HTML and CSS Interview Questions and Answers

Q. Can you have a DIV element nested inside a SPAN element?
A. It is a bad practice to have a DIV element nested inside a SPAN element. You can have a SPAN inside a DIV. The reason being the DIV is a block element and SPAN is an inline element. So, why would you want to have a block element inside an inline element? SPAN is a like sub tag, which applies styles for the specified content in-between the SPAN tag.

Q. How will you decide between using nested HTML table tags and a DIV tag with CSS?
A. Use DIV tags with CSS for laying out the web pages and use TABLE for representing data.

Tabular data represented using html table tag.

To layout web page elements

The traditional way of laying out web pages was to place them inside invisible tables as demonstrated below. This way of laying out is more complicated to do, harder to maintain and makes the web pages to load very slowly.

Bad: Laying out with nested TABLE tags and CSS

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Table Layout</title>

<style type="text/css">
table {
 width: 100%;
 height: 1000px;
}

td.header {
 width: 100%;
 text-align: center;
 background-color: yellow;
}

td.contents {
 width: 80%;
 text-align: center;
 background-color: orange;
}

td.rhsmenu {
 width: 20%;
 text-align: center;
 background-color: green;
}

td.footer {
 width: 100%;
 text-align: center;
 background-color: blue;
}
</style>


</head>
<body>
 <table>
  <tbody>
   <tr height="15%">
    <td class="header" colspan="2">Header Information</td>
   </tr>
   <tr height="65%">
    <td class="contents">Contents go
     here</td>
    <td class="rhsmenu">RHS Panel</td>
   </tr>
   <tr height="20%">
    <td class="footer" colspan="2">Footer Information</td>
   </tr>
  </tbody>
 </table>

</body>
</html>

 The newer way to lay out your page elements is using DIVs and CSS. It can do everything tables can do and much more, and as an added bonus it loads a lot faster than tables ever did. It is easier to maintain, if you dont go overboard with nested DIVs. Use DIV for the conatainer and then use other elements SPAN, P, etc with CSS.

 Good: Laying out with DIVs and CSS tag

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Div Layout</title>

<!-- This can be defined outside in its own file and included into an html file -->
<style type="text/css">
body {
 display: block;
 width: 400px;
 height:400px;
 text-align: center;
}

/* main content container floated to the left*/
#content {
 position: relative;
 width: 80%;
 height: 65%;
 float: left;
 background-color: orange;
 width: 320px;
}

/* rhs menu container floated to the left*/
#rhs-menu {
 position: relative;
 width: 20%;
 height: 65%;
 float: left;
 background-color: green;
}

/* header container floated to the left*/
#header {
 position: relative;
 width: 100%;
 height: 15%;
 float: left;
 background-color: yellow;
}

/* footer with "clear"" to ensure that the footer is always below content and rhs-menu */
#footer {
 position: relative;
 width: 100%;
 height: 20%;
 clear: both;
 background-color: blue;
}

/* align text vertically*/
#content p,#rhs-menu p,#header p,#footer p {
 position: absolute;
 top: 50%;
 left: 50%;
 height: 50%;
 width: 50%;
 margin: -15% 0 0 -25%;
}

/* position the logo using absolute (from top left corner) or relative*/
.logo-text {
 position: absolute; 
 top: 5px;
 left: 10px;
}

</style>

</head>
<body>

 <div id="header"><span class="logo-text">logo goes here </span>
  <p>Header Information</p>
 </div>
 <div id="content">
  <p>Contents go here</p>
 </div>
 <div id="rhs-menu">
  <p>RHS Panel</p>
 </div>
 <div id="footer">
  <p>Footer Information</p>
 </div>

</body>
</html>

Note: It is a best practice to define HTML, CSS, and JavaScript in separate files. The CSS is combined with HTML in these examples for illustration purpose only.

The typical usecase for the "clear" css tag is when you want to put a footer at the bottom of your page, beneath the RHS menu and the content sections. So, by using the CSS tags like float, clear, absolute, relative, and display you can create attractive, maintainable, and faster layouts.

Read More..

SQL Interview Questions and Answers on deleting records

The following is a very popular SQL job interview question.

