Showing posts with label Servlets. Show all posts

Java J2EE Spring Chapter 3: A Sample Servet

We saw what the purpose of a Servlet Container and a Web server is, in the previous chapter. In this chapter, we are going to look at how a Servlet code would look like.

So, lets get started!!!

Servlet Skeleton

If I ask you, what are the components of a Java class, you’ll happily tell me that, there are first package statements and then imports and then the class declaration. Within the

Java J2EE Spring Chapter 2: Web Servers and Servlet Containers

In the previous chapter we looked at the history of the Web (Internet) and how JSPs and Servlets came into being. As you might have already guessed by now, any J2EE application needs a server on which it runs. It is called a Web Server. Also, the Servlet needs something in which it would run (Think of the JVM in which all java applications run) and that is called the Servlet container.

In this

Java J2EE Spring Chapter 1: Servlet & JSP History

Here we are, studying for the SCWCD exam. I would like to congratulate you again for this decision of yours because of which you are going to get yourself SCWCD certified. It's a big step and am gonna be with you step by step to help you get this certification.

Well, it wouldn't be much fun preparing for a certification on JSPs and Servlets without knowing their history. Would it?

This

Spring Framework Session Tracking Example in Servlets

Here is a simple session tracking example in servlets using Tomcat, our pretty pet. We are familiar with using cookies in servlets because we've already done an example and you should note that there are some drawbacks of cookies. One of the major drawbacks that strikes to your mind is they may not stored. Yes

What if cookies are not stored by the browser?
A. Session tracking to the rescue!
A session refers to all the requests made by a user to a web application. This session is unique for every user and is stored in the server itself. For every session, the default lifetime is 20 minutes which can be changed.

An ID will be generated which is usually look like this 4BABD9D86DFF9061DDC3DA4C8A9E2498 (this is just an example) which is unique and random. This is usually stored in a cookie or in some invisible input field, however the session is maintained by the web server.

We need to track all the user's requests made for a particular application, this phenomenon is called as Session Tracking. All the regarded information i.e. the track of user's requests is stored in the web server itself.

Folder structure

Project path: D:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps\sessiont

Project structure



sessiont


            |_ index.html


            |_ WEB-INF


                               |_ web.xml


                               |_ classes


                                              |_ SessionExample.java


                                              |_ SessionExample.class


                                              |_ PrintAttribute.java


                                              |_ PrintAttribute.class

HTML File(s)

index.html


<html>

    <head>

        <title>Get a Hai for me</title>

    </head>



    <body>



    <form action="http://localhost:8080/sessiont/mt" method="get">

        <input type="text" name="user"/>

        <input type="submit" value="Get"/>

    </form>



    </body>

</html>

Deployment Descriptor - web.xml


<web-app>

    <servlet>

        <servlet-name>myser</servlet-name>

        <servlet-class>SessionExample</servlet-class>

    </servlet>

    

    <servlet-mapping>

        <servlet-name>myser</servlet-name>

        <url-pattern>/mt</url-pattern>

    </servlet-mapping>



    <servlet>

        <servlet-name>myser1</servlet-name>

        <servlet-class>PrintAttribute</servlet-class>

    </servlet>

    

    <servlet-mapping>

        <servlet-name>myser1</servlet-name>

        <url-pattern>/rd</url-pattern>

    </servlet-mapping>

</web-app>

Servlet Programs

SessionExample.java



import javax.servlet.*;

import javax.servlet.http.*;

import java.io.*;

public class SessionExample extends HttpServlet

{

    public void doGet(HttpServletRequest 



req,HttpServletResponse res)throws ServletException,IOException

    {

    String st=req.getParameter("user");



    HttpSession ses=req.getSession();

    ses.setAttribute("uname",st);

    

    res.sendRedirect(res.encodeURL("/sessiont/rd"));

    }

}

PrintAttribute.java



import javax.servlet.*;

import javax.servlet.http.*;

import java.io.*;

public class PrintAttribute extends HttpServlet

{

    public void doGet(HttpServletRequest req,HttpServletResponse res)throws ServletException,IOException

    {

    PrintWriter pw=res.getWriter();



    HttpSession ses=req.getSession();

    String st=(String)ses.getAttribute("uname");



    pw.println("<h1> Hai "+st+"</h1>");

    }

}

Output

The following screenshots show you sample output of this application.

