Enterprise Application Development using J2EE · 3 Enterprise Application Development Using J2EE / © Shmulik London 2004 JSP request processing Internet JSP container JSP Page Upon

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Enterprise Application Development Using J2EE / © Shmulik London 2004Interdisciplinary Center Herzeliza Israel

Enterprise Application Development using J2EE

Shmulik London

Web Programming II –JSP (Java Server Pages)

Lecture #6

Enterprise Application Development Using J2EE / © Shmulik London 2004

The Problem

ResultSet result = statement.executeQuery(

"SELECT course_id, name, hours FROM courses");

response.setContentType("text/html");

PrintWriter writer = response.getWriter();writer.println(“<html><body><table border=\"1\">");

writer.println("<tr><td>ID</td><td>Name</td></tr>”) ;

while(result.next()) {

long id = result.getLong(1);

String name = result.getString(2);writer.println("<tr><td>"+id+"</td>”+

“<tr><td>”+name+”</td></tr>”);

}

writer.println(“</table></body></html>”);


The Problem

• Writing HTML in Java is cumbersome and inefficient (both runtime and development cycle)

• We would like Web Designers to do design the page and programmers to do the logic (separation of concerns)


How we approached it in the old days... (ASP)

<HTML><TITLE>Multiplication Table</TITLE><H2>Multiplication Table</H2><TABLE border="1" cellpadding="2" cellspacing="0">

<TR height="20" bgcolor="#f0f0f0"><TD width="20"></ TD><% FOR J=1 TO 10 %>

<TD width="20"><%=J%></TD><% NEXT

FOR I=1 TO 10 %><TR height="20"><TD width="20" bgcolor="#f0f0f0"><% =I%></TD>

<% FOR J=1 TO 10 %><TD width="20"><%=I*J%></TD>

<% NEXTNEXT %>

</TABLE></HTML>

Note: this example is superficial – we don’t need the serverfor the data, we might as well do it in client side JavaScript


ASP request processing

Internet

File-systemstatic contentand templates

CoursesDatabase

IIS ISAPI Filter

ASP Page

The ASP page is parsedand the embedded scriptsare executed to generatedynamic content


And some continuedthis way in JSP…

<HTML>

<TITLE>Multiplication Table</TITLE>

<H2>Multiplication Table</H2><TABLE border="1" cellpadding="2" cellspacing="0">

<TR height="20" bgcolor="f0f0f0"><TD width="20"></T D>

<% for (int j=1; j<=10; j++) { %><TD width="20"><%=j%></TD>

<% } %>

<% for (int i=0; i<=10; i++) { %>

<TR height="20"><TD width="20" bgcolor="f0f0f0"><%= i%></TD><% for (int j=1; j<=10; j++) { %>

<TD width="20"><%=i*j%></TD>

<% }} %>

</TABLE>

</HTML>

2


<HTML>

<TITLE>Multiplication Table</TITLE>

<H2>Multiplication Table</H2><TABLE border="1" cellpadding="2" cellspacing="0">

<TR height="20" bgcolor="f0f0f0"><TD width="20"></T D>

<% for (int j=1; j<=10; j++) { %><TD width="20"><%=j%></TD>

<% } %>

<% for (int i=0; i<=10; i++) { %>

<TR height="20"><TD width="20" bgcolor="f0f0f0"><%= i%></TD><% for (int j=1; j<=10; j++) { %>

<TD width="20"><%=i*j%></TD>

<% }} %>

</TABLE>

</HTML>

Scripting elements makethe code messy and don’t allow for good separationof concerns (design / logic)JSP offer better alternatives. Avoid scripting elements!

But you’re too smart for that…


Scripting Elements

• Imagine large pages, containing both scripting elements, JavaScript / DHTML, CSS, sometimes Applets or ActiveX controls.. server side script that generate client side script!, pages delegates control to each other..

• This results in a jungle that is impossible to maintain


JSP as a Template Engine

JSP Page

Request

Fetch data orcompute

Use the data to fill in a JSP template

Return the result of merging the static htmlof the template with the dynamic data

Servlet


Example (Query Form)

<html><head><title>Course Search</title></head><body>

<h1>Course Search</h1><form action="course-info" method="POST">

<table border="0"><tr>

<td>Enter course code</td><td><input name="code"

type="text" size="10"/></td><td><input type="submit" value="Submit"/></td>

</tr></table>

</form></body></html>


Example (JSP Template)

<%@ page contentType="text/html" %>

<html><body>

<h1>Course Details</h1><b>Name:</b> ${courseName} <br/>

<b>Code:</b> ${courseCode} <br/>

<b>Credit points:</b> ${creditPoints} <br/>...

