Daily Archives: July 3, 2013

Spring Book – Chapter 1 – Introduction

Over the last few years, Spring has grown substantially, surpassing many other frameworks. Spring enables you to concentrate on writing less Spring-Framework-related code and more application code, which is vital in the fast-changing and cost-sensitive world of enterprise applications. Since its initial release in 2004, Spring has reinvented itself multiple times and become prominent in the industry as a strong force in the framework market. This has not only made the Spring Framework renowned, but it has also put healthy pressure or rather competition on well-known industry specifications (Java EE) and the application-server market. In the Java world, this is a very exciting time and a very important turning point.

In this chapter, I introduce Spring Framework as a whole (If I could, I would compel you to use it). Before explaining the nitty-gritty, I give you reasons to choose Spring for your application. Then I explain the Spring framework architecture and its features and, more important, introduce you to the main modules on which Spring Framework is based.

Why Spring?

Spring provides an extensive, portable, open source-application-development framework for Enterprise Java. Starting with Spring, you can build whatever you want: reservations system, banking systems, social networks, and more. Spring expands to meet your needs; you can integrate various security models, databases, web services, mobile clients, messaging systems, and so on that are required in today’s agile enterprise applications. Another key advantage is that Spring fits directly into your current infrastructure, because Spring uses the same Plain Old Java Objects (POJOs) you use every day. Once you start creating applications with Spring, you can deploy it everywhere in the certainty that it will thrive and adapt to the environment with ease.

If you need your application to be better, newer, and speedier, Spring is the right alternative for development. Surveys suggest that more and more Java developers around the world are moving toward Spring. For instance, recent analysis from Evans Data (“Spring Usage Study,” Evans Data Corporation, September 2011) analyzes the ubiquity achieved by Spring as summarized below:

  • Spring is the framework of choice among knowledgeable Java developers.
  • Spring developers report productivity and speed of deployment as the top reasons for using it: 70 percent of Spring users report at least a 50 percent productivity gain by using it, and 73 percent report that the framework allows them to deliver projects twice as fast.
  • It is estimated that more than two thirds of Java developers today are either using Spring or plan to do so within the next two years.
  • More than half of all existing Spring users expect to considerably increase their use of this framework over the next few years.
  • Spring users are more cloud ready and it is considered that heavy Spring adopters are more likely to have already deployed their applications to the cloud.
  • More than half of all existing Spring developers report that they plan to move their Java applications to a lightweight server, such as Apache Tomcat, within one year. ( Get more information from http://www.vmware.com/company/news/releases/vmw-spring-momentum-3-14-12.html )

Shared feedback from developers around the world highlights the following advantages of Spring Framework:

  • Easier to understand. Not rocket science.
  • If you have any issues with the framework code, you can just open the source code and with minimal effort understand it very easily.
  • Makes users highly productive, shortens development time.
  • For junior developers, it’s an excellent learning tool because so many live, proven Java pattern examples can be seen throughout the framework code.
  • Enables developers to cut out tons of redundant code, reducing boilerplate code in their applications. Programmatic catching of exceptions and cleaning up of resources, etc., are things of the past.
  • Spring’s ability to wire objects at runtime is incredible. Injection of right type-safe objects wherever needed is transparently handled by the Spring container.
  • A la carte framework—Plug-in what you want and use it.

What Is Spring Framework?

Spring Framework is built on well-defined goals and a coherent philosophy. Its main aim is to make Java EE development easier. This section explains Spring Framework’s main goals and its role in the development of enterprise applications.

Goal

Spring’s main aim, according to Rod Johnson (see sidebar) is to make Java EE easier to use and promote good programming practice. Even though POJO-based programming model is practiced in many enterprise applications, Spring Framework takes this concept into a different level by incorporating this model into it and making it applicable in a wide range of environments available. Due to this style of programming model, the framework keeps itself open to take advantages provided by the environment it works on without losing portability in the process.

Rather than Spring writing its own bit of code for common functionalities like logging, connection pools, transaction coordinators etc., it allows the developers to appropriately plug in the various packages available as open-source projects (For example, Commons Logging package can be used for all common logging purposes, Commons DBCP package can be used for connection pooling etc.) into the framework with mere configuration and with ease. By doing so it allows using the best package available in the open-source world and also keeps it open for future change as the case may be. All of this Spring does by keeping in mind that it doesn’t gets itself locked to any platform-specific or non-standard technology making it one of reason to use the framework in any enterprise application development.

Spring over the period has grown into a mature framework transforming itself into a one-stop shop capable of handling most of the infrastructural concerns which exists in a typical modern enterprise application. Applications are there because it has to support a business requirement. Spring provides applications with the capability of taking care of your core business objects easily and also allows changing it with minimal impact on the application as a whole according to changing business scenarios.