Q. What is the difference between "Truncate" and "Delete" commands?
A. 

• TRUNCATE TABLE_NAME always locks the table and page but not each row, whereas  DELETE statement is executed using a row lock, each row in the table is locked for deletion.
• Truncate removes all the records in the table whereas delete can be used with WHERE clause to remove records conditionally. That is remove only a handful number of records.
• Truncate performance is much faster than Delete, as its logging is minimal wheres the Delete command logs every record.
• Truncate does not retain the identity, whereas DELETE command retains the identity. When you use Truncate, If the table contains an identity column, the counter for that column is reset to the seed value that is defined for the column.
• Truncate cleans up the object statistics and clears the allocated space whereas Delete retains the object statistics and allocated space.
• TRUNCATE is a DDL (Data Definition Language) and DELETE is a DML (Data Manipulation Language). 
• Data removed by TRUNCATE command cannot be generally rolled back unless the database server specifically supports it. The DELETE command can rollback a transaction.
• The TRUNCATE command does not fire any triggers, whereas the DELETE command fires any triggers defined on the table. For example, to keep an audit trail of records that have been deleted by inserting the deleted records into an audit table via the DELETE triggers.

Q. When will you use a truncate command?
A.TRUNCATE is useful for purging a table with huge amount of data. Alternatively, you can drop the table and recreate it that makes sense. Firing a delete command instead of a truncate command to empty a table with millions of records can result in locking the whole table and also can take longer time to complete, and at times cause the machine to hang.

The truncate command is executed as shown below.

TRUNCATE TABLE table_name

Q. Which command will you use to periodically purge data from your tables as part of a house keeping job?
A.  Use a DELETE command within a transaction with a WHERE clause to remove data that are older than 7 years. Remove  large amount of data in batches as opposed to in a single transaction.

Q. How will you delete a few records from single table
A.

DELETE FROM parent p WHERE p.parent_name = Peter

Q. How will you delete a few records from parent and child tables where the parent table with parent_name = Peter?
A.

Firstly, you need to delete the child records because the integrity constraint wont let you delete the parent record when there are child records.

DELETE child

FROM  parent p, child c

WHERE p.parent_id = c.parent_id

  AND p.parent_name = Peter

Now, the parent table can be deleted as shown below

DELETE FROM  parent p WHERE p.parent_name = Peter

Note: Please note the difference in syntax when you make a join with the child. When there is only a single table involved, it is "DELETE FROM table_name", but when there is a join, it is "DELETE table_name" and then the "FROM" with the join clauses.


Q.  What do you do with the PURGE command?
A. The purge command is used to clear the recycle bin. It is generally used with the DROP command. For example,

drop table tablename purge;

the above  command will clear away the table from database as well as from the recycle bin. After executing  the purge command, you cannot retrieve the table using a flashback query. 

You may also like:

• Database interview Questions and answers
• SQL Interview Questions and Answers
•  SQL interview questions and answers - scenarios based
•  SQL subqueries interview questions and answers
•  SQL Interview Questions and Answers: storing a tree structure in a database table
•  Excel spreadsheet to generate SQL
•  SQL Tutorial with HSQLDB

Read More..

Java new I O Interview Questions and Answers

The Java New IO is very powerful and it is all about performance!, performance!!, and performance!!!. But, you need to get your head around how the buffers work. Here are some questions and answers that will help you do that. Q. How does the Java NIO (i.e New IO) introduced in Java version 1.4 differ from the old IO?
A. The NIO is all about better performance.

