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J2EE Web Fundamentals Lesson 4 Request and Response. Instructor: Dr. Segun Adekile. Outline. Objectives Course Text Book Basham, Bryan; Sierra, Kathy; Bates, Bert (2012-10-30). Head First Servlets and JSP (Kindle Location 1349). O'Reilly Media. Kindle Edition. Request and Response - PowerPoint PPT Presentation
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J2EE Web FundamentalsLesson 4
Request and Response
Instructor: Dr. Segun Adekile
Outline
• Objectives• Course Text Book– Basham, Bryan; Sierra, Kathy; Bates, Bert (2012-
10-30). Head First Servlets and JSP (Kindle Location 1349). O'Reilly Media. Kindle Edition.
• Request and Response– Being a Servlet
Objectives
Agenda
• How the Container Handles a Request• Servlet Lifecycle– Loading– Initialization– Service• HTTP Methods• Request Object• Response Object
• Response Redirect• Request Dispatch
How the Container Handles a Request
How the Container Handles a Request
How the Container Handles a Request
Servlet Lifecycle• The servlet lifecycle is simple
• There is only one main state – initialized
• If the servlet isn’t initialized, then it’s either being initialized (running its constructor or init() method), being destroyed (running its destroy() method), or it simply does not exist
Servlet Lifecycle
Servlet Lifecycle
Servlet Lifecycle
Servlet Loading• When the Container starts, it looks for deployed web apps
and then starts searching for servlet class files– Finding the class is the first step– Loading the class is the second step, and it happens either on Container
startup or first client use. Your Container might give you a choice about class loading, or it might load the class whenever it wants.
Servlet Initialization• The constructor makes only an object• To be a servlet, the object needs to be granted servletness, getting all the unique privileges that come with being a servlet e.g. its ServletContext reference.
• You can override the init() method to add operations such as getting a db connection or registering yourself with other objects.
Servlet Initialization
Servlet Service: Request and Response
Servlet Service - HTTP Methods
Servlet Service - HTTP MethodsIntended use:
• for getting things
• Idempotent
Intended use:
• for sending data to be processed
• Non-idempotent
Servlet Service - HTTP Methods
Sending and using a single parameter
getParameterValues – for multiple values
Servlet Service – Request Object
Lifecycle key points
HTTPServletRequest key points
Servlet Service – Response Object• The response is what goes back to the client.• It is parsed and rendered by the browser.• Typically the response object is used to get an • output stream which is used to write the HTML, which goes back to the client.
Response Redirect
Response Redirect
Request Dispatch
HTTPServletResponse key points