Rod Johnson is an enterprise Java architect specializing in scalable web applications. He has worked with both Java and JEE since their release and is also a core member of JSR 154 Expert Group entrusted with defining the Servlet 2.4 specification. He started developing frameworks for web application in 2000 while working as independent consultant. The Spring project was started by him in 2002, and it first official release was in March 2004. Johnson released this framework with the publication of his book Expert One-on-One Java EE Design and Development (Wrox Press, 2002).

Spring Framework’s Role in Enterprise Applications

Spring Framework includes core support for:

  • Application configuration
  • Enterprise integration
  • Data access
  • Testing
  • Web application-development support
  • Enterprise application-development support

Application Configuration

A typical application comprises various components working together to carry out a particular application-use case. Spring helps you build this configuration with ease. With Spring, components constituting a use case don’t worry about one another and at any point they can be swapped to keep up with the business change (agility).

Enterprise Integration

An enterprise application doesn’t work in isolation. It requires various enterprise services and resources such as security, messaging, caching, transactions, etc., to constitute an end-to-end application to meet real-life application needs. With ease and agility, Spring does this by keeping your application code simple and both unit and integration testable. It can be easily plugged into any standard Java EE application server and also is capable of stand-alone usage.

Data Access

An enterprise application accesses data stored in a relational database to carry out various business functions and to enforce various business validations. Spring makes data access easy and effective. It supports all major data-access technologies, such as Hibernate, JPA, JDBC, etc.; manages these resources transparently from the developer; and also offers tons of APIs, which enables developers to concentrate more on the core business coding and thereby increase productivity.

Testing

Unit and integration testing is essential for any enterprise application. It helps with decompiling objects from the environment where it resides and makes it easier to test the application in isolation from its actual deployment environment. More important, it helps in system/integration testing to see that all the components constituting an enterprise application work properly. This testing can be done in the actual environment as well as in isolation from the actual environment, which is a big plus compared to other framework platforms.

Web Application-Development Support

Spring includes a powerful and highly configurable Model-View-Controller web framework called Spring MVC. Even though very much similar to Apache Struts, it can never be said as derived from it. Frankly saying no copyright infringement spotted.  Now to look into the similarities, Struts Action class is similar to Spring MVC Controller class and this object is multi-threaded in nature will a single instance being used for servicing all the clients.  Spring MVC has some significant advantages over Struts, however—it has a powerful navigation rule framework, Spring Web Flow, which equals its powerful web framework for application development. Even though Spring has its own implementation for a web framework, it has kept its main goal of seamlessly integrating with other famous web frameworks, such as Struts and Java Server Faces (JSF).

Enterprise Application-Development Support

Spring’s core strength lies in its ability to integrate with common and most required services in enterprise applications. It has modules for creating and maintaining web services, scheduling jobs, integrating with messaging services, and so on. This modular coding support ensures good manageability for applications.

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Spring Book – Part 1 – Overview

Spring Framework is a Java platform that provides all-inclusive infrastructure support for developing JEE applications. It handles the almost all the plumbing/boilerplate code required for your application so that you can focus on your business specific logic while building your enterprise application. Simple Plain Old Java Objects (POJOs) becomes powerful objects having middleware services like security, transaction management etc. inside the Spring Container. Part 1 introduces you to the Spring Framework and also tries to introduce various core concepts on which Spring Framework is built on.

In Chapter 1, “Introduction”, you will get to know overview, history, overall architecture, building blocks, and features of the spring framework in detail.

In Chapter 2, “Getting Started with Spring Framework”, I will show you how to get set up for building applications with Spring Framework, and I will introduce the sample application on which the book is based. Chapter 2 also introduces some basic concepts that are essential for understanding Spring in a holistic way.

So here we go, I hope you will enjoy reading this book as much as I did in writing it for you.

Chapter 1: Introduction

Chapter 2: Getting Started With Spring

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Spring Security – Multiple authentication providers

An AuthenticationManager is responsible for passing requests through a chain of AuthenticationProviders. It is very much similar to the filter chain in a typical web application.

These authentication providers are tried in the order shown (which is implied by the use of a List instead of a Set), with each provider able to attempt authentication, or skip authentication by simply returning null. If all implementations return null, the ProviderManager will throw a suitable exception.

Below is the spring bean configuration which can be used for setting up multiple authentication providers in your Spring application using Spring Security.

spring-security.xml

Sample 1:-

Sample 2:-

In the above sample configuration, both the declared authentication providers will be registered with authentication manager.

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Basic EJB FAQ – Part 1

1)Who is EJB technology for?

EJB technology benefits a number of audiences:

Enterprise customers that build and/or deploy EJB-based applications – gain development productivity, can choose from a wide selection of EJB servers, create business logic that runs everywhere and is architecture independent, all this while protecting their existing IT investment!

