web.xml里面各元素标签出现的顺序如下:(注:"?" 表示该标签出现次数最多为1,"*" 表示可以多次出现)
icon? display-name? description? distributable? context-param* filter* filter-mapping* listener* servlet* servlet-mapping* session-config? mime-mapping* welcome-file-list? error-page* taglib* resource-env-ref* resource-ref* security-constraint* login-config? security-role* env-entry* ejb-ref* ejb-local-ref
转自:http://blog.csdn.net/zhannk/article/details/4112440