Google Talk: Run Multiple Instances or Login as Multiple Users

If you have several Google talk accounts, you may want to run multiple instances of Google talk at once. Here’s how to do it.

Many users, including myself, like to have several different personalities on IM–Work, play, etc. By default Google talk with only allow you to run instance of the program at a time. Here’s how to get around that…
Run Google talk with the following switch: /nomutex
If you installed Google talk to the default location, you can easily create a shortcut to this setting.

1. Right-click on the desktop
2. Select New
3. Select Shortcut
4. Paste this into the text box:
"c:\program files\google\google talk\googletalk.exe" /nomutex
5. Click Next6. Name it whatever: Google Talk Multiple, etc.
7. Click OK until you are done.

How to Run Multiple Yahoo! Messengers and Login to Multi Yahoo! Messengers Accounts

For Yahoo! Messenger with Voice 8 users, it’s now possible to run multiple instances of Yahoo!. Messengers (polygamy feature) and log into multiple Y!Msgr accounts with just a simple registry hack. So if you need to open and log-in multiple Yahoo! Messenger accounts as you have a few Yahoo! ID or various other reason, just use the small registry registration file below that once click, will modify and merge the registry setting required to run and execute multiple Yahoo! Messengers at the same time on a computer.

Download ym8multi.zip, extract it and run “ym8multi.reg” contained inside the archive. Once the registry is patched, you can now starting and running multi Yahoo! Messenger with different login or Yahoo! ID accounts. If you want to uninstall the patch/hack, download the ym8multi_uninst.zip uninstaller which contains ym8multi_uninst.reg. Once double click on this uninstaller registration registry value file, it will edit the registry value and set it to disable the ability for Y! M 8 to launch multiple copies of instances.



If you prefer to edit and change the registry setting yourself manually, without using the above registry registration file, simply launch the registry editor (type regedit at Run command), and navigate to the following registry branch:

HKEY_CURRENT_USER\Software\yahoo\pager\Test

Then, on the right pane, right click on the registry editor and select “New”, then create a new DWORD registry value. Name the new registry key as Plural, and assign it the value of 1 (decimal). If some case, the value of 2 should also works. To disable or disallow multiple instances of Yahoo Messengers, simply change and set the “Plural” registry key’s value to 0, or delete the “Plural” key.

Marker Interface in Java

Marker Interface most of the people know the definition, but many of them are not aware of the purpose of the Marker Interface and how it works. Very often I heard the question from my friends that the Marker Interface doesn't have methods then what is the use of Marker Interface.

One of the basic feature of Java Programing Language is that it mandates a separation between Interfaces and Classes. Interfaces are used in Java to specify the behavior of the derived class.

While working on the Java Programing Language many of the programmers might have observed the Interfaces which doesn't have no behavior. In other words they are just empty Interface definitions. These Interfaces are knows as Marker Interfaces.

Basic Definition: Interfaces with empty body.
Example: Serializable, Cloneable, Remote, EventListener


Marker Interfaces are also called as Tag Interfaces because they tag all the derived classes into a category based on their purpose. If we consider a real time example for this scenario, lets pick Cloneable from the abouve examples given. All classes that implement Cloneable Interface can be cloned by calling clone(); method. Now the Java Compiler checks to make sure that if the clone(); method is called on a class and the class implements the Cloneable Interface. If we have the Object obj and call clone(); method on this as

MyObject obj = new MyObject();
MyObject ref = (MyObject)(obj.clone());

Here if the MyObject doesn't implement the Cloneable Interface and Cloneable is not implemented any of the super class that MyObject inherits from, the compiler will mark this line as error. This is because the clone() method may only be called by objects of the type Cloneable.

Here our Cloneable Interface is an Interface with empty body, but still it serving a major role.

To create a copy of any Object, in our case we have MyObject to create a clone for this Object we need to have a clone(); method which should implement Cloneable Interface.

The above scenario clearly states that we are marking the class Cloneable so that the Object can be Cloneable. For this purpose we have Marker Interfaces in Java.

When ever we implement Serializable, Cloneable JVM understands that this thing is to be serialized or cloned and no methods involved in this process.

Hope this article will clear your ambiguities about Marker Interfaces.

JavaServer Faces Interview Questions

1. What is JSF (or JavaServer Faces)?

A server side user interface component framework for Java™ technology-based web applications. JavaServer Faces (JSF) is an industry standard and a framework for building component-based user interfaces for web applications.

JSF contains an API for representing UI components and managing their state; handling events, server-side validation, and data conversion; defining page navigation; supporting internationalization and accessibility; and providing extensibility for all these features.