ISVs and SIs that develop EJB components or applications based on EJB components – Invest in business logic that is widely deployable, across any OS and middleware, don’t need to choose one vendor-specific server platform. Like enterprise customers they also benefit from productivity gains and architecture independence

The EJB specification itself is mostly targeted at the EJB server vendors – It is the blueprint that instructs these vendors on how to build an EJB server that EJB components can execute on successfully

2)What are the design goals of the Enterprise JavaBeansTM architecture?

The Enterprise JavaBeans specification defines a standard architecture for implementing the business logic of multi-tier applications as reusable components. In addition to Enterprise JavaBeans components, the architecture defines three other entities: servers, containers, and clients. This architecture incorporates several design goals:

Enterprise JavaBeans servers are designed to wrap around legacy systems to provide fundamental services for containers and the components they contain.

Enterprise JavaBeans containers are designed to handle details of component life-cycle, transaction, and security management. By interceding between clients and components at the method call level, containers can manage transactions that propagate across calls and components, and even across containers running on different servers and different machines. This mechanism simplifies development of both component and clients.

Component developers are free to focus on business logic, since containers provide services automatically by interceding in component method calls. A simple set of callback interfaces are all that a developer needs to implement to participate in container provided services.

A client’s view of an Enterprise JavaBean remains the same regardless of the container it is deployed in. Any container in which an Enterprise JavaBean is deployed presents the same interfaces to the client. This extends to containers from different vendors, running against different servers and different databases, on diverse systems on a network. This client transparency ensures wide scalability for multi-tier applications.

Along with container managed transactions, the Enterprise JavaBeans architecture enables component- and client-managed transactions. Containers can participate in component or client initiated transactions to enforce transaction rules across method call and component boundaries. Components can also specify transaction types by method, enabling them to mix transaction types within a single object.

A variety of Enterprise JavaBean attributes, including the default component transaction type, can be specified at either development or deployment time, and enforced through mechanisms built into the container architecture.

The Enterprise JavaBeans architecture is based on the Java programming language, so enterprise Beans take full advantage of the “write once, run anywhereTM” standard.

3)What’s the client view of an Enterprise JavaBeans component?

The client view is provided through two interfaces — the home interface and the remote interface. These interfaces are provided by classes constructed by the container when a bean is deployed, based on information provided by the bean. The home interface provides methods for creating a bean instance, while the remote interface provides the business logic methods for the component. By implementing these interfaces, the container can intercede in client operations on a bean, and offers the client a simplified view of the component.

4)Why doesn’t the client interact with an Enterprise JavaBean directly?

To the client, there appears to be direct interaction with an Enterprise Java Bean through the home and remote interfaces. However, Enterprise JavaBeans architecture is designed to enable clients and components to exist in different runtimes on different systems on a network. The container intercedes between client and component, completely concealing both the bean instance and its own actions from the clients.

5)What methods are developers required to implement the Enterprise JavaBeans architecture?

There are three categories of Enterprise JavaBeans methods. First, the bean implements methods corresponding to those in its home interface — methods largely for creating, locating and accessing instances of the bean. Second, a bean implements business logic methods corresponding to those provided by its remote interface. Finally, a bean implements methods for interacting with the container. Since these methods aren’t intended for client access, they are hidden by the container.

6)What specific services does a container provide for an entity bean?

As with session beans, the tools for a container generate additional classes for an entity bean at deployment time to implement the home and remote interfaces. These classes enable the container to intercede in all client calls on the same entity bean. The container also generates the serializable Handle class, providing a way to identify the entity bean within a specific life cycle. These classes can be implemented to mix in container-specific code for performing customized operations and functionality. In addition to these custom classes, each container provides a class to provide metadata to the client. Finally, where specified by a particular bean, a container manages persistence of selected fields of the entity bean.

7)What’s the difference between container-managed and bean-managed persistence?

In container-managed persistence, entity bean data is automatically maintained by the container using a mechanism of its choosing. For example, a container implemented on top of an RDBMS may manage persistence by storing each bean’s data as a row in a table. Or, the container may use Java programming language serialization for persistence. When a bean chooses to have its persistence container managed, it specifies which of its fields are to be retained.

In bean-managed persistence, the bean is entirely responsible for storing and retrieving its instance data. The EntityBean interface provides methods for the container to notify an instance when it needs to store or retrieve its data.

8)How is an entity bean created?

An entity bean can be created in two ways: by direct action of the client in which a create method is called on the bean’s home interface, or by some other action that adds data to the database that the bean type represents. In fact, in an environment with legacy data, entity objects may “exist” before an Enterprise JavaBean is even deployed.

9)How does the client get a reference to an existing entity bean?

A client can get a reference to an existing entity bean in several ways:

Receiving the bean as a parameter in a method call

Looking the bean up through a finder method of the home interface

Obtaining the bean as a handle, a runtime specific identifier generated for a bean automatically by the container

10)How do you determine whether two entity beans are the same?

