What is J2EE

1
What is J2EE?

• J2EE (Java 2 Platform Enterprise Edition) is a
  combination of tools and java technologies
  available to simplify application development and
  deployment on the Internet.
• Technologies include Servlets, JSP(s), Enterprise
  Java Beans and JDBC to name a few.
• Tools include the JDK and Forte for Java

2
What are Java Servlets?

• Servlets are Java technology's replacement for
  CGI programming. They are java programs that run
  on a web server or J2EE container and provide
  dynamic web content.
• Commonly used to extend the functionality of a
  web server.
• Built upon a request-response model (doGet,doPost
  methods)
• Access to Java API(s) bundled with JDK such as
  JDBC.

3
Advantages of Servlets over CGI

• Efficient/Scalable JVM is loaded once and each
  HTTP request is handled by a lightweight java
  thread. CGI executes a heavyweight OS process for
  each user request. The overhead of this OS
  process degrades performance and impacts
  scalability.
• Powerful simplified session tracking (session
  API provides support for getting track of state
  using cookies, URL rewriting and hidden form
  fields) and data sharing that allows easy
  implementation of things like connection pooling.
• Portable runs on any web server with servlet
  support. (All of them)

4
Client Server Architecture
5
HttpServlet Class

• All Servlet classes extend the HttpServlet
  abstract class
• HttpServlet simplies writing HTTP servlets by
  providing a framework for handling the HTTP
  protocol.
• Since HttpServlet is abstract, you must extend it
  and implement at least one of the methods
  (doGet,doPost)
• Your Servlet class is declared as public so the
  web server or J2EE container can access it.

6
Typical Servlet Class

• import javax.servlet. // contains generic
  (protocol-independent) servlet classes
• import javax.servlet.http. // contains HTTP
  servlet classes
• public class TypicalServletClass extends
  HttpServlet
• public void init() throws ServletException
• public void doPost (HttpServletRequest request,
  HttpServletResponse response)
• throws ServletException,
  IOException
• public void doGet (HttpServletRequest request,
  HttpServletResponse response)
• throws ServletException,
  IOException
• public void destroy()

7
Life of a Servlet

• Life cycle is controlled by the web server or
  container in which the servlet is deployed.
• (1) If instance of servlet class does not exist
• Loads the servlet class
• Creates an instance of the servlet class
• Initializes the servlet instance by calling the
  init() method.

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Life of a Servlet (Cont)

• (2) Invokes a service method (doGet(), doPost())
  and passing in a request and response object.
• (3) If the servlet needs to be garbage collected
  (removed from memory), then the destroy() method
  is called by the web server/J2EE container
  (finally)

9
doGet vs. doPost Method

• doGet is called in response to an HTTP GET
  request.
• A GET request is a request to get a resource from
  the server.
• This is the case of a browser requesting a web
  page.
• It also happens with HTML Forms that specify the
  METHOD"GET" in the FORM tag.
• doPost is called in response to an HTTP POST
  request.
• A POST request is a request to post or send form
  data to a resource on the server.
• Both methods are called by the default
  (superclass) implementation of service in the
  HttpServlet base class.
• You override one or both to perform your
  servlet's actions.

10
So Which One do I implement?

• doGet has some limitations in the amount of data
  that can be passed as parameters
• doGet data is sent as a part of the URL and thus
  sensative data may be exposed
• Most implement doPost and and doGet placing the
  code that will perform some action in doPost and
  calling doPost from doGet passing in the request
  and response objects.
• public void doGet(HttpServletRequest request,
  HttpServletResponse response) throws
  ServletException, IOException
• doPost(request, response)

11
Simple Servlet Example

• import java.io. // for system input and output
• import javax.servlet. // contains generic
  (protocol-independent) servlet classes
• import javax.servlet.http. // contains HTTP
  servlet classes
• public class SimpleServletExample extends
  HttpServlet
• public void doPost(HttpServletRequest request,
  HttpServletResponse response) throws
  ServletException, IOException
• response.setContentType("text/html")
• PrintWriter out response.getWriter()
• out.println("ltHTMLgtltHEADgtltTITLEgtWelcome to
  Bradshaw Marinalt/TITLEgtlt/HEADgt")
• out.println("ltBODYgtltH1gtWelcome to Bradshaw
  Marinalt/H1gt ltH3gtCurrent Time ")
• out.println(new java.util.Date())
• out.println("lt/H3gtlt/BODYgtlt/HTMLgt")

