FreeMark的语法，循环，逻辑

一个对象BOOK
1.输出 ${book.name}
空值判断：${book.name?if_exists }或空值判断可以写成<#if book.name?? > 
${book.name?default(‘xxx’)}//默认值xxx
日期格式：${book.date?string('yyyy-MM-dd')}
数字格式：${book?string.number}--20
插入布尔值：
<#assign foo=ture />
${foo?string("yes","no")} <#-- yes -->

2.逻辑判断
<#if condition>...
<#elseif condition>
...
<#else>
...
<#if/>

<#switch value>
<#case refValue1>

3. Sequence内置的计数器: xxx_index
用途：显示序号
模板:

<#list employees as e>
${e_index}. ${e.name}
</#list>

4、FreeMarker的list
List使用样例-List元素为Scalar对象:

<#list scalarList as value0>
    Scalar List值：${value0}
</#list>

List使用样例-List元素为User对象:

<#list userList as listUser>
    List对象User Id值：${listUser.userId}
</#list>

5、freeMarker的Map
<#list scalarMap?keys as mykey>
    Scalar Map key is :${mykey}
    Scalar Map value is:${scalarMap[mykey]}
</#list>
<#list userMap?keys as key1>
    <#assign mapUser="${userMap[key1]}" >
    User Object is :${mapUser}
    <#--
    以下方法有问题
    User is :${mapUser.userId} <br>
    -->
</#list>

6、FreeMarker中list排序
升序：
<#list list?sort_by("time") as v>
</#list>
降序：
<#list list?sort_by("time") as v>
</#list>
    ...
    <#break>
<#case refValue2>
    ...
    <#break>
...
<#case refValueN>
    ...
    <#break>
<#default>
    ...
</#switch>