上下文(Context)ActionContext介绍(在Struts2中).docx

上下文(context)ActionContext介绍（在Struts2中） 一种属性的有序序列，它们为驻留在环境内的对象定义环境。在对象的激活过程中创建上下文，对象被配置为要求某些自动服务，如同步、事务、实时激活、安全性等等。多个对象可以存留在一个上下文内。也有根据上下文理解意思的意思。ActionContext介绍（在Struts2中）在Web应用程序开发中,除了将请求参数自动设置到Action的字段中,我们往往也需要在Action里直接获取请求(Request)或会话(Session)的一些信息,甚至需要直接对JavaServlet Http的请求(HttpServletRequest),响应(HttpServletResponse)操作.我们需要在Action中取得request请求参数username的值:ActionContext context = ActionContext.getContext();Map params = context.getParameters();String username = (String) params.get(username);ActionContext(com.opensymphony.xwork.ActionContext)是Action执行时的上下文,上下文可以看作是一个容器(其实我们这里的容器就是一个Map而已),它存放放的是Action在执行时需要用到的对象一般情况,我们的ActionContext都是通过:ActionContext context = (ActionContext) actionContext.get();来获取的.我们再来看看这里的actionContext对象的创建:static ThreadLocal actionContext = new ActionContextThreadLocal();,ActionContextThreadLocal是实现ThreadLocal的一个内部类.ThreadLocal可以命名为线程局部变量,它为每一个使用该变量的线程都提供一个变量值的副本,使每一个线程都可以独立地改变自己的副本,而不会和其它线程的副本冲突.这样,我们ActionContext里的属性只会在对应的当前请求线程中可见,从而保证它是线程安全的.下面我们看看怎么通过ActionContext取得我们的HttpSession:Map session = ActionContext.getContext().getSession();ServletActionContext(com.opensymphony.webwork. ServletActionContext),这个类直接继承了我们上面介绍的ActionContext,它提供了直接与JavaServlet相关对象访问的功能,它可以取得的对象有:1, javax.servlet.http.HttpServletRequest:HTTPservlet请求对象2, javax.servlet.http.HttpServletResponse;:HTTPservlet相应对象3, javax.servlet.ServletContext:Servlet上下文信息4, javax.servlet.ServletConfig:Servlet配置对象5, javax.servlet.jsp.PageContext:Http页面上下文下面我们看看几个简单的例子,让我们了解如何从ServletActionContext里取得JavaServlet的相关对象:1,取得HttpServletRequest对象:HttpServletRequest request = ServletActionContext. getRequest();2,取得HttpSession对象:HttpSession session = ServletActionContext. getRequest().getSession();ServletActionContext和ActionContext有着一些重复的功能,在我们的Action中,该如何去抉择呢?我们遵循的原则是:如果ActionContext能够实现我们的功能,那最好就不要使用ServletActionContext,让我们的Action尽量不要直接去访问JavaServlet的相关对象.在使用ActionContext时有一点要注意:不要在Action的构造函数里使用ActionContext.getContext(),因为这个时候ActionContext里的一些值也许没有设置,这时通过ActionContext取得的值也许是null.如果我要取得Servlet API中的一些对象,如request,response或session等,应该怎么做?在Strutx 2.0你可以有两种方式获得这些对象:非IoC(控制反转Inversion of Control)方式和IoC方式.A、非IoC方式要获得上述对象,关键Struts 2.0中com.opensymphony.xwork2.ActionContext类.我们可以通过它的静态方法getContext()获取当前Action的上下文对象.另外,org.apache.struts2.ServletActionContext作为辅助类(Helper Class),可以帮助您快捷地获得这几个对象.HttpServletRequest request = ServletActionContext.getRequest();HttpServletResponse response = ServletActionContext.getResponse();HttpSession session = request.getSession();如果你只是想访问session的属性(Attribute),你也可以通过ActionContext.getContext().getSession()获取或添加session范围(Scoped)的对象.B、IoC方式要使用IoC方式,我们首先要告诉IoC容器(Container)想取得某个对象的意愿,通过实现相应的接口做到这点.具体实现,请参考例6 IocServlet.java.例6 classes/tutorial/NonIoCServlet.javapackage tutorial;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;import org.apache.struts2.ServletActionContext;import com.opensymphony.xwork2.ActionContext;import com.opensymphony.xwork2.ActionSupport;Public classNonIoCServletextends ActionSupportprivate String message;public String getMessage() return message;HttpServletRequest request = ServletActionContext.getRequest();HttpServletResponse response = ServletActionContext.getResponse();HttpSession session = request.getSession();Overridepublic String execute() ActionContext.getContext().getSession().put(msg, Hello World from Session!);A2StringBuffer sb =new StringBuffer(Message from request: );sb.append(request.getParameter(msg);sb.append(Response Buffer Size: );sb.append(response.getBufferSize();sb.append(Session ID: );sb.append(session.getId();message = sb.toString();/转换为字符串。