Java serverpages

Copyright @ 2000 Jordan Anastasiade. All rights rese1
JavaServer Pages
In this lesson you will be learning about:
What JSP Technology is and how you can use it.
How to define and write JSP Page.
Syntax of JSP Page.
How do JSP pages work.
How is a JSP page invoked and compiled.
Use of Beans in a JSP Page.
How one could create XML pages using JSP technology.
JavaServer Pages v1.2

JavaServer Pages Technology
JavaServer Pages (JSP) technology provides a simplified,
fast way to create web pages that display dynamically-
generated content.
The JSP 1.2specification is an important part of the Java
2 Platform, Enterprise Edition. Using JSP and
Enterprise JavaBeans technologies together is a great
way to implement distributed enterprise applications
with web-based front ends.
The first place to check for information on JSP
technology is http://java.sun.com/products/jsp/

JSP Page
A JSP page is a page created by the web developer that includes JSP
technology-specific tags, declarations, and possibly scriptlets, in
combination with other static HTML or XML tags.
A JSP page has the extension .jsp; this signals to the web server that
the JSP engine will process elements on this page.
Pages built using JSP technology are typically implemented using a
translation phase that is performed once, the first time the page is
called. The page is compiled into a Java Servlet class and remains in
server memory, so subsequent calls to the page have very fast
response times.
Put .jsp pages into a WAR file (see Web ARchive)
Deploy (upload) the WAR file as a Web Application to your Sun
Java System Application Server Platform.

Overview
JavaServer Pages (JSP) lets you separate the dynamic
part of your pages from the static HTML.
HTML tags and text
<% some JSP code here %>
HTML tags and text
<I>
<%= request.getParameter("title") %>
</I>
You normally give your file a .jsp extension, and
typically install it in any place you could place a normal
Web page

Client and Server with JSP

Translation Time
A JSP application is usually a collection of JSP files,
HTML files, graphics and other resources.
A JSP page is compiled when your user loads it into a
Web browser
1. When the user loads the page for the first time, the files that make up
the application are all translated together, without any dynamic data,
into one Java source file (a .java file)
2. The .java file is compiled to a .class file. In most implementations,
the .java file is a Java servlet that complies with the Java Servlet API.

Simple JSP Page
<%@ page info=“A Simple JSP Sample” %>
<HTML>
<H1> First JSP Page </H1>
<BODY>
<% out.println(“Welcome to JSP world”); %>
</BODY>
</HTML>

How JSP Works?
User Request – JSP File RequestedUser Request – JSP File Requested
ServerServer
File
Changed
File
ChangedCreate Source from JSPCreate Source from JSP
CompileCompile Execute ServletExecute Servlet

JSP Elements
Declarations <%! code %>
<jsp:declaration>
</jsp:declaration >
Expressions <%= expression %>
<jsp:expression>
</jsp:expression>
Scriplets <% code %>
<jsp:scriplet>
</jsp:scriplet >

HTML Comment
Generates a comment that is sent to the client.
Syntax

Example:

Declaration
Declares a variable or method valid in the scripting language used in
the JSP page.
 Syntax
<%! declaration; [ declaration; ]+ ... %>
 Examples
<%! String destin; %>
<%! Public String getDestination()
{return destin;}%>
<%! Circle a = new Circle(2.0); %>
 You can declare any number of variables or methods within one declaration
element, as long as you end each declaration with a semicolon.
 The declaration must be valid in the Java programming language.

Declaration Example
<HTML>
<HEAD><TITLE>JSP Declarations</TITLE></HEAD>
<BODY><H1>JSP Declarations</H1>
<%! private int keepCount = 0; %>
<H2>
Page accessed:
<%= ++keepCount %>
times
</H2>
</BODY>
</HTML>

Predefined Variable – Implicit
Objects
request – Object of HttpServletRequest (request parameters, HTTP headers,
cookies
response – Object of HttpServletResponse
out - Object of PrintWriter buffered version JspWriter
session - Object of HttpSession associated with the request
application - Object of ServletContext shared by all servlets in the engine
config - Object of ServletConfig
pageContext - Object of PageContext in JSP for a single point of access
page – variable synonym for this object

Expression
Contains an expression valid in the scripting language used in the
JSP page.
 Syntax
<%= expression %>
<%! String name = new String(“JSP World”); %>
<%! public String getName() { return name; } %>
<B><%= getName() %></B>
 Description:
An expression element contains a scripting language expression that is
evaluated, converted to a String, and inserted where the expression appears
in the JSP file.
 Because the value of an expression is converted to a String, you can use an
expression within a line of text, whether or not it is tagged with HTML, in a
JSPfile. Expressions are evaluated from left to right.