Type some data in the input field and hit enter

You can observe jsessionid in address bar

Explanation

index.html

The HTML file consists of two input fields, one of type text and the other one of type SUBMIT. The name of the text type input field is user. Whenever user hits enter or click on the submit button, the form is submitted to the web server to the url http://localhost:8080/sessiont/mt and then the class associated with this URL is SessionExample.java. This get's executed.

web.xml

There is nothing to say about web.xml, it is understood and it's obvious. /mt URL is associated with SessionExample and /rd with PrintAttribute classes.

SessionExample.java

HttpSession ses=req.getSession(); The getSession() method in HttpServletRequest class get's the session associated with the request (if there is no session new one will be created). This method returns the javax.servlet.http.HttpSession object.

ses.setAttribute("uname",st); The setAttribute() method takes a key value pair with uname as key (here) and st is the value. These attributes are very important and they carry the information. Here st contains the data that user has typed in the text field (input field of type text) with name as user. This is obtained from getParameter("user"); (see above).

res.sendRedirect(res.encodeURL("/sessiont/rd")); The sendRedirect() method in HttpServletResponse takes a String which contains the URL to be redirected to. Here I made a method call to encodeURL() which is present in HttpServletResponse and takes String as parameter. This parameter is the URL to be encoded. By calling this method and sending the parameter you can observe the jsessionid in the URL (see it in the 2nd output image).

PrintAttribute.java

HttpSession ses=req.getSession(): The same thing as explained above. But here, the Session is already created and now it is sent.

String st=(String)ses.getAttribute("uname"); Here, the session is already created and now we can call getAttribute("uname") which returns the value of the uname.

That's it. In this way we can work out with session tracking in servlets. Simple is that. Also see Cookies example in servlets

Spring Hibernate Display Current Date using GenericServlet

We have a class named Date from java.util.Date package. We can use the Date class methods to display the date. We are going to display this date in the webpage using servlets.

Here we are using init methods to initialize the names and values. with this we can get the names and values from the web.xml file while the program runs. Actually this init(javax.servlet.ServletConfig) method is invoked by the container during initialization phase of the servlet interface.

init() method is a convienience method provided in javax.servlet.GenericServlet class. Generally, it is suggested that init(javax.servlet.ServletConfig) method present in javax.servlet.GenericServlet class should be given a chance to get executed, during servlet's initialization. This method, apart from performing some initialization process, invokes init() method at the end.

Let us come to our Date application using servlet.Using Date calss create a new Date object 'd'. This date object contains the current date. But we can't display the object directly in the webpage. So convert the object to String using toString() method.Then display the date in the form of string in the servlet.

The Structure of our DateApp is :

Date d=new Date();
String s=d.toString();

Use setContentType() method to display in text/html format in the java file of servlet.

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app
    PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
    "http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>
  <servlet>
        <servlet-name>ABC</servlet-name>
        <servlet-class>blog.javabynataraj.DateSrv</servlet-class>
  <init-param>
      <param-name>sno</param-name>
      <param-value>1001</param-value>
  </init-param>
  <init-param>
      <param-name>sname</param-name>
      <param-value>sharukh</param-value>
  </init-param>
    </servlet>

    <servlet-mapping>
        <servlet-name>ABC</servlet-name>
        <url-pattern>/first</url-pattern>
    </servlet-mapping>
</web-app>

in the above web.xml the mappings are done based on serletname 'ABC'.We can give any name but it should be same in and tags. Based on this the logical name /firstwill be called by Servlet.

DateSrv.java

package blog.javabynataraj;
import javax.servlet.*;
import java.io.*;
import java.util.*;
public class  DateSrv extends GenericServlet
{
 
 public void service(ServletRequest req,ServletResponse res)throws ServletException,IOException 
 {
         ServletConfig cg=getServletConfig();
   String s1=cg.getInitParameter("sno");
   String s2=cg.getInitParameter("sname");

  PrintWriter pw=res.getWriter();
  res.setContentType("text/html");
  Date d=new Date();
  String s=d.toString();
  pw.println("<b> Date is"+s +"</b>");
  pw.println("<font color=red ><br> Param1 :"+s1+"<br> param2 is:  "+s2+"</font>");
     pw.close();
 }//service

}//class

In the above web.xml we used urlpattern as '/first' so while running the program type the url-pattern given in web.xml in the addressbar of your browser.

Output:

Download the above Application in jar file.