</body>


Example (Servlet)

protected void doPost(HttpServletRequest request…

String code = request.getParameter(“code”);

String courseName = … fetch data using code

String creditPoints = … fetch data …

request.setAttribute(“courseName”, courseName);

request.setAttribute(“courseCode”, code);

request.setAttribute(“creditPoints”, creditPoints);

RequestDispatcher dispatcher =

request.getRequestDispatcher(

"/course-info.jsp");

dispatcher.forward(request, response);

}

3


JSP request processing

Internet

JSP container

JSP Page

Upon first request the JSP isparsed and is compiled into aServlet. The Servlet include code to dump static HTML code segments that appearedin the original JSP page

JSP compiler

ControllerServlet


Template Engines

• Many web frameworks use the idea of a template engine

– JSP, Velocity, FreeMarker… (Java)

– Django (Python)

– Ruby on Rails (Ruby)

– Grails (Groovy)

– Lift (Scala)

– …


Beyond Placeholders

• Sometimes we need more than just placeholders– Lists / Tables

– Conditional segments

– Common elements – header, footer..

– …

• We use JSP Tags for this– Again not embedded code!


JSP Tags

• JSP defines a set of HTML-like tags that allow to add dynamic content to a page

• In addition it provide a simple way for writing your own custom tags

• You can find numerous of tag libraries (often open source)


Example: include Tag


<html>

<body><jsp:include page="header.html“/>

<jsp:include page="menu.jsp“/>

<h1>My special page</h1>Here is the content of my special page . . .

. . .

<jsp:include page="footer.html"/></body>

</html>

• Includes the content of another page (static or dynamic) in the current page


Example

Using <jsp:include> to include a result of a Servlet

Again: this example is superficial – we don’t need the server for the data, we might as well do it in client side JavaScript

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Example

Using <jsp:include> to include a result of a Servlet

MultiplicationTableServletmultiplication_table.jsp


MultiplicationTableServlet

protected void doGet(

HttpServletRequest request,

HttpServletResponse response)throws IOException {

try {

int rows = Integer.parseInt(request.getParameter("rows"));

int columns = Integer.parseInt(

request.getParameter("columns"));

PrintWriter writer = response.getWriter();

printTable(writer, rows, columns);} catch (NumberFormatException e) {

System.out.println("Illegal parameter value");

}

}


MultiplicationTableServletprivate void printTable(

PrintWriter writer,

int rows, int columns) {

writer.println("<TABLE border=\"1\" cellpading... > ");

writer.println("<TR height=\"20\" bgcolor=...</TD>" );

for (int j=1; j<=columns; j++) {writer.println("<TD width=\"20\">"+j+"</TD>");

}

for (int i=1; i<=rows; i++) {

writer.println("<TR height=\"20\"><TD width=\"20\" " +

"bgcolor=\"f0f0f0\">"+i+"</TD>");

...

}}


multiplication_table.jsp<%@ page contentType="text/html" %>

<h2>Multiplication Table</h2>

<form method="GET" action="multiplication_table.jsp " >Rows <select name="rows"><option value="3">3</optio n>...

</select>

Columns <select name="columns">...

</select>

<input type="submit" value="Go"></form>

<jsp:include page="/multiplication_table_servlet"

flush="true"><jsp:param name="rows"

value="<%=request.getParameter("rows")%>"/>

<jsp:param name="columns"

value="<%=request.getParameter("columns")%>"/></jsp:include>


JSTL

• JSTL - JSP Standard Tag Library

• Collection of tags for functions that are common to many web apps

– flow control, formatting, IO...

– Introduces EL expressions

Note: JSTL introduce many Tags, but not all make sense,Tags that access the database or read files directly from the JSPpage is a bad idea! In general all the logic of fetching the data shouldbe done in lower layer


if Tag<%@ page import="sokoban.web.*"%><%@ page contentType="text/html" %><%@ taglib prefix="c”

uri="http://java.sun.com/jstl/core" %>

<jsp:include page="/header.html"/><p>Welcome to our Sokoban server....

<c:if test="${!(empty sessionInfo.message)}"><p><font color="#CC3300"><c:out value="${sessionInfo.message}" /></font></p>

</c:if>... EL Expressions

5


foreach Tag<%@ page contentType="text/html" %><%@ page isELIgnored ="false" %><%@ taglib prefix="c" uri="http://java.sun.com/jsp/j stl/core" %><html>

<body><h1>Course List</h1><table border="1" cellpadding="3" cellspacing="0">

<tr><th width="80" align="center">Symbol</th><th width="400" align="center">Name</th><th width="120" align="center">Instructor</th>

</tr><c:forEach var="course" items="${courses}">

<tr><td align="center">${course.symbol}</td><td align="center">${course.name}</td><td align="center">${course.instructor}</td>

</tr></c:forEach>

</table></body>

</html>


Servlet Side

public void doGet(HttpServletRequest request … ) …{

...

