Servlet , JSP

Margus Hanni, Nortal AS

Servlet, JSP

11.03.2013

Viited varasematele materjalidele…

2012 – TÜ - Servlets, JSP, Web Containers – Roman Tekhov

2010 – Webmedia - Java EE + containers – Anti Orgla

Kas on asjakohane?

http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html

Kas on asjakohane?

http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html

Hello World - C ja JAVA

#include <stdio.h> int main() { printf("Hello World\n"); return 0; }

public class HelloWorld { public static void main(String[] args) { System.out.println("Hello, World"); } }

Kas on asjakohane?

Võrreldes eelmise aastaga on JAVA populaarsus taas kasvanud

Jätkuvalt on JAVA populaarseim keel ning selles osas arvatavasti lähiajal muutusi ei toimu

JAVA on laialdaselt kasutuses erinevate veebilahenduste loomisel

JAVA EE (Enterprise Edition)

Kogum vahendeid erinevate lahenduste loomiseks:

Veebi rakendused

Veebi teenused

Sõnumivahetus

Andmebaasid

…

http://en.wikipedia.org/wiki/Java_Platform,_Enterprise_Edition

JAVA EE

Kogum vahendeid erinevate lahenduste loomiseks:

Veebi rakendused

Veebi teenused

Sõnumivahetus

Andmebaasis

…

http://en.wikipedia.org/wiki/Java_Platform,_Enterprise_Edition

Web ContainerServletJSP

Web Container

Manages componentlife cycles

Routes requests toapplications

Accepts requests, sends responses

http://tutorials.jenkov.com/java-servlets/overview.html


Web Containers

Apache Tomcat

JBoss

WebLogic

Jetty

Glassfish

Websphere

…

Web Containers

Multiple applicationsinside one container




Application structure


Java source files


Document root


15

Static content


Configuration,executable code


Deployment descriptor


Compiled classes


Dependencies (JAR-s)


Java Server Pages

Deployment descriptor (web.xml)Instructs the container how to deal with this application<?xml version="1.0" encoding="UTF-8"?><web-app xmlns="http://java.sun.com/xml/ns/javaee"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://java.sun.com/xml/ns/javaee

http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"version="3.0">

<welcome-file-list><welcome-file>index.html</welcome-file>

</welcome-file-list>

</web-app>

Deployment descriptor (web.xml)In Servlet API version 3.0 most components of web.xml are replaced by annotations that go directly to Java source code.

We will see examples later

Servlets

On JAVA klass, mis töötleb sissetulevat päringut ning tagastab vastuse

Enamasti kasutatakse HTTP päringute ja vastuste töötlemiseks

Servletid töötavad veebikonteineris, mis hoolitseb nende elutsükli ning päringute suunamise eest

javax.servlet.http.HttpServlet – abstraktne klass, mis sisaldab meetodeid doGet ja doPost HTTP päringute töötlemiseks

Servlet examplepublic class HelloServlet extends HttpServlet {

@Overrideprotected void doGet(HttpServletRequest req,

HttpServletResponse resp) throws ServletException, IOException {

PrintWriter writer = resp.getWriter();writer.println("<html><head><title>Hello</

title></head><body>");writer.println("Hello World!");writer.println("Current time: " + new

Date() + "");writer.println("</body></html>");

}}

HttpServlet methods

For each HTTP method there is corresponding HttpServlet method

doPostdoGetdoPut

…

Servleti töö

Servlet Mapping

Before Servlet 3.0 in web.xml<servlet>

<servlet-name>hello</servlet-name><servlet-class>example.HelloServlet</servlet-class>

</servlet>

<servlet-mapping><servlet-name>hello</servlet-name><url-pattern>/hello</url-pattern>

</servlet-mapping>

Servlet Mapping

In Servlet 3.0 via annotation

@WebServlet("/hello")public class HelloServlet extends HttpServlet {...

Servlet life cycle

http://tutorials.jenkov.com/java-servlets/servlet-life-cycle.html

http://tutorials.jenkov.com/java-servlets/servlet-life-cycle.html

Üldine servleti elutsükkel

Kui veebikonteineris puudub Servleti instants

Laetakse Servleti klass

Luuakse isend

Initsialiseeritakse (init meetod)

Iga päringu jaoks kutsutakse välja service meetod

Servleti kustutamisel kutsutakse välja destroy meetod

Sessions

HTTP is a stateless protocol, but we often need the server to remember us between requests There are some ways