By invoking the EntityBean.isIdentical method. This method should be implemented by the entity bean developer to determine when two references are to the same object. Note that the equals and hashCode methods of Object are undefined for entity beans, since clients don’t directly access bean instances within a container.

11)How does a container manage access from multiple transactions on an entity bean?

Containers manage multiple transactions in one of two ways. First, the container can instantiate multiple instances of the bean and let the transaction management of the DBMS handle transaction processing issues. Or, the container can acquire an exclusive lock on the instance’s state in the database, and serialize access from multiple transactions to this instance.

12)How do enterprise beans handle concurrent and loopback calls on entity beans?

Concurrent calls in the same transaction context on the same Enterprise JavaBean component are illegal and may lead to unpredictable results. A bean can be marked as non-reentrant by its deployment descriptor. This allows the container to detect and prevent illegal concurrent calls from clients. On the other hand, some entity beans may require loopback calls: that is, calls where bean A is invoked, in turn invoking bean B, which then invokes a method call on bean A. This kind of concurrency is tricky and is best avoided.

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Basic Java FAQ – Part 3

101) What is RMI architecture?

Ans: – RMI architecture consists of four layers and each layer performs specific functions:

a) Application layer —- contains the actual object definition

b) Proxy layer —- consists of stub and skeleton

c) Remote Reference layer —- gets the stream of bytes from the transport layer and sends it to the proxy layer

d) Transportation layer —- responsible for handling the actual machine-to-machine communication

102) What is UnicastRemoteObject?

Ans: All remote objects must extend UnicastRemoteObject, which provides functionality that is needed to make objects available from remote machines.

103) Explain the methods, rebind( ) and lookup() in Naming class?

Ans: rebind( ) of the Naming class(found in java.rmi) is used to update the RMI registry on the server machine.

Naming. rebind(“AddSever”, AddServerImpl);

lookup( ) of the Naming class accepts one argument, the rmi URL and returns a reference to an object of type AddServerImpl.

104) What is a Java Bean?

Ans: A Java Bean is a software component that has been designed to be reusable in a variety of different environments.

105) What is a Jar file?

Ans: Jar file allows to efficiently deploying a set of classes and their associated resources. The elements in a jar file are compressed, which makes downloading a Jar file much faster than separately downloading several uncompressed files.

The package java.util.zip contains classes that read and write jar files.

106) What is BDK?

Ans: BDK, Bean Development Kit is a tool that enables to create, configure and connect a set of set of Beans and it can be used to test Beans without writing a code.

107) What is JSP?

Ans: JSP is a dynamic scripting capability for web pages that allows Java as well as a few special tags to be embedded into a web file (HTML/XML, etc). The suffix traditionally ends with .jsp to indicate to the web server that the file is a JSP files. JSP is a server side technology – you can’t do any client side validation with it.

The advantages are:

a) The JSP assists in making the HTML more functional. Servlets on the other hand allow outputting of

HTML but it is a tedious process.

b) It is easy to make a change and then let the JSP capability of the web server you are using deal with compiling it into a servlet and running it.

108) What are JSP scripting elements?

Ans: JSP scripting elements lets to insert Java code into the servlet that will be generated from the current JSP page. There are three forms:

a) Expressions of the form <%= expression %> that are evaluated and inserted into the output,

b) Scriptlets of the form <% code %> that are inserted into the servlet’s service method, and

c) Declarations of the form <%! Code %> that are inserted into the body of the servlet class, outside of any existing methods.

109) What are JSP Directives?

Ans: A JSP directive affects the overall structure of the servlet class. It usually has the following form:

<%@ directive attribute=”value” %>

However, you can also combine multiple attribute settings for a single directive, as follows:

<%@ directive attribute1=”value1″

attribute 2=”value2″

attributeN =”valueN” %>

There are two main types of directive: page, which lets to do things like import classes, customize the servlet superclass, and the like; and include, which lets to insert a file into the servlet class at the time the JSP file is translated into a servlet

110) What are Predefined variables or implicit objects?

Ans: To simplify code in JSP expressions and scriptlets, we can use eight automatically defined variables, sometimes called implicit objects. They are request, response, out, session, application, config, pageContext, and page.

111) What are JSP ACTIONS?

Ans: JSP actions use constructs in XML syntax to control the behavior of the servlet engine. You can dynamically insert a file, reuse JavaBeans components, forward the user to another page, or generate HTML for the Java plugin. Available actions include:

112) How do you pass data (including JavaBeans) to a JSP from a servlet?

Ans: (1) Request Lifetime: Using this technique to pass beans, a request dispatcher (using either “include” or forward”) can be called. This bean will disappear after processing this request has been completed.

