java-jsp-servlet-struts-oracle-sql-interview-quest: July 2011

Sunday, July 31, 2011

Reduce MySQL memory usage

/usr/share/doc/my-server-5.0/examples. I am also attaching a my.cnf here that is taken out from CentOS 4 installation of LxAdmin (which has been famous for its low-memory foot print). It is pretty much based on my-small.cnf. Some important notes:

*

skip-bdb and skip-innodb are added, so you don’t get BSD DB nor InnoDB support. BSD DB support in MySQL is pretty much obsolete, and many open source scripts don’t rely on the presence of InnoDB. A low end VPS is not likely to enjoy the concurrency InnoDB is offering anyway. Transaction and referential integrity? Real ProgrammersTM write their own rollback routines :)
*

key_buffer is only 16K which is far from enough. key_buffer is pretty much one of the most important parameter for MyISAM tables and I usually bump it up to at least 1MB. The same can be said about table_cache — 4 is way too small. A WordPress page will likely touch 10 tables, and much more for apps like Drupal or MediaWiki.
*

Query cache might be a good thing if you intend to run a busy site on such a low end VPS (provided that it has small data set, mostly read, like blogs, news sites, etc). I have my query_cache_limit set to 256K and query_cache_size set to 4M here.

Thursday, July 28, 2011

what is a apachi log4j Explain Log4j / interview question

Explain Log4j / interview question

Logging within the context of program development constitutes inserting statements into the program that provide some kind of output information that is useful to the developer.

Log4j provide mathod

1. error()

2. fatal()

3. info()

4. debug()

5. warn()

Requirtments

log4j.jar -->lib/log4j-1.2.6.jar

log4j.xml

Finally configured the program

when will occur the erro during runtime

Eample of the Program

import org.apache.log4j.Level;
import org.apache.log4j.Logger;
import org.apache.log4j.SimpleLayout;
import org.apache.log4j.FileAppender;
public class simpandfile {
   static Logger logger = Logger.getLogger(simpandfile.class);
   public static void main(String args[]) {
      SimpleLayout layout = new SimpleLayout();

      FileAppender appender = null;
      try {
         appender = new FileAppender(layout,"output1.txt",false);
      } catch(Exception e) {}

      logger.addAppender(appender);
      logger.setLevel((Level) Level.DEBUG);

      logger.debug("Here is some DEBUG");
      logger.info("Here is some INFO");
      logger.warn("Here is some WARN");
      logger.error("Here is some ERROR");
      logger.fatal("Here is some FATAL");
   }
}

Configuring Log4J
As you can see above we added the log4j library. This library does like a configuration file in the source directory or it welcomes you with the following error.
log4j:WARN No appenders could be found for logger (TestClient).
log4j:WARN Please initialize the log4j system properly.
Create a file named log4j.properties in the root directory and insert the following:
### direct log messages to stdout ###
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L – %m%n
### set log levels – for more verbose logging change ‘info’ to ‘debug’ ###
log4j.rootLogger=debug, stdout
log4j.logger.org.hibernate=info
#log4j.logger.org.hibernate=debug
### log HQL query parser activity
#log4j.logger.org.hibernate.hql.ast.AST=debug
### log just the SQL
log4j.logger.org.hibernate.SQL=debug
### log JDBC bind parameters ###
log4j.logger.org.hibernate.type=info
### log schema export/update ###
log4j.logger.org.hibernate.tool.hbm2ddl=info
### log HQL parse trees
#log4j.logger.org.hibernate.hql=debug
### log cache activity ###
log4j.logger.org.hibernate.cache=info
### log transaction activity
#log4j.logger.org.hibernate.transaction=debug
### log JDBC resource acquisition
#log4j.logger.org.hibernate.jdbc=debug
### enable the following line if you want to track down connection ###
### leakages when using DriverManagerConnectionProvider ###
#log4j.logger.org.hibernate.connection.DriverManagerConnectionProvider=trace

log4j.properties


# Set root logger level to DEBUG and its only appender to Appender1.
log4j.rootLogger=INFO, Appender1,Appender2

# Appender1 is set to be a ConsoleAppender.
log4j.appender.Appender1=org.apache.log4j.ConsoleAppender
log4j.appender.Appender2=org.apache.log4j.RollingFileAppender
log4j.appender.Appender2.File=sample.log


# Appender2 uses PatternLayout.
log4j.appender.Appender1.layout=org.apache.log4j.PatternLayout
log4j.appender.Appender1.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n

log4j.appender.Appender2.layout=org.apache.log4j.PatternLayout
log4j.appender.Appender2.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n

log4j.xml


<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/" debug="false">

   <appender name="consoleAppender" class="org.apache.log4j.ConsoleAppender">
      <param name="Threshold" value="INFO" />   
      <layout class="org.apache.log4j.PatternLayout">
         <param name="ConversionPattern" value="%d %-5p  [%c{1}] %m %n" />
      </layout>
   </appender>

