Refer

http://www.onjava.com/pub/a/onjava/excerpt/jebp_3/index1.htm
l?page=4


sandhya S

two types of cookjies are used in hosting support

The browser is expected to support 20 cookies for each Web 
server, 300 cookies total, and may limit cookie size to 4 
KB each.

If you are using any tool debug the code using the tool's 
debugger it will help you a lot

debigging the errors in servlets is very difficult.........
if we want to detect the errors in servlet we have to print 
the object ......... for ex----
           Connection con=DriverManager("url","uid",pwd");
           System.out.println(con);
           if it prints the object address the program is 
connected to database otherwise not connected to database

<jsp:useBean> tag can be used to avail the bean data in 
case you are working with JSP's, or if you use a servlet 
you can set the bean to the request object and forward it 
to the JSP component and there in JSP retreive this object 
and use getter methods and do something like this and it 
works for sure.

Using RequestDispatcher as follows,

RequestDispatcher rd = 
getServletContext().getRequestDispatcher("test.jsp");
rd.forward(req,res);

Try to use this code it may help you
public class MessageImage {
/** Creates an Image of a string with an oblique
* shadow behind it. Used by the ShadowedText servlet
* and the ShadowedTextFrame desktop application.
*/
public static Image makeMessageImage(String message,
String fontName,
int fontSize) {
Frame f = new Frame();
// Connect to native screen resource for image creation.
f.addNotify();
// Make sure Java knows about local font names.
GraphicsEnvironment env =
GraphicsEnvironment.getLocalGraphicsEnvironment();
env.getAvailableFontFamilyNames();
Font font = new Font(fontName, Font.PLAIN, fontSize);
FontMetrics metrics = f.getFontMetrics(font);
int messageWidth = metrics.stringWidth(message);
int baselineX = messageWidth/10;
int width = messageWidth+2*(baselineX + fontSize);
int height = fontSize*7/2;
int baselineY = height*8/10;
Image messageImage = f.createImage(width, height);
Graphics2D g2d =
(Graphics2D)messageImage.getGraphics();
g2d.setFont(font);
g2d.translate(baselineX, baselineY);
g2d.setPaint(Color.lightGray);
AffineTransform origTransform = g2d.getTransform();
g2d.shear(-0.95, 0);
g2d.scale(1, 3);
g2d.drawString(message, 0, 0);
g2d.setTransform(origTransform);
g2d.setPaint(Color.black);
g2d.drawString(message, 0, 0);
return(messageImage);
}

<form action="/servlet/full.class.name">
</form>


This method uses the invoker servlet, provided by many 
servlet containers. The much better way of invoking a 
servlet is by providing an explicit mapping for it. This is 
accomplished by using a pair of tags in your web 
application's web.xml file. This is not the same file as 
mentioned above. That file was located in Tomcat's conf/ 
directory. This web.xml file (which you will probably need 
to create) will reside in your web-application's WEB-INF/ 
directory. For each servlet you want to call, provide a 
pair of tags like the following: 


...
<servlet>
    <servlet-name>HelloWorld</servlet-name>
    <servlet-class>your.package.name.HelloWorld</servlet-
class>
</servlet>
...
<servlet-mapping>
    <servlet-name>HelloWorld</servlet-name>
    <url-pattern>/hello</url-pattern>
</servlet-mapping>
...

you can invoke the servlet by two ways
one is dierctly u can invoke from address bar
like the following
http://<servername>:<port-Number>/<web-application-name>/<url-pattern
of perticular servlet>

eg:- http://localhost:8080/app1/test

second one is u can invoke by using form..
<form action="/app1/test">
.....
.....
</form>

web.xml:-

<servlet>
    <servlet-name>FirstServlet</servlet-name>
    <servlet-class>pack1.pack2.ClassName</servlet-class>
</servlet>
<servlet-mapping>
     <servlet-name>FirstServlet</servlet-name>
     <url-pattern>/test</url-pattern>(test should be equal
to what u typed in the address bar after the web-application
name or should be equal to what u mention in the form action
after the web-application name)
</servlet-mappin>

either using DriverManager.getConnection
(or)
DataSource.getConnection()

DataSource.getConnection()

through servletloginfo()

Servlets communicate with each other with the help of 
RequestDispatcher objects.

RequestDispatcher rd=getServletConfig().getNamedDispatcher
(...);

... name used to identify a servlet i.e. name given in the 
web.xml in the url-pattern

Servlets can communiceate with the help of RequestDispacher.

RequestDispacher rd = getRequestDispacher("passing the 2nd servlet url");
rd.forward(rquest,response);

through session context interface

Store the variable in the session.

we have to set the variable in session object.like
session.setAttribute("somename",varible name);
and then we can get this variable where we want in this 
session 
session.getAttribute("somename");

internally the threads are implemented in servlets

During servicing any request the container will create a
thread or will get a thread from a thread pool.

Web Container will create a Thread for each request!

using Threads

For every request servlet container will create a new 
thread and service method is called

depends on the servlets reload properties.

if in your deployment descriptor or <web.xml> file you have 
set <load-on-startup>1</load-on-startup> then it will  be 
auto matically loaded

We have to Make a WEB-INF folder and under it classes 
folder. In WEB-INF we have to write web.xml .

Our compled servelet class file should be stored in classes 
folder.

Make a war file using jar & deploy in Web.

The structure of the web app. is
demo[root]
 - all jsps will go her
 - WEB-INF
   - web.xml
   - tld files
   - classes
     - all java class files will go here

Compile all the files and create a war file
copy the war file into Tomcat_root\webapps folder
if you use weblogic or webspehere the deployment will be 
different.

we have make dir name is,WEB-INF is the root directory
    WEB-INF
         --classes dir
         --lib dir
         --src dir
         --web.xml
      -html file
      -dhtml file
      -jsp file

lib dir contains
      --jasper-runtime.jar
      --servlet-api.jar
      --jsp-api.jar

your source code put in the src dir

--put the WEB-INF dir in your tomcat server and run the servlet

first we con compile the java code throught javac compiler.
then,its .class file will be created that .class file copy 
and paste the in the directory
c:/program files/apache/tomcat/webapps/servlet/web-inf
/classes.
then back one step backward
change the servlet code with ur file name
and also sevlet mapping code with ur file name
save that file
then open explorar
and type the local host address