Servlet:

request.setAttribute(“theBean”, myBean);

RequestDispatcher rd = getServletContext().getRequestDispatcher(“thepage.jsp”);

rd.forward(request, response);

JSP PAGE:

(2) Session Lifetime: Using this technique to pass beans that are relevant to a particular session

(such as in individual user login) over a number of requests. This bean will disappear when the

session is invalidated or it times out, or when you remove it.

Servlet:

HttpSession session = request.getSession(true);

session.putValue(“theBean”, myBean);

/* You can do a request dispatcher here,

or just let the bean be visible on the

next request */

JSP Page:

3) Application Lifetime: Using this technique to pass beans that are relevant to all servlets and JSP pages in a particular app, for all users. For example, I use this to make a JDBC connection pool object available to the various servlets and JSP pages in my apps. This bean will disappear when the servlet engine is shut down, or when you remove it.

Servlet:

GetServletContext(). setAttribute(“theBean”, myBean);

JSP PAGE:

113) How can I set a cookie in JSP?

Ans: response.setHeader(“Set-Cookie”, “cookie string”);

To give the response-object to a bean, write a method setResponse

(HttpServletResponse response)

– to the bean, and in jsp-file:

<%

bean.setResponse (response);

%>

114) How can I delete a cookie with JSP?

Ans: Say that I have a cookie called “foo,” that I set a while ago & I want it to go away. I simply:

<%

Cookie killCookie = new Cookie(“foo”, null);

KillCookie.setPath(“/”);

killCookie.setMaxAge(0);

response.addCookie(killCookie);

%>

115) How are Servlets and JSP Pages related?

Ans: JSP pages are focused around HTML (or XML) with Java codes and JSP tags inside them. When a web server that has JSP support is asked for a JSP page, it checks to see if it has already compiled the page into a servlet. Thus, JSP pages become servlets and are transformed into pure Java and then compiled, loaded into the server and executed.

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Basic Java FAQ – Part 2

51)How do you set security in applets?

Ans: using setSecurityManager() method

52) What is an event and what are the models available for event handling?

Ans: An event is an event object that describes a state of change in a source. In other words, event occurs when an action is generated, like pressing button, clicking mouse, selecting a list, etc.

There are two types of models for handling events and they are:

a) event-inheritance model and b) event-delegation model

53) What are the advantages of the model over the event-inheritance model?

Ans: The event-delegation model has two advantages over the event-inheritance model. They are:

a)It enables event handling by objects other than the ones that generate the events. This allows a clean separation between a component’s design and its use.

b)It performs much better in applications where many events are generated. This performance improvement is due to the fact that the event-delegation model does not have to be repeatedly process unhandled events as is the case of the event-inheritance.

54)What is source and listener ?

Ans: source : A source is an object that generates an event. This occurs when the internal state of that object changes in some way.

listener : A listener is an object that is notified when an event occurs. It has two major requirements. First, it must have been registered with one or more sources to receive notifications about specific types of events.

Second, it must implement methods to receive and process these notifications.

55) What is adapter class?

Ans: An adapter class provides an empty implementation of all methods in an event listener interface. Adapter classes are useful when you want to receive and process only some of the events that are handled by a particular event listener interface. You can define a new class to act listener by extending one of the adapter classes and implementing only those events in which you are interested.

For example, the MouseMotionAdapter class has two methods, mouseDragged( )and mouseMoved(). The signatures of these empty are exactly as defined in the MouseMotionListener interface. If you are interested in only mouse drag events, then you could simply extend MouseMotionAdapter and implement mouseDragged( ) .

56)What is meant by controls and what are different types of controls in AWT?

Ans: Controls are components that allow a user to interact with your application and the AWT supports the following types of controls:

Labels, Push Buttons, Check Boxes, Choice Lists, Lists, Scrollbars, Text Components.

These controls are subclasses of Component.

57) What is the difference between choice and list?

Ans: A Choice is displayed in a compact form that requires you to pull it down to see the list of available choices and only one item may be selected from a choice.

A List may be displayed in such a way that several list items are visible and it supports the selection of one or more list items.

58) What is the difference between scrollbar and scrollpane?

Ans: A Scrollbar is a Component, but not a Container whereas Scrollpane is a Conatiner and handles its own events and perform its own scrolling.

59) What is a layout manager and what are different types of layout managers available in java.awt?

Ans: A layout manager is an object that is used to organize components in a container. The different layouts are available are FlowLayout, BorderLayout, CardLayout, GridLayout and GridBagLayout.

60) How are the elements of different layouts organized?

Ans: FlowLayout: The elements of a FlowLayout are organized in a top to bottom, left to right fashion.

BorderLayout: The elements of a BorderLayout are organized at the borders (North, South, East and West) and the center of a container.

CardLayout: The elements of a CardLayout are stacked, on top of the other, like a deck of cards.

GridLayout: The elements of a GridLayout are of equal size and are laid out using the square of a grid.

GridBagLayout: The elements of a GridBagLayout are organized according to a grid.

