Ch5 beeing an application
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This document contains notes from a lecture on web technologies. It discusses procedural items like asking some students to speak after class and notifying about assignment grades and deadlines. It also covers technical topics around installing LAMP and Tomcat, using servlets, web application deployment descriptors, context listeners, and ensuring thread safety.
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Ch5 beeing an application
- 1. Τεχνολογίες Παγκόσμιου Ιστού 5η διάλεξη
- 2. Διαδικαστικά Θα ήθελα να μιλήσω με τους παρακάτω στα τελευταία 10’ του μαθήματος petros_dv, tsakatik, mirtwza, giannis156, apostoli, kir.christos, john_efthi, gavriili, somagion, papeslis, gi0rikas, thanoskaratzas, redsoukas, ntogkasxr, thomadak
- 3. Διαδικαστικά • Παρακαλώ δείτε τους βαθμούς της 1η εργασίας και στείλτε στον Έλβις τυχόν αντιρρήσεις σας • Η 2η εργαστηριακή άσκηση θα συζητηθεί την δεύτερη ώρα σήμερα, θα δωθεί αναλυτικά το απόγευμα και θα πρέπει να παραδωθεί στις 8.00 της Δευτέρας.
- 4. Διαδικαστικά Σημαντική βοήθεια για την συνέχεια του μαθήματος και ιδιαίτερα στο θέμα των εργασιών θα βρείτε στα http://stackoverflow.com http://www.roseindia.net
- 5. 2η εργασία • Μελέτησε το 4ο κεφάλαιο και προπάθησε το αντίστοιχο τεστ. • Ξεκίνα την εξοικοίωσή σου με το https://netbeans.org • Εγκατέστησε στο VM σου στον Ωκεανό • LAMP • http://tomcat.apache.org • Wordpress
- 6. LAMP
- 7. Being a Servlet Chapter 4
- 8. From HMTL to servlet class
- 9. What else?
- 10. Be carefull!! getServerPort(), getLocalPort() & getRemotePort()
- 11. Response now Use the response for I/O when • There is no JSP • No JSP is allowed • Do not want to use JSP • Do not send HTML
- 12. Παράδειγμα
- 13. Redirect sendRedirect() method: if (worksForMe) { // handle the request } else { response.sendRedirect(“http://www.oreilly.com”); } Redirect is not dispatch
- 14. Being a Web Application Chapter 5
- 15. Protecting my e-mail address PrintWriter out = response.getWriter(); out.println(“mav@uth.gr”); <servlet> <servlet-name>BeerParamTests</servlet-name> <servlet-class>TestInitParams</servlet-class> <init-param> <param-name>adminEmail</param-name> <param-value>mav@uth.gr</param-value> </init-param> </servlet> out.println(getServletConfig().getInitParameter(“adminEmail”));
- 16. Servlet initializations and ServletConfig The Container (after running the constructor) • Creates a unique ServletConfig • Reads servlet init parameters • Gives them to ServletConfig • Passes ServletConfig to servlet’s init() method
- 17. Δηλαδή
- 19. Re-deploying a servlet • Edit DD • Shut and restart the container • You better be careful what you put as init-param
- 20. Give JSP servlet’s init params • As a request attribute
- 21. Give JSP servlet’s init params • Using Context
- 22. Context & Servlet init parameters
- 23. Context & Servlet init parameters Container • Reads DD and creates name/ value string pairs for each <context-param> • Creates a new instance of ServletContext • Passes (as reference) pairs to ServletContext JSP is a servlet
- 24. What else is in ServletContext?
- 25. We need a listener Which Listens for context initialization events Runs specific code before servlet starts serving Notice, there is no main()!
- 27. Make and use a context listener Create a listener class Put the class in WEB-INF/classes Put <listener> element in DD • Three classes (and one DD) ServletContextListener.java Dog.java ListenerTester.java
- 28. Listener class
- 29. Attribute class Context init parameters as the argument for the constructor servlet will get dog from context call getBreed() print the value of breed
- 30. Servlet class
- 31. The DD (web.xml in WEB-INF)
- 32. Compile and Deploy Compile the three classes Create a new web app in Tomcat Create ListenerTest and WEB-INF Put web.xml in WEB-INF Make a classes directory underneath. Create a directory structure that matches your package structure Put web.xml and the three compiled files into their space Shutdown and restart Tomcat
- 33. The whole story
- 35. Context & Servlet init parameters
- 36. Context & Servlet init parameters Container • Reads DD and creates name/value string pairs for each <context-‐param> • Creates a new instance of ServletContext • Passes (as reference) pairs to ServletContext
- 37. What else is in ServletContext? You may get them but NOT set them later
- 38. Initializing your web application with an object After initializing with a string of course
- 39. We need a listener (a Java object) • That – Listens for context initialization events – Runs specific code before servlet starts serving Notice! There is no main()
- 41. Listen to the Dog
- 42. Make and use a context listener • Create a listener class • Put the class in WEB-‐INF/classes • Put <listener> element in DD • Three classes (and one DD) – ServletContextListener.java – Dog.java – ListenerTester.java
- 43. Listener class
- 44. Attribute class
- 45. Servlet class
- 46. The DD (the web.xml in WEB-‐INF)
- 47. Review
- 48. The whole story (In pictures)
- 49. You can listen all kinds of events
- 50. Attributes • Who can put (and remove)? • Who can see? • For how long? SCOPE
- 51. Attributes are not Parameters!
- 52. The 3 Scopes
- 53. The 3 Scopes (API)
- 54. Beware of Attributes (1/2)
- 55. Beware of Attributes (2/2)
- 58. Lock the Context (not the Service)
- 60. SingleThreadModel No two threats will execute concurrently in the servlet’s service method. Two choices for STM implementation
- 61. Only request attributes and local variables are thread-‐safe • Instance variables aren’t thread-‐safe • Classes aren’t thread-‐safe
- 62. Request attributes & Request dispatching
- 63. What is wrong here?