Java serverpages

Copyright @ 2000 Jordan Anastasiade. All rights reserved. 1

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 TechnologyJavaServer 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 PageA 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.

http://access1.sun.com/techarticles/simple.WAR.html

http://access1.sun.com/techarticles/simple.WAR.html


OverviewJavaServer 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 TimeA 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 Requested

Server

File ChangedCreate Source from JSP

Compile Execute Servlet


JSP ElementsDeclarations <%! 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:




DeclarationDeclares 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 declarationelement, 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


ExpressionContains 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>


ScriptletContains 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()

jspDestroy()

jspService()

Servlet from JSP

Init Event

RequestResponse

Destroy Event


JSP Page DirectiveDirectives 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. page2. include3. taglib

XML form: <jsp:directive.directiveType attribute=“value” />


Page DirectiveDefines 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 DirectiveIncludes 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 RedirectionOne 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 Usageid="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".

application One can use the bean from any JSP page in the same application as the JSP page that created the bean. The bean exists across an entire JSP application, and any page in the application can use the


Different Scope

Application

Session

Request

Page

Least visible

Most visible

Objects accessible only within pageswhere they were created.

Objects accessible from pages processing the request.

Objects accessible from pagesBelonging to the same session.

Objects accessible from pagesBelong 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>

beforeyou 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 Beanspublic 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 JSPpackage 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 "%>"

Internet

Java serverpages