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ServletContext,ActionContext,ServletActionContext

2011-01-23 21:50 429 查看

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);
}

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