2. What are the advantages of JSF?

The major benefits of JavaServer Faces technology are:

• JavaServer Faces architecture makes it easy for the developers to use. In JavaServer Faces technology, user interfaces can be created easily with its built-in UI component library, which handles most of the complexities of user interface management.
• Offers a clean separation between behavior and presentation.
• Provides a rich architecture for managing component state, processing component data, validating user input, and handling events.
• Robust event handling mechanism.
• Events easily tied to server-side code.
• Render kit support for different clients
• Component-level control over statefulness
• Highly 'pluggable' - components, view handler, etc
• JSF also supports internationalization and accessibility
• Offers multiple, standardized vendor implementations

3. What are differences between struts and JSF?

In a nutshell, Faces has the following advantages over Struts:

· Eliminated the need for a Form Bean

· Eliminated the need for a DTO Class

· Allows the use of the same POJO on all Tiers because of the Backing Bean

The primary advantages of Struts as compared to JavaServer Faces technology are as follows:

· Because Struts is a web application framework, it has more sophisticated controller architecture than does JavaServer Faces technology. It is more sophisticated partly because the application developer can access the controller by creating an Action object that can integrate with the controller, whereas JavaServer Faces technology does not allow access to the controller. In addition, the Struts controller can do things like access control on each Action based on user roles. This functionality is not provided by JavaServer Faces technology.

· Struts includes a powerful layout management framework, called Tiles, which allows you to create templates that you can reuse across multiple pages, thus enabling you to establish an overall look-and-feel for an application.

· The Struts validation framework includes a larger set of standard validators, which automatically generate both server-side and client-side validation code based on a set of rules in a configuration file. You can also create custom validators and easily include them in your application by adding definitions of them in your configuration file.

The greatest advantage that JavaServer Faces technology has over Struts is its flexible, extensible UI component model, which includes:

· A standard component API for specifying the state and behavior of a wide range of components, including simple components, such as input fields, and more complex components, such as scrollable data tables. Developers can also create their own components based on these APIs, and many third parties have already done so and have made their component libraries publicly available.

· A separate rendering model that defines how to render the components in various ways. For example, a component used for selecting an item from a list can be rendered as a menu or a set of radio buttons.

· An event and listener model that defines how to handle events generated by activating a component, such as what to do when a user clicks a button.

· Conversion and validation models for converting and validating component data.

4. What are the available implementations of JavaServer Faces?

The main implementations of JavaServer Faces are:

• Reference Implementation (RI) by Sun Microsystems.
• Apache MyFaces is an open source JavaServer Faces (JSF) implementation or run-time.
• ADF Faces is Oracle’s implementation for the JSF standard.

6. What typical JSF application consists of?

A typical JSF application consists of the following parts:

• JavaBeans components for managing application state and behavior.
• Event-driven development (via listeners as in traditional GUI development).
• Pages that represent MVC-style views; pages reference view roots via the JSF component tree.

7. What Is a JavaServer Faces Application?

JavaServer Faces applications are just like any other Java web application. They run in a Servlet container, and they typically contain the following:

• JavaBeans components containing application-specific functionality and data.
• Event listeners.
• Pages, such as JSP pages.
• Server-side helper classes, such as database access beans.

In addition to these items, a JavaServer Faces application also has:

• A custom tag library for rendering UI components on a page.
• A custom tag library for representing event handlers, validators, and other actions.
• UI components represented as stateful objects on the server.
• Backing beans, which define properties and functions for UI components.
• Validators, converters, event listeners, and event handlers.
• An application configuration resource files for configuring application resources.

8. What is Managed Bean?

JavaBean objects managed by a JSF implementation are called managed beans. A managed bean describes how a bean is created and managed. It has nothing to do with the bean's functionalities.

9. What is Backing Bean?

Backing beans are JavaBeans components associated with UI components used in a page. Backing-bean management separates the definition of UI component objects from objects that perform application-specific processing and hold data.

The backing bean defines properties and handling-logics associated with the UI components used on the page. Each backing-bean property is bound to either a component instance or its value. A backing bean also defines a set of methods that perform functions for the component, such as validating the component's data, handling events that the component fires and performing processing associated with navigation when the component activates.

10. What are the differences between a Backing Bean and Managed Bean?

Backing Beans are merely a convention, a subtype of JSF Managed Beans which have a very particular purpose. There is nothing special in a Backing Bean that makes it different from any other managed bean apart from its usage.

What makes a Backing Bean is the relationship it has with a JSF page; it acts as a place to put component references and Event code.

Backing Beans	Managed Beans
A backing bean is any bean that is referenced by a form.	A managed bean is a backing bean that has been registered with JSF (in faces-config.xml) and it automatically created (and optionally initialized) by JSF when it is needed.
	The advantage of managed beans is that the JSF framework will automatically create these beans, optionally initialize them with parameters you specify in faces-config.xml,
Backing Beans should be defined only in the request scope	The managed beans that are created by JSF can be stored within the request, session, or application scopes

Backing Beans should be defined in the request scope, exist in a one-to-one relationship with a particular page and hold the entire page specific event handling code. In a real-world scenario, several pages may need to share the same backing bean behind the scenes. A backing bean not only contains view data, but also behavior related to that data.

11. What is view object?

A view object is a model object used specifically in the presentation tier. It contains the data that must display in the view layer and the logic to validate user input, handle events, and interact with the business-logic tier. The backing bean is the view object in a JSF-based application. Backing bean and view object are interchangeable terms.

12. What is domain object model?

Domain object model is about the business object and should belong in the business-logic tier. It contains the business data and business logic associated with the specific business object.

