JAVA SERVLETServer-side Programming

ADVANCED FEATURES

1

AGENDA

RequestDispacher

SendRedirect

ServletConfig

ServletContext

ServletFilter

SingleThreadedModel

Events and Listeners

Servlets & Database

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REQUESTDISPATCHER

Forward: facility of dispatching the request to another resource

Include: can also be used to include the content of another

resource

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public void forward(ServletRequest request,ServletResponse response) throws ServletException,java.io.IOException

public void include(ServletRequest request,ServletResponse response) throws ServletException,java.io.IOException

RequestDispatcher rd=request.getRequestDispatcher(“Myservlet");

rd.forward(request, response);

REQUESTDISPATCHER

4SRC: https://www.javatpoint.com/requestdispatcher-in-servlet

REQUESTDISPATCHER

public void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

response.setContentType("text/html");

PrintWriter out = response.getWriter();

String userName=request.getParameter("userName");

String password=request.getParameter(“password");

if(userName.equals(“abc") && password.equals(“xyz") {

RequestDispatcher rd=request.getRequestDispatcher(“LoginSuccessServlet");

rd.forward(request, response); }

else{

out.print(“Sorry User Name or Password Error!");

RequestDispatcher rd=request.getRequestDispatcher("/index.html");

rd.include(request, response);

}

}

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SENDREDIRECT

Method of HttpServletResponse interface

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public void sendRedirect(String URL)throws IOException;

response.sendRedirect("http://www.google.com");

SENDREDIRECT

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forward() method sendRedirect() method

It works at server side. It works at client side.

It sends the same request and

response objects to another

servlet.

It always sends a new request.

It can work within the server only. It can be used within and outsidethe server.

Request method Response method

SERVLETCONFIG

An object of ServletConfig is created by the web container for

each servlet.

This object can be used to get configuration information from

Annotation

web.xml file

Server interface/tool

Don't need to change the servlet

8ServletConfig config=getServletConfig();

SERVLETCONFIG

public String getInitParameter(String name)

public Enumeration getInitParameterNames()

public String getServletName()

public ServletContext getServletContext()

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SERVLETCONFIG

Defining init Paramters

Accessing init Parameters

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@WebServlet(urlPatterns = "/ParameterServlet",

initParams = {

@WebInitParam(name = "email", value = abc@xyz.com"),

@WebInitParam(name = "phone", value = “5555555555")})

private String email, phone;

@Override

public void init(ServletConfig config) throws ServletException {

email = config.getInitParameter("email");

phone = config.getInitParameter("phone");}

SERVLETCONFIG

Web.xml

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<web-app>

<servlet>

......

<servlet-name>ParameterServlet</servlet-name>

<servlet-class> myservlet.ParameterServlet</servlet-class>

<init-param><param-name>email</param-name>

<param-value>abc@xyz.com</param-value>

</init-param>......

</servlet>

</web-app>

SERVLETCONTEXT

Created by the web container at time of deploying the project.

Only one ServletContext object per web application.

This object can be used to get configuration information from

Annotation

web.xml file

Server interface/tool

Don't need to change the servlet

12ServletContext application=getServletContext();

SERVLETCONTEXT

public String getInitParameter(String name)

public Enumeration getInitParameterNames()

public void setAttribute(String name,Object object)

public Object getAttribute(String name)

public void removeAttribute(String name)

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SERVLETCONTEXT

Accessing init Parameters

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private String email, phone;

@Override

public void init(ServletConfig config) throws ServletException {ServletContext ctx = config.getServletContext();

email = ctx.getInitParameter("email");

phone = ctx.getInitParameter("phone"); }

SERVLETCONTEXT

Web.xml

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<web-app>

<context-param>

<param-name>email</param-name>

<param-value>abc@xyz.com</param-value>

</context-param>

<context-param>

<param-name>phone</param-name>

<param-value>555555555</param-value>

</context-param>

<servlet>

......

......

</servlet>

</web-app>

FILTER

A filter is an object that can transform the header and content

(or both) of a request or response.

Authentication Filters.

Data compression Filters.

Encryption Filters.

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FILTER

void init(FilterConfig config) throws ServletException

void destroy()

void doFilter(ServletRequest req, ServletResponse res, FilterChain

chain) throws IOException, ServletException

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FILTER

public class LoginFilter implements Filter {public void init(FilterConfig config) throws ServletException {

}

public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws java.io.IOException, ServletException {

String password=req.getParameter("password"); if(password.equals("admin")){ chain.doFilter(req, resp);//sends request to next resource } else{

out.print("username or password error!"); RequestDispatcher rd=req.getRequestDispatcher("index.html"); rd.include(req, resp); } public void destroy( ) {

}} 18

FILTER

<filter>

<filter-name>LoginFilter</filter-name>

<filter-class>LoginFilter</filter-class>

<init-param>

<param-name>test-param</param-name>

<param-value>Initialization Paramter</param-value>

</init-param>

</filter>

<filter-mapping>

<filter-name>LoginFilter</filter-name>

<url-pattern>/MyServlet</url-pattern>

</filter-mapping>

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SINGLETHREADMODEL

Marker Interface

Ensures that servlets handle only one request at a time.

you are guaranteed that no two threads will execute

concurrently in the servlet's service method.

