Web programming for project students Dr Jim Briggs

What is the web? Distributed system Client-server system Characteristics of clients and servers –Servers always on / Clients choose when on –Clients do not need high performance if the work is done on the server Protocol based

Basic architecture of the web

Common web tools Browsers –Microsoft Internet Explorer –Netscape Navigator –Mozilla (Firefox) –Opera –Safari –Konqueror –Lynx Servers –Apache –Internet Information Server (Microsoft) –Sun –Netscape –Omni –Roxen –NCSA

HTTP protocol Specified by – Based on requests and responses A response can contain any document –MIME ( Multipurpose Internet Mail Extensions ) types – A stateless protocol Normally transported via a TCP/IP connection –Default port is TCP 80

HTTP requests Requests –GET –POST –PUT –HEAD Example request GET HTTP/1.1

HTTP responses HTTP/ OK Server: Microsoft-IIS/4.0 Date: Mon, 29 Apr :50:53 GMT Content-Type: text/html Accept-Ranges: bytes Last-Modified: Wed, 10 Apr :12:34 GMT ETag: "085fb85aae0c11:54fb" Content-Length: University of Portsmouth - Our University...

An error response HTTP/ Object Not Found Server: Microsoft-IIS/4.0 Date: Mon, 29 Apr :58:12 GMT Content-Length: Content-Type: text/html University of Portsmouth - Our University...

Dynamic web pages Four models: –Server-side includes –CGI –Server modules –Auxiliary servers

CGI architecture

CGI specification Specified at

Server module

Auxiliary server

Common web languages Java/JSP ASP (.NET) / C# PHP Perl Ruby on Rails

Architecture of a Java web application

Introduction to Java web apps Servlets and JSPs Servlet container –Tomcat A container may run several (independent) web applications (webapps) Each must have a WEB-INF directory: –web.xml configuration file –classes directory –lib directory

Important classes and interfaces 1 All servlets must implement the Servlet interface Class HttpServlet –init/destroy –doGet/doPut –Your servlet will derive from this

Important classes and interfaces 2 2 parameters to a request handling method Class HttpServletRequest –String param = request.getParameter(name); Class HttpServletResponse –PrintWriter out = response.getWriter(); Class HttpSession –Holds data common to related requests

JavaServer Pages (JSP) Distinction: –servlets: HTML embedded in program –JSP: program embedded in HTML Useful where majority of effort is page design Translated automatically into a servlet –Retranslated if changed (no need to restart server) Can be placed anywhere in a web application –but not visible to client if in the WEB-INF directory

JSP elements Scriptlets Actions Directives Standard tags Custom tags Expression language

Scriptlets Any Java code between Expressions – Declarations – DEPRECATED –Do not use - not XML –Much easier to use JSTL

JSP actions Including other files – –Request time inclusion Accessing beans –

JSP directives Page directive – Include directive – –Translation time inclusion

Java Standard Tag Library (JSTL) Taglib directive – Core – SQL XML Format

Custom tags Implement your own tags Create a Tag Library Definition (tld) file Extend predefined classes Specify your library in directive Use like JSTL tags

Expression language Refer to Java Beans and other common classes ${expression} can appear as tag attributes or (since JSP 2.0) in the page itself Several implicit objects: –header ${header["user-agent"]} –param ${param['name']} ${param.name}

Java tools NetBeans –IDE –edit, compile, build, run, debug –lots of wizards –support for Struts –support for Hibernate (through nbxdoclet) Eclipse

Web application system architecture

Model View Controller (MVC)

MVC in Java

Relationship between Struts and Hibernate

Struts information flow

Role of the persistence layer