J2EE Spring Hibernate 1.Web application introduction.

WebApplication is a collection of web resources like HTML files, JavaScript files, image files Servlets, jsps and etc.

In order to make resources of a application as globally accessible resources developed as web resources of web-application each web-resource develops one webpage and this webpage is globally accessible page.
The web-application that is moved to internet network after development is called Website.

A web application contains two types of web-resources.

** Server side Web-resource

** Client side Web-resource

A web resource that comes to browser(client) from web application placed in web-server/application server for execution is called client side web resource.

EX: HTML,JavaScript programs.

The web-resource program that executed in the server(web-server/application server)is called server-side web-resource program.

EX : Servlet,JSP

Don't decide weather web-server program is server-side or client side based on the place where it resides and decide based on the place where it executes.

Spring Framework Handling Choice in HTML form in Servlets

The following illustrates handling choice in HTML form in Servlets. Till now we have seen working with data in the text box now let us see how to work out with the drop downs. A drop down or a choice looks like this.

Here are all the files..

Folder structure

Project folder: C:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps





selectser


           |_ index.html 


           |_ WEB-INF


                             |_ web.xml


                             |_ classes


                                          |_ SelectExample.java


                                          |_ SelectExample.class

HTML File(s)

index.html



 <html>

    <head>

        <title>Select a language</title>

    </head>

    

    <body>

        <form action="http://localhost:8080/selectser/ss" method="post">

            <select name="lang">

                <option value="C">C</option>

                <option value="C++">C++</option>

                <option value="Java">Java</option>

                <option value="Python">Python</option>

            </select>



            <input type="submit" value="SUBMIT"/>

        </form>

    </body>

</html>

Deployment Descriptor - web.xml



<web-app>

    <servlet>

        <servlet-name>sser</servlet-name>

        <servlet-class>SelectExample</servlet-class>

    </servlet>



    <servlet-mapping>

        <servlet-name>sser</servlet-name>

        <url-pattern>/ss</url-pattern>

    </servlet-mapping>

</web-app>

Servlet Programs



import javax.servlet.*;

import javax.servlet.http.*;

import java.io.*;

public class SelectExample extends HttpServlet

{

    public void doPost(HttpServletRequest req,HttpServletResponse res) throws ServletException,IOException

    {

    

    // Get value first

    String val=req.getParameter("lang");

    

    // Get writer from res

    PrintWriter pw=res.getWriter();

    

    pw.println("<h1> You selected "+val+"</h1>");

    }

}

Working? Let's see.

The following output shows that it is working.

HTML Form containing dropdown. Select some value and click SUBMIT

The HTML form

The value enclosed in <h1> tag is printed here

Print what is selected

Explaining things..

index.html

<select name="lang"> The <select> does it all. It encloses a set of options to be selected. It has a name which can be used to retrieve which option is selected.

<option value="C">C</option> The <option> defines an item in the drop down. The value of this is returned when we call the getParameter("lang") provided this option is selected and submitted. Here value is for the programmers to get and the name that is enclosed between the opening and closing of the option tag is for the user to see.

web.xml

<url-pattern>/ss</url-pattern> This is the url pattern. The tomcat observes this and invokes the class associated with it.

<servlet-class>SelectExample</servlet-class> SelectExample is the class associated with the above pattern.

SelectExample.java

String val=req.getParameter("lang"); Get the value of the option that is submitted. Here i have used the lang which is the name you have encountered above. When this is passed, we get the value of the option that is selected.

PrintWriter pw=res.getWriter(); Get the PrintWriter object to write something on the dynamic page for the user.

pw.println("<h1> You selected "+val+"</h1>"); Print the value the user has selected in a <h1> tag.

In this way we can handle a drop down (choice) in HTML form in Servlets. Hope this helps. Feel free to drop a comment.

Java J2EE Spring What is the difference between doGet() and doPost() methods ?

The difference has given below......

doGet	doPost
In doGet Method the parameters are appended to the URL and sent along with header information	In doPost parameters are sent in separate line in the body
Maximum size of data that can be sent using doget is 240 bytes	There is no maximum size for data
Parameters are not encrypted	Parameters are encrypted
DoGet method generally is used to query or to get some information from the server	DoPost is slower compared to doGet since doPost does not write the content length
DoGet should be idempotent. i.e. doget should be able to be repeated safely many times	This method does not need to be idempotent. Operations requested through POST can have side effects for which the user can be held accountable for example updating stored data or buying items online.
DoGet should be safe without any side effects for which user is held responsible.	This method does not need to be either safe.

