There are three places a servlet can save data for its processing – in the request, in the session (if present), and in the servlet context (which is shared by all servlets and JSP pages in the context). Data saved in the request is destroyed when the request is completed. Data saved in the session is destroyed when the session is destroyed. Data saved in the servlet context is destroyed when the servlet context is destroyed.

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.

// Save and get a request-scoped value
req.setAttribute("userName", "testUser");
Object value = req.getAttribute("userName");

// Save and get a session-scoped value
HttpSession session = req.getSession(false);
if (session != null) {
    session.setAttribute("userName", "testUser");
    value = session.getAttribute("userName");
}

// Save and get an application-scoped value, could be accessed by all Servlets/Jsps in that web application
getServletContext().setAttribute("userName", "testUser");
value = getServletContext().getAttribute("userName");

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