13. What is the difference between the domain object model and a view object?

In a simple Web application, a domain object model can be used across all tiers, however, in a more complex Web application, a separate view object model needs to be used. Domain object model is about the business object and should belong in the business-logic tier. It contains the business data and business logic associated with the specific business object. A view object contains presentation-specific data and behavior. It contains data and logic specific to the presentation tier.

14. What do you mean by Bean Scope?

Bean Scope typically holds beans and other objects that need to be available in the different components of a web application.

15. What are the different kinds of Bean Scopes in JSF?

JSF supports three Bean Scopes. viz.,

• Request Scope: The request scope is short-lived. It starts when an HTTP request is submitted and ends when the response is sent back to the client.
• Session Scope: The session scope persists from the time that a session is established until session termination.
• Application Scope: The application scope persists for the entire duration of the web application. This scope is shared among all the requests and sessions.

16. What is the difference between JSP-EL and JSF-EL?

JSP-EL	JSF-EL
In JSP-EL the value expressions are delimited by ${…}.	In JSF-EL the value expressions are delimited by #{…}.
The ${…} delimiter denotes the immediate evaluation of the expressions, at the time that the application server processes the page.	The #{…} delimiter denotes deferred evaluation. With deferred evaluation, the application server retains the expression and evaluates it whenever a value is needed.

note:As of JSF 1.2 and JSP 2.1 ,the syntax of both expression languages has been unified.

17. What are the main tags in JSF?

JSF application typically uses JSP pages to represent views. JSF provides useful special tags to enhance these views. Each tag gives rise to an associated component. JSF (Sun Implementation) provides 43 tags in two standard JSF tag libraries:

• JSF Core Tags Library.
• JSF Html Tags Library.

18. How do you declare the managed beans in the faces-config.xml file?

The bean instance is configured in the faces-config.xml file:

login

com.developersBookJsf.loginBean

request

This means: Construct an object of the class com.developersBookJsf.loginBean, give it the name login, and keep it alive for the duration of the request.

19. How to declare the Message Bundle in JSF?

We can declare the message bundle in two ways:
(Let’s assume com.developersBookJsf.messages is the properties file)

1. The simplest way is to include the following elements in faces-config.xml file:

com.developersBookJsf.messages

message

2. Alternatively, you can add the f:loadBundle element to each JSF page that needs access to the bundle:

20. How to declare the page navigation (navigation rules) in faces-config.xml file?

Navigation rules tells JSF implementation which page to send back to the browser after a form has been submitted. We can declare the page navigation as follows:

/index.jsp

login

/welcome.jsp

This declaration states that the login action navigates to /welcome.jsp, if it occurred inside /index.jsp.

21. What if no navigation rule matches a given action?

If no navigation rule matches a given action, then the current page is redisplayed.

22. What are the JSF life-cycle phases?

The six phases of the JSF application lifecycle are as follows (note the event processing at each phase):

1. Restore view
2. Apply request values; process events
3. Process validations; process events
4. Update model values; process events
5. Invoke application; process events
6. Render response

23. Explain briefly the life-cycle phases of JSF?

1. Restore View: A request comes through the FacesServlet controller. The controller examines the request and extracts the view ID, which is determined by the name of the JSP page.
2. Apply request values: The purpose of the apply request values phase is for each component to retrieve its current state. The components must first be retrieved or created from the FacesContext object, followed by their values.
3. Process validations: In this phase, each component will have its values validated against the application's validation rules.
4. Update model values: In this phase JSF updates the actual values of the server-side model, by updating the properties of your backing beans.
5. Invoke application: In this phase the JSF controller invokes the application to handle Form submissions.
6. Render response: In this phase JSF displays the view with all of its components in their current state.

24. What does it mean by render kit in JSF?

A render kit defines how component classes map to component tags that are appropriate for a particular client. The JavaServer Faces implementation includes a standard HTML render kit for rendering to an HTML client.

25. Is it possible to have more than one Faces Configuration file?

We can have any number of config files. Just need to register in web.xml.
Assume that we want to use faces-config(1,2,and 3),to register more than one faces configuration file in JSF, just declare in the web.xml file

javax.faces.CONFIG_FILES

/WEB-INF/faces-config1.xml,

/WEB-INF/faces-config2.xml,

/WEB-INF/faces-config3.xml

Steps to create Digital Certificate

The following steps will help you to create a Digital Certificate and to create a signed jar/applet.

Open the command prompt and navigate to

D:\Program Files\Java\jdk1.6.0_14\jre\lib\security

To generate certificate

keytool -genkey -alias SravanModugula -keypass smodugula

To change password/keypass

keytool -keypasswd -alias SravanModugula -keypass smodugula -new newsmodugula

To export the generated certificate

keytool -export -alias SravanModugula -file SravanModugula.cer




To print generated certificate on console

keytool -printcert -file SravanModugula.cer

To display the list of available certificates

keytool -list -alias SravanModugula

Alternative way to create a certificate, this command carry's all the information required

keytool -genkey -dname "cn=Sravan Modugula, ou= Java, o=Sun, c=IN"
-alias SravanModugula -keypass SravanKM -keystore -storepass -validity 720


keytool -selfcert -alias SravanModugula -dname "cn=Sravan Modugula, ou=Java, o=Sun, c=IN"

To create a signed jar file

jarsigner "D:\myfolder\your.jar" SravanModugula

To verify the signed jar file

jarsigner -verify -verbose -certs "D:\myfolder\your.jar"

How To Create a Signed Applet

1. Package the applet into a JAR file. The applet must be in a JAR file before a certificate can be attached to it. Use the jar JDK utility. If the applet was previously referenced with the help of a codebase attribute in <> tag, replace the codebase attribute with the archive attribute. The value of the archive attribute is a URL of a JAR file.