However, the elements are of different size and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes.

61) Which containers use a Border layout as their default layout?

Ans: Window, Frame and Dialog classes use a BorderLayout as their layout.

62) Which containers use a Flow layout as their default layout?

Ans: Panel and Applet classes use the FlowLayout as their default layout.

63) What are wrapper classes?

Ans: Wrapper classes are classes that allow primitive types to be accessed as objects.

64) What are Vector, Hashtable, LinkedList and Enumeration?

Ans: Vector : The Vector class provides the capability to implement a growable array of objects.

Hashtable : The Hashtable class implements a Hashtable data structure. A Hashtable indexes and stores objects in a dictionary using hash codes as the object’s keys. Hash codes are integer values that identify objects.

LinkedList: Removing or inserting elements in the middle of an array can be done using LinkedList. A

LinkedList stores each object in a separate link whereas an array stores object references in consecutive locations.

Enumeration: An object that implements the Enumeration interface generates a series of elements, one at a time. It has two methods, namely hasMoreElements( ) and nextElement( ). HasMoreElemnts( ) tests if this enumeration has more elements and nextElement method returns successive elements of the series.

65) What is the difference between set and list?

Ans: Set stores elements in an unordered way but does not contain duplicate elements, whereas list stores elements in an ordered way but may contain duplicate elements.

66) What is a stream and what are the types of Streams and classes of the Streams?

Ans: A Stream is an abstraction that either produces or consumes information. There are two types of Streams and they are:

Byte Streams: Provide a convenient means for handling input and output of bytes.

Character Streams: Provide a convenient means for handling input & output of characters.

Byte Streams classes: Are defined by using two abstract classes, namely InputStream and OutputStream.

Character Streams classes: Are defined by using two abstract classes, namely Reader and Writer.

67) What is the difference between Reader/Writer and InputStream/Output Stream?

Ans: The Reader/Writer class is character-oriented and the InputStream/OutputStream class is byte-oriented.

68) What is an I/O filter?

Ans: An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.

69) What is serialization and deserialization?

Ans: Serialization is the process of writing the state of an object to a byte stream.

Deserialization is the process of restoring these objects.

70) What is JDBC?

Ans: JDBC is a set of Java API for executing SQL statements. This API consists of a set of classes and interfaces to enable programs to write pure Java Database applications.

71) What are drivers available?

Ans: a) JDBC-ODBC Bridge driver

b) Native API Partly-Java driver

c) JDBC-Net Pure Java driver

d) Native-Protocol Pure Java driver

72) What is the difference between JDBC and ODBC?

Ans: a) OBDC is for Microsoft and JDBC is for Java applications.

b) ODBC can’t be directly used with Java because it uses a C interface.

c) ODBC makes use of pointers which have been removed totally from Java.

d) ODBC mixes simple and advanced features together and has complex options for simple queries. But JDBC is designed to keep things simple while allowing advanced capabilities when required.

e) ODBC requires manual installation of the ODBC driver manager and driver on all client machines. JDBC drivers are written in Java and JDBC code is automatically installable, secure, and portable on all platforms.

f) JDBC API is a natural Java interface and is built on ODBC. JDBC retains some of the basic features of ODBC.

73) What are the types of JDBC Driver Models and explain them?

Ans: There are two types of JDBC Driver Models and they are:

a) Two tier model and b) Three tier model

Two tier model: In this model, Java applications interact directly with the database. A JDBC driver is required to communicate with the particular database management system that is being accessed. SQL statements are sent to the database and the results are given to user. This model is referred to as client/server configuration where user is the client and the machine that has the database is called as the server.

Three tier model: A middle tier is introduced in this model. The functions of this model are:

a) Collection of SQL statements from the client and handing it over to the database,

b) Receiving results from database to the client and

c) Maintaining control over accessing and updating of the above.

74) What are the steps involved for making a connection with a database or how do you connect to a database?

Ans: a) Loading the driver : To load the driver, Class.forName( ) method is used.

Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver”);

When the driver is loaded, it registers itself with the java.sql.DriverManager class as an available

database driver.

b) Making a connection with database : To open a connection to a given database,

DriverManager.getConnection( ) method is used.

Connection con = DriverManager.getConnection (“jdbc:odbc:somedb”, “user”, “password”);

c) Executing SQL statements : To execute a SQL query, java.sql.statements class is used.

createStatement( ) method of Connection to obtain a new Statement object.

Statement stmt = con.createStatement( );

A query that returns data can be executed using the executeQuery( ) method of Statement. This method executes the statement and returns a java.sql.ResultSet that encapsulates the retrieved data:

ResultSet rs = stmt.executeQuery(“SELECT * FROM some table”);

d) Process the results : ResultSet returns one row at a time. Next( ) method of ResultSet object can be called to move to the next row. The getString( ) and getObject( ) methods are used for retrieving column values:

while(rs.next( ) ) {

String event = rs.getString(“event”);

Object count = (Integer) rs.getObject(“count”);

75) What type of driver did you use in project?

