Week6 Intro Server Side II

8/11/2019 Week6 Intro Server Side II

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Server-Side Web Development


JavaBeans; basic concepts and syntax

23rdFebruary 2005

Bogdan L. Vrusias

[email protected]


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23rdFebruary 2006 Bogdan L. Vrusias 2006 2

Contents

JavaBean definition and syntax

Sharing JavaBean components

JavaBeans Examples

Session Tracking


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Invoking Java code from JSP

Call Java code directly

Call Java code indirectly

Use beans

Use the Model-View-Controller architecture

Use the JSP expression language (EL)

Use custom tags

Simple application or

small development team

Complex application or

large development team


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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


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JavaBeans: Basics

A bean class must have a zero-argument (default)

constructor.

A bean should have no public instance variables (fields).

Persistent values should be accessed through methodscalled setXxxand getXxx(or isXxxfor Boolean).


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JavaBeans: Basic Tasks

In a JSP there are three main JavaBean constructs:

jsp:useBean

jsp:getProperty

Jsp:setProperty

(CAREFUL)

Otherwise


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JavaBeans: Basic Tasks

Properties of a JavaBean class must simply be accessible using public

methods that conform to certain conventions:

For each readable property, the bean must have a method of the formPropertyClass getProperty() { ... }

For each writable property, the bean must have a method of the form

setProperty(PropertyClass pc) { ... }

NOTE 1: beanNamemust be the same as the one specified in a

useBeanelement (using the idattribute), and there must be a

getPNamemethod in the JavaBeans component. NOTE2:The official version of a Java Bean class extends the Object

class and implements the Serializableclass. But for simplicity

reasons we will not be doing that.


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JavaBean Example I

StringBean.java

package webtech.w6;

public class StringBean {

private String message = "No message";

public String getMessage() {

return(message);

}

public void setMessage(String message) {

this.message = message;

}

}


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JavaBean Example II

StringBean.jsp

...

Initial value (getProperty):

Initial value (JSP expression):

Value after setting property with scriptlet:

...


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Sharing Beans

(Default)

Bean is not shared and a new bean is created for each request

Same as "page" scope but, two JSP pages or a JSP page and a servlet willshare the bean when you use jsp:include

Bean is shared within a session

Bean is shared by all servlets and JSP pages in a Web application


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Sharing Beans: Example

This example demonstrates the use of JavaBeans and how the beans are

shared.

There are four possibilities:

Page

Request

Session

Application

For this example these is one JavaBean that stores two parameters, and five

JSP pages to demonstrate the use of the bean.

To test the bean sharing we will try to pass parameters by directly entering the

parameters within the URL:

scope_page.jsp?sport=cricket&rating=boring

Parameter 1 Parameter 2


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Sharing Beans: The JavaBean

msgBean.javapackage webtech.w6;

public class msgBean {

private String sport = "football";

private String rating = "fun";

public String getRating() {return rating;

}

public void setRating(String newRating) {

rating = newRating;

}

public String getSport() {return sport;

}

public void setSport(String newSport) {

sport = newSport;

}

}


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Sharing Beans: Page Scope Example

scope_page.jsp

The sport:

Has rating:


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Sharing Beans: Request Scope Example

scope_request.jsp

The sport:

Has rating:


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Sharing Beans: Request Scope Example

snippet.jsp

The sport:

Has rating:


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Sharing Beans: Session Scope Example

scope_session.jsp

The sport:

Has rating:


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Sharing Beans: Application Scope Example

scope_application.jsp

The sport:

Has rating:


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Installing JavaBeans

Each JavaBean should be located within your web

application under:WEB-INF/classes

Or, if the bean is within a package (recommended), then:WEB-INF/classes/subdirectoryMatchingPackageName

Or, if the bean is within a .JAR, then place the .JAR in:

WEB-INF/lib


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JSP Session Tracking

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 clientand the server.


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Session tracking is a technique for maintaining user

information across pages:

HTTP information (not used much privacy issues)

Hidden fields (popular but again, privacy issues)

Extended Path information and URL-rewriting ( privacy issues)

Next

S Sid b l


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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")

JavaBeans using the session scope

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23rd February 2006 Bogdan L Vrusias 2006 23

Closing

Questions???

Remarks???

Comments!!!

Evaluation!

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