9 Application Development

9.1 Application Programs & User Interfaces

  1. Client-server-architecture - a personal directory communicates w/a shared databases

    • two big drawbacks:

      1. Security risks b/c user machines had direct access to database 
2. any changes/updates to app/database required all copies of the app to be updated

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  1. 2 approaches to avoid client-server architecture problems:
    • web browsers
    • application programs installed on individual (usual mobile) devices

9.2 Web Fundamentals

  1. WEB BROWSERS = de facto standard user interface to database b/c…
    • they allow large num. of users to access database anywhere
    • avoid the need to download/install specialized code while also providing a good GUI

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  1. HTTP protocol is connectionless
    • connectionless means that once the server replies to a request, the server closes the connection w/the client and forgets all about the requests
    • in contrast, Unix logins and JDBC/ODBC connections stay connected until the client disconnects; this retains user authentication & other info.
    • connectionless reduces load on server since operating systems have tight limits on num. of open connections on a machine

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  1. Info. services like user authentication needs session info.
    • authentication should be done only once per session
    • the solution is to use a cookie \[\\[.1cm]\]
  2. COOKIE - a small piece of text containing identifying info.
    • sent by server to browser on first interaction to identify session
    • the text is part of the HTTP protocol that creates the cookie on further interactions
    • server saves info. about the cookie it issued, & uses it when serving a request like authentication info and displaying user preferences from same machine

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  1. Cookies can be stored permanently or for a limited time

9.3 Servlets

  1. SERVLETS - defines an application programming interfaces for communication btw the web/application servers and application program

    Ex. Methods to get parameter values from web forms & to send HTML text back to client

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  1. Application programs (aka servlet) is loaded into the server
    • each request spawns a new thread in the server & the thread is closed once the request is serviced
    • programmer creates a class that from Http servlet and overrides methods like doGet, doPost

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  1. Servlet API supports handling of sessions
    • sets a cookie on first interaction w/browser & uses it to identify further session

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  1. servlets run inside application servers such as Apache Tomcat, Glassfish, JBoss, BEA Weblogic, IBM websphere, & Oracle Application Servers
    • these app. servers support deployment & monitoring of servlets
    • some can even support objects, parallel processing across multiple application servers, etc.