CS4273: Distributed System Technologies and Programming I
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CS4273: Distributed System Technologies and Programming I
Lecture 11: JavaServer Pages (JSP)
JavaServer Pages (JSP)
Why JSP?
• Get rid of Java programming.
• Separate presentation from business logic.
• Reuse predefined components, such as JavaBean, tag libraries.
How does JSP work?
• The entire JSP page gets translated into a Servlet (once) at the first time
it is invoked.
• It is the Servlet code that gets executed at each request. No interpretation
of JSP occurs at request time. The original JSP page is totally ignored at
request time.
JSP tutorial website:
http://www.jsptut.com/
http://java.sun.com/products/jsp/docs.html
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Example of a Translated JSP
The original JSP
<H1>A Random Number</H1>
<%= Math.random() %>
The resulting Servlet code
public void _jspService(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
HttpSession session = request.getSession(true);
JspWriter out = response.getWriter();
out.println("<H1>A Random Number</H1>");
out.println(Math.random());
...
}
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JSP Notations
JSP can include Java code, applets, servlets, JavaBeans, etc.
• JSP Expressions: <%= expression %>
• JSP Scriptlets (for Java code): <% Java-code %>
• JSP Declarations: <%! declarations %>
• JSP Directives: <%@ directive %>
e.g., <%@ page import = “java.util.*”%>
<%@ include file = “banner.html”%>
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The First JSP example
• JSP files in dir: ~jia/www/java/js/jsp/
• URL for run JSP: http://jserv.cs.cityu.edu.hk:8080/jia/jsp/jspDate.jsp
<%-- file: ~jia/www/java/js/jsp/jspDate.jsp--%>
<html>
<head><title> Simple JSP Test Page</title></head>
<body>
<h1 align=center>Simple JSP Test Page</h1>
<table align=center>
<tr> <td> Now, the time is: </td>
<td> <%= new java.util.Date() %> </td>
</tr>
</table>
</body></html>
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An Example of JSP Scriptlets (Java code)
<HTML>
<BODY>
The time returned from a java utility function:
<%
// This scriptlet declares and initializes "date"
java.util.Date date = new java.util.Date();
out.println( date );
out.println( "<BR>Your machine's address is " );
// request in next line is in servlet style
out.println( request.getRemoteHost());
%>
</BODY>
</HTML>
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An Example of JSP Declaration and Directives
<%-- the next line is a JSP directive -->
<%@ page import="java.util.*" %>
<HTML>
<BODY>
<!-- following is a JSP declaration of function getDate -->
<%!
Date getDate()
{
Date theDate = new Date();
return theDate;
}
%>
<!-- the next line has JSP expression -->
The time returned from java declared function is: <%= getDate() %>
</BODY>
</HTML>
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Another Example of Scriptlet
<%-- filename: welcome.jsp --%>
<html><head>
<title>Example of JSP Scriptlet</title>
</head>
<body>
<% // begin scriptlet
String name =
request.getParameter( "firstName" );
if ( name != null ) {
%>
<h1>Hello <%= name %>, <br />
Welcome to JavaServer Pages!</h1>
<% // continue scriptlet
} // end if
else {
%>
<form action = "welcome.jsp" method = "GET">
<p>Type your first name and press Submit</p>
<p><input type = "text" name = "firstName" />
<input type = "submit" value = "Submit"/>
</p>
</form>
<% // continue scriptlet
} // end else
%> <%-- end scriptlet --%>
</body>
</html>
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JSP Directives
JSP directives are used for specifying page settings at
translation time. Three directives: page, include, and taglib.
• page directive: define the page setting.
e.g., <%@ page import = “java.util.*”%>
• include directive: insert a file at translation-time as if it
were originally part of the JSP (note. jsp:include inserts a
file at request time!).
e.g., <%@ include file = “banner.html”%>
• taglib directive: specify user-defined tag libraries.
e.g., <%@ taglib prefix=”blx” uri=”/blx.tld” %>
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JSP Standard Actions
JSP actions allow some common tasks in JSP. JSP containers process
actions at request time:
• <jsp:include>. Include a file at request time (Note. The include directive
inserts a file at translation time)
e.g., <jsp:include page = “banner.html”>
• <jsp:forward>. Forward the processing to another JSP or servlet. This
terminates the current JSP’s execution.
e.g., <jsp:forward page = “errorProcess.jsp”>
• <jsp:plugin>. Allow a browser-object (applets) or html element
embedded in jsp. It’s passed to browser without being executed in server!
e.g., <jsp:plugin type="applet" code=“myApplet.class”
width="475" height="350"></jsp:plugin>
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JSP Standard Actions (Cont.)
• <jsp:param>. Pass parameters to another JSP or servlet
(used together with include, forward, and plugin).
