J2EE Servlets
Ch. 10 (Architecture)
Ch. 12 (21 Days)
History of Interactive Web

Applets



CGI




Long download times
Code on client machines (maintenance)
Custom code to interact with web server
Security hole
Resource hog for large sites
Java Servlets



Standard, easy interface to web server
Security/authentication
Implements sessions
History (cont.)

Early use of Servlets


Simple, easy to use for web applications
MVC all implemented in one big servlet
•
•
•

Very complex
Difficult to maintain
Not scalable
Current state of Servlet use


Smaller is better.
Used only for:
•
•
•
•
Gathering and validating data input from the user
Coordinating output
Minimal business logic
Web page forwarding
Servlet Features
 Tailored
to interact with Web Server
 Server and platform independent
 Efficient and scalable
 Container provides additional functionality
(i.e., authentication, cookies, etc.)
Interacting with HTML Forms
– Request information from web
server
 Get

Simple
http://www.byui.edu/j2ee?Name=Fred+&tel=3565132
 Post



– Send data to the server
Submit button, etc.
Data is sent in body of message
Safer than Get
HTML Forms (Cont.)
 Put
– Place a file on the server
 Delete
– Remove a web page from server
Servlet Class Diagram
Class Diagram
Servlet Life Cycle
Class Diagram
START
init()
doGet(),
doPost, …
State: Resident
destroy()
END
Processing
Request
Servlet Sequence Diagram
Fig. 12-15
Model 1 - Servlets only
Model/View/Control
submit
Servlet
doGet/doPost
webpage
WebServer
Generate
HTML
Data
Data
base
Servlets in the Enterprise
submit
View/Control
doGet/doPost
Model
Servlet
Input
Control
WebServer
webpage
Output
Performance
and
Flexibility Issues
Data
EJB
Entity
Bean
Example Servlet
publc class HtmlPage extends HttpServlet
{
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException
{
String name = request.getParameter(“name”);
String telephone = request.getParameter(“tel”);
response.setContentType(“text/html”);
Get value of form parameters
…. Business logic ….
PrintWriter out = response.getWriter():
out.println(“<HTML>”);
out.println(“<HEAD><TITLE>First Servlet</TITLE></HEAD>”);
out.println(“<BODY>”);
out.println(“<H1>Hello “ + name + “, Telephone “ + telephone + “</H1>”);
out.println(“</BODY>”);
out.println(“</HTML>”);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws IOException
{
doGet(request, response);
}
}
Sent output to web
browser
Model 2 Architecture
submit
View
doGet/doPost
Model
Business
Data
Access
Objecs
Servlet
input
<<forward>>
WebServer
Control
Methods
<<SessionEJB>>
Data
<<EntityEJB>>
webpage
JSP
page
output
Web Development Life Cycle
Model 2 Architecture
Servlet
Get request
Parameters
Determine
and call
business
function
JSP
Determine
next view
Build view
Web Development Life Cycle
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String username = request.getParameter("username");
String password = request.getParameter("password");
1. Get request parameters
try {
InitialContext context = new InitialContext();
BusinessRulesRemote businessRules =
(BusinessRulesRemote) context.lookup(BusinessRules.REMOTE_JNDI_NAME);
Long personId = businessRules.login(username,password);
} catch (Exception e) {
e.printStackTrace();
}
2.Call business
function
HttpSession session = request.getSession();
session.setAttribute("personid", personId);
RequestDispatcher dispatcher = request.getRequestDispatcher("index.jsp");
dispatcher.forward(request, response);
}
3. Determine next view
Web Development Life Cycle
JSP page
<div id="login">
<span class='highlight'>Welcome to Home Town Bank!</span>
<br>
<a id='logout' href="">Logout</a>
</div>
4.Build next
view
How to use HTTPServlet
HttpServlet
doGet(request HttpServletRequest , response:HttpServletResponse)
doPost(request HttpServletRequest, response:HttpServletResponse)
doPut(request HttpServletRequest , response:HttpServletResponse)
doDelete(request HttpServletRequest , response:HttpServletResponse)
HttpServletRequest
Contains Request Info (Input)
HttpServletResponse
Handles Response (Output)
RequestResponse Interface
Forwarding a Response
RequestResponse Interface
Including other Web Components
Deployment of Servlets
 All
Servlet files zipped together into a web
archive (“war”) file
 Requires
specific directory structure
 Deployment
Descriptor (WSDL)
Deployment Descriptor
<?xml version=“1.0” encoding=“UTF-8:?>
<!DOCTYPE web-app PUBLIC ‘-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN’
‘http://java.sun.com/dtd/web-app_2_3.dtd’>
<web-app>
<display-name>A Simple Application</display-name>
<servlet>
<servlet-name>Verify Data</servlet-name>
<servlet-class>VerifyData</servlet-class>
<init-param>
<param-name>maxValue</param-name>
<param-value>25</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>Verify Data</servlet-name>
<url-pattern>/verifydata</url-pattern>
</servlet-mapping>
<session-config>
<session-timeout>30</session-timeout>
</session-config>
<error-page>
<error-code>404</error-code>
<location>/error404.html</location>
</error-page>
</web-app>
Customizing Deployment
 Define

