The following are the notes for Week 5 Java (Web)

• http, svn, https, ftp etc. converts the url into an IP address and then connect to a web server
• Browser sends a request to the Web Server, the Web Server will send a respond
• HTTP works using different error codes
  • HTTP 404 error - e.g. if the http://www.google.co.uk/index2.html website doesn't exist
• GET and POST are the main request types (HEAD, DELETE, PUT, PUT)
  • both pass over information
  • GET accepts a maximum of 256 characters
  • sending an index.html request is a GET request
  • POST is a request to upload something (/index.html?search=fdm)

• Where the Java code lives
• A request goes into a particular java class, and this class will decide what to do (e.g. check database etc)
  • Classes that handle web requests are called Servlets
• Web Containers deal with threads automatically
• Responsible for Security, Concurrency, Lifecycle management, Application deployment
• Java EE (Enterprise Edition) gives standards to things that you'd want to use in the business (previously we dealt with Java SE)
  • e.g. dealing with web applications, messaging, transactions...
  • Java EE generally runs on a web container

• Servlets process requests, and send responds based on requests
• can even send back HTML
• can send a simple HTML back, or something based on the request
• request will include IP, POST information
• similar to dependency injection
• concerns need to be separated out (web developer and java developer code shouldn't be mixed up)
• To make a Java servlet, you extend the HTTPServlet
• Servlet Lifecycle

1. Container creates an instance of a server
2. Calls the init() method
3. Calls the service() method
4. Calls the destroy() method (usually at shutdown)

• • init() and destroy() method are only called once

• To make a Maven Project for web, you choose webapp instead of quickstart in New Maven Project
• packaging in the pom will be war instead of jar
• tomcat is the web container and web server that we use, so maven can deploy the application
• scope in dependencies determines when to use the dependency
• provided means it is needed during compile time, but don't want to include them with your installation (the server will give it to you)
• need to override the doGet method from the HTTPServlet interface
• url-pattern supports wildcards
• apache-tomcat-7.0.22 is required for this

• JSP are html pages sitting on the server with a little bits and pieces of java code in it
• promotes the MVC architecture
  • JSP will be the View
  • the Servlet is the Controller
  • the Model will be whatever you'd want the model to be
• Lifecycle
  • Client requests a JSP Page
  • the browser sends the request to the web server and then to the web container
  • JSP servlet converts the JSP page into a java servlet file
  • A java servlet file is compiled
  • the web container loads the servlet and calls the JSPInit() and JSPService() methods
  • HTML file will be output to the browser

• How widely an object is available
• Session is something that will live for multiple requests (usually for a given time)
  • Like an Amazon basket
• Application scope is generally used for global variables (that don't change)
• Request scope is only for the duration of one request
• Page scope are only available within the actual JSP Page

• Anything inside Web-INF is protected
• Useful for loggedin page, so a user can't just open the logged in page using the URL

• Listener is an interface
• Uses the Observer pattern
  • you have something you listen for or observe, when a certain state changes, you call the Listener
• For things you only want to do one (e.g. set up log4j, start connections to DB, close files at the end,...)

• <% %> is known as a Scriptlet
• <%:  %> is known as a Directive
• <%! %> is known as a Declaration (for declaring primitives)
• <%= %> is for an Expression (e.g. <% 5 + 6 %> will show 11)