WebWork 之 ActionContext(Action上下文)

朱雀 2021-09-10 06:36 300阅读 0赞

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      <strong><font><a rel="nofollow"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 173%"><font>ActionContext</font></span></a><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 173%">介绍</span></font></strong> 
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      <span style="FONT-SIZE: 9pt">在</span> 
      <span style="FONT-SIZE: 9pt">Web</span> 
      <span style="FONT-SIZE: 9pt">应用程序开发中，除了将请求参数自动设置到</span> 
      <span style="FONT-SIZE: 9pt">Action</span> 
      <span style="FONT-SIZE: 9pt">的字段中，我们往往也需要在</span> 
      <span style="FONT-SIZE: 9pt">Action</span> 
      <span style="FONT-SIZE: 9pt">里直接获取请求</span> 
      <span style="FONT-SIZE: 9pt">(Request)</span> 
      <span style="FONT-SIZE: 9pt">或会话（</span> 
      <span style="FONT-SIZE: 9pt">Session</span> 
      <span style="FONT-SIZE: 9pt">）的一些信息</span> 
      <span style="FONT-SIZE: 9pt">, </span> 
      <span style="FONT-SIZE: 9pt">甚至需要直接对</span> 
      <span style="FONT-SIZE: 9pt">JavaServlet Http</span> 
      <span style="FONT-SIZE: 9pt">的请求（</span> 
      <span style="FONT-SIZE: 9pt">HttpServletRequest</span> 
      <span style="FONT-SIZE: 9pt">）、响应</span> 
      <span style="FONT-SIZE: 9pt">(HttpServletResponse)</span> 
      <span style="FONT-SIZE: 9pt">操作。</span> 
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      <span style="FONT-SIZE: 9pt">我们需要在</span> 
      <span style="FONT-SIZE: 9pt">Action</span> 
      <span style="FONT-SIZE: 9pt">中取得</span> 
      <span style="FONT-SIZE: 9pt">request</span> 
      <span style="FONT-SIZE: 9pt">请求参数“</span> 
      <span style="FONT-SIZE: 9pt">username</span> 
      <span style="FONT-SIZE: 9pt">”的值：</span> 
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      <span style="FONT-SIZE: 9pt">ActionContext context = ActionContext.getContext();</span> 
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      <span style="FONT-SIZE: 9pt">Map params = context.getParameters();</span> 
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      <span style="FONT-SIZE: 9pt">String username = (String) params.get(“username”);</span> 
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      <span style="FONT-SIZE: 9pt">ActionContext</span> 
      <span style="FONT-SIZE: 9pt">（</span> 
      <span style="FONT-SIZE: 9pt">com.opensymphony.xwork.ActionContext</span> 
      <span style="FONT-SIZE: 9pt">）是</span> 
      <span style="FONT-SIZE: 9pt">Action</span> 
      <span style="FONT-SIZE: 9pt">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</span> 
      <span style="FONT-SIZE: 9pt">Map</span> 
      <span style="FONT-SIZE: 9pt">而已），它存放放的是</span> 
      <span style="FONT-SIZE: 9pt">Action</span> 
      <span style="FONT-SIZE: 9pt">在执行时需要用到的对象</span> 
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      <span style="FONT-SIZE: 9pt">一般情况，我们的</span> 
      <span style="FONT-SIZE: 9pt">ActionContext</span> 
      <span style="FONT-SIZE: 9pt">都是通过：</span> 
      <span style="FONT-SIZE: 9pt">ActionContext context = (ActionContext) actionContext.get();</span> 
      <span style="FONT-SIZE: 9pt">来获取的。我们再来看看这里的</span> 
      <span style="FONT-SIZE: 9pt">actionContext</span> 
      <span style="FONT-SIZE: 9pt">对象的创建：</span> 
      <span style="FONT-SIZE: 9pt">static ThreadLocal actionContext = new ActionContextThreadLocal();</span> 
      <span style="FONT-SIZE: 9pt">，</span> 