IO	NIO (New IO)
Stream oriented. This means that you read one or more bytes at a time, from a stream. What you do with the read bytes is up to you. They are not cached anywhere. Furthermore, you cannot move forward and back in the data in a stream. If you need to move forward and back in the data read from a stream, you will need to buffer yourself first.	Buffer oriented. This means better performance. Data is read into a buffer from which it be processed later. You can move forward and back in the buffer. This gives you a bit more flexibility during processing. However, you also need to check if the buffer contains all the data you need in order to fully process it.
Blocking IO. This means when a thread invokes a read() or write(), that thread is blocked until there is some data to read, or the data is fully written. The thread can do nothing else in the meantime.	Non blocking IO. This means better performance. NIOs non-blocking mode enables a thread to request reading data from a channel, and only get what is currently available, or do nothing at all, if no data is currently available. Rather than remain blocked until data becomes available for reading, the thread can proceed with doing something else.
You need to create additional threads to read and write data in parallel. More threads means more CPU context switching and consuming more thread stacks.	Selectors.  This also means better performance. NIOs selectors allow a single thread to monitor multiple channels of input. You can register multiple channels with a selector, then use a single thread to "select" the channels that have input available for processing, or select the channels that are ready for writing. This selector mechanism makes it easy for a single thread to manage multiple channels. This is also known as multiplexing. The Apache MINA package is based on Java NIO to write high performance networking applications. For example, a TCP server.

Here is the diagrammatic overview:

Q. How do you manipulate the buffer in NIO?
A. The NIO buffer  has following 3 state variables -- position, limit, and capacity

• position: The position value keeps track of how much you have gotten from the buffer. It specifies from which array element the next byte will come. Thus, if youve written 1 bytes as shown below with shaded area to a channel from a buffer, that buffers position will be set to 1 (starting from 0), referring to the second element of the array as shown in the diagram.
• limit: The limit variable specifies how much room there is left to put data into -- in the case of reading from a channel into a buffer or how much data there is left to get -- in the case of writing from a buffer into a channel. The position is always less than, or equal to, the limit. The limit is 3 (counting from 0) in the diagram below.
• capacity:  The capacity of a buffer specifies the maximum amount of data that can be stored in the underlying array. The limit can never be larger than the capacity. The capacity is 6 (counting from 0) in the diagram below.

In the above diagram, the position starts with 0, and after reading 1 byte, it becomes 1 byte, and the limit value of 3 states that there are 2 more bytes to be read. 



Q. What do you understand by terms flip( ) and clear( ) in NIO?
A.

Flip

When you are ready to write your data to an output channel. You must call the flip() method. This method does two key things:

1. It sets the limit to the current position.
2. It sets the position to 0.

You are now ready to begin writing data to a channel from the buffer starting from 0 to the limit.


Clear

After you have done your writes, the final step is to call the buffers clear() method. This method resets the buffer in preparation for receiving more bytes. Clear does two key things:

1. It sets the limit to match the capacity.
2. It sets the position to 0.


Also, the get and put methods are used to get and put data to and from the buffer respectively. some coding examples are discussed in Java I/O interview Questions and Answers.


Q. What is in the NIO.2 package introduced in Java 7?
A. The more New I/O APIs for the Java Platform (NIO.2) in Java 7 enhance the New I/O APIs (NIO) introduced in Java 1.4 by adding

• The four asynchronous channels to the java.nio.channels package. 
•  The java.io.File class is upgraded to the java.nio.file.Path that allows logical manipulating of paths in memory without accessing the file system.
• The NIO.2 associates the notion of metadata like is hidden, is it a directory, size, access control, etc with attributes and provides access to them through the java.nio.file.attribute package. Since different file systems have different notions about which attributes should be tracked, NIO.2 groups the attributes into views, each of which maps to a particular file system implementation.
• The NIO.2 provides support for both hard links and symbolic links and the Path class knows how to detect a link and will behave in the default manner if no configuration of behavior is specified.
• The NIO.2 comes with a set of brand new methods for managing files and directories, such as create, read, write, move, delete, and so on. The most of these tasks are found in the java.nio.file.Files class.
• The FileVisitor interface introduced in Java 7 makes recursing through directories and files a breeze.
• The Watch Service API was introduced in Java 7 (NIO.2) as a thread-safe service that is capable of watching  a directory for changes to its content through actions such as create, delete, and modify. This means, with NIO.2, you no longer need to poll the file system for changes or use other in-house solutions to monitor the file system changes.
• Java 7 (NIO.2) introduces a new interface for working with Random Access Files with its SeekableByteChannel and an interface named NetworkChannel that provides network channel classes for tetworking.

Read More..

