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, applic 4000 ation);      }      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);       }