1. What makes J2EE suitable for distributed multitiered Applications?
- The J2EE platform uses a multitiered distributed application model. Application logic is divided into components according to function, and the various application components that make up a J2EE application are installed on different machines depending on the tier in the multitiered J2EE environment to which the application component belongs. The J2EE application parts are:
Client-tier components run on the client machine.
Web-tier components run on the J2EE server.
Business-tier components run on the J2EE server.
Enterprise information system (EIS)-tier software runs on the EIS server.
2. What is J2EE?
J2EE is an environment for developing and deploying enterprise applications. The J2EE platform consists of a set of services, application programming interfaces (APIs), and protocols that provide the functionality for developing multitiered, web-based applications.
3. What are the components of J2EE application?
- A J2EE component is a self-contained functional software unit that is assembled into a J2EE application with its related classes and files and communicates with other components. The J2EE specification defines the following J2EE components.
Application clients and applets are client components.
Java Servlet and JavaServer Pages technology components are web components.
Enterprise JavaBeans components (enterprise beans) are business components.
Resource adapter components provided by EIS and tool vendors.
4. What do Enterprise JavaBeans components contain?
Enterprise JavaBeans components contains Business code, which is logic
that solves or meets the needs of a particular business domain such as banking, retail, or finance, is handled by enterprise beans running in the business tier. All the business code is contained inside an Enterprise Bean which receives data from client programs, processes it (if necessary), and sends it to the enterprise information system tier for storage. An enterprise bean also retrieves data from storage, processes it (if necessary), and sends it back to the client program.
5. Is J2EE application only a web-based?
No, It depends on type of application that client wants. A J2EE application can be web-based or non-web-based. if an application client executes on the client machine, it is a non-web-based J2EE application. The J2EE application can provide a way for users to handle tasks such as J2EE system or application administration. It typically has a graphical user interface created from Swing or AWT APIs, or a command-line interface. When user request, it can open an HTTP connection to establish communication with a servlet running in the web tier.
6. Are JavaBeans J2EE components?
No. JavaBeans components are not considered J2EE components by the J2EE specification. They are written to manage the data flow between an application client or applet and components running on the J2EE server or between server components and a database. JavaBeans components written for the J2EE platform have instance variables and get and set methods for accessing the data in the instance variables. JavaBeans components used in this way are typically simple in design and implementation, but should conform to the naming and design conventions outlined in the JavaBeans component architecture.
7. Is HTML page a web component?
No. Static HTML pages and applets are bundled with web components during application assembly, but are not considered web components by the J2EE specification. Even the server-side utility classes are not considered web components, either.
8. What can be considered as a web component?
J2EE Web components can be either servlets or JSP pages. Servlets are Java programming language classes that dynamically process requests and construct responses. JSP pages are text-based documents that execute as servlets but allow a more natural approach to creating static content.
9. What is the container?
Containers are the interface between a component and the low-level platform specific functionality that supports the component. Before a Web, enterprise bean, or application client component can be executed, it must be assembled into a J2EE application and deployed into its container.
10. What are container services?
A container is a runtime support of a system-level entity. Containers provide components with services such as lifecycle management, security, deployment, and threading.
11. What is the web container?
Servlet and JSP containers are collectively referred to as Web containers. It manages the execution of JSP page and servlet components for J2EE applications. Web components and their container run on the J2EE server.
12. What is Enterprise JavaBeans (EJB) container?
It manages the execution of enterprise beans for J2EE applications.
Enterprise beans and their container run on the J2EE server.
13. What is Applet container?
I Manages the execution of applets. Consists of a Web browser and Java Plugin running on the client together.
14. How do we package J2EE components?
J2EE components are packaged separately and bundled into a J2EE application for deployment. Each component, its related files such as GIF and HTML files or server-side utility classes, and a deployment descriptor are assembled into a module and added to the J2EE application. A J2EE application is composed of one or more enterprise bean,Web, or application client component modules. The final enterprise solution can use one J2EE application or be made up of two or more J2EE applications, depending on design requirements. A J2EE application and each of its modules has its own deployment descriptor. A deployment descriptor is an XML document with an .xml extension that describes a component’s deployment settings.
15. What is a thin client?
A thin client is a lightweight interface to the application that does not have such operations like query databases, execute complex business rules, or connect to legacy applications.
16. What are types of J2EE clients?
Following are the types of J2EE clients:
Applets
Application clients
Java Web Start-enabled rich clients, powered by Java Web Start technology.
Wireless clients, based on Mobile Information Device Profile (MIDP) technology.