Expression Example
<HTML>
<HEAD>
<TITLE>JSP Expressions</TITLE>
</HEAD>
<BODY>
<H2>JSP Expressions</H2>
<UL>
<LI>Current time: <%= new java.util.Date() %>
<LI>Your hostname: <%= request.getRemoteHost()
%>
<LI>Your session ID: <%= session.getId() %>
</UL>
</BODY>
</HTML>

Scriptlet
Contains a code fragment valid in the page scripting
language.
 Syntax
<% code fragment %>
<%
String var1 = request.getParameter("name");
out.println(var1);
%>
This code will be placed in the generated servlet method:
_jspService()

Scriplet Example
<HTML>
<HEAD><TITLE>Weather</TITLE></HEAD>
<BODY>
<H2>Today's weather</H2>
<% if (Math.random() < 0.5) { %>
Today will be a <B>suny</B> day!
<% } else { %>
Today will be a <B>windy</B> day!
<% } %>
</BODY>
</HTML>

JSP Lifecycle
jspInit()jspInit()
jspDestroy()jspDestroy()
jspService()jspService()
Servlet from JSP
Init Event
Request
Response
Destroy Event

JSP Page Directive
Directives are messages to the JSP container and do not produce
output into the current output stream
 Syntax:
<%@ directive attribute=“value” %>
<%@ directive attribute1=“value1”
attribute1 =“value2” … %>
There are three types of directives:
1. page
2. include
3. taglib
XML form:
<jsp:directive.directiveType
attribute=“value” />

Page Directive
Defines attributes that apply to an entire JSP
page.
<%@ page
[ language="java" ]
[ extends="package.class" ]
[ import="{package.class |
package.*}, ..." ]
[ session="true|false" ]
[ buffer="none|8kb|sizekb" ]
[ autoFlush="true|false" ]
[ isThreadSafe="true|false" ]
[ info="text" ]
[ errorPage="relativeURL" ]
[ contentType="mimeType [
;charset=characterSet ]"
[ isErrorPage="true|false" ]
%>

Include Directive
Includes a static file in a JSP file, parsing the file's JSP elements.
 Syntax
<%@ include file="relativeURL" %>
The <%@ include %> directive inserts a file of text or code in a JSP file
at
translation time, when the JSP file is compiled.
<%@ include %> process is static. A static include means that the text of
the included file is added to the JSP file.
The included file can be:
1. JSP file,
2. HTML file,
3. text file.

Taglib Directive
Defines a tag library and prefix for the custom
tags used in the JSP page.
 Syntax
<%@ taglib uri="URIToTagLibrary" prefix="tagPrefix"
%>
<%@ taglib uri="http://thathost/tags" prefix="public"
%>
<public:loop>
</public:loop>
The <%@ taglib %> directive declares that the JSP file uses custom tags,
names the tag library that defines them, and specifies their tag prefix.

Server Redirection
One can forward to a text file (HTML), a CGI script, a servlet or another
JSP page.
One can only forward to a new page, provided no output of the original
page has been sent to the browser.
One may pass as many parameters as one needs with this method by
using the param tag.
The forward action ends execution of the current JSP page and removes
any existing buffered output. The new page has access to application,
request, and session objects as the starting file. A new pageContext
object is generated for the page. To the browser, it will appear you have
the originally requested page, not the page to which you are transferred.
Example:
<jsp:forward page="home/Default.jsp" >
<jsp:param name="source" value="entry"/>
</jsp:forward>

<jsp:forward>
Forwards a client request to an HTML
file, JSP file, or servlet for processing.
Syntax
<jsp:forward page="{relativeURL | <%= expression
%>}" />
<jsp:forward page="{relativeURL | <%= expression
%>}" >
<jsp:param name="parameterName"
value="{parameterValue | <%= expression
%>}" />+
</jsp:forward>