initialization parameters
Context parameters
• Apply to entire web application

Servlet parameters
• Apply to a specific servlet
Deployment Descriptor
<?xml version=“1.0” encoding=“UTF-8:?>
<!DOCTYPE web-app PUBLIC ‘-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN’
‘http://java.sun.com/dtd/web-app_2_3.dtd’>
<web-app>
<display-name>A Simple Application</display-name>
<context-param>
Context
<param-name>location</param-name>
<param-value>BYU-Idaho</param-value>
Intialization
<description>Site Location</description>
Parameter
</context-param>
<servlet>
<servlet-name>Verify Data</servlet-name>
<servlet-class>VerifyData</servlet-class>
<init-param>
Servlet
<param-name>maxValue</param-name>
Intialization
<param-value>25</param-value>
Parameter
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>Verify Data</servlet-name>
<url-pattern>/verifydata</url-pattern>
</servlet-mapping>
<session-config>
<session-timeout>30</session-timeout>
</session-config>
<error-page>
<error-code>404</error-code>
<location>/error404.html</location>
</error-page>
</web-app>
Retrieving Init. Parameters
public void init() throws ServletException
{
super.init();
ServletContext context = this.getServletContext();
String location = context.getInitParameter(“location");
if (maxValue == null)
{
int maxValue = Integer.parseInt(this.getInitParameter(“maxValue");
}
…
…
}
Handling Errors
 HTTP


Error Codes
Http Status code – set error code
Error page – set default error page
 Send
Redirect – redirect to another page
Exceptions – catch and handle all
servlet exceptions
 Servlet
Set HTTP Status Code

Sets the error status code on default error page
HttpServletResponse
public void sendError(int statusCode)
public void sendError(int statusCode, String msg))
….
public void sendRedirect(String url);
Import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
publc class HtmlPage extends HttpServlet
{
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException
{
String name = request.getParameter(“name”);
if (name.length() < 1)
response.sendError(9001, “Invalid name”);
}
}
Default HTTP Error Page
Deployment Descriptor
<?xml version=“1.0” encoding=“UTF-8:?>
<<!DOCTYPE web-app PUBLIC ‘-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN’
‘http://java.sun.com/dtd/web-app_2_3.dtd’>
<web-app>
<display-name>A Simple Application</display-name>
<servlet>
<servlet-name>Verify data</servlet-name>
<servlet-class>VerifyData</servlet-class>
<init-param>
<param-name>maxValue</param-name>
<param-value>25</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>verifyData</servlet-name>
<url-pattern>/verifyData</url-pattern>
</servlet-mapping>
<session-config>
<session-timeout>30</session-timeout>
</session-config>
<error-page>
<error-code>9001</error-code>
<location>/error9001.html</location>
</error-page>
Define output error
page for error code
Send Redirect
 Redirect
to another page to handle error
HttpServletResponse
public void sendError(int statusCode)
public void sendError(int statusCode, String msg))
….
public void sendRedirect(String url);
Import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
publc class HtmlPage extends HttpServlet
{
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException
{
String name = request.getParameter(“name”);
if (name.length() < 1)
response.sendRedirect(“/Servlets/invalidNamePage”);
}
}
Servlet Session Management

