单项选择题 Click the Exhibit button. As a maintenance feature， you have created this servlet to allow you to upload and remove files on yourweb server. Unfortunately， while testing this servlet， you try to upload a file using an HTTP request and onthis servlet， the web container returns a 404 status. What is wrong with this servlet？（）

单项选择题 Given： 10.public void service（ServletRequest request， 11.ServletResponse response） { 12.ServletInputStream sis = 13.// insert code here 14.} Which retrieves the binary input stream on line 13？（）

单项选择题 You need to retrieve the username cookie from an HTTP request. If this cookie does NOT exist， then the cvariable will be null. Which code snippet must be used to retrieve this cookie object？（）