CookiesURL rewriting

Java HttpSession

HttpSession is a common interface for accessing session context

Java Servlet API abstract away the details of how the session is maintained

Java HttpSession

http://java.sun.com/developer/onlineTraining/JSPIntro/contents.html


HttpSession example

HttpSession session = req.getSession();int visit;if (session.isNew()) {

visit = 0;} else {

visit = (Integer) session.getAttribute("visit");}session.setAttribute("visit", ++visit);

HttpSession example


visit = 0;} else {


Either create a new session or get existing

HttpSession example


visit = 0;} else {


Check if the session is fresh or not

HttpSession example


visit = 0;} else {


Retrieve attribute

HttpSession example


visit = 0;} else {


Update attribute

HttpServletRequest

Contains request informationAlso can be used to store attributes

request.setAttribute(“key", value);request.getAttribute(“key”);

HttpServletRequest: parametersrequest.getParameterNames();

Enumeration<String>

String value = request.getParameter("name");

HttpServletRequest: meta datarequest.getMethod();

“GET”, “POST”, …request.getRemoteAddr();

Remote client’s IPrequest.getServletPath();

“/path/to/servlet”…

HttpServletRequest: headers

request.getHeaderNames();Enumeration<String>

request.getHeader("User-Agent");

“Mozilla/5.0 (X11; Linux x86_64) …”

Request Headers

Accept text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8Accept-Encoding gzip, deflateAccept-Language et,et-ee;q=0.8,en-us;q=0.5,en;q=0.3Connection keep-alive

CookieJSESSIONID=C687CC4E2B25B8A27DAB4A5F30980583; __utma=111872281.1173964669.1316410792.1318315398.1338294258.52; oracle.uix=0^^GMT+3:00^p

Host localhost:8080

User-AgentMozilla/5.0 (Windows NT 6.1; WOW64; rv:19.0) Gecko/20100101 Firefox/19.0

HttpServletRequest: cookies

Cookie[] cookies = request.getCookies();

cookie.getName();cookie.getValue();cookie.setValue(“new value”);

Cookie

JSESSIONID C687CC4E2B25B8A27DAB4A5F30980583 C687CC4E2B25B8A27DAB4A5F30980583

utma111872281.1173964669.13...318315398.1338294258.52

111872281.1173964669.13...318315398.1338294258.52

oracle.uix 0^^GMT 3:00^p 0^^GMT+3:00^p

HttpServletResponse

Allows to set response information

response.setHeader("Content-Type", "text/html");

response.addCookie(new Cookie("name", "value"));

Response Headers

Content-Language etContent-Type text/html;charset=UTF-8Date Mon, 11 Mar 2013 06:48:54 GMTServer Apache-Coyote/1.1Transfer-Encoding chunked

HttpServletResponse: content

response.getWriter().println("...");

Write text

response.getOutputStream().write(...);

Write binary

Problem with servlets

Writing HTML in Java is hideousPrintWriter writer = resp.getWriter();writer.println("<html><head><title>Hello</title></head><body>");writer.println("Hello World!");writer.println("Current time: " + new Date() + "");writer.println("</body></html>");

Java Server Pages (JSP)

Write standard markup

Add dynamic scripting elements

Add Java code

JSP example

war/WEB-INF/jsp/hello.jsp

<%@page import="java.util.Date"%>

<html><head><title>Hello</title></head><body>

Hello World!Current time: <%= new Date() %>

</body></html>

JSP mapping

In web.xml<servlet>

<servlet-name>hello2</servlet-name><jsp-file>/WEB-INF/jsp/hello.jsp</jsp-file>

</servlet>

<servlet-mapping><servlet-name>hello2</servlet-name><url-pattern>/hello2</url-pattern>

</servlet-mapping>

The JSP Model 2 architecture

http://en.wikipedia.org/wiki/JavaServer_Pages

JSP life cycle

http://www.jeggu.com/2010/10/jsp-life-cycle.html

http://www.jeggu.com/2010/10/jsp-life-cycle.html

Dynamic content

ExpressionCurrent time: <%= new Date() %>

ScriptletCurrent time: <% out.println(new Date()); %>

package org.apache.jsp.WEB_002dINF.jsp.document;

import javax.servlet.*;import javax.servlet.http.*;import javax.servlet.jsp.*;import java.util.Date;

public final class testdokument_jsp extends org.apache.jasper.runtime.HttpJspBase implements org.apache.jasper.runtime.JspSourceDependent {

private static final javax.servlet.jsp.JspFactory _jspxFactory = javax.servlet.jsp.JspFactory.getDefaultFactory();

private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants;

private javax.el.ExpressionFactory _el_expressionfactory; private org.apache.tomcat.InstanceManager _jsp_instancemanager;

public java.util.Map<java.lang.String,java.lang.Long> getDependants() { return _jspx_dependants; }