Hidden fields in form



Visible to client in source (not secure)
Limited amount of data
URL rewritting
http://www.byui.edu/j2ee?sessionid=9982345

Cookies



Store on client browser
May be disabled by some users
Server side session object

Session info stored on Server
• Unlimited amount of space
• More secure

Automatic management
Creating Cookies
 Implement

transactions with Cookies
Store state data in Cookie
HttpServletResponse
…
public void addCookie(Cookie c)
public Cookie[ ] getCookies()
….
Cookie
public void setValue(String value)
public String getName()
public String getValue()
….
Creating a Cookie
Import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
publc class HtmlPage extends HttpServlet
{
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException
{
try
{
Cookie cookie = new Cookie(“userAddress”, null);
String url = this.getRequextURI();
cookie.addValue(url);
response.addCookie(cookie);
double quantity = Double.parseDouble(request.getParameter(“quantity”));
double totalQuantity += (Double) session.getAttribute(“totalQuantity”);
}
catch (RemoteException remex)
{
response.sendError(response.SC_INTERNAL_SERVER_ERROR);
}
}
}
Retrieving a Cookie
publc class HtmlPage extends HttpServlet
{
String userUrl = new UniqueID();
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException
{
try
{
Cookie cookie = null;
Cookie[] cookies = response.getCookies();
if (cookies != null)
{
for (int i=0; i < cookies.length; i++)
{
cookie = cookies[i];
if (cookie.getName().equals(“userAddress”))
{
String urlAddress = cookie.getValue();
break;
}
}
}
}
catch (RemoteException remex)
{
response.sendError(response.SC_INTERNAL_SERVER_ERROR);
}
}
Sessions
 Implement

transactions with a HttpSession
Retains state of data between page request
HttpSession
HttpServletRequest
…
public HttpSession getSession()
….
public long getId()
public long getLastAccessedTime()
public long getCreationTime()
public long getMaxInactiveInterval()
public Object getAttribute()
public boolean isNew()
….
Getting a Session
Import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
publc class HtmlPage extends HttpServlet
{
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException
{
try
{
HttpSession session = request.getSession();
if (session.isNew())
{
Long personId = (Long) session.getAttribute(“personId”);
}
double quantity = Double.parseDouble(request.getParameter(“quantity”));
session.setAttribute(“quantity”);
}
catch (RemoteException remex)
{
response.sendError(response.SC_INTERNAL_SERVER_ERROR);
}
}
}
Filter Servlets
 Acts
as preprocessor to request/response
for target servlet
…HttpPage
Authenticate
Filter
Servlet
PageHits
Filter
Servlet
HttpPage
Servlet
…VerifyData
VerifyData
Servlet
Filter Servlet
Import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
publc class PageHits extends HttpServlet implements Filter
{
private FilterConfig filterConfig = null;
Must implement
Filter Interface
public void init(FilterConfig filterConfig) throws ServletException
{
this.filterConfig = filterConfig;
}
public void destroy(
{
this.filterConfig = null;
}
Must override init.
method
Must override destroy
method
Filter Servlet (cont.)
public void doFilter(HttpServletRequest request, HttpServletResponse response,
Must override
FilterChain chain) throws IOException, ServletException
doFilter method
{
if (filterConfig == null)
return;
synchronized (this)
{
Integer counter =(Integer) filterConfig.getServletContext().getAttribute("Counter");
if (counter == null)
counter = new Integer(0);
counter = new Integer(counter.intValue()+1);
filterConfig.getServletContext().log("Number of hits is " + counter);
filterConfig.getServletContext().setAttribute("Counter", counter);
}
chain.doFilter(req, resp)
}
Modify Deployment Descriptor
<?xml version=“1.0” encoding=“UTF-8:?>
<<!DOCTYPE web-app PUBLIC ‘-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN’
‘http://java.sun.com/dtd/web-app_2_3.dtd’>
<web-app>
<display-name>A Simple Application</display-name>
<servlet>
<servlet-name>VerifyData</servlet-name>
<servlet-class>VerifyData</servlet-class>
<init-param>
<param-name>maxValue</param-name>
<param-value>25</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>Verify Data</servlet-name>
<url-pattern>/verifyData/</url-pattern>
</servlet-mapping>
<filter>
<filter-name>Page Hits</filter-name>
<display-name>Page Hits</display-name>
<description>Count page hits<description>
<filter-class>PageHits</filter-class>
</filter>
<filter-mapping>
<filter-name>PageHits</filter-name>
<servlet-name>VerifyData</servlet-name>
</filter-mapping>
</web-app>
Listener Servlet