To use the 'jar' command, open an MS-DOS window and navigate to the directory where your classes are stored. Notice that this assumes you have already set up a Path on your machine which allows you to use Java SDK commands from anywhere. The instructions for setting up your Path correctly are contained in chapter 2 of the Murach textbook.

On my machine for this example, I navigate in the DOS window to

C:\My Documents\Baruch\4150\Day14\EmailApplet\classes>

Then I use a jar command which specifies the options, output file name and the files to include:

>jar cfv EmailApplet.jar User.class UserIO.class UserEmailPanel.class EmailApplet.class

(You have to write this all in one line; there is a break above only for the purposes of the Word document layout.) Make sure you preserve case when you list these files, or Java won't be able to find them when it opens the .jar archive.

Once you have created the jar file, you can look at its contents by using 'tf' options:

>jar tf EmailApplet.jar

This will show you the metafiles created for the jar, and the files you added to it.

If you run your HTML file now, you will get a security exception (look in the Java console), and the read/write operations will not be carried out. You need to sign it. But before you can sign it, you need a key.



2. Create a public/private key pair. The command for this is

keytool -genkey

keytool is another SDK utility. It will prompt you for a password to your keystore. The keystore is a file that contains your public/private key-pairs, and the public-keys of others with whom you exchange information. See the documentation in the above link. Don't forget your password! You'll need it again.

You can use any of the options listed in the keytool documentation, but generally all you need is:

keytool -genkey -alias

If you don't specify an alias, it will make a key for you called 'mykey'. This will also work fine.

3. Create a certificate for the key you created in the previous step.

keytool -selfcert -alias

Again, keytool will prompt you for a keystore password and remaining parameters. This certificate is now self-signed by you, meaning that it has not been validated by any third party. This is suitable for demo purposes, and may be acceptable to yourself and those who know you because if there is any doubt that the certificate is really yours they can always call you up and ask you for the digest to verify that it is really you and not some impostor that created the certificate. However, if this applet were to be widely distributed, and you wanted it to be accepted by those who do not know you personally, you would certainly want to pay a modest fee to obtain a certificate that is validated by a trusted certificate authority. The procedure for this is straightforward, but beyond the scope of this simple tutorial.

Finally, you can see the certificates available in your keystore by using the following command:

keytool -list



4. Run jarsigner associate this certificate with the JAR file that contains your applet. You will need to give the name of the public key of the certificate you just created. This creates a digest for each file in your JAR and signs them with your private key. These digests or hashes, the public key, and the certificate will all be included in the "WEB-INF" directory of the JAR.

For my demo, I wanted to make several jars, some signed, some not, and some with signatures, some without, so I needed to use the -signedjar option. If you don't use this option, then the .jar file you are signing will be overwritten with the signed version. After the options, you complete your command line with the name of the file being signed and the alias of the key you want to sign it with. So for example, at one point I used:

jarsigner -signedjar EmailApplet2.jar EmailApplet.jar mykey

You can then check to see that the applet is signed by using the -verify option. It's a good idea also to add the -verbose option, so you can see all the details:

jarsigner -verbose -verify EmailApplet2.jar

Your applet is now signed. The next time you or someone else downloads it in it's page the browser will present a dialog box displaying the credentials you just created for it and asking the user permission to run it. If he/she chooses not to, the applet will throw the same AccessControlException that we saw in the Java Console window the first time we tried to run it in our browser. The difference is that now the user gets to make an informed decision as to whether or not they trust your applet to not harm his/her system.

You will only need to generate the public/private key-pair once, but you may want to automate the steps that create and sign the JAR file, because you will need to repeat those every time you modify anything in your code. Remember to update your HTML ARCHIVE command to point to the right .jar file, so that your web page tries to load the applet that is actually signed.

Be careful how you specify the destination for the file to be written in your Java IO class. If you only use the file name, the file will be written at the user 'home', which in the case of my machine is the Desktop.

Spring Tutorial Interview Questions (Java)

What is Spring?

Spring is a lightweight inversion of control and aspect-oriented container framework.

Explain Spring?

• Lightweight - spring is lightweight when it comes to size and transparency. The basic version of spring framework is around 1MB. And the processing overhead is also very negligible.
• Inversion of control (IoC) - Loose coupling is achieved in spring using the technique Inversion of Control. The objects give their dependencies instead of creating or looking for dependent objects.
• Aspect oriented (AOP) - Spring supports Aspect oriented programming and enables cohesive development by separating application business logic from system services.
• Container - Spring contains and manages the life cycle and configuration of application objects.
• Framework - Spring provides most of the intra functionality leaving rest of the coding to the developer.

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What is IOC (or Dependency Injection)?