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How to call Servlet from HTML

• ltHTMLgt
• ltHEADgt
• ltTITLEgtCall a Simple Servletlt/TITLEgt
• lt/HEADgt
• ltBODYgt
• ltH1gtCall a Simple Servlet that Generates the
  Welcome Pagelt/H1gt
• ltFORM name"form1" method"post"
  action"SimpleServletExample"gt
• ltpgt
• ltinput type"submit" valueCall Servlet"gt
• lt/pgt
• lt/FORMgt
• lt/BODYgt
• lt/HTMLgt

13
What are Java Server Pages

• Java Server Pages (JSP) is a technology that
  allows you to mix static and dynamic HTML
  content. (very similar to ASP)
• Web content rendered by CGI programs are mostly
  static. Even with servlets you generate the
  entire web page with your java code. JSPs allow
  the two to be separated. Presentation is standard
  HTML and java is written within special tags (lt,
  gt)

14
Advantages of Java Server Pages

• vs. Active Server Pages (ASP). ASP is a similar
  technology from Microsoft. The advantages of JSP
  are twofold. First, the dynamic part is written
  in Java, not Visual Basic or other MS-specific
  language, so it is more powerful and easier to
  use. Second, it is portable to other operating
  systems and non-Microsoft Web servers.
• vs. Pure Servlets. JSP doesn't give you anything
  that you couldn't in principle do with a servlet.
  But it is more efficient to write the
  presentation in HTML than to have many println
  statements that generate the HTML. You can
  separate the tasks among different people.

15
Advantages of Java Server Pages

• vs. Server-Side Includes (SSI). SSI is a
  widely-supported technology for including
  externally-defined pieces into a static Web page.
  JSP is better because it lets you use servlets
  instead of a separate program to generate that
  dynamic part. SSI is only intended for simple
  inclusions, not complex tasks that use form data
  and make database connections.
• vs. JavaScript. JavaScript can generate HTML
  dynamically on the client. This is a useful
  capability, but only handles situations where the
  dynamic information is based on the client's
  environment. With the exception of cookies, HTTP
  and form submission data is not available to
  JavaScript. And, since it runs on the client,
  JavaScript can't access server-side resources
  like databases.

16
Simple JSP Example

• lt_at_ page import"java.util." gt
• ltHTMLgt
• ltHEADgtltTITLEgtWelcome to Bradshaw
  Marinalt/TITLEgtlt/HEADgt
• ltBODYgt
• ltH1gtWelcome to Bradshaw Marinalt/H1gt
• ltH3gtCurrent Time
• ltnew java.util.Date()gt
• lt/H3gt
• lt/BODYgt
• lt/HTMLgt

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Deploying Servlets and JSP(s)

• Web Servers
• Microsoft IIS servlet/JSP plugin
• Oracle 9ias built in servlet/JSP support
• Weblogic built in servlet/JSP support
• J2EE Lightweight containers for Java
• Tomcat - built in servlet/JSP support
• Oracles OC4J built in servlet/JSP support

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Additional Resources

• http//java.sun.com/
• http//java.sun.com/products/servlet/index.html
• http//java.sun.com/products/jsp/
• http//jakarta.apache.org/tomcat/

19
Demos

• SimpleServletExample display Welcome screen
  with HTML and make a call to the java.util
  package to get the current date and time.
• SimpleJSP.jsp - display Welcome screen with
  HTML and make a call to the java.util package to
  get the current date and time.
• OracleQueryServlet displays a list of employees
  from a specific department (demonstrates both get
  and post requests)
• SimpleOracleQueryJSP1.jsp - execute query using
  statement class.
• SimpleOracleQueryJSP2.jsp - execute query using
  preparedStatement class and bind variables.
• CallSPSample.jsp - execute a stored procedure
  using the callableStatement class and bind
  variables.