17. What is deployment descriptor?
A deployment descriptor is an Extensible Markup Language (XML) text-based file with an .xml extension that describes a component’s deployment settings. A J2EE application and each of its modules has its own deployment descriptor. For example, an enterprise bean module deployment descriptor declares transaction attributes and security authorizations
for an enterprise bean. Because deployment descriptor information is declarative, it can be changed without modifying the bean source code. At run time, the J2EE server reads the deployment descriptor and acts upon the component accordingly.
18. What is the EAR file?
An EAR file is a standard JAR file with an .ear extension, named from Enterprise ARchive file. A J2EE application with all of its modules is delivered in EAR file.
19. What is JTA and JTS?
JTA is the abbreviation for the Java Transaction API. JTS is the abbreviation for the Jave Transaction Service. JTA provides a standard interface and allows you to demarcate transactions in a manner that is independent of the transaction manager implementation. The J2EE SDK implements the transaction manager with JTS. But your code doesn’t call the JTS methods directly. Instead, it invokes the JTA methods, which then call the lower-level JTS routines. Therefore, JTA is a high level transaction interface that your application uses to control transaction. and JTS is a low level transaction interface and ejb uses behind the scenes (client code doesn’t directly interact with JTS. It is based on object transaction service(OTS) which is part of CORBA.
20. What is JAXP?
- JAXP stands for Java API for XML. XML is a language for representing and describing text-based data which can be read and handled by any program or tool that uses XML APIs. It provides standard services to determine the type of an arbitrary piece of data, encapsulate access to it, discover the operations available on it, and create the appropriate JavaBeans component to perform those operations.
21. What is J2EE Connector?
- The J2EE Connector API is used by J2EE tools vendors and system integrators to create resource adapters that support access to enterprise information systems that can be plugged into any J2EE product. Each type of database or EIS has a different resource adapter. Note: A resource adapter is a software component that allows J2EE application components to access and interact with the underlying resource manager. Because a resource adapter is specific to its resource manager, there is typically a different resource adapter for each type of database or enterprise information system.
22. What is JAAP?
The Java Authentication and Authorization Service (JAAS) provides a way for a J2EE application to authenticate and authorize a specific user or group of users to run it. It is a standard Pluggable Authentication Module (PAM) framework that extends the Java 2 platform security architecture to support user-based authorization.
23. What is Java Naming and Directory Service?
- The JNDI provides naming and directory functionality. It provides applications with methods for performing standard directory operations, such as associating attributes with objects and searching for objects using their attributes. Using JNDI, a J2EE application can store and retrieve any type of named Java object. Because JNDI is independent of any specific implementations, applications can use JNDI to access multiple naming and directory services, including existing naming and
directory services such as LDAP, NDS, DNS, and NIS.
24. What is Struts?
- A Web page development framework. Struts combines Java Servlets, Java Server Pages, custom tags, and message resources into a unified framework. It is a cooperative, synergistic platform, suitable for development teams, independent developers, and everyone between.
25. How is the MVC design pattern used in Struts framework?
In the MVC design pattern, application flow is mediated by a central Controller. The Controller delegates requests to an appropriate handler. The handlers are tied to a Model, and each handler acts as an adapter between the request and the Model. The Model represents, or encapsulates, an application’s business logic or state. Control is usually then forwarded back through the Controller to the appropriate View. The forwarding can be determined by consulting a set of mappings, usually loaded from a database or configuration file. This provides a loose coupling between the View and Model, which can make an application significantly easier to create and maintain. Controller: Servlet controller which supplied by Struts itself; View: what you can see on the screen, a JSP page and presentation components; Model: System state and a business logic JavaBeans.
Q) Based on Scenario:
Calling another web application resource using RequestDispatcher from other web application?
My web application calls response.sendRedirect("/newapp/home.jsp").
It works fine. But i am also passing some request parameters which are exposed through request-header.
Is there a way i can use RequestDispatcher to invoke a jsp in another web-app.
getServletContext().getRequestDispatcher(newURL).forward(request, response)
But it didn't work.
I am doing this in a Struts action class.
Any ideas?
RequestDispatcher can forward request to the resources running within the webapplication. It cannot help in forwarding request to another web application.
