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Building Web Apps with Servlets
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Why web apps? Create apps every bit as dynamic, interactive, and custom tailored as native apps Avoid deployment problems Reach people world wide
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First, let’s review some basics about how the Web works
Static Web Pages
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The architecture of the Web
Head First Servlets and JSP (2nd edition), p. 3
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Typical web browser/server interaction
At the very least, what must to give your browser so that it can request a web page? A URL! Head First Servlets and JSP (2nd edition), p. 4
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Anatomy of a URL Port Path Server Protocol Resource
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So what do requests and responses actually look like anyway?
Head First Servlets and JSP (2nd edition), p. 4
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Example HTTP GET request
HTTP Method Path to resource Protocol version GET /select/selectBeerTaste.jsp HTTP/1.1 Host: User-Agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X… Accept: text/xml,application/xml,application/xhtml+xml… Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO ,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Request headers
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Text version of status code
Example HTTP response Protocol version HTTP status code Text version of status code HTTP/ OK Content-Type: text/html Content-Length: 397 Date: Wed, 19 Nov :25:40 GMT Server: Apache-Coyote/1.1 Connection: close <html> … </html> Response headers Response body
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Let’s see the request/response in a bit more detail…
Head First Servlets and JSP (2nd edition), p. 18
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Head First Servlets and JSP (2nd edition), p. 18
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Dynamic Web Pages (Web Apps)
Now, let’s talk about … Dynamic Web Pages (Web Apps)
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Typical architecture of a web app
Head First Servlets and JSP (2nd edition), p. 27
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Typical architecture of a web app
Head First Servlets and JSP (2nd edition), p. 27
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Typical architecture of a web app
Head First Servlets and JSP (2nd edition), p. 27
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Typical architecture of a web app
Head First Servlets and JSP (2nd edition), p. 27
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But how do you pass parameters?
Recall step #2… But how do you pass parameters? Head First Servlets and JSP (2nd edition), p. 27
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GET requests can embed parameters in the URL
Parameter list Head First Servlets and JSP (2nd edition), p. 14
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Limitations of GET parameters
Total characters limited (varies by server) Parameters are exposed Better not do passwords A better way to pass parameters: The HTTP POST method
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Example HTTP POST request
HTTP Method Path to resource Protocol version POST /select/selectBeerTaste.do HTTP/1.1 Host: User-Agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X… Accept: text/xml,application/xml,application/xhtml+xml… Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO ,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive color=dark&taste=malty Request headers Request body How do you make a POST request? HTML forms. More on that in a minute
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Now, here’s how you implement web apps using …
Servlets
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Servlet web app architecture
Java EE provides You write Head First Servlets and JSP (2nd edition), p. 39
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How do you create a Java EE web app? Use Eclipse
A few key steps: Create Dynamic Web project Create servlet class(es) Configure Deployment Descriptor (DD; aka web.xml) Compile, then deploy, then run Allow me to demonstrate
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Some key features of a servlet
import javax.servlet.*; import javax.servlet.http.*; import java.io.*; public class Ch1Servlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException { PrintWriter out = response.getWriter(); java.util.Date today = new java.util.Date(); out.println(“<html> “ + “<body>” + “<h1 align=center>HF\’s Chapter1 Servlet</h1>” + “<br>” + today + “</body>” + “</html>”); }
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Some key features of a DD
<?xml version=”1.0” encoding=”ISO ” ?> <web-app xmlns= xmlns:xsi=…> <servlet> <servlet-name>Chapter1 Servlet</servlet-name> <servlet-class>Ch1Servlet</servlet-class> </servlet> <servlet-mapping> <url-pattern>/Serv1</url-pattern> </servlet-mapping> </web-app> Name in DD Java class URL path
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To make sure you got it, let’s walk through another servlet request/response
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Head First Servlets and JSP (2nd edition), pp. 95–96
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Head First Servlets and JSP (2nd edition), pp. 95–96
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Head First Servlets and JSP (2nd edition), pp. 95–96
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Head First Servlets and JSP (2nd edition), pp. 95–96
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Head First Servlets and JSP (2nd edition), pp. 95–96
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Head First Servlets and JSP (2nd edition), pp. 95–96
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Summary Web architecture HTTP and HTML Web app architecture
Summary Web architecture HTTP and HTML Web app architecture Servlet web app architecture
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