Accessing the Web Context
The context in which Web components execute is an object that implements the "http://java.sun/j2ee/tutorial/api/javax/servlet/ServletContextTARGET=_blank>ServletContext interface. You retrieve the Web context with the getServletContext method. The Web context provides methods for accessing:
The Web context is used by the Duke's Bookstore filters examples/src/web/bookstore1/filters/HitCounterFilter.javaTARGET=_blank>filters.HitCounterFilter and OrderFilter, discussed in the section "Servlets8103101Filtering Requests and Responses. The filters store a counter as a context attribute. Recall from "Servlets5102985Controlling Concurrent Access to Shared Resources that the counter's access methods are synchronized to prevent incompatible operations by servlets that are running concurrently. A filter retrieves the counter object with the context's getAttribute method. The incremented value of the counter is recorded with the context's log method.
public final class HitCounterFilter implements Filter {
private FilterConfig filterConfig = null;
public void doFilter(ServletRequest request,
ServletResponse response, FilterChain chain)
throws IOException, ServletException {
...
StringWriter sw = new StringWriter();
PrintWriter writer = new PrintWriter(sw);
ServletContext context = filterCongetServletContext();
Counter counter = (Counter)context.
getAttribute("hitCounter);
...
writer.println("The number of hits is: +
counter.incCounter());
...
context.log(sw.getBuffer().toString());
...
}
}