Ans: JDBC-ODBC Bridge driver (is a driver that uses native(C language) libraries and makes calls to an existing ODBC driver to access a database engine).

76) What are the types of statements in JDBC?

Ans: Statement — To be used createStatement() method for executing single SQL statement

PreparedStatement — To be used preparedStatement() method for executing same SQL statement over and over

CallableStatement — To be used prepareCall( ) method for multiple SQL statements over and over

77) What is stored procedure?

Ans: Stored procedure is a group of SQL statements that forms a logical unit and performs a particular task. Stored Procedures are used to encapsulate a set of operations or queries to execute on database. Stored procedures can be compiled and executed with different parameters and results and may have any combination of input/output parameters.

78) How to create and call stored procedures?

Ans: To create stored procedures:

Create procedure procedurename (specify in, out and in out parameters)

BEGIN

Any multiple SQL statement;

END;

To call stored procedures:

CallableStatement csmt = con.prepareCall(“{call procedure name(?,?)}”);

csmt.registerOutParameter(column no., data type);

csmt.setInt(column no., column name)

csmt.execute( );

79) What is servlet?

Ans: Servlets are modules that extend request/response-oriented servers, such as java-enabled web servers. For example, a servlet might be responsible for taking data in an HTML order-entry form and applying the business logic used to update a company’s order database.

80) What are the classes and interfaces for servlets?

Ans: There are two packages in servlets and they are javax.servlet and javax.servlet.http.

Javax.servlet contains:

Interfaces Classes

Servlet Generic Servlet

ServletRequest ServletInputStream

ServletResponse ServletOutputStream

ServletConfig ServletException

ServletContext UnavailableException

SingleThreadModel

Javax.servlet.http contains:

Interfaces Classes

HttpServletRequest Cookie

HttpServletResponse HttpServlet

HttpSession HttpSessionBindingEvent

HttpSessionCintext HttpUtils

HttpSeesionBindingListener

81) What is the difference between an applet and a servlet?

Ans: a) Servlets are to servers what applets are to browsers.

b) Applets must have graphical user interfaces whereas servlets have no graphical user interfaces.

82) What is the difference between doPost and doGet methods?

Ans: a) doGet() method is used to get information, while doPost( ) method is used for posting information.

b) doGet() requests can’t send large amount of information and is limited to 240-255 characters. However, doPost( )requests passes all of its data, of unlimited length.

c) A doGet( ) request is appended to the request URL in a query string and this allows the exchange is

visible to the client, whereas a doPost() request passes directly over the socket connection as part of its HTTP request body and the exchange are invisible to the client.

83) What is the life cycle of a servlet?

Ans: Each Servlet has the same life cycle:

a) A server loads and initializes the servlet by init () method.

b) The servlet handles zero or more client’s requests through service( ) method.

c) The server removes the servlet through destroy() method.

84) Who is loading the init() method of servlet?

Ans: Web server

85) What are the different servers available for developing and deploying Servlets?

Ans: a) Java Web Server

b) JRun

g) Apache Server

h) Netscape Information Server

i) Web Logic

86) How many ways can we track client and what are they?

Ans: The servlet API provides two ways to track client state and they are:

a) Using Session tracking and b) Using Cookies.

87) What is session tracking and how do you track a user session in servlets?

Ans: Session tracking is a mechanism that servlets use to maintain state about a series requests from the same user across some period of time. The methods used for session tracking are:

a) User Authentication – occurs when a web server restricts access to some of its resources to only those clients that log in using a recognized username and password

b) Hidden form fields – fields are added to an HTML form that are not displayed in the client’s browser. When the form containing the fields is submitted, the fields are sent back to the server

c) URL rewriting – every URL that the user clicks on is dynamically modified or rewritten to include extra information. The extra information can be in the form of extra path information, added parameters or some custom, server-specific URL change.

d) Cookies – a bit of information that is sent by a web server to a browser and which can later be read back from that browser.

e) HttpSession- places a limit on the number of sessions that can exist in memory. This limit is set in the session.maxresidents property

88) What is Server-Side Includes (SSI)?

Ans: Server-Side Includes allows embedding servlets within HTML pages using a special servlet tag. In many servlets that support servlets, a page can be processed by the server to include output from servlets at certain points inside the HTML page. This is accomplished using a special internal SSINCLUDE, which processes the servlet tags. SSINCLUDE servlet will be invoked whenever a file with an. shtml extension is requested.

So HTML files that include server-side includes must be stored with an .shtml extension.

89) What are cookies and how will you use them?

