UNIT III SERVER SIDE PROGRAMMING

 3.2 Servlet Lifecycle

Introduction

The Servlet lifecycle defines the stages a servlet goes through during its existence in a web application. Understanding the lifecycle helps in effectively managing resources and optimizing server-side operations. The lifecycle is managed by the servlet container (e.g., Apache Tomcat).

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Stages of the Servlet Lifecycle

• 1. Loading and Instantiation
  • The servlet container loads the servlet class into memory when the web server starts or when the first request is made.
  • A single instance of the servlet is created using the default constructor.
• 2. Initialization (init Method)
  • The container calls the init() method once after the servlet instance is created.
  • This stage is for performing one-time initialization tasks, such as setting up resources or configuration.
  • Code Example:

  
  @Override
  public void init(ServletConfig config) throws ServletException {
      super.init(config);
      System.out.println("Servlet is initialized");
  }
  

• 3. Request Handling (service Method)
  • The service() method is invoked for every client request.
  • It identifies the HTTP request type (e.g., GET, POST) and calls the corresponding method (e.g., doGet, doPost).
  • Code Example:

  
      @Override
      protected void doGet(HttpServletRequest request, HttpServletResponse response) 
              throws ServletException, IOException {
          response.setContentType("text/html");
          PrintWriter out = response.getWriter();
          out.println("<h1>Hello, this is a GET response!</h1>");
      }
  

• 4. Destruction (destroy Method)
  • The destroy() method is called once when the servlet is removed from memory, usually during server shutdown.
  • Use this stage for cleanup tasks, such as releasing resources or closing connections.
  • Code Example:

  
  @Override
  public void destroy() {
      System.out.println("Servlet is destroyed");
  }
  

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Servlet Lifecycle Diagram