Servlet Basics and Lifecycle
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This document provides an overview of servlets and related Java web application concepts. It discusses the servlet lifecycle, how servlets handle HTTP requests and responses, and how they fit into the Java EE context. It also covers servlet containers, the model-view-controller pattern, using servlet contexts and configurations, session management, filters, and multithreading issues.
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Servlet Basics and Lifecycle
- 6. What does your web server do?
- 8. Clients and ser vers know HTML and HTTP • HTML tells the browser how to display the content to the user. • HTTP is the protocol clients and servers use on the web to communicate. • The server uses HTTP to send HTML to the client.
- 9. Anatomy of an HTTP GET request
- 11. Anatomy of an HTTP POST request
- 13. Anatomy of an HTTP response, and what the heck is a “ MIME type”?
- 15. Anatomy of URL
- 16. Why Server is not enough • Dynamic Content • Saving data on the server
- 17. What a container? • Communication support • Lifecycle management • Multithreading support • Declarative security • JSP Support
- 18. How a container handle a dynamic request?
- 22. Servlet inherits the lifecycle methods
- 24. Each request runs in a separate thread!
- 29. Besides parameters, what else can I get from a Request object?
- 40. and getting it in Servlet…
- 41. Setting and getting ServletContext
- 42. Where it fit in JEE context…
- 43. Exercise • Hello World Servlet • Login Application –I • Login Application-II • Use ServletContext and ServletConfig
- 44. MVC Model View Controller Where it fit all??
- 47. MVC Arch
- 49. Application flow MVC • 1- The client makes a request for the form.html page. • 2 - The Container retrieves the form.html page. • 3 - The Container returns the page to the browser, where the user answers the questions on the form and... • 4- Browser request data to the container • 5- container find the correct Servlet based on the URL, an passes the request to the servlet • 6 – The Servlet call BeerServlet for the help
- 50. Application flow MVC • 7- BeerExpert class return an answer, which Servlet add to the request object • 8- The Servlet forward request to the jsp • 9-Jsp get the answer from the request object • 10- JSP generate a page for the container • 11- Container return page to the happy user
- 51. The HTML for the initial form page <html><body> <h1 align=”center”>Beer Selection Page</h1> <form method=”POST” action=”SelectBeer.do”> Select beer characteristics<p> Color: <select name=”color” size=”1”> <option value=”light”> light </option> <option value=”amber”> amber </option> <option value=”brown”> brown </option> <option value=”dark”> dark </option> </select> <br><br> <center> <input type=”SUBMIT”> </center> </form> </body></html>
- 52. Web.xml
- 54. Model…..
- 55. And finally the view…
- 57. Need for listener…. • Init parameter (key, value) are really are strings • What if we need objects ….
- 59. She wants a ServletContextListener
- 61. We will convert dog string to a real dog!!!!
- 62. Making and using a context listener • We need three classes and one DD • The ServletContextListener – MyServletContextListener.java • The attribute class – Dog.java • The Servlet – ListenerTester.java
- 63. Writing the listener class
- 73. Attributes: What is it???
- 80. multithreading issues???? What abut multithreading issues???? Note easy to handle But really not rocket science!!!!
- 84. How do we make context attributes thread-safe? • Idea 1: – Synchronizing the service method is a spectacularly BAD idea • Idea 2: – SingleThreadModel – Idea 3: » Synchronized Block » What to Use????
- 85. Synchronizing the service method is a spectacularly BAD idea
- 86. Solution: You don’t need a lock on the servlet... you need the lock on the context!
- 87. Are Session attributes thread-safe? Not really!!!
- 89. request Attribute : thread safe but…..
- 102. Simple Cookies Example: for session management
- 107. Filters are modular, and configurable in the DD
- 108. Three ways filters are like servlets • The Container knows their API • Just like servlets, filters have a lifecycle. » Like servlets, they have init() and destroy() methods. Similar to a servlet’s doGet()/doPost() method, filters have a doFilter() method. • They’re declared in the DD » A web app can have lots of filters, and a given request can cause more than one filter to execute. The DD is the place where you declare which filters will run in response to which requests, and in which order.
- 109. Building the request tracking filter
- 111. Thanks:- Reference:- Head First Servlet and Jsp