Have a look at the getRequestDispatcher method, it comes in two forms. One allows you to access resources from another context in the same web container
Try this..you can also find several examples on web for httpclient / httpproxy
web.xml
======
<servlet>
<servlet-name>HttpProxy</servlet-name>
<servlet-class>weblogic.servlet.proxy.HttpProxyServlet</servlet-class>
<init-param>
<param-name>redirectURL</param-name>
<param-value>http://AnotherAppHostName:yourPort</param-value>
</init-param>
<init-param>
<param-name>WebLogicHost</param-name>
<param-value>AnotherAppHostName</param-value>
</init-param>
<init-param>
<param-name>WebLogicPort</param-name>
<param-value>yourPort</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>HttpProxy</servlet-name>
<url-pattern>/anotherapp/*</url-pattern>
</servlet-mapping>
In your action or servlet
=================
request.getRequestDispatcher("/anotherapp/yoursevletOrJsp").include(request,response);
Question 2: How can we create deadlock condition on our servlet?
Ans: one simple way to call doPost() method inside doGet() and doGet()method inside doPost() it will create deadlock situation for a servlet. This is rather simple servlet interview questions but yet tricky if you don’t think of it J
Question 3: For initializing a servlet can we use constructor in place of init ().
Ans: No, we can not use constructor for initializing a servlet because for initialization we need an object of servletConfig using this object we get all the parameter which are defined in deployment descriptor for initializing a servlet and in servlet class we have only default constructor according to older version of java so if we want to pass a
Config object we don’t have parametrized constructor and apart from this servlet is loaded and initialized by container so ots a job of container to call the method according to servlet specification they have lifecycle method so init() method is called firstly.
More important Java doesn't allow interfaces to declare constructors. These kinds of servlet interview questions are quite popular on service based companies who just want to dig one level more.
Question 4: Why super.init (config) wiil be the first statement inside init(config) method.
Ans: This will be the first statement if we are overriding the init(config ) method by this way we will store the config object for future reference and we can use by getServletConfig () to get information about config object if will not do this config object will be lost and we have only one way to get config object because servlet pass config object only in init method . Without doing this if we call the servletConfig method will get NullPointerException.
Question5: Can we call destroy() method inside the init() method is yes what will happen?
Ans:Yes we can call like this but if we have not override this method container will call the default method and nothing will happen.after calling this if any we have override the method then the code written inside is executed.
Question 6: How can we refresh servlet on client and server side automatically?
Ans: On client side we can use Meta http refresh and server side we can use server push.
Question 7: How can you get the information about one servlet context in another servlet?
Ans: In context object we can set the attribute which we want on another servlet and we can get that attribute using their name on another servlet.
Context.setAttribute (“name”,” value”)
Context.getAttribute (“name”)
Question 8: Why we need to implement Single Thread model in case of Servlet.
Ans: In J2EE we can implement our servlet on two different ways either by using:
1. Single Thread Model
2. Multithread Model
Depending upon our scenario, if we have implemented single thread means only one instance is going handle one request at a time no two thread will concurrently execute service method of servlet.
Example in banking account where sensitive data is handle mostly this scenario was used this interface is deprecated in Servlet API version 2.4.
As the name signifies multi thread means a servlet is capable to handle multiple requests at same time. This servlet interview question was quite popular few years back on entry level but now its loosing its shine.
Question 9: what is servlet collaboration?
Ans communication between two servlet is called servlet collaboration which is achieved by 3 ways.
1. RequestDispatchers include () and forward() method .
2. Using sendRedirect()method of Response object.
3. Using servlet Context methods
Question 10: What is the difference between ServletConfig and ServletContext?
Ans: ServletConfig as the name implies provide the information about configuration of a servlet which is defined inside the web.xml file or we can say deployment descriptor.its a specific object for each servlet.
ServletContext is application specific object which is shared by all the servlet belongs to one application in one JVM .this is single object which represent our application and all the servlet access application specific data using this object.servlet also use their method to communicate with container.
Q) Difference between interceptors and filters?
The most significant difference is that "interceptors" are a part of the Struts 2 framework, and are only part of requests handling that is done by the STruts 2 framework. "Filters" on the other hand are a part of the Servlet Specifcation; in other words, they are part of the Servlet API. If you are using Struts 2, you should user interceptors for wrapping functionality around your Struts 2 actions. If you are trying to wrap functionality around requests coming to your webapp, but not being handled by Struts 2, then a filter might be more appropriate.
the interceptor stack fires on every request.
filters only apply to the urls for which they are defined.
Filters are part of the Servlet API, Interceptors are Struts 2. (Seems obvious though)
The Interceptor stack fires on requests in a configured package while filters only apply to their mapped URLs.
Interceptors can be configured to execute or not depending on specific target action methods via excludeMethods and includeMethods while Filters lack this feature.
Filters are an implementation of the Intercepting Filter pattern while Interceptors are of the Interceptor pattern.
