powerpoint-slides, based on material written by Deepak Kumar

Transcript powerpoint-slides, based on material written by Deepak Kumar

Java Server Pages (JSP)
A Java Servlets Example
• A simple "HelloWorld" servlet, that also prints the current date.
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloWorld extends HttpServlet {
public void doGet(HttpServletRequest req, HttpServletResponse res) throws
ServletException, IOException {
res.setContentType("text/html");
PrintWriter out = res.getWriter();
out.println("<HTML>");
out.println("<HEAD><TITLE>Hello World</TITLE></HEAD>");
out.println("<BODY>");
out.println("<H1>Hello World</H1>");
out.println("Today is: " + (new java.util.Date().toString()) );
out.println("</BODY></HTML>");
} // doGet
} // HelloWorld
• In order to run it, do the following:
– Place it in a file, HelloWorld.java
– Compile it.
– Place the resulting HelloWorld.class file in the "servlets" directory.
A JSP Example
• The previous page can be written using JSP as shown below:
<HTML>
<HEAD>
<TITLE>Hello World</TITLE>
</HEAD>
<BODY>
<H1>Hello World</H1>
Today is: <%= new java.util.Date().toString() %>
</BODY>
</HTML>
• In order to run it, do the following:
– Place it in a file, HelloWorld.jsp in the same directory as your
.html files
– Run it by pointing browser to:
http://server.address/~youraccount/HelloWorld.jsp
Elements of JSP
• Whenever a .jsp is requested for the first time, the server does
the following:
1. Translates the .jsp page into a servlet
2. Compiles the servlet into a class file
3. Executes the servlet (response is sent to the client)
• Subsequent requests (as long as the .jsp page is unchanged)
use the same loaded class file.
• Anatomy of a JSP Page
– A JSP page is a mixture of standard HTML tags, web page content,
and some dynamic content that is specified using JSP constructs.
Everything except the JSP constructs is called Template Text.
JSP Constructs: JSP Comments
• JSP Comments: Different from HTML
comments

<%-- a JSP comment --%>
• JSP comments are used for documenting
JSP code and are not visible client-side
(using browser's View Source option) where
as HTML comments are visible.
JSP Constructs: JAVA Expressions
• Format: <%= some_java_expression %>
• Example:
<%= new java.util.Date().toString() %>
• Output of the expression is placed in the HTML
template at the same location.
JSP Constructs: Variables in JAVA
Expressions
•
•
There are some pre-defined Java variables/objects available for use in expressions (provide
access to important servlet functionality):
–
request
This is the same object as HttpServletRequest parameter in th get/post methods.
Same methods (like, getParameter, getAttribute, etc) can be applied to it.
–
out
The servlet printwriter.
–
session
Same as servlet session object.
Example:
<HTML>
<HEAD>
<TITLE>JSP Expressions: Predefined Objects</TITLE>
</HEAD>
<BODY>
<H1>Using Predefined Objects</H1>
<UL>
<LI> Your Hostname: <%= request.getRemoteHost() %>
<LI> Your Session ID: <%= session.getId() %>
<LI> The value of INFO parameter: <%= request.getParameter("INFO") %>
</BODY>
</HTML>
JSP Constructs: Scriptlets
•
Scriptlets are arbitrary pieces of Java code inserted in the page using the
format: <% some_java_code %>
Example 1
<HTML>
<HEAD>
<TITLE>JSP: Scriptlets</TITLE>
</HEAD>
<%
String bgColor =
request.getParameter("COLOR");
if (bgColor == null)
bgColor = "WHITE";
%>
<BODY BGCOLOR="<%= bgColor %>" >
<H1>Example Scriptlet: Sets background
color</H1>
</BODY>
</HTML>
Example 2
<HTML>
<HEAD>
<TITLE>JSP: Scriptlets 2</TITLE>
</HEAD>
<% String bgColor = request.getParameter("COLOR"); %>
<% if (bgColor == null) { %>
<BODY BGCOLOR="FFFFFF" >
<% } else { %>
<BODY BGCOLOR="<%= bgColor %>" >
<% } %>
<H1>Example Scriptlet: Conditionally sets background
color</H1>
<% if (bgColor == null) { %>
You did not supply a color, I used white.
<% } else { %>
Here is the color you requested.
<% } %>
</BODY>
</HTML
JSP Constructs: Scriptlets, contd.
•
Using Arrays: One can easily use scriptlets to loop over arrays. In this example, the user is presented with
choice boxes. When s/he presses the submit button, the choices are displayed.
•
Example
<HTML>
<BODY BGCOLOR="WHITE">
<FORM ACTION="choices.jsp">
<INPUT type="checkbox" name="music" value="Classical"> Classical<BR>
<INPUT type="checkbox" name="music" value="Rock"> Rock<BR>
<INPUT type="checkbox" name="music" value="Jazz"> Jazz<BR>
<INPUT type="checkbox" name="music" value="Blues"> Blues<BR>
<INPUT type="checkbox" name="music" value="DC-GoGo"> DC GoGo<BR>
<INPUT type="submit" value="Submit">
</FORM>
<%
String[] selected = request.getParameterValues("music");
if (selected != null && selected.length != 0) {
%>
You like the following kinds of music:
<UL>
<%
for (int i = 0; i < selected.length; i++) {
out.println("<LI>" + selected[i]);
}
%>
<UL>
<% } %>
</BODY>
</HTML>
JSP Constructs: Declarations
•
You can define variables and/or methods: <%! some JAVA declarations %>
•
Example
<HTML>
<BODY>
<%!
private int hitCount = 0;
String randomColor() {
java.util.Random random = new java.util.Random();
int R = (int) (random.nextFloat() * 255);
int G = (int) (random.nextFloat() * 255);
int B = (int) (random.nextFloat() * 255);
return "#" + Integer.toString(R, 16) + Integer.toString(G, 16) + Integer.toString(B, 16); }
%>
<FONT COLOR="<%= randomColor() %>" > This page has been accessed <%= ++hitCount %> times.
</FONT>
</BODY>
</HTML>
JSP Constructs: Summary
• Expressions
• Scriptlets
• Declarations
• Availability of pre-defined objects
JSP Directives
• Format:
– <%@ directive attribute="value" %>
– <%@ directive attr1="value" attr2="value"
... attrN="value" %>
• Directives are used to specify the structure of
the resulting servlet. There are three
directives: page, include, and taglib
JSP: Page Directive
•
There are 11 specifiable attributes for this directive: import, contentType, isThreadSafe, session, buffer,
autoflush, extends, info, errorPage, and language
•
Example
<%@ page language="java" contentType="text/html" %>
<%@ page contentType="application/vnd.ms-excel" %>
<%@ page import="java.util.*" %>
<%@ page import="java.util.*,java.io.*" %>
•
Directives can be placed anywhere in the document, but are often placed at the very top.
<%@ page language="java" contentType="text/html import="java.util.*" %>
<HTML>
<HEAD>
<TITLE>Hello World</TITLE>
</HEAD>
<BODY>
<H1>Hello World</H1>
Today is: <%= new Date().toString() %>
</BODY>
</HTML>
JSP: Other Directives
•
The include Directive
– Is used to include a file in the main document.
•
– There are two versions of this. The first one, shown below, includes
the file at translation time.
<%@ include file="relative URL of file" %>
– The second version, includes the file at request time.
<jsp:include page="ralative URL of file" flush=true />
The taglib directive
– This is used to define custom markup tags. Refer to JSP
documentation for details on this.

powerpoint-slides, based on material written by Deepak Kumar

Transcript powerpoint-slides, based on material written by Deepak Kumar

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