ISOM MIS 3150 Module 3 3-Tier Webapps using JSP/JDBC Arijit Sengupta.

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MIS 3150 Module 33-Tier Webapps using JSP/JDBC

Arijit Sengupta

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Structure of this semester

Database Fundamentals

Relational Model

Normalization

ConceptualModeling Query

Languages

AdvancedSQL

XMLDatabases

Java DB Applications –JDBC/JSP

DataMining

0. Intro 1. Design 3. Applications 4. AdvancedTopics

Newbie Users ProfessionalsDesigners

MIS415

2. Querying

Developers

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Today’s Buzzwords

• 3-Tier applicationsClient – WebServer – ApplicationServer

• Basics of JDBC

• Basics of JSP Containers - Tomcat

• Web Applications using JSP

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3 Tier Architecture

HTTP request

HTTP response

Web server

JSP page

JSP container compiles to

a servlet

URL

request

JavaBeanLibrary

DB

properties,call methods

HTTP page

response

Browser

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JDBC

A platform-independent library of classes allowing database access from any Java application

Take advantages of Polymorphism• JDBC is a set of interfaces

– Driver, Connection, Statement, ResultSet, etc.

• Database vendors (not programmers) will implement these interfaces.

• If we switch from one database to another, we just need to load different driver (plug and play)!

– YOU DON'T NEED TO MODIFY THE REST OF YOUR PROGRAM!

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JDBC

DriverManager Connection Statement ResultSet

Database

Driver

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JDBC

DriverManager Connection Statement ResultSet

Driver

Database

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JDBC (Contd.)

• Register a JDBC driverDriver d = new oracle.jdbc.driver.OracleDriver();DriverManager.registerDriver (d); orDriverManager.registerDriver (new

oracle.jdbc.driver.OracleDriver());

• Or, use the Java reflection abilitiesClass.forName("oracle.jdbc.driver.OracleDriver");

calling Class.forName() will create an instance of a driver and register it with the DriverManager automatically

This is better since we can use a constant:String DRIVER =

"oracle.jdbc.driver.OracleDriver";Class.forName(DRIVER);

• For mysql, use: com.mysql.jdbc.driver

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JDBC

DriverManager Connection Statement ResultSet

Driver

Database

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JDBC (Contd.)

• Make a connectionString URL = "jdbc:oracle:thin:@unixapps1.wright.edu:1521:ORA2"; // For Oracle

String URL = ”jdbc:mysql://localhost/employees"; // For MySQL

Connection conn =

DriverManager.getConnection(URL, USERNAME, PASSWORD);

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JDBC

DriverManager Connection Statement ResultSet

Driver

Database

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JDBC (Contd.)

• Create a statementStatement st = conn.createStatement();

//default:TYPE_FORWARD_ONLY and CONCUR_READ_ONLY

orStatement st =conn.createStatement( ResultSet.TYPE_SCROLL_SENSITIVE,

ResultSet.CONCUR_UPDATABLE);//the resultset will be scrollable and sensitive to changes made by others

//we can update the resultset

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JDBC

DriverManager Connection Statement ResultSet

Driver

Database

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JDBC (Contd.)

• Execute a queryString SQL = "INSERT INTO s" + " VALUES ('222-22-2222')";int result = st.executeUpdate(SQL);

//either the row count for INSERT, UPDATE or DELETE or 0 for SQL statements that return nothing

• Execute a query and create a resultsetString SQL = "SELECT * FROM Student";ResultSet rec = st.executeQuery(SQL);

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JDBC (Contd.)

