The servlet life-cycle | jwt life-cycle | java servlet life-cycle

The servlet life-cycle 

A servlet life cycle can be defined as the entire
process from its creation till the destruction. The
following are the paths followed by a servlet.

The servlet is initialized by calling
the init() method.

The servlet calls service() method to process a
client's request.

The servlet is terminated by calling
the destroy() method.

Finally, servlet is garbage collected by the garbage
collector of the JVM.

The init() Method

The init method is called only once. It is called only when the

servlet is created, and not called for any user requests

afterwards.


So, it is used for one-time initializations, just as with the init
method of applets.

The servlet is normally created when a user first invokes a URL

corresponding to the servlet, but you can also specify that the

servlet be loaded when the server is first started.

When a user invokes a servlet, a single instance of each
servlet gets created, with each user request resulting in a new
thread that is handed off to doGet or doPost as appropriate.

The init method definition 

public void init() throws ServletException

{

// Initialization code...

}

The service() Method

The service() method is the main method to perform the

actual task.

The servlet container (i.e. web server) calls the service()

method to handle requests coming from the client(

browsers) and to write the formatted response back to

the client.

Each time the server receives a request for a servlet, the

server spawns a new thread and calls service. The

service() method checks the HTTP request type

 (GET,POST, PUT, DELETE, etc.) and calls doGet, doPost, doPut,

doDelete, etc. methods as appropriate.

Here is the signature of this method −

public void service(ServletRequest request,

ServletResponse response) throws ServletException,

IOException

{

}

The service () method is called by the container and service method
invokes doGet, doPost, doPut, doDelete, etc. methods as appropriate.
So you have nothing to do with service() method but you override either
doGet() or doPost() depending on what type of request you receive
from the client.

The doGet() and doPost() are most frequently used methods with in
each service request. Here is the signature of these two methods.
The doGet() Method

A GET request results from a normal request for a URL or from an
HTML form that has no METHOD specified and it should be handled by
doGet() method.

Public void doGet(HttpServletRequest request, HttpServletResponse
response) throws ServletException, IOException
{
// Servlet code
}

The doPost() Method
A POST request results from an HTML form that specifically lists POST
as the METHOD and it should be handled by doPost() method.

public void doPost(HttpServletRequest request, HttpServletResponse
response) throws ServletException, IOException
{
// Servlet code
}

The destroy() Method

The destroy() method is called only once at the end

of the life cycle of a servlet.

This method gives your servlet a chance to close

database connections, halt background threads,

write cookie lists or hit counts to disk, and perform

other such cleanup activities.

After the destroy() method is called, the servlet

object is marked for garbage collection. The destroy

method definition looks like this −

public void destroy()

{

// Finalization code...

}