http://blog.csdn.net/ocean1010/article/details/6160159
ServletContext,ActionContext,ServletActionContext
ServletContext
- ServletContext从他的package信息可以看出,它是标准的JavaEE WebApplication类库
| javax.servlet.ServletContext |
- ServletContext提供了标准的Servlet运行环境,其实就是一些servlet和web container进行通信的方法
| public interface ServletContext { // Returns the URL prefix for the ServletContext. public String getServletContextName(); //Returns the ServletContext for the uri. public ServletContext getContext(String uri); //Returns the context-path for the web-application. public String getContextPath(); //Returns the real file path for the given uri. public String getRealPath(String uri); public RequestDispatcher getRequestDispatcher(String uri); public RequestDispatcher getNamedDispatcher(String servletName); |
| public Object getAttribute(String name); public Enumeration getAttributeNames(); public void setAttribute(String name, Object value); public void removeAttribute(String name); |
- 注意:一个ServletContext对应一个命名空间的servlet( 比如/struts下的所有servlet),是被所有servlet共享的.
There is one context per "web application" per Java Virtual Machine. (A "web application" is a collection of servlets and content installed under a specific subset of the server's URL namespace such as /catalog and possibly installed via a .war file.)
- ServletContext被包含在ServletConfig对象中,ServletConfig对象通常被servlet或filter的init()方法读取
ServletConfig.getServletContext() filterconfig.getServletContext()
ActionContext来源于Struts2 与 Struts1的本质不同. struts1时，由一个servlet (servlet org.apache.struts.action.ActionServlet)处理所有的*.do struts2时，由一个filter(org.apache.struts2.dispatcher.FilterDispatcher)处理所有的请求 struts1 仍旧属于servlet范畴,struts1 action 其本质仍是servlet. struts2 action 已经是普通的java bean了,已经跳出了servlet 框架 ActionContext就是为了弥补strtus2 action跳出标准servlet框架而造成的和WEB环境失去联系的缺陷
ActionContext的主要作用:
- 提供Web环境Context
- 解决线程安全问题
- 解决一些和其他框架或容器(siteMesh,webLogic)的兼容问题
分析ActionContext源码
| public class ActionContext implements Serializable { |
| //////////ThreadLocal模式下的ActionContext实例,实现多线程下的线程安全/////////////// static ThreadLocal actionContext = new ThreadLocal(); //Sets the action context for the current thread. public static void setContext(ActionContext context) { actionContext.set(context); } //Returns the ActionContext specific to the current thread. public static ActionContext getContext() { return (ActionContext) actionContext.get(); } |
| ///////////////定义放置"名/值对"的Map容器,这是ActionContext的主要功能/////////////// Map<String, Object> context; // constractor // Creates a new ActionContext initialized with another context. public ActionContext(Map<String, Object> context) { this.context = context; } public void setContextMap(Map<String, Object> contextMap) { getContext().context = contextMap; } public Map<String, Object> getContextMap() { return context; } //Returns a value that is stored in the current ActionContext by doing a lookup using the value's key. public Object get(String key) { return context.get(key); } //Stores a value in the current ActionContext. The value can be looked up using the key. public void put(String key, Object value) { context.put(key, value); } |
| ///////////////////将各种功能属性放置入Map容器中///////////////////// //action name, Constant for the name of the action being executed. public static final String ACTION_NAME = "com.opensymphony.xwork2.ActionContext.name"; // ognl value stack public static final String VALUE_STACK = ValueStack.VALUE_STACK; public static final String SESSION = "com.opensymphony.xwork2.ActionContext.session"; public static final String APPLICATION = "com.opensymphony.xwork2.ActionContext.application"; public static final String PARAMETERS = "com.opensymphony.xwork2.ActionContext.parameters"; public static final String LOCALE = "com.opensymphony.xwork2.ActionContext.locale"; public static final String TYPE_CONVERTER = "com.opensymphony.xwork2.ActionContext.typeConverter"; public static final String ACTION_INVOCATION = "com.opensymphony.xwork2.ActionContext.actionInvocation"; public static final String CONVERSION_ERRORS = "com.opensymphony.xwork2.ActionContext.conversionErrors"; public static final String CONTAINER = "com.opensymphony.xwork2.ActionContext.container"; ////// 各种Action主属性:ActionName, ActionInvocation(调用action的相关信息), ognl value stack/// //Gets the name of the current Action. public String getName() { return (String) get(ACTION_NAME); } //Sets the name of the current Action in the ActionContext. public void setName(String name) { put(ACTION_NAME, name); } //Sets the action invocation (the execution state). public