The basic concept of the Inversion of Control pattern (also known as dependency injection) is that you do not create your objects but describe how they should be created. You don't directly connect your components and services together in code but describe which services are needed by which components in a configuration file. A container (in the case of the Spring framework, the IOC container) is then responsible for hooking it all up.

i.e., Applying IoC, objects are given their dependencies at creation time by some external entity that coordinates each object in the system. That is, dependencies are injected into objects. So, IoC means an inversion of responsibility with regard to how an object obtains references to collaborating objects.

What are the different types of IOC (dependency injection) ?

There are three types of dependency injection:

• Constructor Injection (e.g. Pico container, Spring etc): Dependencies are provided as constructor parameters.
• Setter Injection (e.g. Spring): Dependencies are assigned through JavaBeans properties (ex: setter methods).
• Interface Injection (e.g. Avalon): Injection is done through an interface.

Note: Spring supports only Constructor and Setter Injection

What are the benefits of IOC (Dependency Injection)?

Benefits of IOC (Dependency Injection) are as follows:

Minimizes the amount of code in your application. With IOC containers you do not care about how services are created and how you get references to the ones you need. You can also easily add additional services by adding a new constructor or a setter method with little or no extra configuration.

Make your application more testable by not requiring any singletons or JNDI lookup mechanisms in your unit test cases. IOC containers make unit testing and switching implementations very easy by manually allowing you to inject your own objects into the object under test.

Loose coupling is promoted with minimal effort and least intrusive mechanism. The factory design pattern is more intrusive because components or services need to be requested explicitly whereas in IOC the dependency is injected into requesting piece of code. Also some containers promote the design to interfaces not to implementations design concept by encouraging managed objects to implement a well-defined service interface of your own.

IOC containers support eager instantiation and lazy loading of services. Containers also provide support for instantiation of managed objects, cyclical dependencies, life cycles management, and dependency resolution between managed objects etc.

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What are the advantages of Spring framework?

The advantages of Spring are as follows:

• Spring has layered architecture. Use what you need and leave you don't need now.
• Spring Enables POJO Programming. There is no behind the scene magic here. POJO programming enables continuous integration and testability.
• Dependency Injection and Inversion of Control Simplifies JDBC
• Open source and no vendor lock-in.

What are the different modules in Spring framework?

• The Core container module
• Application context module
• AOP module (Aspect Oriented Programming)
• JDBC abstraction and DAO module
• O/R mapping integration module (Object/Relational)
• Web module
• MVC framework module

What is the structure of Spring framework?

Spring Framework

What is the Core container module?

This module is provides the fundamental functionality of the spring framework. In this module BeanFactory is the heart of any spring-based application. The entire framework was built on the top of this module. This module makes the spring container.

What is Application context module?

The Application context module makes spring a framework. This module extends the concept of BeanFactory, providing support for internationalization (I18N) messages, application lifecycle events, and validation. This module also supplies many enterprise services such JNDI access, EJB integration, remoting, and scheduling. It also provides support to other framework.

What is AOP module?

The AOP module is used for developing aspects for our Spring-enabled application. Much of the support has been provided by the AOP Alliance in order to ensure the interoperability between Spring and other AOP frameworks. This module also introduces metadata programming to Spring. Using Spring's metadata support, we will be able to add annotations to our source code that instruct Spring on where and how to apply aspects.

What is JDBC abstraction and DAO module?

Using this module we can keep up the database code clean and simple, and prevent problems that result from a failure to close database resources. A new layer of meaningful exceptions on top of the error messages given by several database servers is bought in this module. In addition, this module uses Spring's AOP module to provide transaction management services for objects in a Spring application.

What are object/relational mapping integration module?

Spring also supports for using of an object/relational mapping (ORM) tool over straight JDBC by providing the ORM module. Spring provide support to tie into several popular ORM frameworks, including Hibernate, JDO, and iBATIS SQL Maps. Spring's transaction management supports each of these ORM frameworks as well as JDBC.

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What is web module?

This module is built on the application context module, providing a context that is appropriate for web-based applications. This module also contains support for several web-oriented tasks such as transparently handling multipart requests for file uploads and programmatic binding of request parameters to your business objects. It also contains integration support with Jakarta Struts.

What is web module?

Spring comes with a full-featured MVC framework for building web applications. Although Spring can easily be integrated with other MVC frameworks, such as Struts, Spring's MVC framework uses IoC to provide for a clean separation of controller logic from business objects. It also allows you to declaratively bind request parameters to your business objects. It also can take advantage of any of Spring's other services, such as I18N messaging and validation.

What is a BeanFactory?

A BeanFactory is an implementation of the factory pattern that applies Inversion of Control to separate the application's configuration and dependencies from the actual application code.

What is the difference between Bean Factory and Application Context?

On the surface, an application context is same as a bean factory. But application context offers much more..

• Application contexts provide a means for resolving text messages, including support for i18n of those messages.
• Application contexts provide a generic way to load file resources, such as images.
• Application contexts can publish events to beans that are registered as listeners.
• Certain operations on the container or beans in the container, which have to be handled in a programmatic fashion with a bean factory, can be handled declaratively in an application context.
• ResourceLoader support: Spring's Resource interface us a flexible generic abstraction for handling low-level resources. An application context itself is a ResourceLoader, Hence provides an application with access to deployment-specific Resource instances.
• MessageSource support: The application context implements MessageSource, an interface used to obtain localized messages, with the actual implementation being pluggable

What is AOP Alliance?