• <jsp:useBean>. Specify scope of a JavaBean and assign id.
e.g. <jsp:useBean id="numguess"
class="num.NumberGuessBean" scope="session"/>
The next two actions are used with JavaBean instance:
• <jsp:setProperty>
• <jsp:getProperty>
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Example of jsp:forward and jsp:param
<%-- filename: forwardExample.jsp --%>
<html><head>
<title>Forward request to another JSP</title>
</head>
<body>
<% // begin scriptlet
String name =
request.getParameter( "firstName" );
if ( name != null ) {
%>
<jsp:forward page = "forwardJSP.jsp">
<jsp:param name = "date" value =
“<%= new java.util.Date() %>”/>
</jsp:forward>
<%
} // end if
else {
%>
<form action = "forwardExample.jsp"
method = "GET">
<p>Type your first name and press Submit</p>
<p><input type = "text" name = "firstName" />
<input type = "submit" value = "Submit"/></p>
</form>
<%
} // end else
%>
</body>
</html>
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Example of JSP: forward and jsp:param (Cont.)
<%-- filename: forwardJSP.jsp --%>
<html>
<head>
<title>Processing a jsp:forward request</title>
</head>
<body>
<p> Hello <%= request.getParameter( "firstName" ) %>, <br />
Your request was received <br />
and forwarded at <%= request.getParameter( "date" ) %>
</body>
</html>
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Example of JSP: useBean
The program numguess.jsp uses a JavaBean object NumberGuessBean.class, which
is in …/js/WEB-INF/classes/num. See NumberGuessBean.java for lib routines.
<%@ page import ="num.NumberGuessBean"%>
<jsp:useBean id="numguess"
class="num.NumberGuessBean"
scope="session"/>
<jsp:setProperty name="numguess" property="*"/>
<html>
<head><title>Number Guess</title></head>
<body bgcolor="white">
<% if (numguess.getSuccess()) { %>
Congratulations! You got it.
And after just <%= numguess.getNumGuesses()
%> tries.<p>
<% numguess.reset(); %>
Would you <a href="numguess.jsp">
try again</a>?
<% } else if (numguess.getNumGuesses()
== 0) { %>
Welcome to the Number Guess game.<p>
I‘ve a number between 1 and 100.<p>
<form method = GET>
What's your guess?
<input type=text name = guess>
<input type=submit value="Submit">
</form>
….</body> </html>
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Example of JSP Tag Library (taglib)
Directive taglib allows user defined tags, facilitating the use of large amount of Java libraries in jsp
(separate JSP from Java-code implementations). Three files involved for taglib:
1.
JSP file, specifying the use of taglib, e.g., SendMail.jsp:
<%@ taglib prefix=“send" uri=“./taglib.tld" %> // “send” is prefix you can use
<HTML><BODY>
<% String email = request.getParameter( "email" ); %>
<send:email host="yoursmtphost.com" from="you@email.com">
<blx:emailTo><%= email %></blx:emailTo>
</send:email>
2.
Tag Library Descriptor file (.tld) in XML format, taglib.tld, specify format of lib routines, such as
routine names, parameters, etc.:
<tag><name>Sendmail</name>
<tagclass>com.cj.smtp.Sendmail</tagclass>
<teiclass>com.cj.smtp.BoolVariable</teiclass>
…………
3.
Library routines (java class file), sendmail.jar in …WEB-INF/lib (for you only) or jserv:/usr/jt/lib (for
all users). See dir setting in http://www.jsptube.com/servlet-tutorials/web-application-directorystructure.html
Use “jar –tvf blazix.jar” cmd to see the list of routines in class file.
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JSP JDBC Example
<%@ page contentType="text/html;charset=utf-8"%>
<%@ page import="java.sql.*" %>
<HTML><HEAD>
<TITLE>JSP JDBC</TITLE></HEAD>
<BODY>
<center>JSP JDBC</center>
<BR><BR>
<table border=3 align=center >
<%
Class.forName("com.mysql.jdbc.Driver");
String url =
“jdbc:mysql://jserv.cs.cityu.edu.hk:3306/db_jdemo”;
Connection con= DriverManager.getConnection(url,
"jdemo","apple1");
Statement stmt=con.createStatement();
String sql="select COF_NAME, PRICE from
COFFEES";
ResultSet rs=stmt.executeQuery(sql);
while(rs.next()) {
out.print("<TR><TD>"+
rs.getString("COF_NAME")+"</TD>");
out.print("<TD>"+
rs.getString("PRICE")+"</TD></TR>");
}
%>
</table>
<BR><HR>
<% rs.close(); stmt.close(); con.close(); %>
</BODY>
</HTML>
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