Tag: J2EE

Before reading this article, i will suggest readers to go through the version table of J2EE.

One of the most appraised feature of Servlet 3.0 is the support of the annotations to create the Servlet. Before  this the Deployment Descriptor (web.xml) was used to create the servlet mapping , defining init parameters etc. All the settings can be now achieved without any entry in web.xml.

Prerequisite:

1. JDK 5.0 and above.
2. Tomcat 7
3. Eclipse 3.6 – Helios (as of now, it only supports Tomcat 7)

We will start with creating the Servlet class : Continue reading “Create Servlet using Annotation – Servlet 3.0”

SendRedirect

• This is the method of object HttpServlerResponse.
• Request is redirected to client (Browser), and it will process the new URL.
• End User can see on which page, url is redirected.
• In Nutshell, Processing done at client side.

RequestDispatcher

• This object can be accessed from HttpServletRequest.
• Servlet will internally forward the request to another servlet or jsp page.
• End user don’t know that which page is processed internally.
• In Nutshell, Processing done at server side.

Servlet is used in J2EE to create the dynamic web pages under Java Environment.  Like Applets, Servlet also have init() and destroy() methods. In this article i will explain the Life cycle of servlet.

Step 1 : After Compilation of the Servlet, the class file is loaded by the loader.

Step 2 : Then the Container instantiates the Servlet class by calling default Constructor. Read this article to know more that how container works for Servlet.

Continue reading “Life Cycle of Servlet”

1. User clicks a link that has a URL of Servlet.

Continue reading “How container handles the Servlet request”

It is not recommended to override the init() method of the servlet.

Here is an example to override init() method of servlet:

    public class BookDBServlet ... {

        private BookstoreDB books;

        public void init(ServletConfig config) throws ServletException {

            // Store the ServletConfig object and log the initialization
            super.init(config);

            // Load the database to prepare for requests
            books = new BookstoreDB();
        }
        ...
    }

you must write super.init(config) code and after that program specific logic.

Technically you can define constructors in servlet. But, the declared constructor cannot access the ServletConfig object or throw a ServletException.

Then why is it not customary to declare a constructor in a servlet? Because the init() method is used to perform servlet initialization. In JDK 1.0 (servlet were written in this version), constructors for dynamically loaded Java classes such as servlets cannot accept arguments. Therefore init() was used to initialize by passing the implemented object of ServletConfig interface and other needed parameters.
Also, Java constructors cannot be declared in interfaces. So, javax.servlet.Servlet interface cannot have a constructor that accepts a ServletConfig parameter. To overcome this, init() method is used for initialization instead of declaring a constructor.