AOP Alliance is an open-source project whose goal is to promote adoption of AOP
and interoperability among different AOP implementations by defining a common
set of interfaces and components.

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What is Spring configuration file?

Spring configuration file is an XML file. This file contains the classes information and describes how these classes are configured and introduced to each other.

What does a simple spring application contain?

These applications are like any Java application. They are made up of several classes, each performing a specific purpose within the application. But these classes are configured and introduced to each other through an XML file. This XML file describes how to configure the classes, known as the Spring configuration file.

What is XMLBeanFactory?

BeanFactory has many implementations in Spring. But one of the most useful one is org.springframework.beans.factory.xml.XmlBeanFactory, which loads its beans based on the definitions contained in an XML file. To create an XmlBeanFactory, pass a java.io.InputStream to the constructor. The InputStream will provide the XML to the factory. For example, the following code snippet uses a java.io.FileInputStream to provide a bean definition XML file to XmlBeanFactory.
BeanFactory factory = new XmlBeanFactory(new FileInputStream("beans.xml"));
To retrieve the bean from a BeanFactory, call the getBean() method by passing the name of the bean you want to retrieve.
MyBean myBean = (MyBean) factory.getBean("myBean");

What are important ApplicationContext implementations in spring framework?

• ClassPathXmlApplicationContext - This context loads a context definition from an XML file located in the class path, treating context definition files as class path resources.
• FileSystemXmlApplicationContext - This context loads a context definition from an XML file in the filesystem.
• XmlWebApplicationContext - This context loads the context definitions from an XML file contained within a web application.

Explain Bean lifecycle in Spring framework?

1. The spring container finds the bean's definition from the XML file and instantiates the bean.
2. Using the dependency injection, spring populates all of the properties as specified in the bean definition.
3. If the bean implements the BeanNameAware interface, the factory calls setBeanName() passing the bean's ID.
4. If the bean implements the BeanFactoryAware interface, the factory calls setBeanFactory(), passing an instance of itself.
5. If there are any BeanPostProcessors associated with the bean, their post- ProcessBeforeInitialization() methods will be called.
6. If an init-method is specified for the bean, it will be called.
7. Finally, if there are any BeanPostProcessors associated with the bean, their postProcessAfterInitialization() methods will be called

What is bean wiring?

Combining together beans within the Spring container is known as bean wiring or wiring. When wiring beans, you should tell the container what beans are needed and how the container should use dependency injection to tie them together.

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How to add a bean in spring application?

In the bean tag the id attribute specifies the bean name and the class attribute specifies the fully qualified class name.

What are singleton beans and how can you create prototype beans?

Beans defined in spring framework are singleton beans. There is an attribute in bean tag named 'singleton' if specified true then bean becomes singleton and if set to false then the bean becomes a prototype bean. By default it is set to true. So, all the beans in spring framework are by default singleton beans.

What are the important beans lifecycle methods?

There are two important bean lifecycle methods. The first one is setup which is called when the bean is loaded in to the container. The second method is the teardown method which is called when the bean is unloaded from the container.

How can you override beans default lifecycle methods?

The bean tag has two more important attributes with which you can define your own custom initialization and destroy methods. Here I have shown a small demonstration. Two new methods fooSetup and fooTeardown are to be added to your Foo class.

What are Inner Beans?

When wiring beans, if a bean element is embedded to a property tag directly, then that bean is said to the Inner Bean. The drawback of this bean is that it cannot be reused anywhere else.

What is DelegatingVariableResolver?

Spring provides a custom JavaServer Faces VariableResolver implementation that extends the standard Java Server Faces managed beans mechanism which lets you use JSF and Spring together. This variable resolver is called as DelegatingVariableResolver

How to integrate Java Server Faces (JSF) with Spring?

JSF and Spring do share some of the same features, most noticeably in the area of IOC services. By declaring JSF managed-beans in the faces-config.xml configuration file, you allow the FacesServlet to instantiate that bean at startup. Your JSF pages have access to these beans and all of their properties.We can integrate JSF and Spring in two ways:

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DelegatingVariableResolver: Spring comes with a JSF variable resolver that lets you use JSF and Spring together.

The DelegatingVariableResolver will first delegate value lookups to the default resolver of the underlying JSF implementation, and then to Spring's 'business context' WebApplicationContext. This allows one to easily inject dependencies into one's JSF-managed beans.

FacesContextUtils:custom VariableResolver works well when mapping one's properties to beans in faces-config.xml, but at times one may need to grab a bean explicitly. The FacesContextUtils class makes this easy. It is similar to WebApplicationContextUtils, except that it takes a FacesContext parameter rather than a ServletContext parameter.

ApplicationContext ctx = FacesContextUtils.getWebApplicationContext(FacesContext.getCurrentInstance());

What is Significance of JSF- Spring integration ?

