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<HEAD><TITLE>FAQ汇萃 >> Servlet >> 如何设置application 变量</title>
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>> 如何设置application 变量 [<a href=http://www.jsp001.com/forum/showthread.php?goto=newpost&threadid=106>查看别人的评论</a>]<br>
<hr><p>由 webmaster 发布于: 2001-01-21 11:06</p><p> </p><p>application变量是对一个web application有效的全局变量，在保存一些全局有效的值时非常有用。与session变量不同，application变量可以用application.getAttribute()和application.setAttribute()来访问。<br><br>在JSP中，可以自动引用application变量，指代当前的web 应用。（有关web 应用，我将在另外的地方讨论。）<br><br>在引用application 变量时，必须使用同步。并且，需要测试一个application属性是否已经存在。请仔细研究下面的代码，在下面，设置了一个叫“change"的application 属性，保存一个整型值。关于在servlet中使用application变量，方法与下面的代码一致，不过，需要先说明一个application如下:<br><br>servletContext application=getServletContext();<br><br>后面的一段函数是env.java的片断，可以看看在servlet中如何使用application变量的。<br><br>Integer count = null;<br><br>synchronized (application) {<br><br> count = (Integer) application.getAttribute("change");<br><br> if (count == null)<br><br> count = new Integer(0);<br><br> count = new Integer(count.intValue() + 1);<br><br> application.setAttribute("change", count);<br><br>}<br><br><br><br>private void printApplication(PrintWriter pw, HttpServletRequest req)<br><br> throws IOException<br><br> {<br><br> ServletContext application = getServletContext();<br><br><br><br>pw.println("<h1>Application Information:</h1>");<br><br> pw.println("<table>");<br><br> pw.print("<tr><td>Major Version<td>");<br><br> pw.println(application.getMajorVersion());<br><br> pw.print("<tr><td>Minor Version<td>");<br><br> pw.println(application.getMinorVersion());<br><br>pw.print("<tr><td>Server Info<td>");<br><br> pw.println(application.getServerInfo());<br><br> pw.print("<tr><td>Real Path (of pathinfo)<td>");<br><br> pw.println(application.getRealPath(req.getPathInfo()));<br><br> pw.print("<tr><td>Mime-type (of pathinfo)<td>");<br><br> pw.println(application.getMimeType(req.getPathInfo()));<br><br> pw.println("</table>");<br><br><br><br> pw.println("<h1>Application Variables:</h1>");<br><br> pw.println("<table>");<br><br><br><br> Enumeration e = application.getAttributeNames();<br><br>while (e.hasMoreElements()) {<br><br> String name = (String) e.nextElement();<br><br> pw.print("<tr><td>");<br><br> pw.print(name);<br><br> pw.print("<td>");<br><br> pw.println(application.getAttribute(name));<br><br> }<br><br><br><br> pw.println("</table>");<br><br>}<br><br><br><br>%><br><br><br><br><html><br><br><head><title>Counter</title></head><br><br><body bgcolor=#ffffff><br><br><br><br><h1>Welcome, visitor: <%= count %></h1><br><br><br><br></body><br><br></html><br></p></td>
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