Using singleton design pattern is a best way to access a valuable resource. In this case we do use Singleton design pattern and stops clients classes to create multiple instances of the Class.

But there is a loophole in this pattern and one can create instance of the Singleton class using object cloning.

So we should prevent cloning of object in this class as well if required.

Code given below gives a brief idea of how to stop client class to clone an object.

package com.sun;

/** * @author Sunil Chauraha */

class Clone1 implements  Cloneable{

@Override protected Object clone() throws CloneNotSupportedException

throw new CloneNotSupportedException(“Cloning of this class is not supported by me…”);

}
public class CloneTest  {

public static void main(String[] args) {

try{

Clone1 clone1 = new Clone1();

Clone1  clone2 = (Clone1)clone1.clone();

}catch (CloneNotSupportedException e) {

System.err.println(e.getMessage()+”: “+e);

}

}

}

36. How we can instantiate a bean of abstract class having 2 subclasses.

37. How can we maintain a collection having the same order of insertion and unique values of object.

38. How can we use JPA in spring.

39. We have a singleton class and constructor is private, how can we create a bean in spring.

40. What is the mechanism used by Java for maintaining set and HashSet objects.

41. What is the significance of equals and hashCode methods in java and object comparison.

package com.sun;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import com.sun1.TestClass;
public class MainClass {
@SuppressWarnings(“unchecked”)
public static void main(String[] args) {
System.out.println(“Testing classloading…”);
try{
Class clazz = Class.forName(“com.sun1.TestClass”);
Method [] methods = clazz.getDeclaredMethods();
TestClass tc = new TestClass();
for (Method method : methods) {
try{
method.invoke(tc, new Object[]{“Sunil Chauraha”});
}catch(InvocationTargetException e){
System.err.println(e.getMessage());
}catch (IllegalAccessException e) {
System.err.println(e.getMessage());
}
}
}catch(ClassNotFoundException cnf){
System.err.println(cnf.getMessage()+” : “+cnf);
}
}
}

package com.sun1;
public class TestClass {
public void pring(String value){
System.out.println(“The value passed is : “+value);
}
}

Here are the links for uml plug in configuration with eclipse.

http://www.seasar.org/en/tutorial/eclipse/uml_omondo/index.html

http://www.vogella.de/articles/UML/article.html#umltools_diagram

My dear friend please think something outstanding or wonderful thing that can decrease the rate of increase in temperature………

There are so many situations where we need to create many or one instance of our class.  Like we will have a single database connection manger.

There are many ways to create a singleton design (i.e. Using User Defined exception class, using static class).

rather there is the most useful way that most programmer uses.  That is static method having a private default constructor.

Jakarta poi has some utilities to read contents of a file using its api.

Every line of the doc file is considered as a paragraph.

For this i used  poi-3.0-FINAL.jar.

This asks for the login and password of any gmail accound and uses gmail smtp to send emails…

**************************************************************************************

package com.sunil.mail;
import java.security.Security;
import java.util.Properties;

import javax.mail.Message;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

import org.apache.log4j.Logger;

public class SimpleJavaMail {

private Session mailSession;
protected PasswordAuthentication authentication;
private String user = null;
private String password = null;
private Properties props;

public SimpleJavaMail(){
Security.addProvider(new com.sun.net.ssl.internal.ssl.Provider());
props = new Properties();
props.setProperty(“mail.transport.protocol”, “smtp”);
props.setProperty(“mail.host”, “smtp.gmail.com”);
props.put(“mail.smtp.auth”, “true”);
props.put(“mail.smtp.port”, “465″);
props.put(“mail.smtp.socketFactory.port”, “465″);
props.put(“mail.smtp.socketFactory.class”, “javax.net.ssl.SSLSocketFactory”);
props.put(“mail.smtp.socketFactory.fallback”, “false”);
props.put(“mail.user”, “xxxxxxx@gmail.com”);
props.put(“mail.password”, “xxxxx”);
props.setProperty(“mail.smtp.quitwait”, “false”);
}

public void initMail(String user, String password) {
this.user = user;
this.password = password;
mailSession = createMailSession();
}

