Objectives ƒ How to program Web applications using JSP ƒ How to extend the JSP syntax using tag libraries ƒ The relation to Servlets

An Introduction to XML and Web Technologies

Programming Web Applications with JSP

Anders Møller & Michael I. Schwartzbach © 2006 Addison-Wesley An Introduction to XML and Web Technologies

The JSP Framework

A Tiny Example

ƒ Servlets make heavy use of Java and require sophisticated programming ƒ JSP views a Web application as a collection of active pages ƒ The pages are HTML with snippets of code ƒ JSP pages are translated into servlets

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JSP

Hello World!

You are visitor number since the last time the service was restarted.

This page was last updated: 3

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JSP Templates

JSP Expressions

ƒ A text file with snippets of Java code: • expressions • statements • declarations ƒ JSP directives ƒ Implicitly declared variables: • • • • • • •

Addition The sum of and is

HttpServletRequest request; HttpServletResponse response; HttpSession session; ServletContext application; ServletConfig config; JspWriter out; PageContext pageContext;

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JSP Statements

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JSP Declarations

Numbers

An Introduction to XML and Web Technologies

An Introduction to XML and Web Technologies

Addition The sum of and is

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Be Careful About Declarations (1/2)

Be Careful About Declarations (2/2)

JSP

Hello World!

You are visitor number since the last time the service was restarted.

This page was last updated:

JSP

Hello World!

You are visitor number since the last time the service was restarted.

This page was last updated:

This page counter is always 1... An Introduction to XML and Web Technologies

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An Introduction to XML and Web Technologies

JSP Directives

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Other Directives

header.jsp

ƒ ƒ ƒ ƒ ƒ



footer.jsp

contentType="type" info=”description" errorPage="path" isErrorPage="boolean" import="package"

The sum of and is An Introduction to XML and Web Technologies

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Using Error Pages

Translation into Servlets

Division / equals

JSP

Hello World!

You are visitor number since the last time the service was restarted.

This page was last updated:

Error Something bad happened: An Introduction to XML and Web Technologies

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The Generated Servlet (1/5)

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The Generated Servlet (2/5)

package org.apache.jsp;

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

import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.jsp.*;

JspFactory _jspxFactory = null; PageContext pageContext = null; HttpSession session = null; ServletContext application = null; ServletConfig config = null; JspWriter out = null; Object page = this; JspWriter _jspx_out = null; PageContext _jspx_page_context = null;

public final class hello_jsp extends org.apache.jasper.runtime.HttpJspBase implements org.apache.jasper.runtime.JspSourceDependent { int hits = 0; private static java.util.Vector _jspx_dependants; public java.util.List getDependants() { return _jspx_dependants; } An Introduction to XML and Web Technologies

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The Generated Servlet (3/5)

The Generated Servlet (4/5)

try { _jspxFactory = JspFactory.getDefaultFactory(); response.setContentType("text/html"); 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;

An Introduction to XML and Web Technologies

response.addDateHeader("Expires", 0); out.write("\n"); out.write("JSP\n"); out.write("

Hello World!

\n"); out.write("\n"); out.write("You are visitor number "); synchronized(this) { out.println(++hits); } out.write("\n"); out.write("since the last time the service was restarted.\n"); out.write("

\n"); out.write("This page was last updated: "); out.print(new java.util.Date().toLocaleString()); out.write("\n"); out.write("\n");

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The Generated Servlet (5/5)

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Literal Translation

} catch (Throwable t) { if (!(t instanceof SkipPageException)){ out = _jspx_out; if (out != null && out.getBufferSize() != 0) out.clearBuffer(); if (_jspx_page_context != null) _jspx_page_context.handlePageException(t); } } finally { if (_jspxFactory != null) _jspxFactory.releasePageContext(_jspx_page_context); }

Have a nice day! Have a lousy day! if (Math.random() < 0.5) { out.write("\n"); out.write(" Have a nice day!\n"); } else { out.write("\n"); out.write(" Have a lousy day!\n"); } out.write("\n”);

} }

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Problematic Whitespace

Advanced Features ƒ ƒ ƒ ƒ ƒ

This is a tiny test

XML version of JSP The expression language Tag files JSTL The Model-View-Controller pattern

This is a tiny test

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JSP Pages Are Not XML

XML Version of JSP response.addDateHeader("Expires", 0); JSP request.getParameter("color")

Hello World!

int hits = 0; You are visitor number synchronized(this) { out.println(++hits); } since the last time the service was restarted.