Ans: Cookies are a mechanism that a servlet uses to have a client hold a small amount of state-information associated with the user.

a) Create a cookie with the Cookie constructor:

public Cookie(String name, String value)

b) A servlet can send a cookie to the client by passing a Cookie object to the addCookie() method of

HttpServletResponse:

public void HttpServletResponse.addCookie(Cookie cookie)

c) A servlet retrieves cookies by calling the getCookies() method of HttpServletRequest:

public Cookie[ ] HttpServletRequest.getCookie( ).

90) Is it possible to communicate from an applet to servlet and how many ways and how?

Ans: Yes, there are three ways to communicate from an applet to servlet and they are:

a) HTTP Communication(Text-based and object-based)

b) Socket Communication

c) RMI Communication

(You can say, by using URL object open the connection to server and get the InputStream from

URLConnection object).

Steps involved for applet-servlet communication:

1) Get the server URL.

URL url = new URL();

2) Connect to the host

URLConnection Con = url.openConnection();

3) Initialize the connection

Con.setUseCatches(false):

Con.setDoOutput(true);

Con.setDoInput(true);

4) Data will be written to a byte array buffer so that we can tell the server the length of the data.

ByteArrayOutputStream byteout = new ByteArrayOutputStream();

5) Create the OutputStream to be used to write the data to the buffer.

DataOutputStream out = new DataOutputStream(byteout);

91) What is connection pooling?

Ans: With servlets, opening a database connection is a major bottleneck because we are creating and tearing down a new connection for every page request and the time taken to create connection will be more.Creating a connection pool is an ideal approach for a complicated servlet. With a connection pool, we can duplicate only the resources we need to duplicate rather than the entire servlet. A connection pool can also intelligently manage the size of the pool and make sure each connection remains valid. A number of connection pool packages are currently available. Some like DbConnectionBroker are freely available from Java Exchange Works by creating an object that dispenses connections and connection Ids on request.

The ConnectionPool class maintains a Hastable, using Connection objects as keys and Boolean values as stored values. The Boolean value indicates whether a connection is in use or not. A program calls

getConnection( ) method of the ConnectionPool for getting Connection object it can use; it calls

returnConnection( ) to give the connection back to the pool.

92) Why should we go for interservlet communication?

Ans: Servlets running together in the same server communicate with each other in several ways.

The three major reasons to use interservlet communication are:

a) Direct servlet manipulation – allows to gain access to the other currently loaded servlets and perform certain tasks (through the ServletContext object)

b) Servlet reuse – allows the servlet to reuse the public methods of another servlet.

c) Servlet collaboration – requires to communicate with each other by sharing specific information (through method invocation)

93) Is it possible to call servlet with parameters in the URL?

Ans: Yes. You can call a servlet with parameters in the syntax as (?Param1 = xxx || m2 = yyy).

94) What is Servlet chaining?

Ans: Servlet chaining is a technique in which two or more servlets can cooperate in servicing a single request. In servlet chaining, one servlet’s output is piped to the next servlet’s input. This process continues until the last servlet is reached. Its output is then sent back to the client.

95) How do servlets handle multiple simultaneous requests?

Ans: The server has multiple threads that are available to handle requests. When a request comes in, it is assigned to a thread, which calls a service method (for example: doGet(), doPost( ) and service( ) ) of the servlet. For this reason, a single servlet object can have its service methods called by many threads at once.

96) What is the difference between TCP/IP and UDP?

Ans: TCP/IP is a two-way communication between the client and the server and it is a reliable and there is a confirmation regarding reaching the message to the destination. It is like a phone call.

UDP is a one-way communication only between the client and the server and it is not a reliable and there is no confirmation regarding reaching the message to the destination. It is like a postal mail.

97) What is Inet address?

Ans: Every computer connected to a network has an IP address. An IP address is a number that uniquely identifies each computer on the Net. An IP address is a 32-bit number.

98) What is Domain Naming Service(DNS)?

Ans: It is very difficult to remember a set of numbers(IP address) to connect to the Internet. The Domain Naming Service(DNS) is used to overcome this problem. It maps one particular IP address to a string of characters. For example, www.mascom.com implies com is the domain name reserved for US commercial sites, moscom is the name of the company and www is the name of the specific computer, which is mascom’s server.

99) What is URL?

Ans: URL stands for Uniform Resource Locator and it points to resource files on the Internet.

URL has four components:

http://www.Pentafour.com:80/index.html

http – protocol name, Pentafour – IP address or host name, 80 – port number and index.html – file path.

100) What is RMI and steps involved in developing an RMI object?

Ans: Remote Method Invocation (RMI) allows java object that executes on one machine and to invoke the method of a Java object to execute on another machine.

The steps involved in developing an RMI object are:

a) Define the interfaces

b) Implementing these interfaces

c) Compile the interfaces and their implementations with the java compiler

d) Compile the server implementation with RMI compiler

e) Run the RMI registry

f) Run the application

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