Spring Framework Cookies in Servlets with Example

The following tutorial brings you an understanding of how-to use cookies in Java servlets, one of the interesting and important concepts to go around. In this post, i'll explain about cookies pragmatically for a better understand. All complete files of the application along with folder structure are discussed.

Folder Structure

Webapps folder: C:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps

Project structure



cookies


           |_ index.html  


           |_ WEB-INF


                              |_ web.xml  


                              |_ classes


                                             |_ CookieExample.java


                                             |_ CookieExample.class


                                             |_ GetCookie.java


                                             |_ GetCookie.class

Now it's time to know what those files really contain. Isn't it? Let's see

HTML Files

index.html



<html>

    <head>
        <title>Cookies Example in Servlets</title>
    </head>

<body bgcolor=wheat>

<center>
    <h1>Cookies Example in Java</h1>

    <form action="http://localhost:8080/cookies/co" method="Post">
        First name: <input type="text" name="fname">
        Last name: <input type="text" name="lname">
        <input type="submit"value="SUBMIT">
    </form>

</center>

</body> 

</html>

Deployment Descriptor

web.xml



<web-app>

    <servlet>
        <servlet-name>mys</servlet-name>
        <servlet-class>CookieExample</servlet-class>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>mys</servlet-name>
        <url-pattern>/co</url-pattern>
    </servlet-mapping>


    <servlet>
        <servlet-name>mls</servlet-name>
        <servlet-class>GetCookie</servlet-class>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>mls</servlet-name>
        <url-pattern>/st</url-pattern>
    </servlet-mapping>

</web-app>

Servlet Programs

CookieExample.java



import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class CookieExample extends HttpServlet
{
    public void doPost(HttpServletRequest req,HttpServletResponse res) throws ServletException,IOException
    {
    String fname=req.getParameter("fname");    
    String lname=req.getParameter("lname");

    Cookie f=new Cookie("first_name",fname);
    Cookie l=new Cookie("last_name",lname);

    res.addCookie(f);
    res.addCookie(l);

    res.sendRedirect("http://localhost:8080/cookies/st");
    }
}

GetCookie.java



import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class GetCookie extends HttpServlet
{
    public void doGet(HttpServletRequest req,HttpServletResponse res) throws ServletException,IOException
    {
    PrintWriter pw=res.getWriter();
    
    pw.println("<h1>");
    Cookie[] c=req.getCookies();
        for(Cookie k:c)
        {
        pw.println(k.getValue());
        }
    pw.println("</h1>");
    }
}

Working? Yes it works.

Invoke the Tomcat at the port installed in your PC or if you are accessing it from another PC, probably then, tomcat installed in that PC. Write the programs, create folders in accordance with the given structure and there will be what you want. Don't forget to compile the classes!!

In my PC, Tomcat is installed in the port 8080 and i will access it as, the project name is cookies i will type the same URL in the address bar of my favorite browser.

http://localhost:8080/cookies

As the default file is index.html the above URL will suffice to load the index.html file, an addition of /index.html is not necessary at the end.

You'll see the following output.

An application on cookies in Java servlets

index.html file in Firefox

Click on the SUBMIT then,

Value of a cookie is retrieved from another servlet

Output produced by GetCookie class

Let me explain

The HTML file

The html file is as usual, a very normal HTML file you might undergo when working out with most servlet programs. The HTML file here consists of input fields with names fname and lname which are used to get the values in them. The other input field is a SUBMIT button which submits the HTML form to the url specified in the <form> tag. The type of method i used here is post.

The web.xml

web.xml file contains two <servlet> and <servlet-mapping> tags (importantly) which are written for two classes. One is the main class i.e. the class that gets the request made by the user, i.e. the data sent by the user can be caught be this servlet. Another class is GetCookie which is a class that gets the cookies stored by the previous servlet.

Servlet Programs

CookieExample.java

req.getParameter("fname") and req.getParameter("lname"): These methods take in the name of the input field and return the value in them. The values are stored in fname and lname respectively.

