What is Java Servlet

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I read many articles to understand java servlet but I did not succeed   Can you please give brief introduction of java servlets  in easy language    Like what is servlet  What are the advantges  And all that    I can t understand the difference between server-side programming languages  PHP  ASP  and servlets

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If you are beginner  I think this tutorial may give basic idea about What Servlet is       Some valuable points are below from the given link   Servlet technology is used to create web application which resides at server side and generates dynamic web page   Servlet can be described in many ways  depending on the context    Servlet is a technology i e  used to create web application  Servlet is an API that provides many interfaces and classes including documentations  Servlet is an interface that must be implemented for creating any servlet  Servlet is a class that extend the capabilities of the servers and respond to the incoming request  It can respond to any type of requests  Servlet is a web component that is deployed on the server to create dynamic web page  Reference Here

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A servlet is simply a class which responds to a particular type of network request - most commonly an HTTP request  Basically servlets are usually used to implement web applications - but there are also various frameworks which operate on top of servlets  e g  Struts  to give a higher-level abstraction than the  here s an HTTP request  write to this HTTP response  level which servlets provide   Servlets run in a servlet container which handles the networking side  e g  parsing an HTTP request  connection handling etc   One of the best-known open source servlet containers is Tomcat

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As this article describes  a Servlet is a standardized way of extending a Java server  and accessing its capabilities   Each Servlet can be seen as a tiny server  hence the name   that gets access to the request and response modelled in Java code  along with other context data  like the Session   With these in hand  the Java code of the servlet can interface with whatever it needs to to render a response  including handing off to a JSP page for generating a HTML view

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What is a Servlet    A servlet is simply a class which responds to a particular type of network request - most commonly an HTTP request   Basically servlets are usually used to implement web applications - but there are also various frameworks which operate on top of servlets  e g  Struts  to give a higher-level abstraction than the  here s an HTTP request  write to this HTTP response  level which servlets provide  Servlets run in a servlet container which handles the networking side  e g  parsing an HTTP request  connection handling etc   One of the best-known open source servlet containers is Tomcat  In a request response paradigm  a web server can serve only static pages to the client To serve dynamic pages  a we require Servlets  Servlet is nothing but a Java program This Java program doesn   t have a main method  It only has some callback methods  How does the web server communicate to the servlet  Via container or Servlet engine  Servlet lives and dies within a web container  Web container is responsible for invoking methods in a servlets  It knows what callback methods the Servlet has    Flow of Request   Client sends HTTP request to Web server Web server forwards that HTTP request to web container  Since Servlet can not understand HTTP  its a Java program  it only understands objects  so web container converts that request into valid request object Web container spins a thread for each request  All the business logic goes inside doGet   or doPost   callback methods inside the servlets Servlet builds a Java response object and sends it to the container  It converts that to HTTP response again to send it to the client   How does the Container know which Servlet client has requested for    There   s a file called web xml This is the master file for a web container You have information about servlet in this file-    servlets   Servlet-name Servlet-class  servlet-mappings- the path like  Login or  Notifications is mapped here in    Servlet-name url-pattern  and so on  Every servlet in the web app should have an entry into this file So this lookup happens like- url-pattern -  servlet-name -  servlet-class   How to  install  Servlets    Well  the servlet objects are inherited from the library- javax servlet     Tomcat and Spring can be used to utilize these objects to fit the use case   Ref- Watch this on 1 5x- https   www youtube com watch v tkFRGdUgCsE   This has an awesome explanation

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A servlet at its very core is a java class  which can handle HTTP requests  Typically the internal nitty-gritty of reading a HTTP request and response over the wire is taken care of by the containers like Tomcat  This is done so that as a server side developer you can focus on what to do with the HTTP request and responses and not bother about dealing with code that deals with networking etc  The container will take care of things like wrapping the whole thing in a HTTP response object and send it over to the client  say a browser    Now the next logical question to ask is who decides what is a container supposed to do  And the answer is  In Java world at least It is guided  note I did not use the word controlled  by specifications  For example Servlet specifications  See resource 2  dictates what a servlet must be able to do  So if you can write an implementation for the specification  congratulations you just created a container  Technically containers like Tomcat also implement other specifications and do tricky stuff like custom class loaders etc but you get the idea    Assuming you have a container  your servlets are now java classes whose lifecycle will be maintained by the container but their reaction to incoming HTTP requests will be decided by you  You do that by writing what-you-want-to-do in the pre-defined methods like init    doGet    doPost   etc  Look at Resource 3   Here is a fun exercise for you  Create a simple servlet like in Resource 3 and write a few System out println   statements in it s constructor method  Yes you can have a constructor of a servlet   init    doGet    doPost   methods and run the servlet in tomcat  See the console logs and tomcat logs   Hope this helps  happy learning   Resources   Look how the HTTP servlet looks here Tomcat example   Servlet Specification  Simple Servlet example  Start reading the book online PDF It also provides you download of the whole book  May be this will help  if you are just starting servlets may be it s a good idea to read the material along with the servlet API  it s a slower process of learning  but is way more helpful in getting the basics clear

