Skip to main content

Servlet Life Cycle

Java Servlet Life Cycle

A servlet is a Java programming language class that is used to extend the capabilities of servers that host applications accessed by means of a request-response programming model. Although servlets can respond to any type of request, they are commonly used to extend the applications hosted by web servers. For such applications, Java Servlet technology defines HTTP-specific servlet classes.
The javax.servlet and javax.servlet.http packages provide interfaces and classes for writing servlets. All servlets must implement the Servlet interface, which defines life-cycle methods. When implementing a generic service, you can use or extend the GenericServlet class provided with the Java Servlet API. The HttpServlet class provides methods, such as doGet and doPost, for handling HTTP-specific services.

Servlet Life Cycle

The life cycle of a servlet is controlled by the container in which the servlet has been deployed. When a request is mapped to a servlet, the container performs the following steps.
1.      If an instance of the servlet does not exist, the web container
a.      Loads the servlet class.
b.      Creates an instance of the servlet class.
c.       Initializes the servlet instance by calling the init method.
2.      Invokes the service method, passing request and response objects.
3.      If the container needs to remove the servlet, it finalizes the servlet by calling the servlet’s destroy method.

Lets try to understand the Servlet Life Cycle in details

1.      A web browser sends an HTTP request to a web server by any one of the following ways.
a.      A user clicks on a hyperlink displayed in an HTML page.
b.      A user fills out a form in an HTML page and submits it.
c.       A user enters a URL in the browser’s address field and presses Enter.

2.      The container "sees" that the request is for a servlet, so the web container creates two objects.
a.      HttpServletRequest
b.      HttpServletResponse

3.      The Web Container finds the correct servlet based on the URL in the request , the container then creates or allocate a thread for that request and calls the service() method of the servlet, passing the request and response objects as arguments.

4.      The service() method figures out which servlet method to call based on HTTP method sent by the client.If the client sent GET , then corresponding doGet() method is called.

5.      The servlet uses the response object to write the response to the client.

6.      The service() method completes, the threads dies or returns to  back to the pool.The request and response object are garbage collected.The client gets the response.



Servlet Life Cycle

Servlet Life Cycle

Comments

Post a Comment

Popular posts from this blog

Mockito interview Questions

1.       Question 1. What Is Mockito? Answer : Mockito allows creation of mock object for the purpose of Test Driven Development and Behavior Driven development. Unlike creating actual object, Mockito allows creation of fake object (external dependencies) which allows it to give consistent results to a given invocation. 2.       Question 2. Why Do We Need Mockito? What Are The Advantages? Answer : Mockito differentiates itself from the other testing framework by removing the expectation beforehand. So, by doing this, it reduces the coupling. Most of the testing framework works on the "expect-run-verify". Mockito allows it to make it "run-verify" framework. Mockito also provides annotation which allows to reduce the boilerplate code. 3.       Question 3. Can You Explain A Mockito Framework? Answer : In Mockito, you always check a particular class. The dependency in that class is injected using mock object. So, for example, if you have service class
2 comments
Read more

JAVA Expert Interview Questions Answers 2017

Java Basics ::  Interview Questions and Answers Home  »  Interview Questions  »  Technical Interview  »  Java Basics  » Interview Questions 1.     What is the difference between a constructor and a method? A constructor is a member function of a class that is used to create objects of that class. It has the same name as the class itself, has no return type, and is invoked using the new operator. A method is an ordinary member function of a class. It has its own name, a return type (which may be void), and is invoked using the dot operator. 2.     What is the purpose of garbage collection in Java, and when is it used? The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources can be reclaimed and reused. A Java object is subject to garbage collection when it becomes unreachable to the program in which it is used. 3.     Describe synchronization in respect to multithreading. With respect to
3 comments
Read more

Java Example Program to Convert List to Set

import java.util.ArrayList; import java.util.HashSet; import java.util.Set; public class ListToSet {  /**   * @author Amarjit Kumar   * @category interview questions   *   * Description: Convert List to set in java with example program   *   */  public static void main(String[] args) {   ArrayList<String> arrList= new ArrayList<>();   arrList.add("Java");   arrList.add("Java");   arrList.add("List to String");   arrList.add("Example Program");   Set<String> strSet = new HashSet<String>(arrList);   System.out.println(strSet);   System.out.println(arrList);  } } /*  * Java program to convert list to set. Convert ArrayList of string to HashSet  * in java example program How to convert List to Set in java Set<String> strSet  * = new HashSet<String>(arrList); HashSet having a constructor which will take  * list as an argument. Lets see how to convert list to Set using java program.
Post a Comment
Read more