basic jsp celsina bignoli [email protected]. problems with servlets servlets contain –request...
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Problems with Servlets
• Servlets contain – request processing, – business logic – response generation
all lumped together!
• Problems:– good Java knowledge is needed to develop and
maintain the application– changing look and feel or a new client type
require changes to the Servlet code– cannot use web page development tools
Advantages of JSP
• separates request processing and business logic from the presentation– places all static HTML in a JSP page and adds
a few JSP elements to generate the dynamic content
• allows the separation of tasks between Java programmers and WEB page authors
• makes it easier to change presentation without affecting business layer and viceversa
A Simple JSP Page
• Static: HTML/XML elements• Dynamic: scriptlets
• Special JSP elements
Example.jsp
<%@ page import=“java.text.*, java.util.*”%>
<head><title><Date Example</title></head><html>
<%Date d=new Date();String today = DateFormat.getInstance().format(d);
%>Today is:<em><%=today%></em></body></html>
HTML
Scriptlet
<body>
JSP tag
JSP Processing- Translation Phase
Servlet Container
JSPPage(.jsp)
JSPPage(.jsp)
ServletSource(.java)
ServletSource(.java)
JSPTranslator
ServletClass(.class
)
ServletClass(.class
)
JavaCompiler
JVM
Translation Phase
Request Processing Phase
TextBuffer
TextBuffer
request response
JSP Processing- Request Processing Phase
Servlet Container
JSPPage(.jsp)
JSPPage(.jsp)
ServletSource(.java)
ServletSource(.java)
JSPTranslator
ServletClass(.class
)
ServletClass(.class
)
JavaCompiler
JVM
Translation Phase
Request Processing Phase
TextBuffer
TextBuffer
request response
package jsp;
import javax.servlet.*; import javax.servlet.http.*;…import java.text.*; import java.util.*;
public class example_jsp extends org.apache.jasper.runtime.HttpJspBase{ …}
example_jsp.java
extends: javax.servlet.http.HttpServlet
JSP Translation - Example
public void _jspService(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { … try { out = pageContext.getOut(); out.write("<html>\r\n"); out.write("<head><title><Date Example</title></head>\r\n"); out.write("<body>\r\n"); Date d=new Date(); String today = DateFormat.getInstance().format(d); out.write("\r\n"); out.write("Today is:\r\n"); out.write("<em>"); out.print(today); out.write("</em>\r\n"); out.write("</body>\r\n"); out.write("</html>"); } …}
service() method - Example
JSP Elements
• Directives• Comments• Actions
– standard actions– custom actions and JSTL
• Expression Language (EL)• Scripting• JavaBean components
JSP Directive Elements
• Specify attribute of the page itself– type of content– buffering requirements– resources used– how runtime errors should be handled
• Do not affect content of a response but how the container should handle it.
• Enclosed between <%@ and and %>• Have a name and one or more attribute/value
pairs – attribute and values are case-sensitive– values must be enclosed in single or double
quotes
Page Directive
<%@page contentType=“text/html” %>
• other possible values for contentType– text/plain– text/xml– text/vnd.wap.wml
• other possible attributes– errorPage– isErrorPage– session– pageEncoding– buffer– autoFlush
Taglib Directive
<%@taglib prefix=“c” uri=“http://java.sun.com/jsp/jstl/core” %>
• declares a JSTL custom tag library used in the page
• the prefix is the name used for the library in the JSP page
• the uri uniquely identifies the library
JSP Comments
<%-- comment goes here --%>
• delimited by <%-- and --%>
• ignored when the page is processed
• never sent to the browser
JSP Actions
• represent dynamic actions to be performed at runtime<prefix: action-name attr1=“value1” attr2=“value2”>
action_body
</brefix:action-name>
• or<prefix: action-name attr1=“value1” attr2=“value2”>
• allows dor actions in different libraries to have the same name
• allow contaienr to determine which library an action belongs
Standard Actions
<isp:useBean>
makes a java bean component available to a page<jsp:getProperty>
gets a property value from a JavaBean components and adds it to the response
<jsp:setProperty>
Set a JavaBean property value<jsp:include>
Include the response from a servlet or JSP page during the request processing phase
<jsp:forward>
Forwards the processing of a request to a servlet or JSP page
Standard Actions (2)
<isp:param>
adds a parameter to a request handed over to another servlet or JSP page
<jsp:plugin>
Used to run applets on the browser<jsp:attribute>
Set the value of an action attribute<jsp:body>
Sets the action element body<jsp:element>
Dynamically generate an XML element<jsp:text>
to encapsulate text “verbatim”
JSP Standard Tag Library (JSTL)
• group of libraries each containing related actions• Core• XML processing• Internationalization• Relational Database Access• Functions
JSP Expression Language
• based on both ECMAScript and XPath
• built-in support for JavaBean access and manipulation, collection of objects, automatic type conversion etc…
• EL expressions enclosed within ${ and }
• ${anObject.aProperty}
• <c:if test=“${user.salary > 10000}”>
…
</C:if>
Scripting Elements
• fragments of java code embedded in a JSP page
• Declarations
• Expressions
• Scriptlets
• heavily used in early JSP pages but rarely in newer developments (and discouraged)
Declarations
• used to insert methods, constants and variable declarations in JSP pages
<%!
private static String EXAMPLE=“/example2”;
private static String SHOP_PAGE=“/estore.jsp”;
private static String CART_PAGE=“/shopcart.jsp”;
private String dispPrice(String price)
{
// method body
}
%>
Expressions
• an embedded Java expression that is evaluated and converted to a text String
• The text string is placed in the JSP output at the location in which the element appears
<table>
<tr>
<td> <%= curItem.getName() %> </td>
<td> <%= String.valueOf(dispPrice(curItem.getPrice())) %>
</td>
</tr>
</table>
Scriptlets
• used to include complete fragments of java code in a JSP page
• cau use the out implicit object (of type javax.servlet.jsp.JspWriter) to write output
<%
if (state.isLocal())
out.print(totalCost * localTax)
else
out.print(totalCost)
%>
Problems with Scriptlets
• discouraged since they do not promote separation of presentation from data/logic
• look as a Servlet inside-out
• make JSP page as hard to write/maintain as corresponding Servlet
Model-View-Controller Design
• Separation of– data and business logic (Model)– data presentation (View)– data interaction (Controller)
• The user interacts with the Controller to ask for things to be done.
• Controller forward the request to the Model• the result of the request is displayed by the
View
Model-View-Controller Design
Controller(Servlet)
View(JSP)
Model(JavaBean)
Data
Data
Data TierJSP/Servlet Container
Request
Response
Browser