Servlets 面试题与答案

问题 16. What is filter? Can filter be used as request or response?

A filter is a reusable piece of code that can transform the content of HTTP requests,responses, and header information. Filters do not generally create a response or respond to a request as servlets do, rather they modify or adapt the requests for a resource, and modify or adapt responses from a resource.

问题 17. When using servlets to build the HTML, you build a DOCTYPE line, why do you do that?

问题 18. What is new in ServletRequest interface ? (Servlet 2.4)

The following methods have been added to ServletRequest 2.4 version:
public int getRemotePort()
public java.lang.String getLocalName()
public java.lang.String getLocalAddr()
public int getLocalPort()

问题 19. Request parameter How to find whether a parameter exists in the request object?

1.boolean hasFoo = !(request.getParameter("foo") == null || request.getParameter("foo").equals(""));
2. boolean hasParameter = request.getParameterMap().contains(theParameter);
(which works in Servlet 2.3+)

问题 20. How can I send user authentication information while making URL Connection?

You'll want to use HttpURLConnection.setRequestProperty and set all the appropriate headers to HTTP authorization.