ResultSet results = statement.executeQuery(“SELECT * FROM courses”);

List<CourseInfo> courses = new ArrayList<CourseInfo >();

while (results.next()) {

CourseInfo course = new CourseInfo();course.setSymbol(results.getString(“symbol”));

course.setName(results.getString(“name”));

...

}

request.setAttribute(“courses”, courses);request.getRequestDispatcher(“/course-list.jsp”).

forward(request, response);

}

Note: there might be too many results to be sent in a single request, it is always a good idea tolimit the number of results and page through them


Tag Libraries

• JSP allows you to add additional tags through tag-libraries

• You can wrap a commonly used presentation code in a new tag and provide it to the web-designer

• You can find numerous tag libraries (notably JSTL) or develop your own


Custom Tag Example

Repeated HTML code

Again, this example is superficial – we are better off using JavaScript here as expanding the tag in the server will result-in large html sent to the client, and redundant server load


Custom JSP Tag<%@ page contentType="text/html" %>

<%@ taglib prefix="examples“

uri="http://www.idc.ac.il/j2ee/examples" %><h2>Recommended EJB Books</h2>

<table border=0>

<tr>

<td><examples:rank rank="5"/></td>

<td>Enterprise JavaBeans / Reichard Monson-Haefel</t d></tr>

<tr>


<td>Mastering Enterprise JavaBeans / Ed Roman</td></tr>

<tr>


<td>EJB Design Patterns / Floyd Marinescu</td></tr>


Custom JSP Tagpackage examples.web.tags;

import java.io.*;

import javax.servlet.jsp.*;import javax.servlet.jsp.tagext.*;

public class RankTag extends TagSupport {

private static final int MAX_RANK = 5;

private int rank;

public void setRank(int rank) {this.rank = rank;

}

6


Custom JSP Tagpublic int doStartTag() throws JspException {

JspWriter writer = pageContext.getOut();try {

writer.println("<table border=0 width=50>");writer.println("<tr height=20 width=50>");for (int i=0; i<MAX_RANK; i++) {

writer.println(i<rank ?“<td width=10><image “+“src=\"res/icons/star.gif\"</td>") :“<td width=10> </td>");

}}writer.println("</tr></table>");

} catch (IOException e) {e.printStackTrace();

}return EVAL_PAGE;

}}


Custom JSP Tag<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE taglib PUBLIC "-//Sun Microsystems, ...<taglib>

<tlibversion>1.1</tlibversion><jspversion>1.1</jspversion><shortname>examples</shortname><uri>http://www.idc.ac.il/j2ee/examples</uri>

<tag><name>rank</name><tagclass>examples.RankTag</tagclass><attribute>

<name>rank</name><required>true</required><rtexprvalue>false</rtexprvalue>

</attribute></tag>

</taglib>


Web Application Framework

• Real applications consists of many Web-pages both dynamic & static

• Pages forward/redirect request to other pages, include other pages, and call components to perform logic

• We need a consistent framework for organizing all presentation and logic components and the interaction between them


WAFs

• Such a framework is referred to as WAF (Web Application Framework)

• There are many Java based WAFs, on top of JSP and/or Servlets

• We’ll describe a general design for working with JSP & Servlets. It is used in Struts2 and other WAFs


Model2

• Model2* applies a design pattern known as MVC to the problem

– The client directs all requests to a single controller Servlet

– The controller process the request, acts on the model and forwards the request to another Servlet/JSP for rendering

– The target Servlet/JSP render the response according to attributes passed by the controller via request/session attributes


Model2 (MVC)

JSP Pages (View)

Servlet (Controller)

JavaBeans / EJB / Database (Model)

Forward request after setting attributes in request or session

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Example (ex3)

login.jsp game.jsp MIDletResponseServlet

MapRenderingServlet

ControllerServlet


Passing parameters

public class ControllerServlet extends HttpServlet {

public void doGet(HttpServletRequest request, ...) { ...

request.setAttribute(“price”, new Float(price));

... forward


...

Price: ${price}...