Top 20 Java technical interview questions and answers for experienced Java developers

If you are an interviewer -- it really pays to ask well rounded questions to judge the real experience of the candidate as opposed to just relying on the number of years. If you are an interviewee -- You have no control over what questions will be asked in Java job interviews, but there are a few Java interview questions that are very frequently asked in job interviews, and it really pays to prepare for those questions. Here are a few such questions. This is based on some of my recent interviews. Brushing up on these answers will boost your success rate in Java job interviews.

The focus is on judging your experience. So, go through your resume and reflect back on your hands-on experience. Many of these answers will also serve you well in selling your technical strengths to open ended questions like -- tell me about yourself? , why do you like software development?, when reviewing others work, what do you look for?, what was your most significant accomplishment?, etc

Q1. Can you describe the high level architecture of the application that you had worked on recently? or Can you give a 100 feet birds eye view of the application you were involved in as a developer or designer?

A1. The purpose is to judge your overall experience. Here are a few links that will prepare for this most sought-after question, especially for the experienced professionals.

• 3 to n-tier enterprise Java architecture, the MVC-2 design pattern, the distinction between physical and logical tiers, and the layered architecture.The logical tiers shown in the diagrams for the above link are basically layers, and the layers are used for organizing your code. Typical layers include Presentation, Business and Data – the same as the traditional 3-tier model. But when  talk about layers, we’re only talking about logical organization of code. Physical tiers however, are only about where the code gets deployed and run as war, ear or jar. Specifically, tiers are places where layers are deployed and where layers run. In other words, tiers are the physical deployment of layers.
• high level architectural patterns and the pros and cons of each approach. Discusses a number different architectual styles like MVC, SOA, UI Component, RESTful data composition, HTML data composition, Plug-in architecture, and Event Driven Architecture (EDA). Also, covers a sample enterprise architecture, which is a hybrid of a number of architectural styles.
• knowing the difference between a component and a service. Covers the differences between components and services and CBA (Component Based Architecture) Vs, SOA (Service Oriented Architecture). Also, briefly covers single page web design and SCA (Service Component Architecture)
• Understanding of various types of application integration styles. Enterprise applications need to be integrated with other systems, and this post covers different integration styles like sharing the same database, feed based, RPC style (e.g. web services), and exchanging JMS messages.
• Good working knowledge of popular and sought-after technologies and frameworks like Maven, Spring, Hibernate, JSF, etc. Covers a number of tutorials using sought-after frameworks and technologies like like Spring, Maven, JSF, JDBC, and RESTful web service.

Q2. How would you go about deciding between SOAP based web service and RESTful web service?
A2. Web services are very popular and widely used to integrate disparate systems. It is imperative to understand the differences, pros, and cons between each approach. Recently, I have been asked these questions very frequently, here is the answer that discusses the pros and cons of SOAP vs. RESTful web services in detail.  

Q3.How will you go about ensuring that you build a more robust application? or How do you improve quality of your application?
A3. This question is very popular with the interviewers because they want to hire candidates who write good quality application. Here are some useful links to prepare for this question.

• Java interview questions and answers on code quality. Gives a high level over view as to things you can do and tools you can use to improve code quality. A common popular job interview question answered is -- What is the difference between fake objects, mock objects, and stubs?
• Unit testing with mock objects interview questions and answers. Tutorial that explains how to write JUnit tests with mock objects using the Mockito and Power mock frameworks.
• Unit testing Spring MVC controllers for web and RESTful services with spring-test-mvc. Tutorial for writing Spring MVC unit tests.
• Selenium and Web Driver for unit testing Java GUI. Tutorial for writing functional unit tests for web applications to test display logic.

• Hibernate Interview Questions and Answers: integration testing the DAO layer. Tutorial for unit testing the DAO layer using hibernate.
• Java Interview Questions and Answers - performance testing your Java application. A high level overview as to how you can go about monitoring performance. Many applications face performance issues and this is a very popular question with the interviewers. 
• Using JMeter for performance testing Java application.A JMeter tutorial for conducting performance tets

Q4. What are some of the best practices regarding SDLC? Have you worked in an agile development environment? Did you use test driven development and continuous integration?
A4. 

• Know the SDLC and the best practices . Gives a high level overview of SDLC.

