Servlet lifecycle

The process of adding a wrapper to its context causes the wrapper's start() method to be invoked. A key task of this method is to set its available member to zero.

This member indicates the time (in milliseconds) when a servlet is expected to be ready to serve requests. If this is zero, the servlet is ready and able to serve. If it is a positive value, then the servlet is expected to be available at the specified future time, and requests for it are handled by returning an SC_SERVICE_UNAVAILABLE response. On the other hand, a servlet whose available member is set to Long.MAX_VALUE is considered to be permanently unavailable, and requests are responded to with an SC_NOT_FOUND error.

As we saw in the last chapter, servlets can also be marked as needing to be loaded during the context's startup process using the<load-on-startup> element in the web deployment descriptor.

Loading a servlet

A context loads a wrapper by invoking its load() method.

A non-null instance member...