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14/07/2009 1 ServletProgramming 1 By VõVăn Hải Http://www.vovanhai.wordpress.com Developing Web Applications An Overview 2 Client – Server Model Advantages of Web Application • Easier access to information • Lower maintenance and deployment costs • Platform independency • Wider visibility 3 14/07/2009 2 Architecture of Web Applications 4 Traditional n-Tier Architecture Application Logic= Presentation logic + Business Logic (No physical demarcation between the two) Infrastructure services provide additional functionalities required by application, such as messaging services and transactional services. 5 Component n-tier Architecture Component A Component B Component C Database Interfaces Application object broken into components that can communicate with each other, through interfaces 6 14/07/2009 3 Layered Architecture Component A Component B Component C Database M I D D L E W A R E JDBC-ODBC Bridge, perhaps 7 Communication/ Protocols Http Protocol Request Message structures Response Message structures 8 HTTP Protocol Hypertext Transfer Protocol (HTTP) is an application level protocol Enables Web servers and browsers to send and receive data HTTP Request – Client sends a request to the Web server using HTTP request methods: GET – Enables to access static resources POST – Enables to access dynamic resources HEAD – Enables to view the headers of HTTP response HTTP Response – Web server sends response to the client after processing the request 9 14/07/2009 4 Server Side Technologies Common Gateway Interface (CGI). Server-side JavaScript (SSJS). Personal Home Page (PHP). Java Servlet Active Server Page (ASP) Java Server Page (JSP). 10 Common Gateway Interface (CGI) Written using Perl programming language Enables the Web server to send information to other files and Web browsers Enables to obtain information and use it on the server machine Helps to process the inputs to the form on the Web page Disadvantages •Reduced efficiency •Reloading Perl interpreter 11 Active Server Pages (ASP) Uses server side scripting architecture that is used to develop database driven Web applications Runs under Internet Information Services (IIS) Saved with a .asp extension Provides programming tools with functionalities that enable the user to develop ASP applications faster Enables the user to develop Web applications using languages such as VB Script and JScript. Provides an array of objects and components that provide benefits such as speed, security, modularity, and extensibility <%@ LANGUAGE = ”JavaScript” %> <html> <body> <% Response.Write(“ Welcome ”)%> </body> </html> Declares page language as JavaScript Displays Welcome message 12 14/07/2009 5 PHP Hypertext Preprocessor Server side scripting language that provides tools for developing dynamic Web pages PHP is similar to JSP and ASP Enables to connect the Web forms to the database Requires a simple text editor to develop the code Provides security by executing the PHP code on the server Enables the use of PHP on operating systems, such as, Windows, Mac, and Unix 13 Servlets Enables the user to run Java code on the Web server Enables to develop Web pages and process inputs from the Web pages Enables to add dynamic content to Web pages A single servlet instance can process multiple requests Contains built-in functionality for reading HTML form data, handling cookies, tracking user sessions, and setting HTTP headers 14 Example of Servlets import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class Example extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { PrintWriter out = response.getWriter(); out.println(“<html><body>”); out.println(“ Example of Servlets”); out.println(“</body></html>”); } } import Java class HTML code in servlets 15 14/07/2009 6 Web.xml <servlet> <description></description> <display-name>Display Servlet Name</display-name> <servlet-name>Servlet Name</servlet-name> <servlet-class>ServletClass</servlet-class> </servlet> <servlet-mapping> <servlet-name>Servlet Name</servlet-name> <url-pattern>/url_pattern</url-pattern> </servlet-mapping> </servlet> 16 Java Server Pages (JSP) JSP is a server-side technology based on servlets Contains static template data and JSP elements Enables to build cross-platform database driven Web applications The tag library in JSP simplifies the task of creating dynamic Web content Saved with a .jsp extension <html> <head> <title>Hello World</title> </head> <body> Today’s date is <%= new java.util.Date() %> </body> </html> 17 Web Development Process Includes six stages: Planning – Implies the stage at which the user needs to gather requirements and define target audience Analysis – Implies the stage at which the user needs to evaluate the information and verify the correctness and consistency of information Design – Implies the stage at which the user needs to create sample layout and send the layout for approval Implementation – Implies the stage at which the user needs to establish the framework of site, create template and standard HTML pages Promotion – Implies the stage at which re-engineering and re- designing of the Web site is done Site maintenance and updating – Implies the stage at which bug fixing and improvement of site is done 14/07/2009 7 GenericServlet Class 19 HTTPServlet Class 20 Web Application Directory Structure 21 14/07/2009 8 Servlet Requests and Response 22 ServletRequest Interface TheServletRequest Interface Provides access tospecific information about the request Contains both actual request (as protocol, URL, and type) and raw request (as headers and input stream), and client specific request parameters (entered data on web form) TheServletRequest Interface methods public String getParameter(String name) public Enumeration getParameterNames() public String[] getParameterValues() public Object getAttribute(String name) public int