      <span style="FONT-SIZE: 9pt">ActionContextThreadLocal</span> 
      <span style="FONT-SIZE: 9pt">是实现</span> 
      <span style="FONT-SIZE: 9pt">ThreadLocal</span> 
      <span style="FONT-SIZE: 9pt">的一个内部类。</span> 
      <span style="FONT-SIZE: 9pt">ThreadLocal</span> 
      <span style="FONT-SIZE: 9pt">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</span> 
      <span style="FONT-SIZE: 9pt">ActionContext</span> 
      <span style="FONT-SIZE: 9pt">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。</span> 
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      <span style="FONT-SIZE: 9pt">下面我们看看怎么通过</span> 
      <span style="FONT-SIZE: 9pt">ActionContext</span> 
      <span style="FONT-SIZE: 9pt">取得我们的</span> 
      <span style="FONT-SIZE: 9pt">HttpSession</span> 
      <span style="FONT-SIZE: 9pt">：</span> 
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      <span style="FONT-SIZE: 9pt">Map session = ActionContext.getContext().getSession()</span> 
      <span style="FONT-SIZE: 9pt">；</span> 
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      <strong><font><a rel="nofollow"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 173%">ServletActionContext</span></a></font></strong> 
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      <span style="FONT-SIZE: 9pt">ServletActionContext</span> 
      <span style="FONT-SIZE: 9pt">（</span> 
      <span style="FONT-SIZE: 9pt">com.opensymphony.webwork. ServletActionContext</span> 
      <span style="FONT-SIZE: 9pt">），这个类直接继承了我们上面介绍的</span> 
      <span style="FONT-SIZE: 9pt">ActionContext</span> 
      <span style="FONT-SIZE: 9pt">，它提供了直接与</span> 
      <span style="FONT-SIZE: 9pt">JavaServlet</span> 
      <span style="FONT-SIZE: 9pt">相关对象访问的功能，它可以取得的对象有：</span> 
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     <div style="MARGIN: 0cm 0cm 0pt 39pt; TEXT-INDENT: -18pt"> 
      <span style="FONT-SIZE: 9pt">1、<span style="FONT: 7pt Times New Roman">&nbsp;&nbsp;&nbsp;</span></span> 
      <span style="FONT-SIZE: 9pt">javax.servlet.http.HttpServletRequest</span> 
      <span style="FONT-SIZE: 9pt">：</span> 
      <span style="FONT-SIZE: 9pt">HTTPservlet</span> 
      <span style="FONT-SIZE: 9pt">请求对象</span> 
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     <div style="MARGIN: 0cm 0cm 0pt 39pt; TEXT-INDENT: -18pt"> 
      <span style="FONT-SIZE: 9pt">2、<span style="FONT: 7pt Times New Roman">&nbsp;&nbsp;&nbsp;</span></span> 
      <span style="FONT-SIZE: 9pt">javax.servlet.http.HttpServletResponse;</span> 
      <span style="FONT-SIZE: 9pt">：</span> 
      <span style="FONT-SIZE: 9pt">HTTPservlet</span> 
      <span style="FONT-SIZE: 9pt">相应对象</span> 
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      <span style="FONT-SIZE: 9pt">3、<span style="FONT: 7pt Times New Roman">&nbsp;&nbsp;&nbsp;</span></span> 
      <span style="FONT-SIZE: 9pt">javax.servlet.ServletContext</span> 
      <span style="FONT-SIZE: 9pt">：</span> 
      <span style="FONT-SIZE: 9pt">Servlet </span> 
      <span style="FONT-SIZE: 9pt">上下文信息</span> 
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      <span style="FONT-SIZE: 9pt">4、<span style="FONT: 7pt Times New Roman">&nbsp;&nbsp;&nbsp;</span></span> 
      <span style="FONT-SIZE: 9pt">javax.servlet.ServletConfig</span> 
      <span style="FONT-SIZE: 9pt">：</span> 
      <span style="FONT-SIZE: 9pt">Servlet</span> 
      <span style="FONT-SIZE: 9pt">配置对象</span> 