void setActionInvocation(ActionInvocation actionInvocation) { put(ACTION_INVOCATION, actionInvocation); } public ActionInvocation getActionInvocation() { return (ActionInvocation) get(ACTION_INVOCATION); } // Sets the OGNL value stack. public void setValueStack(ValueStack stack) { put(VALUE_STACK, stack); } //Gets the OGNL value stack. public ValueStack getValueStack() { return (ValueStack) get(VALUE_STACK); } ////////////////各种 request请求包含的内容//////////////////// //Returns a Map of the HttpServletRequest parameters public Map<String, Object> getParameters() { return (Map<String, Object>) get(PARAMETERS); } public void setParameters(Map<String, Object> parameters) { put(PARAMETERS, parameters); } public void setSession(Map<String, Object> session) { put(SESSION, session); } public Map<String, Object> getSession() { return (Map<String, Object>) get(SESSION); } public void setApplication(Map<String, Object> application) { put(APPLICATION, application); } public Map<String, Object> getApplication() { return (Map<String, Object>) get(APPLICATION); } public void setConversionErrors(Map<String, Object> conversionErrors) { put(CONVERSION_ERRORS, conversionErrors); } public Map<String, Object> getConversionErrors() { Map<String, Object> errors = (Map) get(CONVERSION_ERRORS); if (errors == null) { errors = new HashMap<String, Object>(); setConversionErrors(errors); } return errors; } //Sets the Locale for the current action. public void setLocale(Locale locale) { put(LOCALE, locale); } public Locale getLocale() { Locale locale = (Locale) get(LOCALE); if (locale == null) { locale = Locale.getDefault(); setLocale(locale); } return locale; } public void setContainer(Container cont) { put(CONTAINER, cont); } public Container getContainer() { return (Container) get(CONTAINER); } public <T> T getInstance(Class<T> type) { Container cont = getContainer(); if (cont != null) { return cont.getInstance(type); } else { throw new XWorkException("Cannot find an initialized container for this request."); } } } |
ServletActionContext 其实是ActionContext的子类,其功能脱胎于ActionContext,对ActionContext的方法做了一定的包装,提供了更简便直观的方法
| public class ServletActionContext extends ActionContext implements StrutsStatics { |
| /////////////////Servlet Context 提供了多种操作ActionContext的静态方法,使获得Web对象更方便 //HTTP servlet request public static void setRequest(HttpServletRequest request) { ActionContext.getContext().put(HTTP_REQUEST, request); } public static HttpServletRequest getRequest() { return (HttpServletRequest) ActionContext.getContext().get(HTTP_REQUEST); } //HTTP servlet response public static void setResponse(HttpServletResponse response) { ActionContext.getContext().put(HTTP_RESPONSE, response); } public static HttpServletResponse getResponse() { return (HttpServletResponse) ActionContext.getContext().get(HTTP_RESPONSE); } //servlet context. public static ServletContext getServletContext() { return (ServletContext) ActionContext.getContext().get(SERVLET_CONTEXT); } public static void setServletContext(ServletContext servletContext) { ActionContext.getContext().put(SERVLET_CONTEXT, servletContext); } |
1.ActionContext
xwork框架的ActionContext是Action执行时的上下文，存放Action执行时需要用到的对象。在使用webwork时，其中放有Parameter、Session、ServletContext、Locale等信息。这样，webwork负责将Servlet相关数据转换为与ServletAPI无关的Map对象（即ActionContext），使得xwork的Action实现与web层、逻辑层与表现层的解耦。
2.ServletActionContext
提供直接与Servlet容器交互的途径。通过它，可以取得HttpServletRequest、HttpServletResponse 、ServletConfig、ServletContext、PageContext 对象。但是，使用ServletActionContext意味着Action与ServletAPI的紧密耦合。
3.由于WebWork对request，parameter，Session和Application都进行了封装，将这些隐含的对象封装成了相应的Map，如RequestMap，ParameterMap，SessionMap和ApplicationMap，而这些Map就组成
了ActionContext，因此我们通常都不再需要与request，session这些底层的对象打交道了，这也是我一开始觉得迷惑的地方，因为我找不到Session了。事实上，对于SessionMap的处理即是对Session的
处理了。我们可以通过ActionContext的静态方法getContext返回一个ActionContext的实例，然后再调用其getSession方法获得SessionMap，接着就可以利用put和get方法对session进行读写的操作了。
Map params = new HashMap();;
params.put(String, String);;
......
Map extraContext = new HashMap();;
extraContext.put(ActionContext.PARAMETERS,params);
Map session = new HashMap();;
session.put("foo", "bar");;
extraContext.put(ActionContext.SESSION, session);
ActionContext ctx = ActionContext.getContext();
Map session = ctx.getSession();
session.put("username",loginInfo.getUsername());
ActionContext ctx = ActionContext.getContext();
Map params = ctx.getParameters();
String username = ctx.getParameters("username");
OgnlValueStack stack = new OgnlValueStack();
stack.push(new User());//首先将欲赋值对象压入栈中
stack.setValue("name","erica");//为栈顶对象的指定属性名赋值