freemarker 解析map#if map ?exists#list map?keys as attr ${attr}: ${map[attr]}/#list/#if获取
freemarker 解析map
<#if map ?exists><#list map?keys as attr> ${attr}: ${map[attr]}</#list></#if>获取reuqest的参数：
<#list RequestParameters?keys as key>
${RequestParameters[key]}
</#list>