getContentLength() public ServletInputStream getInputStream() throws IOException public String getServerName() 23 HttpServletRequest Interface HttpServletRequest Interface Extends ServletRequest Interface Add a few more methods for handling HTTP-specific request data HttpServletRequest Interface methods public Cookie[] getCookies() public String getHeader(String name) public String getMethod() public String getPathInfo() public String getAuthType() 24 14/07/2009 9 Reading Request Headers From Request getHeader() getHeaders() getHeaderNames() 25 ServletResponse Interface TheServletResponse Interface Create and manipulate a servlet’s output which is response to the client Retrieve an output stream to send data to the client, decide on the content type Define objects passed as an argument to service() method TheServletResponse Interface methods public String getContentType() public PrintWriter getWriter() throws IOException public ServletOutputStream getOutputStream() throws IOException public void setContentType(String str) 26 HttpServletResponse interface HttpServletResponseInterface Extends ServletResponse Interface Define HttpServlet objects to pass as an argument to the service() method to the client HttpServletResponseInterface methods ◦ addCookie() ◦ addHeader() ◦ containsHeader() ◦ sendError() 27 14/07/2009 10 Sending Text & Binary data getOutputStream() getWriter() print(boolean b) println(char c) 28 Response Header 29 Sending Header addHeader(): add a response header with a given name and value addDateHeader() addIntHeader() containsHeader() 30 [...]... context ◦ To pass parameters form client to servlets ◦ To setup communication Initialising servlets ◦ Container locate the servlet class ◦ Container load the servlet ◦ Create an instance of the servlet ◦ Invoke init() method to initialise the servlet 35 36 12 14/07/2009 RequestDispatcher (1) forward(): used to forward request from one servlet to another servlet 37 RequestDispatcher (2) include():... important if Servlet- 2 performs some system update (such as credit-card processing) 39 13 14/07/2009 Error Handling in Servlets(1) 40 Error Handling in Servlets Reporting Errors •public void sendError (int sc) throws IOException •public void HttpServletResponse.setStatus (int sc) Logging Errors: public void log (String msg[, Throwable t]) 41 Logging Error 42 14 14/07/2009 Error Handling in Servlets Servlet. .. form that targets Servlet- 2, which then redirects to JSP-3 With a redirect, the user's address bar will read "http://[host]/JSP-3" If the user clicks the Reload/Refresh button, only JSP-3 will be re-executed, not Servlet- 2 If you use a RequestDispatcher to forward from Servlet- 2 to JSP-3, the user's address bar will read "http://[host] /Servlet- 2" A reload/refresh will execute both Servlet- 2 and JSP-3... 31 Servlet Lyfe Cycle The life cycle is defined by: • init() – called only one by the server in the first request • service() – process the client’s request • destroy() – called after all requests have been processed or a server-specific number of seconds have passed 32 HTTP Request Processing Life Cycle 33 11 14/07/2009 Servlets and Servlet Context 34 Initialising servlets Need for initialising servlet. .. servlet to another servlet 37 RequestDispatcher (2) include(): used to include the contents of another servlet, JSP page or a HTML file to a servlet 38 RequestDispatcher vs sendRedirect 1) If you use a RequestDispatcher, the target servlet/ JSP receives the same request/response objects as the original servlet/ JSP Therefore, you can pass data between them using request.setAttribute() With a sendRedirect(),... … 57 57 19 14/07/2009 Filter config example 58 FilterMapping elements : name of the filter : pattern useed to resolve URLs to which filter applies : name of servlet whose request and response will be serviced by the filter 59 Configuring FilterChain 60 20 14/07/2009 Sample Filter 61 Securing Web Application 62 Security Concepts Need of SecuringWeb... value=session.getAttribute("name"); 52 Filter 53 Filters Components that add functionality to the request and response processing of a Web Application Intercept the requests and response that flow between a client and a Servlet/ JSP The Filter can Authorize request Request headers and mod ify data Modify response headers and data Authenticating the user, comprising files, encrypting data and converting images... security to resource with the help of the server configuration Works as a different layer from the web component which it works Advantages: Gives scope to the programmer to ignore the constraints of the programming environment Updating the mechanism does not require total change in Security model It is easily maintainable Limitation Access is provided to all or denied Access is provided by the... same authentication mechanism It can not use both form-based and basic authentication for different page 75 25 14/07/2009 Programmatic Security Authenticates users and grant access to the users Servlet either authenticates the user or verify that the user has authenticates earlier Advantages Ensue total portability Allowed password matching strategies Limitation Much harder to code . Name< /servlet- name> < ;servlet- class>ServletClass< /servlet- class> < /servlet& gt; < ;servlet- mapping> < ;servlet- name> ;Servlet Name< /servlet- name> <url-pattern>/url_pattern</url-pattern> < /servlet- mapping> < /servlet& gt; 16 Java. servlets 15 14/07/2009 6 Web.xml < ;servlet& gt; <description></description> <display-name>Display Servlet Name</display-name> < ;servlet- name> ;Servlet Name< /servlet- name> < ;servlet- class>ServletClass< /servlet- class> < /servlet& gt; < ;servlet- mapping> < ;servlet- name> ;Servlet. 14 Example of Servlets import java.io.*; import javax .servlet. *; import javax .servlet. http.*; public class Example extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse