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A simple html form('dbdemo.htm') which invokes
dbdemo.jsp follows:
dbdemo.htm
<html>
<body>
<form
method=post action=dbdemo.jsp>
type the selectquery here
<input type=text size=60
name='text1'> <br>
<input type=submit>
</form>
</body>
</html>
dbdemo.jsp
<html>
<body>
<%@page import="java.sql.*"
%>
<%
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
String url = "jdbc:odbc:telephone";
// an access database registered in odbc
Connection con = DriverManager.getConnection(url);
Statement stm =
con.createStatement(); //
container for sql
String
sql = request.getParameter('text1'); // sql
ResultSet rs
= stm.executeQuery ( sql);
while(rs.next())
{
out.println(rs.getString(1)+"<br>");
// name
out.println(rs.getString(2)+"<br>");
// telephone number
out.println("========");
}
%>
</body>
</html>
--------------------------------------------------------------------------------------------------------------------------
As for sending mail from webserver, using
JavaMail API, the following code shows how the required data
such as 'from', 'to', 'subject' and 'message' are
collected by the servlet and then processed for sending the mail.
------------------------------------------------------------------------------------------------------------------
mailservlet.htm
<html>
<body>
<form
method=post
action="http://localhost:8080/servlet/mailservlet">
sender
<input type=text name=text1><br>
Reciever <input type=text
name=text2><br>
Subject <input
type=text name=text3><br>
Message <textarea
name='area1' rows=5 cols=30>
</textarea>
<input type=submit>
</form>
</body>
</html>
mailservlet.java
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import javax.mail.*;
import javax.mail.internet.*; //
important
import javax.mail.event.*;
// important
import java.net.*;
import java.util.*;
public class servletmail extends HttpServlet
{
public void
doPost(HttpServletRequest request,HttpServletResponse response)
throws ServletException, IOException
{
PrintWriter
out=response.getWriter();
response.setContentType("text/html");
try
{
Properties props=new Properties();
props.put("mail.smtp.host","localhost");
// 'localhost' for testing
Session session1
= Session.getDefaultInstance(props,null);
String s1 = request.getParameter("text1"); //sender (from)
String s2 = request.getParameter("text2");
String s3 = request.getParameter("text3");
String s4 = request.getParameter("area1");
Message message
=new MimeMessage(session1);
message.setFrom(new InternetAddress(s1));
message.setRecipients
(Message.RecipientType.TO,InternetAddress.parse(s2,false));
message.setSubject(s3);
message.setText(s4);
Transport.send(message);
out.println("mail has been sent");
}
catch(Exception ex)
{
System.out.println("ERROR....."+ex);
}
}
}
Using javamail requires that we provide
classpath to mail.jar & activation.jar. These should
have been already installed in our machine. Otherwise, we will not be able
to compile the servlet. For testing the servlet, we should have
installed some mail server in our machine. For compiling the servlet,
we have to set classpath to c:\jsdk2.0\src (java servlet development kit).
(We are using Tomcat server. The TOMCAT
server is a webserver especially created for executing servlets and JSP .
It is a joint effort by SunMicroSystems & Apache Foundation.
Tomcat can be run on Apache server or independently. Tomcat will work in
Windows platform also. The current version is Tomcat 4. Tomcat 5 is
expected shortly).
We can move dbdemo.htm and dbdemo.jsp
to :
c:\tomcat\webapps\root
directory.
In another dos window,
c:\tomcat\bin>SET
TOMCAT_HOME=C:\TOMCAT
>SET JAVA_HOME=C:\JDK1.3
>startup ( this will start the tomcat server in port 8080)
Start InternetExplorer and type the url as
'http://localhost:8080/dbdemo.htm. We will get the form. Type the sql and
submit the form. We will get the resultset sent by the server. We need not
compile the jsp file. It is automatically compiled at the server.
For running a servlet, copy the servlet's
class file to: c:\tomcat\webapps\root\web-inf\classes
directory.
For javamail , we have to copy mail.jar
& activation.jar to classes folder.
copy the invoking html file to: c:\tomcat\webapps\root
directory.
In the browser type the URL as
'http://localhost:8080/mailservlet.htm'. Enter the required data and
submit the form to the server. The mail will be sent as specified by us.
That is as brief a tour as possible of the first group of
technologies in the J2EE basket. This is an essential foundation because ,
even when we use RMI/EJB , the correct practice is to invoke the RMI
through a servlet. In the JSP example seen above, the code was exposed to
the web-administarator. The better method is to encapsulate the code as
a bean and invoke it. This way, only the class file will be seen by
the server-administaror. The JSP page also will be easier to read and
maintain.In the following example , we will adopt that method.
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