Cookie f=new Cookie("first_name", fname): This is the constructor of the javax.servlet.http.Cookie takes in a name (the name of the cookie) and value (value to set in the cookie). The other method is also the same but stores a different value under a different name.

res.addCookie(f), res.addCookie(l): Creating a cookie isn't enough. You'll have to set them in the client's web browser so are these methods.

res.sendRedirect("http://localhost:8080/cookies/st"): Redirect to the specified URL. This URL is associated with GetCookie class (refer web.xml). You can also simply write /cookies/st instead of such lengthy URL.

What is a cookie?

A cookie is a name-value pair which is stored in a user's browser for the sake of the user by the web server when the servlet program says to do so.

GetCookie.java

Here i am writing doGet() because in the above servlet, sendRedirect() method is called stating to redirect to the URL pattern associated with GetCookie. It is a doGet() call in fact.

PrintWriter pw=res.getWriter(): The java.io.PrintWriter class is used to write (print) something on the dynamic page that is generated. To get a PrintWriter object we need to call the getWriter() method present in the HttpServletResponse.

pw.println("<h1>"): Open the <h1> tag.

Cookie[] c=req.getCookies(): To get cookies stored by this application we need to call the getCookies() method present in the HttpServletRequest class. This gives an array of cookies (Cookie[]).

pw.println(k.getValue()): Get value stored in each cookie and print them. The for-each loop is explained by me before.

pw.println("</h1>"): Close the <h1> tag.

Java J2EE Spring Difference between ServletContext and ServletConfig ?

What is the Difference between ServletConfig and ServletContext.?

ServletConfig:

public interface ServletConfig

ServletConfig encapsulates servlet configuration and gives access to the application (servlet context) object. Servlet initialization parameters appear in the servlet configuration file. Each servlet class may have several different servlet instances, one for each servlet parameters:

One ServletConfig per servlet
It is used to pass deploy-time info to servlet and configured in the deployment descriptor file.
it is used to access ServletContext
It is within the Servlet element in Deployment descriptor.
It is accessed by using getServletConfig().getInitParameter("myname");
It is available only to the servlet in which init-param is configured.

Example:

ServletContext:

public interface ServletContext

ServletContexts encapsulate applications. Applications are generalized virtual hosts; a URL prefix defines a distinct application. So /myapp and /yourapp could define different applications. As a degenerate case, each virtual host has its own ServletContext.

It returns the current context of a web application running in a particular JVM..
If the web application is distributed,it is one per JVM.
It is used to access the elements configured in deployment descriptor.
It is accessed by using getServletContext().getInitParameter("myname");
It is available to any servlet or jsp that is part of web application.

Example:

Spring Framework Pre Check web.xml for Errors in Servlets

Sometimes we might be disgusted when we encounter errors related to web.xml while executing our web application, we might not understand it at times even when we look at the Tomcat logs. So in this post i'll discuss about how to pre check the web.xml for errors.
As web.xml is an xml file, the default application for xml files is Internet Explorer, so open web.xml in Internet Explorer. That's it.

See following, i had intentionally written an error in web.xml (not properly closing the <web-app>.


<web-app>

    <servlet>

        <servlet-name>mys</servlet-name>

    <servlet-class>CookieExample</servlet-class>

    </servlet>

    

    <servlet-mapping>

        <servlet-name>mys</servlet-name>

        <url-pattern>/co</url-pattern>

    </servlet-mapping>

<web-app>

When i open this in Internet Explorer, the screenshot will look like..

web.xml error in Internet Explorer

When i write it correctly, closing the tag properly, it will look like..

Correct way of writing web.xml showed in Internet Explorer

web.xml is displayed in Internet Explorer

Unlike the previous screenshot, in this screenshot you have the web.xml correctly displayed which means that the xml file is well parsed with no errors.

However, errors that are not related to the syntax such as change servlet name in tags i.e. different servlet names in servlet-mapping and servlet tags cannot be identified unless you are familiar with.

This is just a tip that helps you detect xml parsing related errors. Hope this helps.

Spring Hibernate Servlet - Servlet Communication

Servlet - Servlet Communication

Communication between Java servlets is called as Servlet communication. It is nothing but, sending users request and the response object passed to a servlet to another servlet. You may ask, what is the use of passing these objects. Well, i have an answer. As seen in the servlet examples written till date, one common method we are using, getParameter(), used to get the user input value in a specified field. So, when a request object is passed from one servlet to another servlet, then you can use this method to get the input that the user has given in a HTML/JSP form. Following example, gives better understand of what is said now.