   <appender name="fileAppender" class="org.apache.log4j.RollingFileAppender">
      <param name="Threshold" value="INFO" />
      <param name="File" value="sample.log"/>
      <layout class="org.apache.log4j.PatternLayout">
         <param name="ConversionPattern" value="%d %-5p  [%c{1}] %m %n" />
      </layout>
   </appender>

   <logger name="javabeat.net.log4j" additivity="false" >   
      <level value="INFO" />
      <appender-ref ref="consoleAppender"/>      
      <appender-ref ref="fileAppender"/>      
   </logger>

</log4j:configuration>

Log4jPropertyTest.java


package javabeat.net.log4j;

import org.apache.log4j.Logger;
import org.apache.log4j.PropertyConfigurator;

/**
 * source : www.javabeat.net
 */
public class Log4jPropertyTest {
    private static Logger logger = Logger.getLogger(Log4jPropertyTest.class);
    public static void main (String args[]){        
        PropertyConfigurator.configure("log4j.properties");
        logger.info("Test Log");
    }
}

Log4jXmlTest.java


package javabeat.net.log4j;

import org.apache.log4j.Logger;
import org.apache.log4j.xml.DOMConfigurator;

/**
 * source : www.javabeat.net
 */
public class Log4jXmlTest {
    private static Logger logger = Logger.getLogger(Log4jXmlTest.class);
    public static void main (String args[]){        
        DOMConfigurator.configure("log4j.xml");
        logger.info("Test Log");
    }

}

What is a Trigger explain tips oracle mysql advantage

Explain Trigger

A trigger is a pl/sql block structure which is fired when a DML statements like Insert, Delete, Update is executed on a database table. A trigger is triggered automatically when an associated DML statement is executed.

Types of PL/SQL Triggers

There are two types of triggers based on the which level it is triggered.

1) Row level trigger - An event is triggered for each row upated, inserted or deleted.

2) Statement level trigger - An event is triggered for each sql statement executed.

PL/SQL Trigger Execution Hierarchy

The following hierarchy is followed when a trigger is fired.

1) BEFORE statement trigger fires first.

2) Next BEFORE row level trigger fires, once for each row affected.

3) Then AFTER row level trigger fires once for each affected row. This events will alternates between BEFORE and AFTER row level triggers.

4) Finally the AFTER statement level trigger fires.

Create Table Stu_Table

Create Table Stu_Table( Stu_Id int, Stu_Name varchar(15),Stu_Class int);

Create Table Stu_Log

create table stu_log( user_id VARCHAR(15), description VARCHAR(100));

Create Trigger Stu_Update
The below Query create a Trigger 'stu_update' on
table stu_table.

delimiter $$

CREATE TRIGGER stu_update

AFTER UPDATE ON stu_table FOR EACH ROW
BEGIN
 INSERT into stu_log(user_id, description)
        VALUES (user(), CONCAT('Update Student Record 
        (',old.stu_id,' ',old.stu_name,' ',old.stu_class,
 ') to (',new.stu_id,' ',new.stu_name,' ',new.stu_class,')'));
END$$
delimiter ;

Insert Data Into Stu_Table

insert into stu_table values(1, 'Komal',10);
insert into stu_table values(2, 'Ajay',10);
insert into stu_table values(3, 'Santosh',10);
insert into stu_table values(4, 'Rakesh',10);
insert into stu_table values(5, 'Bhau',10);

Stu_Table

+--------+----------+-----------+
| Stu_Id | Stu_Name | Stu_Class |
+--------+----------+-----------+
| 1      | Komal    | 10        |
| 2      | Ajay     | 10        |
| 3      | Santosh  | 10        |
| 4      | Rakesh   | 10        |
| 5      | Bhau     | 10        |
+--------+----------+-----------+

Update Stu_Table

update stu_table set Stu_Class = stu_class+1;

Stu_Table

+--------+----------+-----------+
| Stu_Id | Stu_Name | Stu_Class |
+--------+----------+-----------+
| 1      | Komal    | 11        |
| 2      | Ajay     | 11        |
| 3      | Santosh  | 11        |
| 4      | Rakesh   | 11        |
| 5      | Bhau     | 11        |
+--------+----------+-----------+

View Advantage and disadvantage oracle

View Advantage and disadvantage oracle

A view is simply the representation of a SQL statement that is stored in memory so that it can easily be re-used

Benefits of Oracle Views

Oracle views offer some compelling benefits. These include:

* Commonality of code being used. Since a view is based on one common set of SQL, this means that when it is called it’s less likely to require parsing. This is because the basic underlying SQL that is called is always the same. However, since you can add additional where clauses when calling a view, you still need to use bind variables. Additional where clauses without a bind variable can still cause a hard parse!

