Posts Tagged ‘servlet config’

How To Get Servlet Init Parameters In JSP

How To Get Servlet Init Parameters In JSP

We know that we can declare init parameters for JSP file in web.xml file as we do in the case of servlet.The entry in the web.xml file will be as follows:

<servlet>
    <servlet-name>myJSP</servlet-name>
    <jsp-file>/MyJsp.jsp</jsp-file>
    <init-param>
            <param-name>paramName</param-name>
            <param-value>paramValue</param-value>
     </init-param>
</servlet>
<servlet-mapping>
     <servlet-name>myJSP</servlet-name>
      <url-pattern>/MyJsp.jsp</url-pattern>
</servlet-mapping>

Now comes the question that how can be access or retrieve those initialization parameters in the JSP page.Among the life cycle methods of a JSP page jspInit() method is one of the methods which can be overridden.The jspInit() method is called by the init() method of the servlet which is the result of the translation of the JSP page.To access the initialization parameters is one of the cases where we override the jspInit() method.When we need to declare a method we use the declarative tag as follows :

<%!
 public void jspInit()
 {
   ServletConfig sConfig = getServletCOnfig();
   String str= sConfig.getInitParameter(“paramName”);
   getSerrvletContext().setAttribute(“name”,str);
 }
%>

Here we have overridden the jspInit() method in the declarative tag.Since this method is called by the init method of the translated servlet code we can access the servlet config object with the help of getServletConfig() method as it is passed by the server to the servlet through init() method. This method (jspInit()) will appear as an overridden method in the translated servlet.The point should be noted here that init() method in the servlet calls this jpInit() life cycle method of the  jsp page so it can access the servlet config object.The life cycle method _jspService() is not permitted to be overridden .Initialization parameters for the the JSP page can be understood as the configuration parameters to be accessed by the translated servlet.After all a JSP page is a servlet at the end of the day and it is the translated servlet only which processes the requests from the clients.

 

 

 

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Life Cycle Of A Servlet Explained Handling Servlet Life-Cycle Events Servlet Life Cycle Servlet Interview Questions Java Servlet Programming

Life Cycle Of A Servlet 

A servlet is a java code which runs at the server side to process request and return response to the client.

In other words, a servlet is an extension to the server which processes request and returns response as an HTML page to the client. Like applets we donot have main method in a servlet. As in case of applet,its life cycle is taken care by the browser itself,similarly in case of servlet its life cycle of a servlet is managed by the server/container.

 

Life Cycle Of A Servlet denotes the phases it goes through. These phases are symbolized by the life cycle methods in the servlet.As server manages the Life Cycle Of A Servlet, these life cycle methods are called by the server itself. Let us have a look at different Life Cycle methods Of A Servlet. These are as follows :

 

  1. init
  2. service
  3. destroy

 

1. init : The init method is the first Life Cycle method Of A Servlet. It is this method which after being called by the server makes a servlet eligible for being called a servlet. After the servlet class constructor is called,the init method is called by the server. The method looks like :

public void init(ServletConfig sc) throws ServletException {
  // Initialization code...
}

 

Here we can see that the ServletConfig object is passed to the init method. This object is created by serverand passed to the init method. Having received the ServletConfig object ,a servlet is said to be a servlet.

2. service : This life cycle method is called every time a request is sent to the servlet .This means that the servlet’s init method has been called and servlet is ready to process requests.This method looks like :

public void service(ServletRequest request,
                    ServletResponse response)
      throws ServletException, IOException{
}

3.destroy : This is the last phase in the Life Cycle Of A Servlet. Before the servlet object is garbage collected at the server side this method is called to relinquish the resources at the server side. This method looks like :

public void destroy() {
    // Finalization code...
  }

It can be noted that the init method is called only once in the Life Cycle Of A Servlet, service is called as many times as many the requests are fired and destroy is called only once in the Life Cycle Of A Servlet.

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