• Process the resultsetwhile(rec.next())

{ System.out.println(rec.getString("snum"));} orwhile(rec.next())

{ System.out.println(rec.getString(1)); // first column of the resultset} There are methods like getString(), getInt(), etc. that take either a

column name or column position

• See http://java.sun.com/j2se/1.3/docs/guide/jdbc/index.html for all JDBC Class documentation

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Tomcat – a J2EE Container

• Open Source – integrated as an Apache.org project

• Can be obtained from http://tomcat.apache.org

• Provides full JSP 2.0/Servlet 2.4 functionality

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Elements of a Java Server Page

Directives: <%@ %>• Provide global information to the page• Import statements• Scripting language

Declarations: <%! %>• For page-wide variable and method declarations

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Elements of a Java Server Page

• Scriptlets: <% %>This is the Java code embedded in the web

pages

• Expressions: <%= %>Formats the expression as a string to be

included in the output of the web page

• Comments: <%-- --%>• User readable comments, contents

ignored and removed by the JSP Compiler

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JSP Directives

General syntax: <%@ directive {attribute = "value"} %>

• Possible values for directives are:Page - Information for the page

• Include - Specifies the files whose contents are to be included in the outpute.g., <%@ include file="header.html" %>

• TaglibThe URI for a library of custom tags that

may be used in the page

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JSP Page Directive

• The page directive may take the following values: <%@ page language = "java" %> This variable tells the JSP engine what language will

be used in the file

• • "java" is the only language supported by JSP in the current specification

• <%@ page import = "java.util.*, ItemValue" %> Comma separated list of classes and packages that

are used in the JSP page Should appear at the top of the file

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JSP Page Directive (Contd.)

<%@ page session = "true | false" %> true indicates that session data is available to

the page By default, this is set to true

<%@ page buffer = "none | 16kb | sizekb" %> Determines the size of the output stream buffer Defaults to 8kb Use with autoFlush

<%@ page autoFlush = "true | false" %> When set to true, flushes the output buffer

when it is full, rather than raising an exception

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JSP Page Directive (contd.)

<%@ page errorPage = "mypage/error_handler.jsp" %>Specifies the relative path of the page,

where control would be transferred if any exceptions are thrown from this page

The error handling JSP page should have its isErrorPage directive set to true

<%@ page isErrorPage = "true | false" %>Marks the page as an error handler

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JSP Declarations

• Class and instance variables (of the generated servlet class) may be specified using the JSP Declaration tag:<%! String name = “Web Applications";int index = 10;int count = 0; %>

• Methods may also be specified:<%! private int getNextIndex() { return index ++; } %>

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JSP Scriptlets

• JSP scriptlets are defined as block of Java code embedded between a pair of

• tags, <% and %>.• Example:

<%java.util.Date d = new java.util.Date();out.println(d);%>

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JSP Expressions

• Useful for embedding the result of a Java expression in a HTML pageThe expression is encoded between the

tags <%= and %>The value of the expression is converted

to a string and then displayedConversion of primitive types to string

happens automaticallyExample:The date is <%= new java.util.Date() %>

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JSP Implicit Objects

• When writing scriptlets and expressions, the following objects (called implicit objects) are available by default:

• request javax.servlet.http.HttpServletRequest• response javax.servlet.http.HttpServletResponse• out javax.servlet.jsp.JspWriter• session javax.servlet.http.HttpSession• application javax.servlet.ServletContext• exception java.lang.Throwable

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Reading inputs from Forms/URLS

• Remember that parameters are passed to Web applications via one of two methods: GET method: parameters are passed directly through the

URL, encoded using the urlencoding method• Quick to create and test – can be created without a form• Can be bookmarked• URL shows in plaintext – not secure

POST method: parameters are encoded and sent to the server separately from the URL

• Can only be created via forms (or advanced applications)• Secure – parameters cannot be seen

• Reading a single parameter via name:String value = request.getParameter(paramname);String [] values =

request.getParameterValues(paramname); /* for multivalued parameters like

checkboxes/multiple selectable lists */• Better way – using “Beans” - shortly

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JSP Session Example

<html><head><title>Visitor Count -- JSP Session</title></head> <body bgcolor="#FFFFFF"><h2>Visitor Count</h2><p>This JSP page demonstrates session management by

incrementing a counter each time a user accesses a page.</p>

<%! private int totalHits = 0;%><% session = request.getSession(true); Integer ival = (Integer)session.getValue("jspsession.counter"); if (ival == null) ival = new Integer(1); else ival = new Integer(ival.intValue() + 1); session.putValue("jspsession.counter", ival);%><p align="center"> You have hit this page <%= ival %> time<%= (ival.intValue() == 1) ? "" : "s" %>, out of a total of <%= ++totalHits %> page hit<%= (totalHits == 1) ? "" : "s" %>!</p></body></html>

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JSP Actions

• Actions are tags that may affect the runtime behavior of the JSP or affect the current out stream; they may also use, modify and/or create objects.