Servlet Communication - Folder Structure

webapps

|_ servletcom

|_ index.html

|_ WEB-INF

|_ web.xml

|_ classes

|_ FirstServlet.java

|_ FirstServlet.class

|_ FinalServlet.java

|_ FinalServlet.class

Servlet Communication - index.html

<html>
<head>
<title>Servlet-Servlet Communication</title>
</head>
<body>

<form action="/servletcom/pass" method="post">

Name: <input type="text" name="uname" width="20" />
Password: <input type="password" name="pass" width="20" />
<input type="submit" name="submit" value="Login" />

</form>

</body>
</html>

form: User input is taken in a form containing input fields.

action="/servletcom/pass": /pass is the url pattern in web.xml and the servletcom is the name of the project (folder name). The project folder name must be specified here for sure, else the statement means to search in the webapps directory but not within the project.

method="post": Invisible submission, at the background.

name="uname": Used to get the value in this field in Servlet class.

name="pass": Used to get the value in this field in Servlet class.

Servlet Communication - web.xml

<web-app>

<servlet>
<servlet-name>comservlet</servlet-name>
<servlet-class>FirstServlet</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>comservlet</servlet-name>
<url-pattern>/pass</url-pattern>
</servlet-mapping>

<servlet>
<servlet-name>lservlet</servlet-name>
<servlet-class>FinalServlet</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>lservlet</servlet-name>
<url-pattern>/we</url-pattern>
</servlet-mapping>

</web-app>

Here i wrote 2 classes, for servlet communication, as /pass is the url pattern pointing that the corresponding action controlling class is FirstServlet, and also, the user's data sent to this url pattern, FirstServlet will be called first by the servlet container. Next one, /we, when servlet container gets request to the url-pattern /we, the FinalServlet class will be invoked.

For better understand, See Understanding web.xml in Java Servlets

Servlet Communication - FirstServlet.java

import javax.servlet.http.*;
import javax.servlet.*;
import java.io.*;
public class FirstServlet extends HttpServlet
{
public void doPost(HttpServletRequest req,HttpServletResponse res) throws ServletException,IOException
{

String uname=req.getParameter("uname");
String pass=req.getParameter("pass");

getServletContext().getRequestDispatcher("/we").forward(req,res);

}
}

getServletContext(): Gets the ServletContext object. ServletContext is an interface, and may be an implementation class of ServletContext is written and it's object is sent. ServletContext is created by the Servlet Container (Tomcat here) and by using this method we will call it. This object contains common data for the entire web application, so reusable and also helps in communicating with the servlet container because it was generated by the Servlet Container (could also be one of the reason).

getRequestDispatcher(): This is a method of the ServletContext interface.This returns RequestDispatcher object which is again an interface and may be some implementation class is written and its object is sent (to us). The purpose of this method is to pass the request to another servlet. It takes String as parameter, which is the url-pattern pointing the servlet that we are going to send the request to (here FinalServlet).

forward(req,res): This is a method in RequestDispatcher interface, that helps us to forward user's request to another servlet (the servlet that the RequestDispatcher object points out to) (FinalServlet here).

Servlet Communication - FinalServlet.java

import javax.servlet.http.*;
import javax.servlet.*;
import java.io.*;
public class FinalServlet extends HttpServlet
{

public void doPost(HttpServletRequest req,HttpServletResponse res) throws ServletException,IOException
{

String uname=req.getParameter("uname");
String pass=req.getParameter("pass");

PrintWriter pw=res.getWriter();
pw.println("<h1>Your username is "+uname+"</h1>");
pw.println("<h1>Your password is "+pass+"</h1>");

}

}

javax.servlet.http.*: Contains HttpServlet, HttpServletRequest, HttpServletResponseclasses (used here).

javax.servlet.*: Contains ServletException (used here).

java.io.*: Contains PrintWriter, IOException (used here).

pw.println("<h1>Your username is "+uname+"</h1>"): Present in the PrintWriter class, prints username (the value that user gives in field named uname).

pw.println("<h1>Your password is "+pass+"</h1>"): Present in the PrintWriter class, prints password (the value that user gives in field named pass).

Note: The req,res objects are given by the FirstServlet.java and those are used here. These objects are passed from FirstServlet.java to FinalServlet.java by Servlet container (Tomcat here).

