Skip to main content

Servlet Works

How Servlet works?

It is important to learn how servlet works for understanding the servlet well. Here, we are going to get the internal detail about the first servlet program.

The server checks if the servlet is requested for the first time.

If yes, web container does the following tasks:

  • loads the servlet class.
  • instantiates the servlet class.
  • calls the init method passing the ServletConfig object

else

  • calls the service method passing request and response objects

The web container calls the destroy method when it needs to remove the servlet such as at time of stopping server or undeploying the project.

How web container handles the servlet request?

The web container is responsible to handle the request. Let's see how it handles the request.

  • maps the request with the servlet in the web.xml file.
  • creates request and response objects for this request
  • calls the service method on the thread
  • The public service method internally calls the protected service method
  • The protected service method calls the doGet method depending on the type of request.
  • The doGet method generates the response and it is passed to the client.
  • After sending the response, the web container deletes the request and response objects. The thread is contained in the thread pool or deleted depends on the server implementation.

What is written inside the public service method?

The public service method converts the ServletRequest object into the HttpServletRequest type and ServletResponse object into the HttpServletResponse type. Then, calls the service method passing these objects. Let's see the internal code:

  1. public void service(ServletRequest req, ServletResponse res)  
  2.         throws ServletException, IOException  
  3.     {  
  4.         HttpServletRequest request;  
  5.         HttpServletResponse response;  
  6.         try  
  7.         {  
  8.             request = (HttpServletRequest)req;  
  9.             response = (HttpServletResponse)res;  
  10.         }  
  11.         catch(ClassCastException e)  
  12.         {  
  13.             throw new ServletException("non-HTTP request or response");  
  14.         }  
  15.         service(request, response);  
  16.     }  

What is written inside the protected service method?

The protected service method checks the type of request, if request type is get, it calls doGet method, if request type is post, it calls doPost method, so on. Let's see the internal code:

  1. protected void service(HttpServletRequest req, HttpServletResponse resp)  
  2.         throws ServletException, IOException  
  3.     {  
  4.         String method = req.getMethod();  
  5.         if(method.equals("GET"))  
  6.         {  
  7.             long lastModified = getLastModified(req);  
  8.             if(lastModified == -1L)  
  9.             {  
  10.                 doGet(req, resp);  
  11.             }   
  12.     ....  
  13.     //rest of the code  
  14.         }  
  15.     }  


Anurag Rana

Comments

Popular posts from this blog

JAVA Scrollbar, MenuItem and Menu, PopupMenu

ava AWT Scrollbar The  object  of Scrollbar class is used to add horizontal and vertical scrollbar. Scrollbar is a  GUI  component allows us to see invisible number of rows and columns. AWT Scrollbar class declaration public   class  Scrollbar  extends  Component  implements  Adjustable, Accessible   Java AWT Scrollbar Example import  java.awt.*;   class  ScrollbarExample{   ScrollbarExample(){               Frame f=  new  Frame( "Scrollbar Example" );               Scrollbar s= new  Scrollbar();               s.setBounds( 100 , 100 ,  50 , 100 );               f.add(s);               f.setSize( 400 , 400 );               f.setLayout( null );               f.setVisible( true );   }   public   static   void  main(String args[]){           new  ScrollbarExample();   }   }   Output: Java AWT Scrollbar Example with AdjustmentListener import  java.awt.*;   import  java.awt.event.*;   class  ScrollbarExample{        ScrollbarExample(){               Frame f=  new  Frame( "Scro

Difference between net platform and dot net framework...

Difference between net platform and dot net framework... .net platform supports programming languages that are .net compatible. It is the platform using which we can build and develop the applications. .net framework is the engine inside the .net platform which actually compiles and produces the executable code. .net framework contains CLR(Common Language Runtime) and FCL(Framework Class Library) using which it produces the platform independent codes. What is the .NET Framework? The Microsoft .NET Framework is a platform for building, deploying, and running Web Services and applications. It provides a highly productive, standards-based, multi-language environment for integrating existing investments with next-generation applications and services as well as the agility to solve the challenges of deployment and operation of Internet-scale applications. The .NET Framework consists of three main parts: the common language runtime, a hierarchical set of unified class librari

C++ this Pointer, static, struct and Enumeration

C++ this Pointer In C++ programming,  this  is a keyword that refers to the current instance of the class. There can be 3 main usage of this keyword in C++. It can be used  to pass current object as a parameter to another method. It can be used  to refer current class instance variable. It can be used  to declare indexers. C++ this Pointer Example Let's see the example of this keyword in C++ that refers to the fields of current class. #include <iostream>    using   namespace  std;   class  Employee {       public :           int  id;  //data member (also instance variable)               string name;  //data member(also instance variable)            float  salary;          Employee( int  id, string name,  float  salary)             {                   this ->id = id;                  this ->name = name;                  this ->salary = salary;            }             void  display()             {                 cout<<id<< "  " <<name<&