<natures>
</natures>

Change this value to

<natures>
        <nature>org.eclipse.jdt.core.javanature</nature>
</natures>

public void getJSONInfo(HttpServletRequest request, HttpServletResponse response) throws Exception {
    JSONObject result = new JSONObject();
    try {
        Object obj = new Object();
        // To get JSON data from obj
       JSONObject jsonObj = JSONObject.fromObject(obj);
       result.put("result", "success");
       result.put("jsonInfo", jsonObj);
   } catch (Exception e) {
       result.put("result", "error");
  } finally {
      // Write this jsonObj in HttpServletResponse
      response.getWriter().print(result);
      response.flushBuffer();
   }
}

While on the client side, I am using jquery to make AJAX request,

function getJSONInfo() {
    $.ajax({
       url: '../location?q=getJSONInfo',
       type: "POST",
       cache: false,
       dataType: "json",
       success: function(response){
           alert(response.jsonInfo);
       },
       error: function(msg){
       }
    });
}

As we can see from the example, an ajax request is made to get JSONInfo and result is displayed in popup window.

Sending data in JSON format from client to server will be covered in part2

	mail.transport.protocol = smtp
	mail.smtp.host = mailHost
	mail.smtp.port = 25
	mail.smtp.auth = true

The exception I am getting while sending email

Exception in thread "main" javax.mail.SendFailedException: Sending failed;
        nested exception is:
	javax.mail.MessagingException: 530 5.7.0 Must issue a STARTTLS command first m1sm949464nzf
 	at javax.mail.Transport.send0(Transport.java:219)
	at javax.mail.Transport.send(Transport.java:81)
	at example.SendMailUsingAuthentication.postMail(SendMailUsingAuthentication.java:77)
	at example.SendMailUsingAuthentication.main(SendMailUsingAuthentication.java:35)

$ cd
$ tar xvzf apache-tomcat-6.0.14.tar.gz

Move tomcat to ~/opt directory

sudo mv apache-tomcat-6.0.18 ~/opt/tomcat

Now you can start tomcat by executing startup.sh script located in tomcat/bin directory.

<< Back to Setting up j2ee developer environment …

$ mkdir ~/opt

Go to the directory where you have downloaded eclipse

$ tar -xvf eclipse-SDK-3.4.1-linux-gtk.tar.gz && mv eclipse ~/opt

Make a bin folder in user’s home directory

$ mkdir ~/bin

Next create an executable for Eclipe at ~/bin/eclipse

$ vi ~/bin/eclipse

Add the following lines in this file

export MOZILLA_FIVE_HOME="/usr/lib/mozilla/"
export ECLIPSE_HOME="$HOME/opt/eclipse"
$ECLIPSE_HOME/eclipse $*

Finally make script executable

$ chmod +x ~/bin/eclipse

You can now execute that file to start up Eclipse.

<< Back to Setting up j2ee developer environment ...

$ sudo apt-get install sun-java6-jdk

Provide password for root. It will show you agreement. Select and wait for installation to be completed.
We should set JAVA_HOME environment variable after successful installation of jdk.

$ vi ~/.bashrc

Insert following line in above file

export JAVA_HOME=/usr/lib/jvm/java-6-sun

<< Back to Setting up j2ee developer environment ...

Currently above are the popular versions, please update version if a newer version is available. Also, I have tried to list down all the necessary links and commands so that you can save time in finding these links or commands.

if you find something missing, please post a comment.

This is how you can debug this exception:

1. Check which service is binding the port by command “netstat –b”

This will list down all port and the application which binds the port like:

Proto Local Address Foreign Address State PID

TCP hddlntd100000:1090 test.test.cim:1026 ESTABLISHED 2248 [OUTLOOK.EXE]

1. Now check for the port which is shown as already in use. Like if the message resulted by BindException is “Port already in use: 1098”, then 1098 is in use by other application.
2. Identify the application running on the given port. Like Outlook is acquiring port 1090.
3. Either close the application which is acquiring the port directly by exiting the application like in case of Outlook or go to task manager and do end task for the given application/service. If application/service closes successfully you are done, now retry whatever had caused BindException earlier.

To make a class singleton, its constructor is made private or protected so that it can not be instantiated. Instead, a getInstance () method is written to return a new instance of that class if it doesn’t exist or return the reference of that object if it already exists. If it’s a multithreaded environment make sure to synchronize the getInstance() menthod.
Conventional way of writing a singleton class is :

public class Singleton {
private static Singleton INSTANCE = null;
// to prohibit instantiation
private Singleton() {
}

public static Singleton getInstance() {
if (INSTANCE == null) {
// lazy initialisation
INSTANCE = new Singleton();
}
return INSTANCE;
}
}

You can synchronise on getInstance() method for a multi threaded environment.

Another thread-safe Java programming language lazy-loaded solution is:

public class Singleton {
private Singleton() {}

// lazy initialisation
private static class SingletonHolder {
private final static Singleton INSTANCE = new Singleton();
}

public static Singleton getInstance() {
return SingletonHolder.INSTANCE;
}
}

Remember a singleton class is one instance per JVM. So if you have your application running in a cluster of servers. Every server will have its own JVM, therefore its own instance of singleton class. In this case, purpose of making a class singleton is not fulfilled. Hence this pattern should be used with care.