Controller Servlet

Rendering JSP page


Using JavaBeans

• JSP allows to separate presentation from logic by using JavaBeans– You ‘embed’ a JavaBean in your page

– Set its properties, typically according to request parameters values

– The bean calculates the value of other properties accordingly

– Retrieve the value of the calculated property and include it in the page


Using JavaBeans

DeveloperWorks withJava & HTML

Web-DesignerWorks withdesigner tools

JSP Page

JavaBeans Component(logic)


Mortgage Calculator Example


MortgageCalcBean/**

* A JavaBean component for calculating a mortgage

* monthly payment*/

public class MortgageCalcBean implements Serializabl e {

// The requested amount of the loan

private double loanAmount;

// The annual interest

private double interest;

// The requested period of the load in years.

private int years;

Hold the value of the properties of the bean

8


MortgageCalcBeanpublic double getLoanAmount() {

return loanAmount;

}

public void setLoanAmount(double loanAmount) {

this.loanAmount = loanAmount;

}

public double getInterest() {

return interest;

}

public void setInterest(double interest) {

this.interest = interest;

}

Setter/Getter methods, define the properties of the bean


MortgageCalcBeanpublic double getMonthlyPayment() {

double monthlyPayment = calculateMonthlyPayment();

return monthlyPayment;}

private double calculateMonthlyPayment() {

double monthlyInterest = interest * 0.01 / 12;

int months = years * 12;double debt = Math.pow(1+monthlyInterest, months);

double monthlyPayment =

loanAmount*debt*monthlyInterest/(debt-1);

monthlyPayment =Math.floor(monthlyPayment*100)/100.0;

return monthlyPayment;

}

}

Read only property to return the result


mortgage_calculator.jsp<%@ page contentType="text/html" %>

<h1 align="center">Simple Mortgage Calculator</h1><p>

Below is a simple calculator for calculating the

monthly payment of the mortgage. Please enter the

required loan amount, the interest you expect to ge t

for the loan and the period of the loan in years;then press the 'calculate' button.

</p>

... tabs, tables to enhance the look of the page


mortgage_calculator.jsp<jsp:useBean id="calc" class="MortgageCalcBean"/>

<jsp:setProperty name="calc"

property="loanAmount" param="loanAmount"/><jsp:setProperty name="calc" property="interest" ...

<jsp:setProperty name="calc" ...

<form method="POST" action="mortgage_calc.jsp" >

Amount: <input type="text" name="loanAmount"

value="<%=calc.getLoanAmount()%>"><br>Interest: <input type="text" name="interest"

value="<%=calc.getInterest()%>"><br>

Years: <input type="text" name="years"

value="<%=calc.getYears()%>"><br><input type="submit" value="Calculate">

</form>

Monthly Payment $<jsp:getProperty name="calc" property="monthlyPaymen t"/>


Packaging

• A web-application consists of many elements

– Static HTML pages and resources (images, clips, ...)

– JSP pages and tag-libraries

– Servlets, Java classes, JARs

– Configuration files (descriptors)


Packaging

• J2EE defines a standard form for packaging web-applications

– The packaging unit is called a web-module

– It has standard folder structure and contains standard descriptor files

– The module is packaged as a WAR file (Web Achieve) – essentially a zip of the folder

– It can either be packaged standalone or as part of a J2EE application together with other web modules and ejb modules

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Packaging


Example

resources

libraries required by JSTL

web-pagesJSP & static

Servlet and supporting classes

tag librarydefinition for JSTL

web applicationdescriptor

JBoss specificweb applicationdescriptor


web.xml<web-app>

<servlet><servlet-name>CourseListServlet</servlet-name><servlet-class>CourseListServlet</servlet-class>

</servlet><servlet-mapping>

<servlet-name>CourseListServlet</servlet-name><url-pattern>/course_list</url-pattern>

</servlet-mapping>...<env-entry>

<env-entry-name>jdbc/IDCDB</env-entry-name><env-entry-value>!org.gjt.mm.mysql.Driver!jdbc:mysql://localhost:...</env-entry-value><env-entry-type>java.lang.String</env-entry-type>

</env-entry></web-app>


application.xml

<?xml version="1.0" encoding="ISO-8859-1"?>

<!DOCTYPE application PUBLIC '-//Sun Microsystems, ...

<application>

<display-name>Examples</display-name><module>

<web>

<web-uri>examples.war</web-uri><context-root>/examples</context-root>

</web>

</module></application>


Apache Ant and other insects...

• Manual packaging is tedious & error-prone

• Application server tools & IDEs provide varying level of support for packaging, deployment and editing descriptor files -often not enough

• We’ll use Apache Ant, which is a generic build tool and de-facto standard building Java applications

• More on Ant in a separate presentation...

Documents

Enterprise Application Development using J2EE · 3 Enterprise Application Development Using J2EE / © Shmulik London 2004 JSP request processing Internet JSP container JSP Page Upon