<jsp:useBean>
Locates or instantiates a bean with a specific
name and scope.
<jsp:useBean
id="beanInstanceName"
scope="page|request|session|application"
{ class="package.class" |
type="package.class" |
class="package.class" type="package.class" |
beanName="{package.class | <%= expression %>}“
}
{ /> |
> other elements
</jsp:useBean>
}

Attributes and Usage
id="beanInstanceName"
A variable that identifies the bean in the scope you specify. The name
is case sensitive and must conform to the naming conventions of the
scripting language used in the JSP page
scope="page|request|session|application“
page One can use the bean within the JSP page with the
<jsp:useBean> element or any of the page's static include files, until
the page sends a response back to the client or forwards a request to
another resource
request One can use the bean from any JSP page processing the same
request, until a JSP page sends a response to the client or forwards the
request to another resource. One can use the request object to access
the bean, for example,
request.getAttribute(beanInstanceName).
session One can use the bean from any JSP page in the same session
as the JSP page that created the bean. The bean exists across the entire
session, and any page that participates in the session can use it. The
page in which you create the bean must have a page directive with
session="true".

Different Scope
ApplicationApplication
SessionSession
RequestRequest
PagePage
Least visible
Most visible
Objects accessible only within pages
where they were created.
Objects accessible from pages
processing the request.
Belonging to the same session.
Belong to the same application.

<jsp:setProperty>
Sets a property value or values in a bean.
 Syntax
<jsp:setProperty name="beanInstanceName"
{ property="*" |
property="propertyName" [ param="parameterName" ] |
property="propertyName" value="{string | <%= expression
%>}"
}
/>
 Examples
<jsp:setProperty name="mybean" property="*" />
<jsp:setProperty name="mybean" property="username" />
<jsp:setProperty name="mybean" property="username" value="Steve" />
The <jsp:setProperty> element sets the value of one or more properties in a
bean,
using the bean's setter methods. You must declare the bean with<jsp:useBean>
before
you set a property value with <jsp:setProperty>.

<jsp:getProperty>
Gets the value of a bean property so that you
can display it in a result page.
 Syntax
<jsp:getProperty name="beanInstanceName“
property="propertyName" />
 Example:
<jsp:useBean id="calendar" scope="page" class="employee.Calendar" />
<h2>
Calendar of <jsp:getProperty name="calendar" property="username" />
</h2>
The <jsp:getProperty> element gets a bean property value using the
property's getter methods and displays the property value in a JSP
page. You must create or locate a bean with <jsp:useBean> before
you use <jsp:getProperty>.

Jsp with Beans
public class MessageBean {
private String message = "No Message";
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
}

JavaBeans with JSP Page
<jsp:useBean id="firstBean" scope="session"
class="packBeans.MessageBean"/>
<jsp:setProperty name="firstBean"
property="message"
value="This is a message from a bean" />
<H1>Message:
<I><font color="#0000FF" size=+3>
<jsp:getProperty name="firstBean" property="message" />
</I></font>
</H1>

Handling Forms with JSP
package packBeans;
public class NameBean {
private String name;
public NameBean() {
name = null;
}
public String getName() {
return name;
}
public void setName(String aName) {
name = aName;
}
}

JSP Form
<jsp:useBean id='nb' scope='session' class=‘packBeans.NameBean'/>
<jsp:setProperty name='nb' property="*"/>
<HTML>
<BODY>
<H1>Please enter your name to be registered to JSP Course?</H1>
<FORM method="get">
<INPUT type="text" name="name" size="25">
<INPUT type="submit" value="Submit">
</FORM>
<% if ( request.getParameter("name") != null ) } %>
<%=
"Click<a href=GetName.jsp> here</a> to confirm your registration"
%>
<% } %>
</BODY>
</HTML>

JSP Results
<jsp:useBean id='nb'
scope="session“class=“packBeans.NameBean"/>
<HTML>
<HEAD>
<TITLE>Registered Name</TITLE>
</HEAD>
<BODY>
<jsp:getProperty name="nb" property="name"/>
</BODY>
</HTML>

JSP and JavaBeans

Conclusion
JavaServer Pages (JSP) lets you separate the dynamic
part of your pages from the static HTML.
1. One can simply write the regular HTML in the normal
manner, using whatever Web-page-building tools you
normally use.
2. One can enclose then the code for the dynamic parts in
special tags, most of which
start with "<%"
and end with "%>"

Java serverpages

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