* Security. Views have long been used to hide the tables that actually contain the data you are querying. Also, views can be used to restrict the columns that a given user has access to. Using views for security on less complex databases is probably not a bad thing. As databases become more complex, this solution becomes harder to scale and other solutions will be needed.

* Predicate pushing. Oracle supports pushing of predicates into a given view. Assume we had a set of layered views, like this:

create view viewsample as
select ct_name,ct_description,first_name
from category,employee group by first_name

select * from viewsample

1)Simple Views:

•The view which is created by selecting only one table.
•A Simple view does not contain functions.
•You can always perform DML operations through Simple views.

2)Complex Views:
•The view which is created by selecting more than one tables.
•A Complex view contains functions.
•You cannot always perform DML through Complex views.

Rules for performing DML Operations on a view:

•You can perform DML operations on Simple views.
•You cannot always perform DML through Complex views.
•You cannot delete a row if the view contains the following:

Group functions such as SUM, MIN, MAX, AVG and ......
A GROUP BY clause.
The DISTINCT keyword.

• You cannot update data in a view if it contains,

Group functions such as SUM, MIN, MAX, AVG and ......
A GROUP BY clause.
The DISTINCT keyword.
Columns defined by expressions such as SALARY*1.2
The ROWNUM pseudo column.

• You cannot insert data in a view if it contains,

Group functions such as SUM, MIN, MAX, AVG and ......
A GROUP BY clause.
The DISTINCT keyword.
Columns defined by expressions such as SALARY*1.2
The ROWNUM pseudo column.
There are NOT NULL columns in the base tables that are not selected by the view.

Saturday, July 2, 2011

Hash map exception in java ClassCastException

On execution of the code, the code show you an exception indicating an string cannot be converted into double.

PROGRAM

import java.util.*;

import java.util.Iterator;

public class Hashmapexception {

public static void main(String[] args) {

HashMap hashMap = new HashMap();

hashMap.put("ABS", new Double(3434.34));

hashMap.put("ABD", new Double(123.22));

hashMap.put("cccc", "jdshgjhs");

Set set = hashMap.entrySet();

Iterator i = set.iterator();

while (i.hasNext()) {

Map.Entry me = (Map.Entry) i.next();

System.out.println(me.getKey() + " : " + me.getValue());

}

double balance = ((Double) hashMap.get("cccc")).doubleValue();

hashMap.put("cccc", new Double(balance + 1000));

System.out.println("balance : " + hashMap.get("cccc"));

}

OUTPUT

Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Double

at Hashmapexception.main(Hashmapexception.java:20)

Java Result: 1

Hash table exception in java java.util.NoSuchElementException Hashtable Enumerator

Hash table exception in java java.util.NoSuchElementException Hashtable Enumerator

import java.util.*;

import java.util.Hashtable;

import java.util.Enumeration;

public class HashTableException {

  public static void main(String args[]) {

  try {

  Hashtable hashtable = new Hashtable();

  hashtable.put("Girish", new Integer(1));

  hashtable.put("Tewari", new Integer(2));



  Integer one = (Integer) hashtable.get("One");

  System.out.println("Elements in the Hashtable");

  Enumeration e = hashtable.keys();

  while (e.hasMoreElements()) {

  System.out.println(e.nextElement());

  System.out.println(e.nextElement());

  System.out.println(e.nextElement());

  }

  } catch (Exception ex) {

  System.out.println

("Exception generated by hash table is "+ex.getMessage());

  }

  }

}

OUTPUT

java.util.NoSuchElementException: Hashtable Enumerator

What is a NoClassDefFoundError in java exception Reason and when will occur the error

What is a NoClassDefFoundError in java exception Reason and when will occur the error

NoClassDefFoundError is another common exception thrown by the class loader during the loading phase. The JVM specification defines NoClassDefFoundError as follows:

Thrown if the Java virtual machine or a ClassLoader instance tries to load in the definition of a class (as part of a normal method call or as part of creating a new instance using the new expression) and no definition of the class could be found.

The searched-for class definition existed when the currently executing class was compiled, but the definition can no longer be found.

Essentially, this means that a NoClassDefFoundError is thrown as a result of a unsuccessful implicit class load.

Note :
Another One Reason occure the “ NoClassDefFoundError”

Our Server have the jre 1.5 But you local system jre 1.6

Your local system class file generated by jdk 1.6 . that file uploed to the server . Then show the error. Because server have jdk 1.5. So version one problem.

