_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications1  Wiley and the book authors 2001 E-Commerce: Fundamentals and Applications Chapter 4 : Server-Side Programming I Servlet Fundamentals

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications2  Wiley and the book authors 2001 Outline Common server-side programming techniques Basic concepts of Java Servlets - an innovative server-side programming technology Advantages of servlets over other technologies for developing Web-based applications Simple Java servlet programs

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications3  Wiley and the book authors 2001 Revisiting the Three-tier Model Web-based e-commerce applications are usually built according to the “Three-tier Model” (Fig. 4.1), which includes: The First-tier: Web Client  Discussed in Chapter 3 The Second-tier: Server-side Application (SSA)  Discussed in this chapter The Third-tier: Database Management Systems (DBMS)  Discussed in Chapter 5

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications4  Wiley and the book authors 2001 Three-Tier Model (Fig. 4.1) Database Cluster Client Browser First-tier : Web Clients Second-tier : Server-side Web Applications Web Server Application Server Third-tier (DBMS) : Database Cluster(s) SQL Server Other databases Oracle databases DB2 databases Internet Database Connectivity

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications5  Wiley and the book authors 2001 Server-side programming technologies There are numerous ways to implement server- side applications. Common examples include: CGI (Common Gateway Interface) ASP (Active Server Page) Java Servlets

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications6  Wiley and the book authors 2001 Common Gateway Interface (CGI) Early Web page designs were “static” in the sense that a client can only request for a static HTML document from the Web server (Fig. 4.2). Later, CGI programming techniques were introduced to remove this constraint by providing dynamic Web pages via server-side interaction, as shown in Fig. 4.3.

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications7  Wiley and the book authors 2001 Static Web Page Retrieval (Fig. 4.2)  HTTP Request  HTTP Document  Retrieve Document  Request for Web Document Web Documents Web Browser Web Server

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications8  Wiley and the book authors 2001 CGI-based Web Application (Fig. 4.3)  Get Data  HTTP Request  HTTP Document  Output (HTML)  HTML forms to invoke CGI scripts CGI Scripts/ Applications Web Browser Web Server Database  Return data

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications9  Wiley and the book authors 2001 Common Gateway Interface (CGI) Fig. 4.3 explains the retrieval of a static Web page. The Web browser goes to the designated URL on a specific Web server to retrieve the required static HTML document when it receives a client request. Note the content is independent of the request, in the sense, everyone who makes a request to that particular URL gets the same document.

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications10  Wiley and the book authors 2001 Active Server Page (ASP) ASP is a "scripting" technique that runs on Web servers rather than Web clients.This contrasts with VBScript and JavaScript which run on web clients. It basically generates HTML documents for the Web client. Execution of the ASP code by the server returns the corresponding HTML document to the client. Fig. 4.4 shows the schematic diagram of ASP model.

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications11  Wiley and the book authors 2001 ASP Model (Fig. 4.4) ASP Engine  HTTP Request  HTTP Document Web Browser Web Server Database

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications12  Wiley and the book authors 2001 Disadvantages of CGI programs Each new request activates a new process to run the CGI program Creating a process requires time and resource so CGI programs is not as scaleable a solution Also, CGI programs may raise security problems.

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications13  Wiley and the book authors 2001 Java Servlet A servlet is a small piece of server-side application, which can be viewed as the server- side analog of an applet. In a typical servlet application, a servlet-enabled Web server receives an HTTP request from the client. It then forwards the request to the servlet engine for performing the necessary operations as specified by the program. Finally it returns a response (e.g., HTML document) to the client via the Web server (Fig. 4.5)

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications14  Wiley and the book authors 2001 Typical Web-based Servlet Interaction (Fig. 4.5) Servlet Engine HTTP Request HTTP Response Web Browser Web Server Database

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications15  Wiley and the book authors 2001 Why using Servlets? In this book, they cover a solution called Java servlet for three reasons:  it is more effective and efficient  it is more secure  it contains a lot of standard libraries ("do not need to reinvent the wheel") Effectively, Java servlet does what CGI programs do but simpler, more efficient and more secure

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications16  Wiley and the book authors 2001 How to run servlets? To run servlets, there are TWO options: To use a servlet-enabled Web server, i.e. a Web server that can support the servlet APIs directly. To use a "plug-in" servlet engine in a non-servlet- enabled Web server.

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications17  Wiley and the book authors 2001 Generic vs. HTTP Servlet Model The Java servlet API has two main packages, namely javax.Servlet and javax.Servlet.http.  The javax.Servlet package consists of interfaces and classes that can be implemented and used by all servlets by overriding service() method - Generic Servlets.  The javax.Servlet.http package are for HTTP-specific servlets. Hence it is mainly used for building Web- based applications by overriding doPost()/doGet() methods - HTTP Servlets.

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications18  Wiley and the book authors 2001 Methods to create HTTP servlets Besides the doGet() and doPost() methods, a variety of methods corresponding to different HTTP commands are available (see Table 4.3 in the book). Essentially, these methods allow a servlet to perform actions according to the type of HTTP request received.

_______________________________________________________________________________________________________________ E-Commerce: Fundamentals and Applications19  Wiley and the book authors 2001 Building the Virtual Bookstore (VBS) We will demonstrate how to build a simple Virtual Bookstore (VBS) by using Java servlets as the core server-side programming tool, which include:  Client-side programming using HTML and JavaScript in Chapter 3.  Server-side programming using Java servlets in this Chapter 4-6.  JDBC programming with servlets to implement database connectivity, in Chapter 5.  Session tracking technique using the servlet session tracking API to implement user login and shopping cart applications, in Chapter 6.