Servlet is automatically executed when
some external event occurs
HTTPSessionActivationListener
Session is activated/passivated
HTTPSessionAttributeListener
Session attribute is added/removed
HTTPSessionListener
Session attribute is created/destroyed
HTTPSessionContextAttributeListener Servlet contextattribute is
added/removed
HTTPSessionContextListener
Servlet context changes
Create Listener Servlet
Import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
publc class Listener extends HttpServlet implements ServletContextListener
{
private ServletContext context = null;
Must implement
Listner Interface
public void contextIntialized(ServletContextEvent event)
{
context = event.getServerContext();
Integer counter = new Integer(0);
context.setAttribute(“Counter”, counter);
context.log(“Created Counter”);
Must override
contextInitialized
method
}
public void contextDestroyed(ServletContextEvent event)
{
event.getServletContext().removeAttribute(“Counter”);
}
}
Must override
contextInitialized
method
Modify Deployment Descriptor
<?xml version=“1.0” encoding=“UTF-8:?>
<<!DOCTYPE web-app PUBLIC ‘-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN’
‘http://java.sun.com/dtd/web-app_2_3.dtd’>
<web-app>
<display-name>A Simple Application</display-name>
<servlet>
<servlet-name>Verify data</servlet-name>
<servlet-class>VerifyData</servlet-class>
<init-param>
<param-name>maxValue</param-name>
<param-value>25</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>Verify Data</servlet-name>
<url-pattern>/verifyData/</url-pattern>
</servlet-mapping>
<filter>
<filter-name>Page Hits</filter-name>
<display-name>Page Hits</display-name>
<description>Count page hitsdescription>
<filter-class>PageHits</filter-class>
</filter>
<filter-mapping>
<filter-name>PageHits</filter-name>
<servlet-name>Verify data</servlet-name>
</filter-mapping>
<listener>
< listener-class>Listener</ listener -class>
</listener>
</web-app>
Modify Filter Servlet
public void doFilter(HttpServletRequest request, HttpServletResponse response,
FilterChain chain) throws IOException, ServletException
{
if (filterConfig == null)
return;
synchronized (this)
{
Integer counter =( Integer) filterConfig.getServletContext().getAttribute(“Counter”);
if (counter = null)
No longer needed
counter = new Integer(1);
counter = new Integer(counter.intValue()+1);
filterConfig.getServletContext().log(“Number of hits is “ + counter);
filterConfig.getServletContext().setAttribute(“Counter”, counter); counter);
}
chain.doFilter(request, response);
}
}
Modified Filter Servlet
public void doFilter(HttpServletRequest request, HttpServletResponse response,
FilterChain chain) throws IOException, ServletException
{
if (filterConfig == null)
return;
synchronized (this)
{
Integer counter =( Integer) filterConfig.getServletContext().getAttribute(“Counter”);
counter = new Integer(counter.intValue()+1);
filterConfig.getServletContext().log(“Number of hits is “ + counter);
filterConfig.getServletContext().setAttribute(“Counter”, counter); counter);
}
chain.doFilter(request, response);
}
}