Example Error Code

500 Servlet Exception
java.lang.NoClassDefFoundError: yellowpages/helper/AllCategoryDAO
at yellowpages.action.AllCategoryAction.execute(AllCategoryAction.java:27)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:413)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:225)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1858)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:446)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:114)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:91)
at com.caucho.server.dispatch.ServletFilterChain.doFilter(ServletFilterChain.java:103)
at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:181)
at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:266)
at com.caucho.server.hmux.HmuxRequest.handleRequest(HmuxRequest.java:435)
at com.caucho.server.port.TcpConnection.run(TcpConnection.java:602)
at com.caucho.util.ThreadPool$Item.runTasks(ThreadPool.java:690)
at com.caucho.util.ThreadPool$Item.run(ThreadPool.java:612)
at java.lang.Thread.run(Thread.java:619)

Subject	Written By	Posted
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Thamodara Jegan	09/02/2005 03:08AM
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Sridevi Aruncahalam	11/28/2005 06:25AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	LuChen Lo	12/16/2005 11:45AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	LuChen Lo	12/16/2005 12:13PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	karthicraj rajendran	08/10/2009 02:27PM
Class.forName("com.mysql.jdbc.Driver"); con=DriverManager.getConnection("jdbc:mysql://lo calhost:3306/karthicraj","mysql","mysql");	karthicraj rajendran	08/10/2009 02:33PM
Re: Class.forName("com.mysql.jdbc.Driver"); con=DriverManager.getConnection("jdbc:mysql:// localhost:3306/karthicraj","mysql","mysql");	karthicraj rajendran	09/10/2009 11:15AM
Class.forName("com.mysql.jdbc.Driver"); con=DriverManager.getConnection("jdbc:mysql:// localhost:3306/karthicraj","mysql","mysql");	karthicraj rajendran	09/10/2009 11:32AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Mani Mani	08/12/2009 06:15AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Oliver f	09/25/2007 04:22PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Alina Apes	06/02/2009 11:53AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	jeevan reddy	05/31/2011 08:02AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	irfan u	04/20/2007 12:14AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Chandra G	07/31/2007 09:01AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	isuru udayanga	10/29/2008 07:17PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	sourabh sharma	01/08/2010 12:28AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	ram kumar	02/12/2010 11:00PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	amarjeet kumar	04/04/2011 01:47AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	suryaprakashnaidu pattipati	05/07/2010 01:36AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	gaurav gulanjkar	12/03/2010 10:52AM
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Alex Burno	03/16/2006 07:57AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	jayaraj selvakumar	09/28/2007 04:20AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Eman Hossny	11/29/2007 04:01PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	subari	04/01/2006 05:23AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Doni Osmon	01/04/2007 08:56PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Vincent Hughitt	05/06/2007 03:15PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	PraveenKumar Subramanian	11/13/2007 04:05PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Srinivas Marripudi	11/30/2007 11:56AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Amlan Banerjee	03/20/2010 11:48AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	arvind M	05/26/2010 07:46AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	kiran c	03/29/2008 10:53PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Tracey Bain	05/17/2007 03:18AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	khushboo kapoor	02/06/2008 02:03AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	rfg gxdg	04/22/2008 12:35AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Caesar Kennedy Olima	05/12/2008 11:22AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	aye seint	05/15/2008 12:23AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Fernando Mendoza	05/21/2008 10:50PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	wenbin Tang	07/09/2010 02:07AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Aimable Ruhumuliza	07/04/2008 11:13AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	vysakh kay	08/13/2010 09:15AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	ramesh babu	07/28/2008 11:07AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	subash thirimanna	12/14/2008 08:25PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	rekha jayaprakash	03/14/2009 12:59AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Kent Vanninen	08/11/2009 11:51AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	ramesh kumar	09/03/2009 07:37AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Gabriel Lopes	12/04/2009 08:15AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	amar singh	05/24/2010 09:31AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	tanusri reddy	05/24/2010 10:41PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	teresa du plessis	06/29/2010 08:18PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	M.J. S.	07/13/2010 02:42PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Aboobakkar Siddiq	10/04/2010 05:55AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Mohammad Amin Sarkandi	03/12/2011 04:56PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	cabbeen long	03/13/2011 08:29PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	anjan rao	10/08/2010 08:16AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Thomas Frank	11/08/2010 01:11PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Rahul Shingala	02/21/2011 04:32AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	zhang chunyan	03/14/2011 04:53AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	deni borin	03/17/2011 08:00AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	luke archer	03/28/2011 03:39PM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Saniya Deshpande	04/01/2011 12:17AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	price pk	06/02/2011 03:35AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	roopa kumar	06/16/2011 03:44AM
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	Muhammad Afzal	06/21/2011 02:10AM
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	keerthana gopal	07/01/2011 01:16AM
Re: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver	keerthana gopal	07/01/2011 01:31AM