Q5: Can you write code? How would you go about implementing .....?
A5:  You will be asked to write a small function or a program. The interviewer will be looking for things like

• How well you analyze the requirements and the solution? Ask relevant questions if the requirements are not clear. Think out loud so that the interviewer knows that how you are approaching the problem.The approach is more important that arriving at the correct solution.
• List all possible alternatives.
• Write pseudo code.
• Write unit tests.
• Where required, brainstorm with the interviewer.
• Find ways to improve your initial solution. Talk through thread safety and best practices where applicable.

Here are some links to popular coding questions and answers.

• Java coding interview questions and answers:. Covers a number of coding questions with answers. These are some of the popular coding interview questions like reversing a string, calculating the Fibonacci number, recursion vs iteration, equals versus ==, etc.

Q6. How would you go about designing a car parking station?
A6.
Map out the requirements:

• The car park needs to cater for different types of car parks like regular, handicapped, and compact.
• It should keep track of empty and filled spaces.
• It should also cater for valet parking.

Map out the classes that would be required. Use a UML class diagram. Here are some points to get started.

• A CarPark class to represent a parking station.
• A ParkingSpace can be an abstract class or an interface to represent a parking space, and RegularParkingSpace, HandicappedParkingSpace, CompactParkingSpace, etc are subtypes of a ParkingSpace. This means a RegularParkingSpace is a ParkingSpace.
• A CarPark has a (i.e. composition) finite number of ParkingSpaces. A CarPark also keeps track of all the parking spaces and a separate list of all the vacant parking spaces.
• A Vehicle class uses a (i.e. delegation) ParkingSpace.  The Vehicle class will hold attributes using enum classes like  VehicleType and ParkingType. The vehicle types could be Compact, Regular, and Handicapped. The parking types could be Self or Valet. Depending on the requirements, the self or valet types could be designed as subtypes of the Vehicle class.

Q7: Can you design the classes that represent a restaurant?
A7: Very popular. Good understanding of OO design is vital to job interview success. Learn the SOLID design principles, know why you favor composition over inheritance, and dont under estimate the power of coding to interface.

• Java OO Interview Questions and Answers. A step-by-step tutorial explaining how you would go about designing your classes. The "Core Java Career Essentials" PDF covers more examples on SOLID design principles with working code.

How would you go about identifying thread safety issues in an application? How would you go about identifying memory leaks issues? How would you go about identifying performance issues?, etc to judge your experience. I am yet to work on a project that didnt face problems relating to thread safety, memory leaks, and performance issues. Hence, it really pays to market your skills and experience in fixing issues relating to these common challenges.


Q8. How will you go about fixing memory leaks in Java?
A8. Again, a very common problem, and a thorough answer will go a long way in securing your next Java job.

• Detecting and fixing memory leak issues in Java. Tools and techniques to detect memory leaks in Java.
• Memory profiling in Java. Tutorial on memory profiling a Java application.

Q9: How will you go about fixing performance issues in Java?
A9:

• Detecting performance issues in Java. A basic tutorial covering -- how to detect performance issues.
• Also, refer to the JMeter tutorials in this blog as to learn how you can put load on your application to simulate concurrent users.

Q10: How will you go about detecting and fixing thread-safety issues in Java?
A10: Debugging concurrency issues and fixing any thread starvation, dead lock, and contention requires skills and experience to identify and reproduce these hard to resolve issues. Here are some techniques to detect concurrency issues.

• Manually reviewing the code for any obvious thread-safety issues. There are static analysis tools like Sonar, ThreadCheck, etc for catching concurrency bugs at compile-time by analyzing their byte code.

• List all possible causes and add extensive log statements and write test cases to prove or disprove your theories.

• Thread dumps are very useful for diagnosing synchronization problems such as deadlocks. The trick is to take 5 or 6 sets of thread dumps at an interval of 5 seconds between each to have a log file that has 25 to 30 seconds worth of runtime action. For thread dumps, use kill -3 in Unix and CTRL+BREAK in Windows. There are tools like Thread Dump Analyzer (TDA), Samurai, etc. to derive useful information from the thread dumps to find where the problem is. For example, Samurai colors idle threads in grey, blocked threads in red, and running threads in green. You must pay more attention to those red threads.

