Document

Download Report

Transcript Document 

Introduction to Server-Side
Web Development
Introduction to Server-Side Web
Development
JSP Final Remarks
10th March 2005
Bogdan L. Vrusias
[email protected]
Introduction to Server-Side
Web Development
Contents
• Java Collections API and Casting
• JavaBeans – Final Remarks
• Session Tracking
10th March 2005
Bogdan L. Vrusias © 2005
2
Introduction to Server-Side
Web Development
Java Collection API
• Array
• Vector
• Hashtable
• ArrayList
• LinkedList
• ...
import java.util.*;
10th March 2005
Bogdan L. Vrusias © 2005
3
Introduction to Server-Side
Web Development
Array Example
int[] anArray;
anArray = new int[10];
for (int i = 0; i < anArray.length; i++) {
anArray[i] = i;
System.out.print(anArray[i] + " ");
}
boolean[] answers = { true, false, true, false };
MyObject[] anObjectArray = new MyObject[5];
10th March 2005
Bogdan L. Vrusias © 2005
4
Introduction to Server-Side
Web Development
Multidimensional Array Example
int[][] aMatrix = new int[4][];
for (int i = 0; i < aMatrix.length; i++) {
aMatrix[i] = new int[5];
for (int j = 0; j < aMatrix[i].length; j++) {
aMatrix[i][j] = i + j;
}
}
for (int i = 0; i < aMatrix.length; i++) {
for (int j = 0; j < aMatrix[i].length; j++) {
System.out.print(aMatrix[i][j] + " ");
}
System.out.println();
}
10th March 2005
Bogdan L. Vrusias © 2005
5
Introduction to Server-Side
Web Development
Vector Example
Vector v = new Vector();
v.addElement("Hello");
v.addElement(new Integer(99));
v.addElement(99);
// Error
for (int i=0; i < v.size(); i++)
System.out.println(v.elementAt(i));
// or v.get(i)
Integer a = (Integer) v.elementAt(1);
10th March 2005
Bogdan L. Vrusias © 2005
6
Introduction to Server-Side
Web Development
Hashtable Example
Hashtable nums = new Hashtable();
nums.put("one", new Integer(1));
nums.put("two", new Integer(2));
Integer n = (Integer)nums.get("two");
if (n != null) {
System.out.println("two = " + n);
}
for (Enumeration e = nums.keys (); e.hasMoreElements ();)
{
System.out.println (e.nextElement ().toString ());
}
if (nums.containsKey ("one")) {...}
10th March 2005
Bogdan L. Vrusias © 2005
7
Introduction to Server-Side
Web Development
Java Type Conversion / Casting
If v is a Vector type collection object then:
Getting a String from Vector
String s = (String)v.elementAt(x);
Vector of Vector objects
Vector v = (Vector)v.elementAt(x);
Getting a String from Vector of Vector objects
String s =
((Vector)v.elementAt(x)).elementAt(y).toString();
10th March 2005
Bogdan L. Vrusias © 2005
8
Introduction to Server-Side
Web Development
Invoking Java code from JSP
Simple application or
small development team
• Call Java code directly
• Call Java code indirectly
• Use beans
• Use the Model-View-Controller architecture
Complex application or
large development team
10th March 2005
• Use the JSP expression language (EL)
• Use custom tags
Bogdan L. Vrusias © 2005
9
Introduction to Server-Side
Web Development
Servlets vs. JSP
• JSPs and servlets are two different ways to accomplish the
same goal: generating dynamic HTML pages using Java
code. One puts Java code in your HTML, and one puts
HTML in your Java code.
• Functionally, they are equivalent. In fact, under the covers,
the web server takes a JSP and converts it to the
corresponding servlet and dynamically compiles it.
• BUT servlets have the following deficiencies:
– It is hard to write and maintain the HTML
– You cannot use standard HTML tools
– The HTML is inaccessible to non-Java developers
10th March 2005
Bogdan L. Vrusias © 2005
10
Introduction to Server-Side
Web Development
JSP Example
<HTML>
<HEAD><TITLE>Hello World</TITLE></HEAD>
<body>
<jsp:useBean id="dateBean"
class="webtech.DateFormatBean" />
<p>The date is: <%= dateBean.getDate() %></p>
<%
dateBean.setDate("9-Mar-2005");
%>
<p>The new date is: <%= dateBean.getDate() %></p>
</body></html>