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Servlet is a java class to respond a HTTP request and produce a HTTP response       when we make a page with the use of HTML then it would be a static page so to make it dynamic we use SERVLET  in simple words one can understand  To make use of servlet is overcomed by JSP it uses the code and HTML tag both in itself

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Servlet is server side technology which is used to create dynamic web page in web application  Actually servlet is an api which consist of group of classes and interfaces  which has some functionality  When we use Servlet API we can use predefined functionality of servlet classes and interfaces   Lifecycle of Servlet   Web container maintains the lifecycle of servlet instance   1   Servlet class loaded  2   Servlet instance created  3   init   method is invoked  4   service   method invoked  5   destroy   method invoked  When request raise by client browser  then web-container checks whether the servlet is running or not if yes then it invoke the service   method and give the response to browser    When servlet is not running then web-container follow the following steps    1  classloader load the servlet class    2  Instantiates the servlet  3  Initializes the servlet  4 invoke the service   method  after serving the request web-container wait for specific time  in this time if request comes then it  call only  service   method otherwise it call destroy   method

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I think servlet is basically a java class which acts as a middle way between HTTP request and HTTP response Servlet is also used to make your web page dynamic  Suppose for example if you want to redirect to another web page on server then you have to use servlets  Another important thing is that servlet can run on localhost as well as a web browser

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You just got the answer for a normally servlet  However  I want to share you about something about Servlet 3 0      What is first a Servlet       A servlet is a Web component that is managed by a container and   generates dynamic content  Servlets are Java classes that are compiled   to byte code that can be loaded dynamically into and run by a Java   technology-enabled Web server or Servlet container       Servlet 3 0 is an update to the existing Servlet 2 5 specification    Servlet 3 0 required API of the Java Platform  Enterprise Edition 6    Servlet 3 0 is focussed on extensibility and web framework   pluggability  Servlet 3 0 bring you up some extensions such as Ease of   Development  EoD   Pluggability  Async Support and Security   Enhancements      Ease of Development      You can declare Servlets  Filter  Listeners  Init Params  and almost   everything can be configured by using annotations      Pluggability      You can create a sub-project or a module with a web-fragment xml  It   means that it allows to implement pluggable functional requirements   independently       Async Support      Servlet 3 0 provides the ability of asynchronous processing  for   example  Waiting for a resource to become available  Generating   response asynchronously       Security Enhancements      Support for the authenticate  login and logout servlet security   methods   I found it from Java Servlet Tutorial

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Servlets are Java classes that run certain functions when a website user requests a URL from a server  These functions can complete tasks like saving data to a database  executing logic  and returning information  like JSON data  needed to load a page    Most Java programs use a main   method that executes code when the program in run  Java servlets contain doGet   and doPost   methods that act just like the main   method  These functions are executed when the user makes a GET or POST request to the URL mapped to that servlet  So the user can load a page for a GET request  or store data from a POST request    When the user sends a GET or POST request  the server reads the  WebServlet at the top of each servlet class in your directory to decide which servlet class to call  For example  let s say you have a ChatBox class and there s this at the top    WebServlet   chat   public class ChatBox extends HttpServlet     When a user requests the  chat URL  your ChatBox class with be executed

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In addition to the above  and just to point out the bleedin  obvious     To many this is hyper obvious  but to someone used to writing apps which are just run and then end  a servlet spends most of its time hanging around doing nothing    waiting to be sent something  a request  and then responding to it   For this reason a servlet has a lifetime  it is initalised and then waits around  responding to anything thrown at it  and is then destroyed   Which implies that it has to be created  and later destroyed  by something else  a framework   that it runs in its own thread or process  and that it does nothing unless asked to  And also that  by some means or other  a mechanism must be implemented whereby this  entity  can  listen  for requests   I suggest that reading about threads  processes and sockets will throw some light on this  it s quite different to the way a basic  hello world  app functions   It could be argued that the term  server  or  servlet  is a bit of an overkill  A more rational and simpler name might be  responder   The reason for the choice of the term  server  is historical  the first such arrangements were  file servers   where multiple user client terminals would ask for a specific file from a central machine  and this file would then be  served up  like a book or a plate of fish and chips

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Java Servlets are server-side Java program modules that procedure and answer customer demands and actualize the servlet interface  It helps in improving Web server usefulness with negligible overhead  upkeep and support    A servlet goes about as a mediator between the customer and the server  As servlet modules keep running on the server  they can get and react to demands made by the customer  Demand and reaction objects of the servlet offer a helpful method to deal with HTTP asks for and send content information back to the customer    Since a servlet is coordinated with the Java dialect  it additionally has all the Java highlights  for example  high movability  stage autonomy  security and Java database availability

[java] What is Java Servlet?

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