Spring - JSF integration is useful when an event handler wishes to explicitly invoke the bean factory to create beans on demand, such as a bean that encapsulates the business logic to be performed when a submit button is pressed.

How to integrate your Struts application with Spring?

To integrate your Struts application with Spring, we have two options:
Configure Spring to manage your Actions as beans, using the ContextLoaderPlugin, and set their dependencies in a Spring context file.
Subclass Spring's ActionSupport classes and grab your Spring-managed beans explicitly using a getWebApplicationContext() method.

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What are the different types of bean injections?

There are two types of bean injections.
1. By setter
2. By constructor

What is Auto wiring?

You can wire the beans as you wish. But spring framework also does this work for you. It can auto wire the related beans together. All you have to do is just set the autowire attribute of bean tag to an autowire type.

What are different types of Autowire types?

There are four different types by which autowiring can be done.

• byName
• byType
• constructor
• autodetect

What are the different types of events related to Listeners?

There are a lot of events related to ApplicationContext of spring framework. All the events are subclasses of org.springframework.context.Application-Event. They are

• ContextClosedEvent - This is fired when the context is closed.
• ContextRefreshedEvent - This is fired when the context is initialized or refreshed.
• RequestHandledEvent - This is fired when the web context handles any request.

What is an Aspect?

An aspect is the cross-cutting functionality that you are implementing. It is the aspect of your application you are modularizing. An example of an aspect is logging. Logging is something that is required throughout an application. However, because applications tend to be broken down into layers based on functionality, reusing a logging module through inheritance does not make sense. However, you can create a logging aspect and apply it throughout your application using AOP.

What is a Jointpoint?

A joinpoint is a point in the execution of the application where an aspect can be plugged in. This point could be a method being called, an exception being thrown, or even a field being modified. These are the points where your aspect's code can be inserted into the normal flow of your application to add new behavior.

What is an Advice?

Advice is the implementation of an aspect. It is something like telling your application of a new behavior. Generally, and advice is inserted into an application at joinpoints.

What is a Pointcut?

A pointcut is something that defines at what joinpoints an advice should be applied. Advices can be applied at any joinpoint that is supported by the AOP framework. These Pointcuts allow you to specify where the advice can be applied.

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What is an Introduction in AOP?

An introduction allows the user to add new methods or attributes to an existing class. This can then be introduced to an existing class without having to change the structure of the class, but give them the new behavior and state.

What is a Target?

A target is the class that is being advised. The class can be a third party class or your own class to which you want to add your own custom behavior. By using the concepts of AOP, the target class is free to center on its major concern, unaware to any advice that is being applied.

What is a Proxy?

A proxy is an object that is created after applying advice to a target object. When you think of client objects the target object and the proxy object are the same.

What is meant by Weaving?

The process of applying aspects to a target object to create a new proxy object is called as Weaving. The aspects are woven into the target object at the specified joinpoints.

What are the different points where weaving can be applied?

• Compile Time
• Classload Time
• Runtime

What are the different advice types in spring?

• Around : Intercepts the calls to the target method
• Before : This is called before the target method is invoked
• After : This is called after the target method is returned
• Throws : This is called when the target method throws and exception
• Around : org.aopalliance.intercept.MethodInterceptor
• Before : org.springframework.aop.BeforeAdvice
• After : org.springframework.aop.AfterReturningAdvice
• Throws : org.springframework.aop.ThrowsAdvice

What are the different types of AutoProxying?

• BeanNameAutoProxyCreator
• DefaultAdvisorAutoProxyCreator
• Metadata autoproxying

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What is the Exception class related to all the exceptions that are thrown in spring applications?

DataAccessException - org.springframework.dao.DataAccessException

What kind of exceptions those spring DAO classes throw?

The spring's DAO class does not throw any technology related exceptions such as SQLException. They throw exceptions which are subclasses of DataAccessException.

What is DataAccessException?

DataAccessException is a RuntimeException. This is an Unchecked Exception. The user is not forced to handle these kinds of exceptions.

How can you configure a bean to get DataSource from JNDI?

How JDBC can be used more efficiently in spring framework?

JDBC can be used more efficiently with the help of a template class provided by spring framework called as JdbcTemplate.

How JdbcTemplate can be used?

With use of Spring JDBC framework the burden of resource management and error handling is reduced a lot. So it leaves developers to write the statements and queries to get the data to and from the database.

JdbcTemplate template = new JdbcTemplate(myDataSource);

A simple DAO class looks like this.

public class StudentDaoJdbc implements StudentDao {
private JdbcTemplate jdbcTemplate;

public void setJdbcTemplate(JdbcTemplate jdbcTemplate) {
this.jdbcTemplate = jdbcTemplate;
}
more..
}

The configuration is shown below.

How do you write data to backend in spring using JdbcTemplate?

The JdbcTemplate uses several of these callbacks when writing data to the database. The usefulness you will find in each of these interfaces will vary. There are two simple interfaces. One is PreparedStatementCreator and the other interface is BatchPreparedStatementSetter.

Explain about PreparedStatementCreator?

PreparedStatementCreator is one of the most common used interfaces for writing data to database. The interface has one method createPreparedStatement().