private Session createMailSession() {
Session session = null;
try {
session = Session.getDefaultInstance(props,    new javax.mail.Authenticator(){
protected PasswordAuthentication getPasswordAuthentication(){
return new PasswordAuthentication(user,password);
}
});
} catch (Exception e) {
e.printStackTrace();
}
return session;
}

public synchronized void sendMail(String subject, String body, String sender, String recipients)
throws Exception{
String host;
String mailUserName = (String) getProps().get(“mail.user”);
String mailPassword = (String) getProps().get(“mail.password”);
host = (String) getProps().get(“mail.host”);
host = host.toLowerCase();
initMail(mailUserName, mailPassword);
MimeMessage message = new MimeMessage(mailSession);
message.setSender(new InternetAddress(sender));
message.setSubject(subject);
message.setContent(body, “text/plain”);
if (recipients.indexOf(‘,’) > 0){
message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(recipients));
}else{
message.setRecipient(Message.RecipientType.TO, new InternetAddress(recipients));
}
Transport.send(message);
}

public Properties getProps() {
return props;
}

public void setProps(Properties props) {
this.props = props;
}

public static void main(String[] args) {
try{
String subject = “Test mail…”;
String body = “Hi Buddy…”;
String sender = “noname@noname.com”;
String recipients = “sunilxxxx@gmail.com”;
SimpleJavaMail mailJava = new SimpleJavaMail();
mailJava.sendMail(subject, body, sender, recipients);
} catch (Exception e) {
Logger.getLogger(SimpleJavaMail.class.getName()).error(e);
e.printStackTrace();
}
System.out.println(“Mail sent!”);
}

}

Here is a small example.

We can use to run a dos command using java code.

/***************Code ******************/

import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStreamReader;

class SunilCmd {

static public void main(String args[]) {
try {
StringBuffer sb = new StringBuffer();
BufferedReader buff = new BufferedReader(new InputStreamReader(    Runtime.getRuntime().exec(“cmd.exe /C dir”).getInputStream()));
/* Here Runtime.getRuntime creates environment to run the command */
/* .exec executes the parameters given inside the method */

/*
* here “cmd.exe /C” will invoke the DOS in exclusive mode and “dir”
* is a command that will be executed…..
*/

String line = buff.readLine();
while (line != null) {
sb.append(line + “\n”);
line = buff.readLine();
}
System.out.println(sb);
File f = new File(“output.txt”);
/**
*All the output will be written into output.txt file
*/
FileOutputStream fos = new FileOutputStream(f);
fos.write(sb.toString().getBytes());
fos.close();
} catch (Exception ex) {
ex.printStackTrace();
}
}

}

private FacesContext getFacesContext(ServletRequest request, ServletResponse response) {
// Try to get it first
FacesContext facesContext = FacesContext.getCurrentInstance();
if (facesContext != null) return facesContext;

FacesContextFactory contextFactory = (FacesContextFactory)FactoryFinder.getFactory(FactoryFinder.FACES_CONTEXT_FACTORY);
LifecycleFactory lifecycleFactory = (LifecycleFactory)FactoryFinder.getFactory(FactoryFinder.LIFECYCLE_FACTORY);
Lifecycle lifecycle = lifecycleFactory.getLifecycle(LifecycleFactory.DEFAULT_LIFECYCLE);

// Either set a private member servletContext = filterConfig.getServletContext();
// in you filter init() method or set it here like this:
// ServletContext servletContext = ((HttpServletRequest)request).getSession().getServletContext();
// Note that the above line would fail if you are using any other protocol than http

// Doesn’t set this instance as the current instance of FacesContext.getCurrentInstance
facesContext = contextFactory.getFacesContext(servletContext, request, response, lifecycle);

// Set using our inner class
InnerFacesContext.setFacesContextAsCurrentInstance(facesContext);

// set a new viewRoot, otherwise context.getViewRoot returns null
UIViewRoot view = facesContext.getApplication().getViewHandler().createView(facesContext, “yourOwnID”);
facesContext.setViewRoot(view);

return facesContext;
}