10th March 2005
Bogdan L. Vrusias © 2005
11
Introduction to Server-Side
Web Development
JavaBeans
• JavaBeans is a portable (platform-independent) component model
written in Java and was developed in collaboration with industry
leaders.
• JavaBeans components are Java classes that can be easily reused and
composed together into applications.
• Any Java class that follows certain design conventions can be a
JavaBeans component.
• JavaServer Pages technology directly supports using JavaBeans
components with JSP language elements.
10th March 2005
Bogdan L. Vrusias © 2005
12
Introduction to Server-Side
Web Development
JavaBeans: Advantages
• No Java syntax in the JSP
– Stronger separation between content and presentation
– Good for separating Web and Java developers
• Simple object sharing
– Due to the JSP bean constructs
• Convenient correspondence between request parameters
and object properties
– Simple process of reading request parameters
• JavaBeans will minimize the code on the JSP.
10th March 2005
Bogdan L. Vrusias © 2005
13
Introduction to Server-Side
Web Development
JavaBean Example I
StringBean.java
package webtech;
public class StringBean {
private String message = "No message";
public String getMessage() {
return(message);
}
public void setMessage(String message) {
this.message = message;
}
}
10th March 2005
Bogdan L. Vrusias © 2005
14
Introduction to Server-Side
Web Development
JavaBean Example II
StringBean.jsp
<jsp:useBean id="sBean" class="webtech.StringBean" />
<jsp:getProperty name="sBean" property="message" />
<%= sBean.getMessage() %>
<jsp:setProperty name="sBean" property="message"
value=“message 1" />
<jsp:getProperty name="sBean" property="message" />
<% sBean.setMessage(“message 2"); %>
<%= sBean.getMessage() %>
10th March 2005
Bogdan L. Vrusias © 2005
15
Introduction to Server-Side
Web Development
Sharing Beans
• <jsp:useBean … scope="page"/> (Default)
– Bean is not shared and a new bean is created for each request
• <jsp:useBean … scope="request"/>
– Same as "page" scope but, two JSP pages or a JSP page and a servlet will
share the bean when you use jsp:include
• <jsp:useBean … scope="session"/>
– Bean is shared within a session
• <jsp:useBean … scope="application"/>
– Bean is shared by all servlets and JSP pages in a Web application
10th March 2005
Bogdan L. Vrusias © 2005
16
Introduction to Server-Side
Web Development
JSP Sessions I
• A session can be defined as a series of related interactions between a
single client and the server, which take place over a period of time.
• A session object can be used for storing and retrieving information.
• Every time the client accesses the resources on the server, the client
provides the session ID that was assigned by the server.
• A session has a one-to-one association between a client and the server.
10th March 2005
Bogdan L. Vrusias © 2005
17
Introduction to Server-Side
Web Development
JSP Sessions II
• Session tracking is a technique for maintaining user
information across pages.
• Unsecured / Not recommended:
– HTTP information (not used much… privacy issues)
– Hidden fields (very popular… but again privacy issues)
<input type="hidden" name="myKey"
value="myValue" >
– Extended Path information and URL-rewriting ( privacy issues)
<a href="/myPage.jsp?login=james&item=book_1">
Next</a>
10th March 2005
Bogdan L. Vrusias © 2005
18
Introduction to Server-Side
Web Development
JSP Sessions III
• More secure / Recommended:
– Cookies (data can be encrypted)
Cookie uid = new Cookie("uid", "234ff543333c");
response.addCookie(uid);
– Session (data can be encrypted)
session.putValue("user_id", user_id);
session.getValue("user_id")
10th March 2005
Bogdan L. Vrusias © 2005
19
Introduction to Server-Side
Web Development
Closing
• Questions???
• Remarks???
• Comments!!!
• Evaluation!
10th March 2005
Bogdan L. Vrusias © 2005
20