PreparedStatement createPreparedStatement(Connection conn)
throws SQLException;

When this interface is implemented, we should create and return a PreparedStatement from the Connection argument, and the exception handling is automatically taken care off. When this interface is implemented, another interface SqlProvider is also implemented which has a method called getSql() which is used to provide sql strings to JdbcTemplate.

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Explain about BatchPreparedStatementSetter?

If the user what to update more than one row at a shot then he can go for BatchPreparedStatementSetter. This interface provides two methods

setValues(PreparedStatement ps, int i) throws SQLException;

int getBatchSize();

The getBatchSize() tells the JdbcTemplate class how many statements to create. And this also determines how many times setValues() will be called.

Explain about RowCallbackHandler and why it is used?

In order to navigate through the records we generally go for ResultSet. But spring provides an interface that handles this entire burden and leaves the user to decide what to do with each row. The interface provided by spring is RowCallbackHandler. There is a method processRow() which needs to be implemented so that it is applicable for each and everyrow.

void processRow(java.sql.ResultSet rs);

What are the types of the transaction management Spring supports ?

Spring Framework supports:
Programmatic transaction management.
Declarative transaction management.

What are the benefits of the Spring Framework transaction management ?

The Spring Framework provides a consistent abstraction for transaction management that delivers the following benefits:
Provides a consistent programming model across different transaction APIs such as JTA, JDBC, Hibernate, JPA, and JDO.
Supports declarative transaction management.
Provides a simpler API for programmatic transaction management than a number of complex transaction APIs such as JTA.
Integrates very well with Spring's various data access abstractions.

Why most users of the Spring Framework choose declarative transaction management ?

Most users of the Spring Framework choose declarative transaction management because it is the option with the least impact on application code, and hence is most consistent with the ideals of a non-invasive lightweight container.

Explain the similarities and differences between EJB CMT and the Spring Framework's declarative transaction management ?

The basic approach is similar: it is possible to specify transaction behavior (or lack of it) down to individual method level. It is
possible to make a setRollbackOnly() call within a transaction context if necessary.

The differences are:

• Unlike EJB CMT, which is tied to JTA, the Spring Framework's declarative transaction management works in any environment. It can work with JDBC, JDO, Hibernate or other transactions under the covers, with configuration changes only.
• The Spring Framework enables declarative transaction management to be applied to any class, not merely special classes such as EJBs.
• The Spring Framework offers declarative rollback rules: this is a feature with no EJB equivalent. Both programmatic and declarative support for rollback rules is provided.
• The Spring Framework gives you an opportunity to customize transactional behavior, using AOP. With EJB CMT, you have no way to influence the container's transaction management other than setRollbackOnly().
• The Spring Framework does not support propagation of transaction contexts across remote calls, as do high-end application servers.

When to use programmatic and declarative transaction management ?

Programmatic transaction management is usually a good idea only if you have a small number of transactional operations.
On the other hand, if your application has numerous transactional operations, declarative transaction management is usually worthwhile. It keeps transaction management out of business logic, and is not difficult to configure.

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Explain about the Spring DAO support ?

The Data Access Object (DAO) support in Spring is aimed at making it easy to work with data access technologies like JDBC, Hibernate or JDO in a consistent way. This allows one to switch between the persistence technologies fairly easily and it also allows one to code without worrying about catching exceptions that are specific to each technology.

What are the exceptions thrown by the Spring DAO classes ?

Spring DAO classes throw exceptions which are subclasses of DataAccessException(org.springframework.dao.DataAccessException).Spring provides a convenient translation from technology-specific exceptions like SQLException to its own exception class hierarchy with the DataAccessException as the root exception. These exceptions wrap the original exception.

What is SQLExceptionTranslator ?

SQLExceptionTranslator, is an interface to be implemented by classes that can translate between SQLExceptions and Spring's own data-access-strategy-agnostic org.springframework.dao.DataAccessException.

What are the differences between EJB and Spring ?

Feature	EJB	Spring
Transaction management	Must use a JTA transaction manager. Supports transactions that span remote method calls.	Supports multiple transaction environments through its PlatformTransactionManager interface, including JTA, Hibernate, JDO, and JDBC. Does not natively support distributed transactions-it must be used with a JTA transaction manager.
Declarative transaction support	Can define transactions declaratively through the deployment descriptor. Can define transaction behavior per method or per class by using the wildcard character *. Cannot declaratively define rollback behavior-this must be done programmatically.	Can define transactions declaratively through the Spring configuration file or through class metadata. Can define which methods to apply transaction behavior explicitly or by using regular expressions. Can declaratively define rollback behavior per method and per exception type.
Persistence	Supports programmatic bean-managed persistence and declarative container managed persistence.	Provides a framework for integrating with several persistence technologies, including JDBC, Hibernate, JDO, and iBATIS.
Declarative security	Supports declarative security through users and roles. The management and implementation of users and roles is container specific. Declarative security is configured in the deployment descriptor.	No security implementation out-of-the box. Acegi, an open source security framework built on top of Spring, provides declarative security through the Spring configuration file or class metadata.
Distributed computing	Provides container-managed remote method calls.	Provides proxying for remote calls via RMI, JAX-RPC, and web services.