Project Presentation on Advance Java

PROGRAMMING IN ADVANCE JAVA
(J2EE)
Created By : Vikas Goyal

Basic Concepts Of Advance Java
 JVM : Java Virtual Machine
 Assertion
 JDBC : Java Database Connectivity
 Java Servlet
 JSP : Java Server Pages

JVM : Java Virtual Machine
 Java application are typically compiled to byte code
(class file) that can run on any java virtual machine
(JVM) regardless of computer architecture.
 Before understanding what is JVM let us first know
what virtual machine is.
 A Virtual Machine is a layer of abstraction that gives
a program one simplified interface for interacting
with a variety of physical computers and their
operation system.

JVM : Java Virtual Machine
 As the name indicates, JVM is not a real hardware
machine but a software layer which resembles an
hardware platform.
 JVM converts java byte code into machine language
and execute it.
 The byte code can be executed on any platform
where there exists JVM

Diagram for JVM

Components of JVM
 Byte code verifier : It checks for unusual code.
 Class loader : It loads the java class into JVM. It also reads
byte code and creates the instance of java.lang.class
 Execution engine : It helps JVM to convert byte code into
machine code.
 Garbage collector : It is the process of automatically freeing
objects that are no longer referenced by the program.
 Security manager : It constantly monitors the code.

Assertion
 An assertion is a statement in Java that enables you to
test your assumptions about your program.
 Each assertion contains a boolean expression that you
believe will be true when the assertion executes.
 By verifying that the boolean expression is indeed true,
the assertion confirms your assumptions about the
behavior of your program, increasing your confidence
that the program is free of errors.

Why use assertions?
 Programming by contract
 Pre-conditions
 Assert precondition as requirement of client
 Post-conditions
 Assert post-condition as effect of client method

Syntax of using Assertion :
 There are two ways to use assertion.
 First way is : assert expression;
 Second way is : assert expression1 : expression2;

Simple Example of Assertion in Advance Java

JDBC : Java Database Connectivity
 JDBC provides Java applications with access to most
database systems via SQL.
 Before APIs like JDBC and ODBC, database
connectivity was tedious
With JDBC, the application programmer uses the
JDBC API
The developer never uses any proprietary APIs
• Any proprietary APIs are implemented by a JDBC
driver
• There are 4 types of JDBC Drivers

Type 1 - JDBC-ODBC Bridge
Type 2 - JDBC-Native Bridge
Type 3 - JDBC-Net Bridge
Type 4 - Direct JDBC Driver
Type 1 only runs on platforms where ODBC is available
ODBC must be configured separately
Type 2 Drivers map between a proprietary Database API and
the JDBC API
Type 3 Drivers are used with middleware products
Type 4 Drivers are written in Java
In most cases, type 4 drivers are preferred

Java Servlet
16
 Servlets are the Java technology for serving HTTP
requests.
 They are particularly used for serving HTTP requests, but
they can be used as a basis for serving other requests,
too.
 Basic servlet functionalities implemented by the basic
HTTP servlet classes have the features for accessing
HTTP request data and managing cookies and sessions.
 Typically some other technology is used for user interface
or representation part.
 Basic servlets are not that handy for representation matters.

Important To Know
17
 javax.servlet.Servlet
 Interface defining methods that all servlets implement
 javax.servlet.GenericServlet
 An abstract class for all Servlets
 javax.servlet.HttpServlet
 An abstract class for servlets serving HTTP requests.
 Most importantly, a Http servlet needs to implement the
doPost() and doGet() methods, which are called when a post or
get request is received.
 This is the basis for getting started with the implementation
http servlets.

Java Servlet Web Application
18
 Servlet development (learning) life cycle
 Development
 Defining servlet classes, methods and properties
 Deployment
 Servlet mapping to web environment
 (Deployment on Tomcat)
 Execution
 Understand its execution life cycle

“web.xml” Configuration
19
 Using the file
“web.xml” for more
specific mapping
 The file is in the
“WEB-INF” folder
 Example
 Servlet class
 HelloWorld.class
 Application context:
 http://localhost:8988/servletintro/
 Invoker class mapping
 http://localhost:8988/servletintro/servlet/HelloWorld
 Specific mapping
 http://localhost:8988/servletintro/hello
 For more mapping examples, see example “web.xml”
<servlet>
<servlet-name>HelloW</servlet-name>
<servlet-class>HelloWorld</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>HelloW</servlet-name>
<url-pattern>hello</url-pattern>
</servlet-mapping>

Servlet Example

JSP : Java Server Pages
 Four different elements are used in constructing JSPs
 Scripting Elements
 Implicit Objects
 Directives
 Actions
 JSPs run in two phases
 Translation Phase
 Execution Phase
 In translation phase JSP page is compiled into a servlet
 called JSP Page Implementation class
 In execution phase the compiled JSP is processed

 JSP Actions :
 Processed during the request processing phase.
 As opposed to JSP directives which are processed during translation
 Standard actions should be supported by J2EE compliant web servers
 Custom actions can be created using tag libraries
 The different actions are
 Include action : <jsp:include page=“inlcudedPage.jsp”>
 Forward action : <jsp:forward page=“Forwarded.html”>
Param action : <jsp:forward page=“Param2.jsp”>
<jsp:param name=“FirstName” value=“Sanjay”>
</jsp:forward>

o useBean action : <jsp:useBean id=“myName” scope=“request”
class=“java.lang.String”>
<% firstName=“Sanjay”; %>
</jsp:useBean>
 setProperty action:<jsp:setProperty name=“myBean” property=“firstName”
value=“Sanjay”/>
 getProperty action:<jsp:getProperty name=“myBean” property=“firstName” />


o plugIn action:
<jsp: plugin type=“applet” code=“MyApplet.class” codebase=“/”>
<jsp:params>
<jsp:param name=“myParam” value=“122”/>
</jsp:params>
<jsp:fallback><b>Unable to loadapplet</b></jsp:fallback>
</jsp:plugin>

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