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				Saving Data in a JSP Page (Java Developers Almanac Example)
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				The Java Developers Almanac 1.4
				
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				        Java Server Pages
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				  e1048. Saving Data in a JSP Page
				
				When a JSP page needs to save data for its processing, it must
				specify a location, called the scope.  There are four scopes
				available - page, request, session, and application.  Page - scoped data
				is accessible only within the JSP page and is destroyed when the page
				has finished generating its output for the request.  Request-scoped
				data is associated with the request and destroyed when the request is
				completed.  Session-scoped data is associated with a session and
				destroyed when the session is destroyed.  Application-scoped data is
				associated with the web application and destroyed when the web
				application is destroyed.  Application-scoped data is not accessible
				to other web applications.
				
				 Data is saved using a mechanism called attributes.  An
				attribute is a key/value pair where the key is a string and the value
				is any object. It is recommended that the key use the reverse domain
				name convention (e.g., prefixed with com.mycompany) to minimize
				unexpected collisions when integrating with third party modules.  
				
				 This example uses attributes to save and retrieve data in each
				of the four scopes:
				
				
				    <%
				        // Check if attribute has been set
				        Object o = pageContext.getAttribute("com.mycompany.name1", PageContext.PAGE_SCOPE);
				        if (o == null) {
				            // The attribute com.mycompany.name1 may not have a value or may have the value null
				        }
				    
				        // Save data
				        pageContext.setAttribute("com.mycompany.name1", "value0");  // PAGE_SCOPE is the default
				        pageContext.setAttribute("com.mycompany.name1", "value1", PageContext.PAGE_SCOPE);
				        pageContext.setAttribute("com.mycompany.name2", "value2", PageContext.REQUEST_SCOPE);
				        pageContext.setAttribute("com.mycompany.name3", "value3", PageContext.SESSION_SCOPE);
				        pageContext.setAttribute("com.mycompany.name4", "value4", PageContext.APPLICATION_SCOPE);
				    %>
				    
				    <%-- Show the values --%>
				    <%= pageContext.getAttribute("com.mycompany.name1") %> <%-- PAGE_SCOPE --%>
				    <%= pageContext.getAttribute("com.mycompany.name1", PageContext.PAGE_SCOPE) %>
				    <%= pageContext.getAttribute("com.mycompany.name2", PageContext.REQUEST_SCOPE) %>
				    <%= pageContext.getAttribute("com.mycompany.name3", PageContext.SESSION_SCOPE) %>
				    <%= pageContext.getAttribute("com.mycompany.name4", PageContext.APPLICATION_SCOPE) %>
				
				See also e1067 Saving Data Using JSTL in a JSP Page.
				
				
				
				
				             Related Examples
				
				
				
				
				e1046. 
				    The Quintessential JSP Page
				
				
				
				e1047. 
				    Running Java Code in a JSP Page
				
				
				
				e1049. 
				    Implementing a Form in a JSP Page
				
				
				
				e1050. 
				    Implementing a Form That Prevents Duplicate Submissions in a JSP Page
				
				
				
				e1051. 
				    Precompiling a JSP Page
				
				
				
				e1052. 
				    Preventing the Creation of a Session in a JSP Page
				
				
				
				
				
				
				
				
				        See also: 
				
				    Java Server Pages Headers
				  
				
				
				    Java Server Pages Input
				  
				
				
				    Java Server Pages Output
				  
				
				
				
				
				
				
				
				
				
				© 2002 Addison-Wesley.