• There are tools like JDB (i.e. Java DeBugger) where a “watch” can be set up on the suspected variable. When ever the application is modifying that variable, a thread dump will be printed.

• There are dynamic analysis tools like jstack and JConsole, which is a JMX compliant GUI tool to get a thread dump on the fly. The JConsole GUI tool does have handy features like “detect deadlock” button to perform deadlock detection operations and ability to inspect the threads and objects in error states. Similar tools are available for other languages as well.

Java Interview Questions 11- 13 for experienced developers

Read More..

Servlets interview questions and answers

Q. How do you get your servlet to stop timing out on a really long database query? A. There are situations despite how much database tuning effort you put into a project, there might be complex queries or a batch process initiated via a Servlet, which might take several minutes to execute. The issue is that if you call a long query from a Servlet or JSP, the browser may time out before the call completes. When this happens, the user will not see the results of their request. There are proprietary solutions to this problem like asynchronous servlets in WebLogic, Async Beans in WebSphere etc but you need a solution that is portable. Let us look at portable solutions to this issue.

Solution 1: Client-pull or client-refresh (aka server polling): You can use the tag for polling the server. This tag tells the client it must refresh the page after a number of seconds.

<META http-equiv=”Refresh” content=”10; url=”newPage.html” />

Once you can have the browser poll your Servlet on a regular basis to re-fetch a page, then your servlet can check for a value of a variable say in a HttpSession to determine if the page returned will have the results expected by the user or resend the tag with a “Please wait …” message and retry fetching the page again later.

Solution 2: JEE Solution: Instead of spawning your own threads within your Servlet, you could use JMS (Java Messaging Service). This involves following steps:

1. You need to have two servlets, a RequestingServlet and a DisplayingServlet. The initial client request is sent to the RequestingServlet. Both the RequestingServlet and DisplayingServlet polled by the browser via tag discussed above or JavaScript. Both these Servlets should send the tag with their responses until final display of the query results.
2. RequestingServlet places the query on the “request” queue using JMS.
3. You need to have a MessageDrivenBean (aka MDB) say QueryProcessorMDB, which dequeues the query from the “request” queue and performs the long-running database operation. On completion of processing long-running database operation, the QueryProcessorMDB returns the query results to the “reply” queue (use javax.jms.QueueSender & javax.jms.ObjectMessage). Note: MDBs are invoked asynchronously on arrival of messages in the queue.
4. DisplayingServlet checks the “reply” queue for the query results using JMS (use javax.jms.QueueReceiver & javax.jms.ObjectMessage) every few seconds via tag described above or a JavaScript.

Advantages: Firstly, implementing your long-running database operation to be invoked from onMessage( ) method of your QueryProcessorMDB decouples your application whereby if a database failure occurs, the request query message will be placed back in the “request” queue and retried again later. Secondly MDBs can be clustered (with or without additional JVMs) to listen on the same “request” queue. This means cluster of MDBs will be balancing the load of processing long running database operations. This can improve the throughput due to increased processing power.


Q. What is the difference between forwarding a request and redirecting a request?
A. Both methods send you to a new resource like Servlet, JSP, etc

Forward:

• Forward action takes place within the server without the knowledge of the browser. Accepts relative path to the servlet or context root.
• No extra network trip.

Redirect:

• Sends a header back to the browser, which contains the name of the resource to be redirected to. The browser will make a fresh request from this header information. Need to provide absolute URL path.
• This has an overhead of extra remote trip but has the advantage of being able to refer to any resource on the same or different domain and also allows book marking of the page.

Q. What are the considerations for servlet clustering?
A.

Objects stored in a session should be serializable to support in-memory replication of sessions. Also consider the overhead of serializing very large objects. Test the performance to make sure it is acceptable. Design for idempotence. Failure of a request or impatient users clicking again can result in duplicate requests being submitted. So the Servlets should be able to tolerate duplicate requests. Avoid using instance and static variables in read and write mode because different instances may exist on different JVMs. Any state should be held in an external resource such as a database.  Avoid storing values in a ServletContext. A ServletContext is not serializable and also the different instances may exist in different JVMs. Avoid using java.io.* because the files may not exist on all backend machines. Instead use getResourceAsStream().

