部分参考《Struts2技术内幕》
ActionContext 作为ValueStack的上下文环境 <|——ServletActionContext
|——context：OgnlContext implements Map ActionContext.getContextMap(),ognl上下文
|——_root：CompountRoot extends ArrayList ：ognl的根
| 内容：( HashMap：ActionContext.getValueStack().set(key,vlaue)用到的HashMap
| 当前Action实例
| DefaultTextProvider：)
|——classResolver：CompoundRootAccessor指定处理class loading的处理类
|——converter：OgnlTypeConverterWrapper指定处理类型转换的处理类
|——memberAccess：SecurityMemberAccess指定处理属性访问策略的处理方式
|——_value：HashMap ：使用一个Map来维护ognl的上下文
===========ActionContext.context._value中的数据========================
Web原生对象：
Com.opensymphony.xwork2.dispatcher.HttpServletRequest——StrutsRequestWrapper
Com.opensymphony.xwork2.dispatcher.HttpServletResponse——ResponseFacade implements HttpServletResponse
Com.opensymphony.xwork2.dispatcher.ServletContext——ApplicationContextFacade
XWork封装对象：
Com.opensymphony.xwork2.ActionContext.application——ApplicationMap<K,V>
<——ActionContext.getApplication()
Com.opensymphony.xwork2.ActionContext.session——SessionMap<K,V>
<——ActionContext.getSession()
Com.opensymphony.xwork2.ActionContext.parameters——TreeMap<K,V> <——ActionContext.getParameters() 返回 HttpServletRequest(get|post,String[],有重复参数名也不覆盖)参数的map
Com.opensymphony.xwork2.util.ValueStack.ValueStack——OgnlValueStack <——ActionContext.getValueStack()
application——ApplicationMap<K,V>
session——SessionMap<K,V>
parameters——HashMap：
request——RequestMap
attri——AttributeMap
action——当前Action类
自定义key——自定义值：使用ActionContext.put(key,value)，ActionContext.get(key)
Com.opensymphony.xwork2.ActionContext.name——fmCS：Action标签的name属性
<—— ActionContext.getName()
Com.opensymphony.xwork2.ActionContext.container——ContainerImpl：struts2的容器
<—— ActionContext.getContainer()
Com.opensymphony.xwork2.ActionContext.actionInvocation——DefaultActionInvocation
<——ActionContext.getActionInvocation()
Com.opensymphony.xwork2.ActionContext.conversionErrors——HashMap
<——ActionContext.getConversionErrors()
Com.opensymphony.xwork2.ActionContext.local——Lcale <——ActionContext.getLocale()
Struts2.actionMapping——ActionMapping
Xwork.NullHandler.createNullObjects——boolean
Xwork.MethodAccessor.denyMethodExecution——Boolean
Report.conversion.errors——Boolean
Current.property.path——
Last.property.accessed——
Last.bean.accessed——
======================================================================
OgnlValueStack：对ognl中的root对象的扩展，具有栈结构
|——context：OgnlContext，差不多就是ActionContext
|——root：CompoundRoot：对valuestack的操作用到的是这里的数据
ValueStack中的[n]表示除栈结构中前N个元素之后构成的元素集合。通过CompoundRoot的cutStack()实现。
使用装饰者模式
StrutsRequestWrapper——|>HttpServletRequestWrapper——|>ServletRequestWrapper
|——request：RequestFacade
|——request：Request
|——attributes：HashMap<K,V>
StrutsRequestWrapper有子类HttpServletRequestWrapper，实现HttpServletRequest接口
使用适配器模式
ApplicationMap
|——context：ApplicationContextFacade
|——entries：HashSet<Set>
public class ApplicationMap extends AbstractMap implements Serializable
Struts2 API解释：A simple implementation of the Map interface to handle a collection of attributes and init parameters in a ServletContext object. The entrySet() method enumerates over all servlet context attributes and init parameters and returns a collection of both. Note, this will occur lazily - only when the entry set is asked for
SessionMap
|——entries
|——request：StrtusRequestWrapper
|——session：StandardSessionFacade
public class SessionMap extends AbstractMap implements Serializable
Struts2 API解释：A simple implementation of the Map interface to handle a collection of HTTP session attributes. The entrySet() method enumerates over all session attributes and creates a Set of entries. Note, this will occur lazily - only when the entry set is asked for.
RequestMap
|——entries
|——request：StrutsRequestWrapper
public class RequestMap extends AbstractMap implements Serializable
Struts2 API解释：A simple implementation of the Map interface to handle a collection of request attributes.
AttributeMap
public class AttributeMap implements Map
Struts2 API解释：
A Map that holds 4 levels of scope.
The scopes are the ones known in the web world.:
Page scope
Request scope
Session scope
Application scope
A object is searched in the order above, starting from page and ending at application scope.
===================================================================
Struts2下的FreeMarker：
参考Struts2API类FreemarkerResult的createModel方法：
Build the instance of the ScopesHashModel, including JspTagLib support
Objects added to the model are
//1）Application - servlet context attributes hash model
atc.getApplication().put("fmApplication", "application 测试");
${Application.fmApplication}
//2）Request - request attributes hash model
ServletActionContext.getRequest().setAttribute("servletRequestFM", "原生Request 测试");
${Request.servletRequestFM}
//3）Session - session attributes hash model
atc.getSession().put("fmSession", "session 测试");
${Session.fmSession}
//4）stack - the OgnLValueStack instance for direct access
atc.put("fmActionContext", "actionContext 测试");
${stack.context.fmActionContext}
atc.getValueStack().set("fm_set_ValueStack", "valueStack set 测试");
${stack.root[0].fm_set_ValueStack}
//5）action - the action itself
private String fmStr="action 域 FreeMarker 测试"; getter,setter
${action.fmStr}
//6）request - the HttpServletRequst object for direct access
//7）response - the HttpServletResponse object for direct access
//8）ognl - the instance of the OgnlTool
//9）JspTaglibs - jsp tag lib factory model
//10）struts - instance of the StrutsUtil class
//11）exception - optional : the JSP or Servlet exception as per the servlet spec (for JSP Exception pages)