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      <span style="FONT-SIZE: 9pt">5、<span style="FONT: 7pt Times New Roman">&nbsp;&nbsp;&nbsp;</span></span> 
      <span style="FONT-SIZE: 9pt">javax.servlet.jsp.PageContext</span> 
      <span style="FONT-SIZE: 9pt">：</span> 
      <span style="FONT-SIZE: 9pt">Http</span> 
      <span style="FONT-SIZE: 9pt">页面上下文</span> 
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     <div style="TEXT-INDENT: 18pt"></div> 
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      <span style="FONT-SIZE: 9pt">下面我们看看几个简单的例子，让我们了解如何从</span> 
      <span style="FONT-SIZE: 9pt">ServletActionContext</span> 
      <span style="FONT-SIZE: 9pt">里取得</span> 
      <span style="FONT-SIZE: 9pt">JavaServlet</span> 
      <span style="FONT-SIZE: 9pt">的相关对象：</span> 
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     <div style="MARGIN: 0cm 0cm 0pt 39pt; TEXT-INDENT: -18pt"> 
      <strong><span style="FONT-SIZE: 9pt">1、<span style="FONT: 7pt Times New Roman">&nbsp;&nbsp;&nbsp;</span></span></strong> 
      <span style="FONT-SIZE: 9pt">取得</span> 
      <span style="FONT-SIZE: 9pt">HttpServletRequest</span> 
      <span style="FONT-SIZE: 9pt">对象：</span> 
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      <span style="FONT-SIZE: 9pt">HttpServletRequest request = ServletActionContext. getRequest();</span> 
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     <div style="MARGIN: 0cm 0cm 0pt 39pt; TEXT-INDENT: -18pt"> 
      <strong><span style="FONT-SIZE: 9pt">2、<span style="FONT: 7pt Times New Roman">&nbsp;&nbsp;&nbsp;</span></span></strong> 
      <span style="FONT-SIZE: 9pt">取得</span> 
      <span style="FONT-SIZE: 9pt">HttpSession</span> 
      <span style="FONT-SIZE: 9pt">对象：</span> 
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      <span style="FONT-SIZE: 9pt">HttpSession session = ServletActionContext. getRequest().getSession();</span> 
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      <span style="FONT-SIZE: 9pt">ServletActionContext</span> 
      <span style="FONT-SIZE: 9pt">和</span> 
      <span style="FONT-SIZE: 9pt">ActionContext</span> 
      <span style="FONT-SIZE: 9pt">有着一些重复的功能，在我们的</span> 
      <span style="FONT-SIZE: 9pt">Action</span> 
      <span style="FONT-SIZE: 9pt">中，该如何去抉择呢？我们遵循的原则是：如果</span> 
      <span style="FONT-SIZE: 9pt">ActionContext</span> 
      <span style="FONT-SIZE: 9pt">能够实现我们的功能，那最好就不要使用</span> 
      <span style="FONT-SIZE: 9pt">ServletActionContext</span> 
      <span style="FONT-SIZE: 9pt">，让我们的</span> 
      <span style="FONT-SIZE: 9pt">Action</span> 
      <span style="FONT-SIZE: 9pt">尽量不要直接去访问</span> 
      <span style="FONT-SIZE: 9pt">JavaServlet</span> 
      <span style="FONT-SIZE: 9pt">的相关对象。在使用</span> 
      <span style="FONT-SIZE: 9pt">ActionContext</span> 
      <span style="FONT-SIZE: 9pt">时有一点要注意：不要在</span> 
      <span style="FONT-SIZE: 9pt">Action</span> 
      <span style="FONT-SIZE: 9pt">的构造函数里使用</span> 
      <span style="FONT-SIZE: 9pt">ActionContext.getContext()</span> 
      <span style="FONT-SIZE: 9pt">，因为这个时候</span> 
      <span style="FONT-SIZE: 9pt">ActionContext</span> 
      <span style="FONT-SIZE: 9pt">里的一些值也许没有设置，这时通过</span> 
      <span style="FONT-SIZE: 9pt">ActionContext</span> 
      <span style="FONT-SIZE: 9pt">取得的值也许是</span> 
      <span style="FONT-SIZE: 9pt">null</span> 
      <span style="FONT-SIZE: 9pt">。</span> 
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