return SUCCESS;/与LoginAction类似的方法。例6 classes/tutorial/IoCServlet.javapackage tutorial;import java.util.Map;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;import erceptor.ServletRequestAware;import erceptor.ServletResponseAware;import erceptor.SessionAware;import com.opensymphony.xwork2.ActionContext;import com.opensymphony.xwork2.ActionSupport;publicclassIoCServletextends ActionSupportimplements SessionAware,ServletRequestAware, ServletResponseAware private String message;private Map att;private HttpServletRequest request;private HttpServletResponse response;public String getMessage() return message;public void setSession(Map att) this.att = att;publicvoid setServletRequest(HttpServletRequest request) this.request = request;publicvoid setServletResponse(HttpServletResponse response) this.response = response;Overridepublic String execute() att.put(msg, Hello World from Session!);HttpSession session = request.getSession();StringBuffer sb =new StringBuffer(Message from request: );sb.append(request.getParameter(msg);sb.append(Response Buffer Size: );sb.append(response.getBufferSize();sb.append(Session ID: );sb.append(session.getId();message = sb.toString();return SUCCESS;例6 Servlet.jspHello World!Message from session: 例6 classes/struts.xml中NonIocServlet和IoCServlet Action的配置/Servlet.jsp/Servlet.jsp运行Tomcat,在浏览器地址栏中键入http:/localhost:8080/Struts2_Action /NonIoCServlet.action?msg=Hello%20World!或http:/localhost:8080/Struts2_Action/IoCServlet.action?msg=Hello%20World!在Servlet.jsp中,我用了两次property标志,第一次将escape设为false为了在JSP中输出转行,第二次的value中的OGNL为#session.msg,它的作用与session.getAttribute(msg)等同.附：ActionContext的常用方法（来自Struts2.0API）（一）getpublicObjectget(Objectkey)Returns a value that is stored in the current ActionContext by doing a lookup using the values key.Parameters:key- the key used to find the value.Returns:the value that was found using the key or null if the key was not found.（二）putpublic voidput(Objectkey,Objectvalue)Stores a value in the current ActionContext. The value can be looked up using the key.Parameters:key- the key of the value.value- the value to be stored.（三）getContextpublic staticActionContextgetContext()Returns the ActionContext specific to the current thread.Returns:the ActionContext for the current thread, is never null.（四）getSessionpublicMapgetSession()Gets the Map of HttpSession values when in a servlet environment or a generic session map otherwise.Returns:the Map of HttpSession values when in a servlet environment or a generic session map otherwise.(五)setSessionpublic voidsetSession(Mapsession)Sets a map of action session values.Parameters:session- the session values.Struts2的action类继承com.opensymphony.xwork2.ActionSupport类的常用方法addFieldError/该方法主要用于验证的方法之中public voidaddFieldError(StringfieldName,StringerrorMessage)Description copied from interface:ValidationAwareAdd an error message for a given field.Specified by:addFieldErrorin interfaceValidationAwareParameters:fieldName- name of fielderrorMessage- the error me