to object ServletContext Same object for every client

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jsp:setProperty <jsp:setProperty name=“beanName”

propertyDetails /> Set the property of beans that we define with

useBean propertDetails is one of the following:

property=“*” all properties are set with parameter of same name in the

request object property=“propertyName”

Set with the parameter of the same name

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jsp:setProperty propertyAyrıntıları (continue)

property=“propertyName” param=“parameterName” Set with the parameter given

property = “propertyName” value=“propertyValue” Set with the property given . It can be constant string or an

expression

String values are converted to types of properties by using the related conversion methods.

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jsp:getProperty

<jsp:getProperty name=“name” property=“propertyName” />

Take the value of property, convert it to String and writes in output stream

name: name of bean object property: property of bean

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A JSP<html><jsp:useBean id="topla" class="test.Toplama" /><jsp:setProperty name="topla" property="sayi1"

value="2" /><jsp:setProperty name="topla" property="sayi2"

value="5" /><% topla.topla(); %>toplam : <jsp:getProperty name="topla"

property="toplam" /></html>

package test;public class Toplama{

private int sayi1;private int sayi2;private int toplam;

public Toplama() {super();

}public int getSayi1() {

return sayi1;}public int getSayi2() {

return sayi2;}public int getToplam() {

return toplam;}public void setSayi1(int i) {

sayi1=i;}public void setSayi2(int i) {

sayi2=i;}public void topla() {

toplam=sayi1+sayi2;}

}

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jsp:include

Static or dynamic page can be added into jsp file <jsp:include page=“filename” flush=“true” />

ya da

<jsp:include page=“urlSpec” flush=“true”>

<jsp:param name=“paramname” value=“paramvalue” />

...

</jsp:include>

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jsp:forward <jsp:forward page=“url” />

ya da

<jsp:forward page=“url”>

<jsp:param name=“paramname” value=“paramvalue” />

…

</jsp:forward> Request is passed to another JSP, servlet or static address Jsp that is used erased from buffer and if new parameters

added , request is reorganised and target page is loaded

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A Simple JSP

testdb.jsp

<%@ page contentType="text/html; charset=ISO-8859-9" %> <%@ page import="java.sql.*" %><HTML><HEAD><META http-equiv="Content-Style-Type"

content="text/css"><TITLE>DataBase Erişim Örneği</TITLE></HEAD>

<BODY BGCOLOR="#FFFFFF"><table border="1"><th>NO</th><th>AD</th><th>SOYAD</th>

<% try{ Connection connection = null; Statement statement = null; ResultSet results = null; Class.forName("com.ibm.as400.access.AS400JDBCDriver"); String url = "jdbc:as400://192.168.0.201"; //AS400 IP adresi String query="SELECT * from OYKINSNKT.PERSONEL"; connection = DriverManager.getConnection(url,"adm","pass"); statement= connection.createStatement(); results = statement.executeQuery(query); while (results.next()){ %><tr> <td><%= results.getString(1) %> </td> <td><%= results.getString(2) %> </td> <td><%= results.getString(3) %> </td></tr><%} connection.close(); }catch(Exception ex){out.println(ex);}%>

</table></BODY></HTML>