Servlet
term is used in 2 different contexts with 2 different meaning.
In the broader context, it represents technology provided
by SUN Microsystems for developing web
application in java. It is web component that is deployed on the server to create dynamic web pages.
In the narrow context, it represent a class for web
application component that is created using the technology and that is
responsible for processing request on a web server.
CGI based application had following
problems:
1-
CGI
scripts were platform dependent.
Execution of CGI
script was process based. Process based execution limits scalability due to
limited hardware resources such as RAM, Processor etc..
Servlet as
a technology removes both the problems associated with CGI. By providing platform independent and thread based request processing model.
As a technology servlet represents set of classes and interfaces provided by SUN Microsystems. These interfaces define the standard communication model between web server and servlets.
As a technology servlet represents set of classes and interfaces provided by SUN Microsystems. These interfaces define the standard communication model between web server and servlets.
javax.servlet package contains classes and interface of servlet API.
At the core of servlet
API is an interface named javax.servlet.Servlet
which provides life cycle methods of servlet. It need to implemented.
Life cycle methods of Servlet
interface:
1-init(): It is used by the web developer to perform initialization operation. This method is invokes only once just after Servlet object is created. It is used by the server to provide the reference of a ServletConfig object to the servlet.
ServletConfig is an interface of servlet API, implementation of which is provided by web server vendors.
public void init(ServletConfig config);
2- service(): This is a request processing method. This method is invoked each time a request for the Servlet is received.It is used by the Servlet for processing the request.
public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException;
1-init(): It is used by the web developer to perform initialization operation. This method is invokes only once just after Servlet object is created. It is used by the server to provide the reference of a ServletConfig object to the servlet.
ServletConfig is an interface of servlet API, implementation of which is provided by web server vendors.
public void init(ServletConfig config);
2- service(): This is a request processing method. This method is invoked each time a request for the Servlet is received.It is used by the Servlet for processing the request.
public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException;
In the
service() method object of type ServletRequest
and ServletResponse are provided by the web server as parameter.
ServletRequest and ServletResponse
are interface of Servlet API. Implementation of these provided
by web server vendors. These interfaces defines a standard mode of
communication between Servlet and server.
1.1-
ServletRequest object is created and request data is stored in it.
1.2- ServletResponse
object is created to receive response from the Servlet.
1.3- service()
method is invoked and references of ServletRequest and
ServletResponse objects are provided.
1.4- Request
data is read form the ServletRequest object by the Servlet for
processing.
1.5- Processing
logic is applied and result is store in ServletResponse object.
1.6- After
the completion of service() method server reads the contents of
ServletResponse object .
1.7- Response
is sent to the client.
3- destroy(): This method is invoked only one just
before Servlet is unloaded. It is used by the application developers to perform
cleanup operations.
public void destroy();
Non Life cycle methods of Servlet
interface:
1- getServletConfig() :
This methos is used to obtain the reference of the
1- getServletConfig() :
This methos is used to obtain the reference of the
ServletConfig object from a Servlet object.
public ServletConfig getServletConfig();
2- getServletInfo() :
This method is used by the application developer to
This method is used by the application developer to
describes there servlets.
public String getServletInfo();
Note: web
Server create object for a requested Servlet, so there is need to predefine
method (Life cycle methods) that is call by web server to communicate with
Servlet and provides services
|
No comments:
Post a Comment