public void _jspInit() { _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory(); _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig()); }

public void _jspDestroy() { }

public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response) throws java.io.IOException, javax.servlet.ServletException {

final javax.servlet.jsp.PageContext pageContext; javax.servlet.http.HttpSession session = null; final javax.servlet.ServletContext application; final javax.servlet.ServletConfig config; javax.servlet.jsp.JspWriter out = null; final java.lang.Object page = this; javax.servlet.jsp.JspWriter _jspx_out = null; javax.servlet.jsp.PageContext _jspx_page_context = null;

try { response.setContentType("text/html; charset=UTF-8"); pageContext = _jspxFactory.getPageContext(this, request, response, null, true, 8192, true); _jspx_page_context = pageContext; application = pageContext.getServletContext(); config = pageContext.getServletConfig(); session = pageContext.getSession(); out = pageContext.getOut(); _jspx_out = out;

out.write("\r\n"); out.write("\r\n"); out.write("Current time: "); out.print( new Date() ); out.write(""); } catch (java.lang.Throwable t) { if (!(t instanceof javax.servlet.jsp.SkipPageException)){ out = _jspx_out; if (out != null && out.getBufferSize() != 0) try { out.clearBuffer(); } catch (java.io.IOException e) {} if (_jspx_page_context != null) _jspx_page_context.handlePageException(t); else throw new ServletException(t); } } finally { _jspxFactory.releasePageContext(_jspx_page_context); } }}

Dynamic content

Declaration<%!

private Date currentDate(){return new Date();

} %>

Current time: <%= currentDate() %>

JSP Eeldefineeritud muutujad

request- HttpServletRequest

response – HttpServletResponse

out – Writer

session – HttpSession

application – ServletContext

pageContext – PageContext

JSP Märgendid

jsp:include Veebipäring antakse ajutiselt üle mingile teisele JSP lehele.

jsp:forward Veebpäring antakse jäädavalt üle mingile teisele JSP lehele.

jsp:getProperty Loeb mingi JavaBeani muutuja väärtuse.

jsp:setProperty Määrab mingi JavaBeani muutuja väärtuse.

jsp:useBean Loob uue või taaskasutab mingit JSP lehele kättesaadavat JavaBeani.

Expression Language (EL)

Easy way to access JavaBeans in different scopes

Rea summa: ${rida.summa * rida.kogus}

Basic Operators in ELOperator Description

. Access a bean property or Map entry

[] Access an array or List element

( ) Group a subexpression to change the evaluation order

+ Addition

- Subtraction or negation of a value

* Multiplication

/ or div Division

% or mod Modulo (remainder)

== or eq Test for equality

!= or ne Test for inequality

< or lt Test for less than

> or gt Test for greater than

<= or le Test for less than or equal

>= or gt Test for greater than or equal

&& or and Test for logical AND

|| or or Test for logical OR

! or not Unary Boolean complement

empty Test for empty variable values

http://www.tutorialspoint.com/jsp/jsp_expression_language.htm

Scopes

Many objects allow you to store attributes

ServletRequest.setAttribute

HttpSession.setAttribute

ServletContext.setAttribute

Andmete skoobid

ServletContext – veebikontekst, üks ühe rakenduse ja JVM-i kohta

Sessioon – üks iga kasutajasessiooni kohta (erinev browser = erinev sessioon)

Request – konkreetse päringu skoop

Andmete kirjutamiseks/lugemiseks on meetodid setAttribute/getAttribute

Scopes



Scopes

<% application.setAttribute("subject", "Web information systems");session.setAttribute("topic", "Servlets");request.setAttribute("lector", "Roman");pageContext.setAttribute("lector", "Roman");%>

Subject: ${subject}Topic: ${topic}Lector: ${lector}

Väljund: Subject: Web information systems Topic: Servlets Lector: Roman

Scopes

<% application.setAttribute("subject", "Web information systems");session.setAttribute("topic", "Servlets");request.setAttribute("lector", "Roman");pageContext.setAttribute("lector", "Roman");pageContext.setAttribute("subject", "Meie uus teema");application.setAttribute("subject", "Meie järgmine teema");%>


Mis on väljundiks?