Another Note: Do not forget to compile the class and re/start tomcat! ;)

Spring Hibernate doPost() in doGet() in Java Servlets - What's the difference?

doPost() in doGet() in Servlets

Till now we have seen working with doPost() and doGet(). Now let us see how to write doPost() in doGet() before that lets us talk about them for some time. doPost() does invisible data submission whereas doGet() does visible data submission, through url. While doGet() is not recommended for everything, doPost() is used to carry passwords. But some tricky people, tries to pass data through url, though doPost() was to be done. However, this doesn't happen unless they use some extension like Tamper Data. To give them (only the people who thinks of doing so), you can write doPost() within doGet(). Let us look at the example for a better understand.

doPost() in doGet() - Folder Structure

webapps

|_ dopostindoget

|_ WEB-INF

| |_ classes

| | |_ doPostIndoGet.java

| | |_ doPostIndoGet.class

| |_ web.xml

|_ index.html

doPost() in doGet() - index.html

<html>
<head>
<title>doPost in doGet</title>
</head>
<body>

<form action="/dopostindoget/dpdg" method="post">

Name: <input type="text" name="uname" width="20" />
Password: <input type="password" name="pass" width="20" />
<input type="submit" name="submit" value="Login" />

</form>

</body>
</html>

form: User input is taken in a form containing input fields.

action="/postservlet/ps": /ps is the url pattern in web.xml and the postservlet is the name of the project (folder name). The project folder name must be specified here for sure, else the statement means to search in the webapps directory but not within the project.

method="post": Invisible submission, at the background.

name="uname": Used to get the value in this field in Servlet class.

name="pass": Used to get the value in this field in Servlet class.

doPost() in doGet() - web.xml

<web-app>

<servlet>

<servlet-name>testservlet</servlet-name>
<servlet-class>doPostIndoGet</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>testservlet</servlet-name>
<url-pattern>/dpdg</url-pattern>

</servlet-mapping>

</web-app>

Cant understand web.xml? See Understanding web.xml in Java Servlets

doPostIndoGet.java

doPostIndoGet Result

doPostIndoGet Tricked. See Address Bar.

import javax.servlet.http.*;
import javax.servlet.*;
import java.io.*;
public class doPostIndoGet extends HttpServlet
{
public void doGet(HttpServletRequest req,HttpServletResponse res) throws ServletException,IOException
{
doPost(req,res);
}

public void doPost(HttpServletRequest req,HttpServletResponse res) throws ServletException,IOException
{

String user=req.getParameter("uname");
String password=req.getParameter("pass");

PrintWriter pw=res.getWriter();

pw.println("<h1> Welcome "+user+"</h1> <br/>");
pw.println("<h2> Your Password is "+password+"</h2>");

}

}

doPost(): For url type submission, submission through url, observe method="post" in index.html

PrintWriter: Part of the java.io package.

req.getParameter("uname"): Get the value (user input value) in the input field nameduname.

req.getParameter("pass"): Get the value (user input value) in the input field named pass.

pw.println("<h1>Welcome "+user+"</h1> <br/>"): Present in the PrintWriter class, write Welcome along with user within <h1> with a line break. (here).

pw.println("<h2> Your Password is "+password+"</h2>"): Display password withinh2 tag.

Note: Do not forget to compile the class and re/start tomcat! ;)

Folder structure

Project structure

HTML File(s)

index.html

Deployment Descriptor - web.xml

Servlet Programs

SessionExample.java

PrintAttribute.java

Output

Explanation

index.html

web.xml

SessionExample.java

PrintAttribute.java

Folder structure

HTML File(s)

index.html

Deployment Descriptor - web.xml

Servlet Programs

Working? Let's see.

Explaining things..

index.html

web.xml

SelectExample.java

Folder Structure

Project structure

HTML Files

index.html

Deployment Descriptor

web.xml

Servlet Programs

CookieExample.java

GetCookie.java

Working? Yes it works.

Let me explain

The HTML file

The web.xml

Servlet Programs

CookieExample.java

GetCookie.java

Servlet - Servlet Communication

Servlet Communication - Folder Structure

Servlet Communication - index.html

Servlet Communication - web.xml

Servlet Communication - FirstServlet.java

Servlet Communication - FinalServlet.java

doPost() in doGet() in Servlets

doPost() in doGet() - Folder Structure

doPost() in doGet() - index.html

doPost() in doGet() - web.xml

doPostIndoGet.java

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