- https://chatgpt.com/c/d7dba5ab-7f7a-4c1c-a443-f67f15ca09a2 :green_circle:

Servlet 3

new feature/s

• programmatically register servlets,filter and lister into it ServletContext / SC , using WebApplicationInitializer

• eliminating need of web.xml

• public class MyWebAppInitializer implements WebApplicationInitializer { @Override public void onStartup(ServletContext servletContext) throws ServletException { ServletRegistration.Dynamic servlet = servletContext.addServlet("exampleServlet", new ExampleServlet()); servlet.addMapping("/example"); } }

• Anno based - @WebServlet, @WebFilter, @WebListener
• allows asynchronous request processing

  @WebServlet(urlPatterns = "/asyncServlet", asyncSupported = true)
  public class AsyncServlet extends HttpServlet {
      @Override
      protected void doGet(HttpServletRequest request, HttpServletResponse response)
              throws ServletException, IOException {
          AsyncContext asyncContext = request.startAsync();
          asyncContext.start(() -> {
              try {
                  // Simulate long-running task
                  Thread.sleep(5000);
                  response.getWriter().write("Async Response");
                  asyncContext.complete();
              } catch (Exception e) {
                  e.printStackTrace();
              }
          });
      }
  }
  

• programmatically configure security settings, but will use sb-security-starter.
• Enhanced file upload capabilities with the @MultipartConfig

---

@webListener

• used to perform actions in response to various events in a web application
• event eg : creation and destruction of the sessions and request objects
• based on event already parent listener present, just create subclass out of it
  • HttpSessionListener
  • ServletRequestListener
  • ...

    @WebListener
    public class MyServletRequestListener implements ServletRequestListener {
    
        @Override
        public void requestInitialized(ServletRequestEvent sre) {
            System.out.println("Request initialized");
            // Perform tasks such as logging request details, initializing request-specific data, etc.
        }
    
        @Override
        public void requestDestroyed(ServletRequestEvent sre) {
            System.out.println("Request destroyed");
            // Perform tasks such as cleaning up request-specific data, logging request end, etc.
        }
    }
    

Servlet Context / SC

• like spring IAC - AC or hibernate - PC, we have web container - SC
• sample code:

    - InputStream inputStream = servletContext.getResourceAsStream("/WEB-INF/resource.txt");
  
    - String paramValue = servletContext.getInitParameter("paramName");
  
    - servletContext.setAttribute("attributeName", attributeValue);
      Object attributeValue = servletContext.getAttribute("attributeName");
      servletContext.removeAttribute("attributeName");
  
    - servletContext.addServlet("dynamicServlet", new MyServlet()); 
  

@WebFilter

• Components that can perform filtering tasks on request and response objects
• before and after the request is processed by a servlet.
• logging,
• authentication,
• input validation,
• transformation of response content. - intercept

  @WebFilter(
      urlPatterns = "/*",
      initParams = {
          @WebInitParam(name = "paramName", value = "paramValue")
      }
  )
  public class ConfigurableFilter implements Filter {
  
      private String paramValue;
  
      @Override
      public void init(FilterConfig filterConfig) throws ServletException {
          paramValue = filterConfig.getInitParameter("paramName");
      }
  
      @Override
      public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
              throws IOException, ServletException {
          // Use the initialization parameter in the filter logic
          System.out.println("Initialization Parameter: " + paramValue);
  
          // Pass the request and response to the next filter or servlet in the chain
          chain.doFilter(request, response);
      }
  
      @Override
      public void destroy() {
          // Cleanup code, if needed
      }
  }