Advanced Java, J2EE : Day 2

Day 2

Maven Project
JDBC with MYSQL application
Convert the application to web application using servlet, JSP, Session Handling

Maven

→ Dependency Management, including transitive dependency

→ Consistency across all team members(No need to manually download from different websites. Maven will do that for us)

→ Standard structure for Application for different IDE

→ Automation for compile, test, build, and bundle via goals

Java provides interfaces and database vendors provide the implementation class

Steps to connect to MySQL

Load Vendor class to JVM(Class.forName(‘oracle.jdbc.OracleDriver’))
Establish Database Connection

java.sql.Connection con = DriverManager.getConnection(URL, UserName, Password)
Send SQL statements(statement, Callable Statement, Prepared statement)
ResultSet(Cursor to iterate data)
Close the connection → Finally Block

Web Application Development

Static Content
Servlet → Server Side Java Code
JSP → Static + Dynamic
Filter → Interceptor design pattern for security, logging
Listener → Activity based on events

Engine/Container/helper_application : Tomcat, Jetty, JRocket.

Servlet Containers have thread pools

Servlets

threadLocal APIs and threadpools

ArrayBlocking Queue

Servlets!

web.xml → Deployment Descriptor

<servlet>
	<servlet-name>One</servlet-name>
	<servlet-class><pkg.RegisterServlet/servlet-clas>
</servlet>

<servlet-mapping>
	<servlet-name>One</servlet-name>
	<url-pattern>/register</url-pattern>
</servlet-mapping>

From Servlet API 2.5 onwards we use Annotation

res.sendRedirect is used for client Side Redirection with 302 header

package com.cisco.prj.web;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.cisco.prj.dao.DaoException;
import com.cisco.prj.dao.ProductDao;
import com.cisco.prj.dao.ProductDaoJdbcImpl;
import com.cisco.prj.entity.Product;
 
@WebServlet("/products")
public class ProductServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
 
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		response.setContentType("text/html"); // MIME type
		PrintWriter out = response.getWriter(); // opens character stream to browser
		//ServletOutputStream out = response.getOutputStream(); // byte stream
		out.print("<html>");
		out.print("<body>");
		out.print("<h1>Products</h1>");
		out.print("<table border=\"1\">");
		out.print("<tr><th>Name</th><th>Price</th><th>Quantity</th></tr>");
		ProductDao productDao = new ProductDaoJdbcImpl();
		
		try {
			List<Product> list = productDao.getProducts();
			for(Product p : list) {
				out.print("<tr>");
					out.print("<td>" + p.getName() + "</td>");
					out.print("<td>" + p.getPrice() + "</td>");
					out.print("<td>" + p.getQuantity() + "</td>");
				out.print("</tr>");
			}
		} catch (DaoException e) {
			e.printStackTrace();
			response.sendRedirect("error.jsp?msg=" + e.getMessage());
		}
		
		out.print("</table></body></html>");
		
		
		
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		ProductDao productDao = new ProductDaoJdbcImpl();
		Product p = new Product();
		p.setName(request.getParameter("name"));
		p.setPrice(Double.parseDouble(request.getParameter("price")));
		p.setQuantity(Integer.parseInt(request.getParameter("quantity")));
		
		try {
			productDao.addProduct(p);
			response.sendRedirect("index.html");
		} catch (DaoException e) {
			response.sendRedirect("error.jsp?msg=" + e.getMessage());
		}
	}

}

ResourceBundle res = ResourceBundle.getBundle("config"); Used to access Resource properties File

Class.forName(DRIVER);

JSP Pages and JSTL

Internally, It is servlet too.

Can have static and dynamic content

Translation Phase → Change JSP to Servlet [JSPc : JSP → Java]

Request Processing phase

${p.id} is same as p.getId() in JSTL

Servlet, JSP, Client Side Redirection and Server Side Redirection

Session Tracking ==> Http Protocol is a stateless protocol [ request and response objects are short-lived; created and destroyed for every client request] Session Tracking is the ability to server side code to keep track of conversational state of client ==> HttpSession API

Filter → Protected resource

→ Based on Interceptor pattern. Usecase could be to check if user has logged In

Req/Res → once per HTTP

Session → Once per user, destroyed on logout

Servlet Context → Once per application, shared by all users of the application ==> Chatting Application ==> Bid application

Used @WebFilter annotation and Implements FilterClass. Also implements doFilter(ServletRequest request, ServletResponse response,FilterChain chain) method

chain.doFilter(request, response); Passed the request and response down the FilterChain chain

package com.cisco.prj.web;

import java.io.IOException;

import javax.servlet.DispatcherType;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

 
@WebFilter(urlPatterns = "*.jsp",dispatcherTypes = {
		DispatcherType.REQUEST, 
		DispatcherType.FORWARD
})
public class SecuirtyFilter implements Filter {
 
    public SecuirtyFilter() {
    }

	public void destroy() {
	}

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		HttpServletRequest req = (HttpServletRequest) request;
		HttpServletResponse res = (HttpServletResponse) response;
		HttpSession ses = req.getSession(false);
		String uri = req.getRequestURI();
		System.out.println(uri);
		if( (ses != null && ses.getAttribute("email") != null) || uri.endsWith("login.jsp")) {
			chain.doFilter(request, response);
		} else {
			res.sendRedirect("login.jsp");
		}
		
	}

	public void init(FilterConfig fConfig) throws ServletException {
	}

}

Listeners

→ Gets invoked based on events happening within servlet engine

ServletContxextListener

ContextInitialized(), contextDestroyed()
HttpSessionListener

SessionCreated(), SessionDestroyed()
HttpSessionAttributeListener

package com.cisco.prj.web;

import java.util.HashMap;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

@WebListener
public class ContextLoaderListener implements ServletContextListener {

    public ContextLoaderListener() {
    }

    public void contextDestroyed(ServletContextEvent sce)  { 
    }

    public void contextInitialized(ServletContextEvent sce)  { 
    	System.out.println("Context created!!!");
    	// initialize users and place them in ServletContext
    	HashMap<String, String> users = new HashMap<String, String>();
    	users.put("gavin@apache.com", "secret123");
    	users.put("tim@msn.com", "secret123");
    	users.put("roger@cisco.com", "secret123");
    	
    	sce.getServletContext().setAttribute("users", users);
    }
	
}