Jobcrawler's Blog

EJB: some basic concept

jobcrawler — Thu, 26 Nov 2009 03:50:00 +0000

#There are two types of session beans: stateful and stateless.

#Because stateless session beans can support multiple clients, they can offer better scalability for applications that require large numbers of clients.

#A stateless session bean can implement a web service, but other types of enterprise beans cannot.

#A session bean represents a single client inside the Application Server.

# Like an interactive session, a session bean is not persistent. (That is, its data is not saved to a
database.) When the client terminates, its session bean appears to terminate and is no longer
associated with the client.

#The state of an object consists of the values of its instance variables.(stateful session bean).

# A stateless session bean does not maintain a conversational state with the client. When a client
invokes the methods of a stateless bean, the bean’s instance variables may contain a state specific to that client, but only for the duration of the invocation.

#A message-driven bean is an enterprise bean that allows Java EE applications to process messages asynchronously.

#A message-driven bean’s instances retain no data or conversational state for a specific client.

#Message-driven beans have the following characteristics:
They execute upon receipt of a single client message.
They are invoked asynchronously.
They are relatively short-lived.
They are stateless.

#Session beans allow you to send JMS messages and to receive them synchronously, but not asynchronously.To receive messages asynchronously, use a message-driven bean.

#When you design a Java EE application, one of the first decisions you make is the type of client access allowed by the enterprise beans: remote, local, or web service.

#If you aren’t sure which type of access an enterprise bean should have, choose remote access. This decision gives you more flexibility.

#The Webserver: Just Receive the request from the client and forward to Webcontainer and do the Response vice versa.
Web Container: Creates HTTP Request and Response for the Servlet calls the appropriate servlet service
method (doGet or doPost) to service the client request.

Interpreter Vs. Compiler

jobcrawler — Thu, 12 Nov 2009 10:42:17 +0000

A compiler is a special program that processes statements written in a particular programming language and converts them into machine language, a “binary program” or “code,” that a computer processor uses.

Interpreters translate code one line at time, executing each line as it is “translated,”

Store Data in a Session

jobcrawler — Tue, 10 Nov 2009 15:56:45 +0000

session[:data] = @data

@data = session[:data]

Linking to Another Action

jobcrawler — Tue, 10 Nov 2009 05:30:46 +0000

<%= link_to “Go to lunch.”, :action => “lunch” %>

Selecting Which View to Render

jobcrawler — Tue, 10 Nov 2009 05:10:21 +0000

You use the render method to draw a view, and render(:action => :lunch) draws
the view associated with the lunch action.

You can use the render method alone if you’re through processing and just want to jump to the view
connected to your action:
def work
if Time.now.hour == 12
render(:action => :lunch)
else
render
end

Escaping Sensitive Text

jobcrawler — Tue, 10 Nov 2009 05:02:49 +0000

Problem when you type something like this : I say that here

Solution is:

<%= h(“I say that here

It is possible to make one variable be another:

jobcrawler — Sun, 08 Nov 2009 14:57:48 +0000

using namespace std;
#include 

int main ()
{
   double a = 3.1415927;

   double &b = a;                            // b is a

   b = 89;

   cout << "a contains: " << a << endl;     // Displays 89.

   return 0;
}

(If you are used to pointers and absolutely want to know what happens, simply think double &b = a is translated to double *b = &a and all subsequent b are replaced by *b.)

A global variable can be accessed even if another variable with the same name has been declared inside the function:

jobcrawler — Sun, 08 Nov 2009 14:54:28 +0000

using namespace std; #include double a = 128; int main () { double a = 256; cout << "Local a: " << a << endl; cout << "Global a: " << ::a << endl; return 0; }

lesson 1

jobcrawler — Sun, 08 Nov 2009 14:50:56 +0000

using namespace std;
#include 

int main ()
{

   for (int i = 0; i < 4; i++)
   {
      cout << i << endl;
   }

   cout << i << endl;           // Bad practice!
   i += 5;                      // Bad practice!
   cout << i << endl;           // Bad practice!

   return 0;
}

A Simple C++ program

jobcrawler — Sun, 08 Nov 2009 14:47:17 +0000

using namespace std;
#include 

int main()
{
   int a;                    // a is an integer variable
   char s [100];             // s points to a string of max 99 characters

   cout << "This is a sample program." << endl;

   cout << endl;             // Just a line feed (end of line)

   cout << "Type your age : ";
   cin >> a;

   cout << "Type your name: ";
   cin >> s;

   cout << endl;

   cout << "Hello " << s << " you're " << a << " old." << endl;
   cout << endl << endl << "Bye!" << endl;

   return 0;
}