Java Servlet Presentation
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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);
}
}
