Classes
GenericServlet Class: Provides the
logic/implementation for life cycle methods of Servlet. This class implements
interfaces like Servlet and ServletConfig
ServletlnputStream Class: Extends
InputStream [with its readLine() method] that provides user to read data from
client request
ServletOutputStream Class: Extends
OutputStream [with its print() method] that provides user to write data to a
client response
ServletException Class: Thrown when the
problem occur with servlet A UnavailableException Class: Thrown when the
servlet is not available. This class extends ServletException
Reading Servlet Parameters
Example 3
- This example explains how to get the list of parameters that are passed to servlet in its Request from client. (We will use the classes/interfaces that we learned in earlier slides)
- Create following files in a folder (Please check next slide for code)
- Java FileReadParamsServlet.java Contains logic to get the params details
- DD web.xml Contains deployment details. Deployment Descriptor
- HTMLFile index.html Contains html that allows user to enter details
- Compile the Java File as you did in earlier example
- Create below structure with files that you created above
- Folder "ReadParamsServlet" contains
- I__"WEB-INF" Folder and index.html
- I__"WEB-INF" Folder contains "classes" Folder and web.xml File.
- I__"classes" Folder contains "ReadParamsServlet.class" File
- Deploy the ReadParamsServlet folder inside webapps folder of Tomcat
- Bounce the Server
- Send request using "http://localhost:8550/ReadParamsServlet/index.html"
ReadParamsServlet.java: This prepares the response as HTML
file that displays request parameters
import java.io.*;
import java.util.*;
import javax.servlet.*;
public class ReadParamsServlet
extends GenericServlet {
public void
service(ServletRequest request, ServletResponse response) throws
ServletException, IOException {
PrintWriter pw =
response.getWriter();
Enumeration list =
request.getParameterNames();
while(list.hasMoreElements())
{
String paramname =
(String)list.nextElement();
pw.print(paramname + " =
");
String paramvalue =
request.getParameter(paramname); pw.println(paramvalue);
}
pw.close();
}
}
PrintWriter out =
response.getWriter();
response.setContentType("text/html");
out.println("<html>");
out.println("<head>");
out.println("<title>InitParams!
</title>");
outprintln("</head>");
out.println("<body>");
out.println("<h1>Init
Params from Serylet!</h1>");
Iterator<Map.Entry> iter
= initParamsCollection.entrySet().iterator();
while (iter.hasNextQ)
Map.Entry entry = iter.next();
String key =
(String)entry.getKey();
String value =
(String)entry.getValue();
out.println("InitParameter
:" +key +" Its Value:"+value+ …..")
}
out.println("</body>");
out.println("</html>");
out.close();
}
}
- web.xml
- <servlet> tag maps your servlet class with internal name
- <servlet-mapping> tag maps internal name with url-pattern that your invoke
-<web-app
xmlns="http://java.sun.com/xml/ns/j2ee"
xmins:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
version="2.4">
-<servlet>
<servlet-name>paramsservlet</servlet-name>
<servlet-class>ReadParamsServiet</servlet-class>
</servlet>
<servlet-mapping>
-<servlet-name>paramsservlet</servlet-name>
<url-pattern>/RegisterStudent.do</url-pattern>
</servlet-mapping>
</web-app>
- index.html
<html>
<body>
<center>
<hl
align="center">Welcome to Student Registration Page...</h1>
<form
name="StudentForm" method="post"
action="RegisterStudent.do">
<table>
<tr>
<td><B>Name of
Student : </td>
<td><input
type=textbox name="StudentNameParam" size="25"
value=""></td>
</tr>
<tr>
<td><B>Registration
# : </td>
<td><input
type=textbox name="RollNumberParam" s' value="">
</td>
</tr>
<tr>
<td><B>Father's
Name : </td>
<td><input
type=textbox name="FatherName" size="25"
value="">'</td>
</tr>
</table>
</form>
</center>
</body>
</html>
</html>