• JSP specification defines the following standard actions:<jsp:useBean><jsp:setProperty><jsp:getProperty>

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JSP Actions

<jsp:include><jsp:forward><jsp:param><jsp:plugin>

• New action types are introduced by means of custom tags

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What is a JavaBean?

• A Java class that (at a minimum)has an empty constructorhas getters and setters for each of the

properties in the classimplements the serializable interface

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JSP Actions and Attributes

• JSP actions can define named attributes and associated values

<%@ page import="People" errorPage="exception.jsp“ %>

<jsp:useBean id="myperson" class="People" /><% myperson.setName("Ramesh"); %><h1>My name is: <%=myperson.getName()%></h1><%-- Let's now use the bean syntax --%>Name using Bean is:<jsp:getProperty name="myperson"

property="name" />

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Beans and HTML forms

• You may connect HTML form parameters to Bean properties<jsp:setProperty name="id" property="accountHolder"

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

• There is a shorthand for the above:<jsp:setProperty name="id"

property="accountHolder" />

This works if the property name was exactly the same as the form parametername

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Beans and HTML forms

• If the form parameter name and the property name do not match, then use the following variant of "jsp:setProperty"<jsp:setProperty name=“myperson" property=“age“ param=“myage" />

• Another powerful variation of "jsp:setProperty" examines all the parameter names from the request object and if some of them match with property names, it sets the appropriate properties<jsp:setProperty name=“myperson" property="*" />

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Beans and HTML (contd.)

<%-- Trying the all powerful syntax --%>

<jsp:setProperty name="myperson" property="*" />

Name is: <%=myperson.getName()%>

Age is: <%=myperson.getAge()%>

Weight is: <%=myperson.getWeight()%>

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Including Files

• JSP supports two kinds of file inclusion: Static (using the directive "include") Dynamic (or Request-Time)

• Static inclusion is specified using the "include" directive e.g., <%@ include file="header.html" %> In static inclusion, the contents of "header.html" are

included in the output of the containing JSP file during the JSP page compilation

If the contents of the "header.html" file change, these changes are not visible to the user of the containing JSP file

Static inclusion is fast (because inclusion is done at compile time)

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Including Files (contd.)

• Dynamic inclusion is supported by the use of the tag "jsp:include" e.g., <jsp:include page = "news/headlines.jsp" flush

= "true" /> Each time the containing JSP file is accessed, the JSP

engine includes the contents of the latest copy of the file "news/headlines.jsp“

You may also pass parameters to the included file, e.g:

<jsp:include page = "news/headlines.jsp" flush="true">

<jsp:param name="prefers" value="international"/>

...</jsp:include>

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Forwarding Files

• A request to a JSP file may be forwarded, transparently to the user, to another JSP file<jsp:forward page = "target" />This is used to redirect request from one page

to another pageThe calling JSP file relinquishes control to the

forwarded pageThe calling JSP cannot send any data back to

the browser before invoking this tag If data had already been sent by the calling JSP,

invoking the "jsp:forward" tag causes an exception to be thrown

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Forwarding Requests

• You may also pass parameters to the forwarded page<jsp:forward page="catalog.jsp" /><jsp:param name="color" value="red"/> ...</jsp:forward>

• Parameters passed in this fashion may be accessed by the forwarded JSP (catalog.jsp) by the following call: request.getParameter("color");

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Forwarding Requests

• Request forwarding is typically used for authentication<% if(request.getParameter("login-info") == null)

%><jsp:forward page="login.jsp"/><%else{ /* Generate Error message – no login */}%>

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Summary

• JSP – JDBC provides a stable and well-tested platform for 3-tier web application design

• Supports all major databases and all platforms• With Servlet compilation, performance is high• Many major applications like Wiki, major

Government/Funding organizations like NSF – are running on Java/JSP technology.

• Web services are well-supported• J2EE provides a well-designed software design

and development platform for enterprise systems.