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Applications require some of the attributes to be initialized much before the application is made available to the user or process the request. This tip will help us achieve the task. Code: JSP 1.1


		Code Snippet

Code Written By: Sridhar M S

Typical example can be application version that needs to be present across the application which has to be initialized before hand. Adpoting this approach eliminates the process of retrieval of that value from data-store or a permanent storage location everytime it is required. Attributes such as Application Name, timeout for some process etc can be initialized using this approach.

The ServletContextListener interface from javax.servlet package can perform this operation for us.

We need to register the class that implements this interface as a listener element in the web.xml, and implement the methods contextInitialized(ServletContextEvent sce) and contextDestroyed(ServletContextEvent sce) as required.
 
The class that implements this interface will receive notification when the context is initialized as well as when it gets destroyed.

Code fragment:

public class InitializeData implements ServletContextListener {

	public void contextInitialized(ServletContextEvent event) {
		ServletContext context = event.getServletContext();
		setInitialAttribute(context,"app.version",value); 
		//value can be either from a properties file or from a datasource or any-other source
	}

	public void contextDestroyed(ServletContextEvent event){
		//code that needs to be done when the context is destroyed.
		//can be like destroying the thread or closing resources etc.
	}

	private void setInitialAttribute(ServletContext context,String initParamName,String initialValue) {
		context.setAttribute(initParamName, initialValue);
	}
	
	//other methods can also come in
}

The attribute that is set can be retrieved across the application using the getServletContext().getAttribute("app.version") and made use appropriately.


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