Scopes

<% application.setAttribute("subject", "Web information systems");session.setAttribute("topic", "Servlets");request.setAttribute("lector", "Roman");pageContext.setAttribute("lector", "Roman");pageContext.setAttribute("subject", "Meie uus teema");application.setAttribute("subject", "Meie järgmine teema");%>


Subject: Meie uus teema Topic: Servlets Lector: Roman

Scopes

<% application.setAttribute("subject", "Web information systems");session.setAttribute("topic", "Servlets");request.setAttribute("lector", "Roman");pageContext.setAttribute("lector", "Roman");%>


Less visible

JavaBeans

public class Person implements Serializable {

private String name;

public Person() {}

public String getName() {return name;

}

public void setName(String name) {this.name = name;

}}

Implements Serializable

Public default constructor

getX and setX methods for each property X

JavaBeans in EL

Person person = new Person();person.setName("Roman");request.setAttribute("person", person);

Person: ${person.name}

Java Standard Tag Library (JSTL)Set of standard tools for JSP<%List<String> lectors = Arrays.asList("Siim", "Roman", "Margus");pageContext.setAttribute("lectors", lectors);%>

<c:set var="guestLector" value="Margus" />

<c:forEach var="lector" items="${lectors}">Name: ${lector}<c:if test="${lector eq guestLector}“>(guest)</c:if> 

</c:forEach>

Problem with JSP

Writing Java in JSP is hideous

Current time: <%= currentDate() %>

Model-View-Controller (MVC)

http://java.sun.com/blueprints/patterns/MVC-detailed.html

http://java.sun.com/blueprints/patterns/MVC-detailed.html

Servlet controller, JSP view

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

req.setAttribute("currentDate", new Date());

req.getRequestDispatcher("/WEB-INF/jsp/hello.jsp").forward(req, resp);}

Model data

Controller gets invoked


protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

req.setAttribute("currentDate", new Date());

req.getRequestDispatcher("/WEB-INF/jsp/hello.jsp").forward(req, resp);}

Select and invoke view

Controller gets invoked


WEB-INF/jsp/hello.jsp

<html>...

<body>Current time: $

{currentDate}</body>

</html>View uses thedata from model

Filters

Allows you to do something before, after or instead of servlet invocation.

http://docs.oracle.com/javaee/5/tutorial/doc/bnagb.html

Filter chain

http://docs.oracle.com/javaee/5/tutorial/doc/bnagb.html

Filter example

public class LoggingFilter implements Filter {

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { long start = System.currentTimeMillis();

chain.doFilter(request, response);

long end = System.currentTimeMillis(); System.out.println("Time spent: " + (end - start)); }}

Filter example

public class LoggingFilter implements Filter {

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

long start = System.currentTimeMillis();

chain.doFilter(request, response);

long end = System.currentTimeMillis(); System.out.println("Time spent: " + (end - start)); }}

Invoke next filter inchain or the servletif this was the last filter

Filter declaration

Before Servlet 3.0 in web.xml

<filter><filter-name>loggingFilter</filter-name><filter-class>example.LoggingFilter</filter-

class></filter>

<filter-mapping><filter-name>hello</filter-name><url-pattern>/*</url-pattern>

</filter-mapping>

Filter declaration


@WebFilter("/*")public class LoggingFilter implements Filter {...

Life cycle event listeners

javax.servlet.ServletContextListenerjavax.servlet.ServletContextAttributeListenerjavax.servlet.ServletRequestListenerjavax.servlet.ServletRequestAttributeListenerjavax.servlet..http.HttpSessionListenerjavax.servlet..http.HttpSessionAttributeListener

Listener example

public class LoggingRequestListener implements ServletRequestListener {

@Overridepublic void requestInitialized(ServletRequestEvent event) { System.out.println("Received request from " + event.getServletRequest().getRemoteAddr());}

@Override public void requestDestroyed(ServletRequestEvent event) {}

}

Listener declaration

Before Servlet 3.0 in web.xml

<listener><listener-class>example.LoggingRequestListener</listener-class>

</listener>

Listener declaration


@WebListenerpublic class LoggingRequestListener implements ServletRequestListener {...

Should I bother?

• There are a lot of fancy Java web frameworks that simplify application building.

• Should I still learn these basic technologies, will I ever use them?

Should I bother?

• You are still going to deploy your application to a web container.

• Most traditional frameworks use JSP as the view technology.

What about servlets?

• Most frameworks are based on the Servlet API• You will probably still encounter things like

HttpSession, HttpServletRequest etc inside your code.

• You might want to write filters and listeners.• You probably won’t write much servlets. But

sometimes they can still be handy for simple tasks.

Sources of wisdom

Tutorialhttp://docs.oracle.com/javaee/6/tutorial/doc/http://docs.oracle.com/javaee/5/tutorial/doc/

APIhttp://docs.oracle.com/javaee/6/api/http://docs.oracle.com/javaee/5/api/

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

http://docs.oracle.com/javaee/5/tutorial/doc/

http://docs.oracle.com/javaee/6/api/

Documents

Servlet , JSP