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EVENT AND LISTENER

The servlet specification includes the capability to track key

events in your Web applications through event listeners.

Three levels of servlet events

Servlet context level

Session level

Request level

Each of these two levels has two event categories:

Lifecycle changes

Attribute changes

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EVENT AND LISTENER

ServletRequestListener

ServletRequestAttributeListener

ServletContextListener

ServletContextAttributeListener

HttpSessionListener

HttpSessionAttributeListener

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EVENT AND LISTENER

Listener that tracks the number of concurrent users

HttpSessionListener interface

void sessionCreated(HttpSessionEvent evt)

void sessionDestroyed(HttpSessionEvent evt)

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EVENT AND LISTENER

public class CountUserListener implements HttpSessionListener{

ServletContext ctx=null;

static int total=0,current=0;

public void sessionCreated(HttpSessionEvent e) {

total++;

current++;

ctx=e.getSession().getServletContext();

ctx.setAttribute("totalusers", total);

ctx.setAttribute("currentusers", current);

}

public void sessionDestroyed(HttpSessionEvent e) {

current--;

ctx.setAttribute("currentusers",current);

}

}24

EVENT AND LISTENER

public class First extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

response.setContentType("text/html");

PrintWriter out = response.getWriter();

String n=request.getParameter("username");

out.print("Welcome "+n);

HttpSession session=request.getSession();

session.setAttribute("uname",n);

ServletContext ctx=getServletContext();

int t=(Integer)ctx.getAttribute("totalusers");

int c=(Integer)ctx.getAttribute("currentusers");

out.print("<br>total users= "+t);

out.print("<br>current users= "+c);

out.print("<br><a href='logout'>logout</a>");

out.close();

}

}

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EVENT AND LISTENER

public class LogoutServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse

response)throws ServletException, IOException {

response.setContentType("text/html");PrintWriter out = response.getWriter();

HttpSession session=request.getSession(false);session.invalidate();

out.print("You are successfully logged out");

out.close();}

}26

EVENT AND LISTENER

<web-app version="2.5" >

<listener>

<listener-class>CountUserListener</listener-class>

</listener>

<servlet>

<servlet-name>First</servlet-name>

<servlet-class>First</servlet-class>

</servlet>

<servlet>

<servlet-name>LogoutServlet</servlet-name>

<servlet-class>LogoutServlet</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>First</servlet-name>

<url-pattern>/First</url-pattern>

</servlet-mapping>

<servlet-mapping>

<servlet-name>LogoutServlet</servlet-name>

<url-pattern>/logout</url-pattern>

</servlet-mapping>

</web-app>

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EVENT AND LISTENER

<form action=“First">

Name:<input type="text" name="username"><br>

Password:<input type="password" name="userpass"><br>

<input type="submit" value="login"/>

</form>

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SERVLETS - DATABASE ACCESS

PrintWriter out = response.getWriter();

try {

String driver = "com.mysql.jdbc.Driver";

String url = "jdbc:mysql://localhost:3306/students";

String username = "root";

String password = "password";

String query = "select * from mtcse";

Class.forName(driver);

Connection con = DriverManager.getConnection(url, username,

password);

Statement stmt = con.createStatement();

ResultSet rs = stmt.executeQuery(query);

out.println("<TABLE BORDER=1>");

ResultSetMetaData rsmd = rs.getMetaData();

int columnCount = rsmd.getColumnCount();

out.println("<TR>");

for (int i = 1; i <= columnCount; i++) {

out.print("<TH>" + rsmd.getColumnName(i));

}

out.println();29

while (rs.next()) {

out.println("<TR>");

for (int i = 1; i <= columnCount; i++) {

if (rsmd.getColumnType(i) == java.sql.Types.INTEGER) {

out.print("<TD>" + rs.getInt(i));

} else {

out.print("<TD>" + rs.getString(i));

}

}

out.println();

}

out.println("</TABLE>");

} catch (ClassNotFoundException cnfe) {

out.println("Error loading driver: " + cnfe);

} catch (SQLException sqle) {

out.println("Error connecting: " + sqle);

} catch (Exception ex) {

out.println("Error with input: " + ex);

} finally {

out.println("</BODY></HTML>");

out.close();

}

REFERENCES

https://docs.oracle.com/javaee/7/JEETT.pdf

https://www.javatpoint.com/servlet-tutorial

30

THANK YOU

31SRC: https://tunza.eco-generation.org/resourcesView.jsp?boardID=worldReport&viewID=13336