This page was last updated: new java.util.Date().toLocaleString()

JSP Color

Hello World!

You are visitor number since the last time the service was restarted.

This page was last updated:

ƒ This page generates HTML, not XHTML ƒ is not well-formed XML An Introduction to XML and Web Technologies

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• Uses • No schema seems to be available • No validation of the output • No validation of Java code • but it’s there... 24

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The Expression Language

An Expression Example

ƒ We want to avoid explicit Java code in JSP templates

Addition The sum of ${param.x} and ${param.y} is ${param.x+param.y}

ƒ The syntax ${exp} may be used in • template text • attribute values in markup

ƒ The expression may access • variables in the various scopes • implicit objects, such as param

ƒ The usual operators are available 25

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Tag Files

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Content as a Value: A New Image Tag

Define abstractions as new tags

image.tag:

wrap.tag: ${title} The sum of ${param.x} and ${param.y} is ${param.x+param.y}

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widget.jpg

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Declaring Variables: A Date Context Tag

Using the Date Context

date.tag: An Introduction to XML and Web Technologies

In the US today is ${month}/${date}/${year}, but in Europe it is ${date}/${month}/${year}.

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Quick Poll Tags (1/2)

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Quick Poll Tags (2/2)

The question has been set to "${question}". ${question}? yes no

You have voted ${vote}. In favor: ${yes}
Against: ${no}
Total: ${total} Sorry, the polls have closed.

See the tag files in the book... An Introduction to XML and Web Technologies

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Tag Libraries

JSTL 1.1

ƒ Libraries of tags capturing common patterns: • • • • • • • • • •

ƒ JSP Standard Tag Library covers:

pagination of large texts date and times database queries regular expressions HTML scraping bar charts cookies e-mail WML ...

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• • • • • • • • • 33

Selecting Some Recipes

assigning to variables writing to the output stream catching exceptions conditionals iterations URL construction string formatting SQL queries XML manipulation

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Using JSTL for the Menu Select Some Recipes


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Using JSTL for the Table (1/3)

Using JSTL for the Table (2/3)

Nutrition Overview

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Using JSTL for the Table (3/3)

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Evaluation of Tags

Title	Calories	Fat	Carbohydrates	Protein	Alcohol
					0%

An Introduction to XML and Web Technologies

An Introduction to XML and Web Technologies

ƒ Make Web applications available to a wider range of developers ƒ May be used to structure applications ƒ A myriad of domain-specific languages ƒ Brittle implementation, hard to debug

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The ModelModel-ViewView-Controller Pattern

The Benefit of MVC

View

Model

Separation of concerns!

provides views to clients

encapsulates data representation and business logic

(high cohesion – low coupling)

Controller

handles interactions with clients An Introduction to XML and Web Technologies

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An Introduction to XML and Web Technologies

Using MVC

Summary

ƒ Controller: one servlet ƒ View: JSP pages ƒ Model: pure Java (e.g. JavaBeans)

ƒ JSP templates are HTML/XHTML pages with embedded code ƒ The simple expression language is often sufficient in place of full-blown Java code ƒ Tag files and libraries allow code to be hidden under a tag-like syntax

[Example in the book: Business Card Server]

ƒ MVC provides separation of programming and HTML design tasks An Introduction to XML and Web Technologies

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Essential Online Resources ƒ Sun’s home page for JSP: http://java.sun.com/products/jsp/

ƒ JSTL: http://java.sun.com/products/jsp/jstl/

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