freemarker 的ObjectWrapper Settings

關於 struts2 和freemarker合做來處理 map 類型的狀況：
struts2 官方以下說：

Once you get familiar with FreeMarker, you will find certain subtletieswith it that may become frustrating. The most common thing you'll likely run in to is the BeansWrapper provided by FreeMarker. If you don't know what this is, don't worry. However, if you do, know this:

The StrutsBeanWrapper extends the default FreeMarker BeansWrapper and provides almost no change in functionality, except for how it handles maps. Normally, FreeMarker has two modes of operation: either support for friendly map built-ins (?keys, ?values, etc) but only support for String keys; OR no special built-in support (ie: ?keys returns the methods on the map instead of the keys) but support for String and non-String keys alike. Struts provides an alternative implementation that gives us the best of both worlds.

It is possible that this special behavior may be confusing or can cause problems. Therefore, you can set the struts.freemarker.wrapper.altMap property in struts.properties to false, allowing the normal BeansWrapper logic to take place instead.

這裏大體的意思就是，freemarker關於map的處理方式有兩種，都是 使用freemarker內建的map?keys

我之前只是使用map?keys返回 這個map當中全部的key的列表，

struts提供了<constant name="struts.freemarker.wrapper.altMap" value="false"/> 參數供咱們設置：

當值爲true的時候，map?keys返回 map中key的列表 不（這時候map的key只能是String類型的）。當值設置爲fase的時候，map?keys返回的是map這個類的全部方法和內容，例如map?keys?size返回22，由於map有22個方法。也能夠使用

此時（map的key能夠是string或者不是string類型的）