Q. How do you perform I/O operations in a Servlet/JSP?
A.

Problem: Since web applications are deployed as WAR files on the application server’s web container, the full path and relative paths to these files vary for each server.

Solution -1: You can configure the file paths in web.xml using tags and retrieve file paths in your Servlets/JSPs. But this technique requires changes to the web.xml deployment descriptor file, to point to the correct path.


Solution -2: You can overcome these configuration issues by using the features of java.lang.ClassLoader and javax.servlet.ServletContext classes. There are various ways of reading a file using the ServletContext API methods such as getResource(String resource),getResourceAsStream(String resource), getResourcePaths(String path) and getRealPath(String path). The getRealPath(String path) method translates virtual URL into real path.

//Get the file “products.xml” under the WEB-INF folder of  your application as inputstream
InputStream is = config.getServletContext().getResourceAsStream(“/products.xml”);

Alternatively you can use the APIs from ClassLoader as follows. The file “products.xml” should be placed under WEB-INF/classes directory where all web application classes reside.

//Get the URL for the file and create a stream explicitly 
URL url = config.getServletContext().getResource(“/products.xml”);
BufferedReader br = new BufferedReader(new InputStreamReader(url.openStream));
                        OR
//use the context class loader 
URL url  = Thread.currentThread().getContextClassLoader().getResource(“products-out.xml”); 
BufferedWriter bw = new BufferedWriter(new FileWriter(url.getFile());

Q. How do you send a file to a browser from your web application? I.e. how do you download a file from your web application?
A. Files can be downloaded from a web application by using the right combination of headers.

//set the header to a non-standard value for attachments to be saved by the browser with the //Save-As dialog so that it is unrecognized by the browsers because often browsers try to do //something special when they recognize the content-type. 
response.setContentType(“application/x-download”); 
//use Content-Disposition “attachment” to invoke “Save As” dialog and “inline” for displaying //the file content on the browser without invoking the “Save As” dialog.
response.setHeader(“Content-disposition”, “attachment;filename=” + fileName);

Q. How do you send a file from a browser to your web application? i.e. How do you upload a file to your web application?
A. There are better and more secured ways to upload your files instead of using using web. For example FTP, secure FTP etc. But if you need to do it via your web application then your default encoding and GET methods are not suitable for file upload and a form containing file input fields must specify the encoding type “multipart/form-data” and the POST method in the

tag as shown below:

<form enctype=”multipart/form-data” method=”POST”  action=”/MyServlet”>
     <input type=”file” name=”products” />
     <input type=”submit” name=”Upload” value=”upload” />
</form>    

When the user clicks the “Upload” button, the client browser locates the local file and sends it to the server using HTTP POST. When it reaches your server, your implementing servlet should process the POST data in order to extract the encoded file. Unfortunately, application servers implementing the Servlet and JSP specifications are not required to handle the multipart/form-data encoding. Fortunately there are number of libraries available such as Apache Commons File Upload, which is a small Java package that lets you obtain the content of the uploaded file from the encoded form data. The API of this package is flexible enough to keep small files in memory while large files are stored on disk in a “temp” directory. You can specify a size threshold to determine when to keep in memory and when to write to disk.

Note: The above questions and answers are extracted from the book Java/J2EE Job Interview Companion. Only a few questions and answers are extracted.

Read More..

Top 10 Servlet Interview Question Answers J2EE

This time its servlet interview questions, I was thinking what to pick for my interview series and than I thought about J2EE and Servlet is my favorite on that space. Servlet is an important part of any J2EE development and serves as Controller on many web MVC frameworks and that’s why it’s quite popular on J2EE interviews. These Servlet questions are based on my experience as well as collected by friends and colleague and they are not only good for interview practice but also shows a new direction of learning for any one who is not very familiar with servlet technology.

As said earlier this interview question article is part of my earlier series java interview questions , UNIX command interview questions and Java threading interview questions.

You can find answers of all these questions on google but I have also listed my answers fo r quick reference.

Read more »

Read More..