下面也是一个搜索引擎界面的例子,通过修改前面HTTP状态代码的例子得到。在这个Servlet中,用户界面是动态生成而不是由静态HTML文件提供的。Servlet除了负责读取表单数据并把它们发送给搜索引擎之外,还要把包含表单数据的Cookie发送给客户端。以后客户再次访问同一表单时,这些Cookie的值将用来预先填充表单,使表单自动显示最近使用过的数据。 SearchEnginesFrontEnd.java 该Servlet构造一个主要由表单构成的用户界面。第一次显示的时候,它和前面用静态HTML页面提供的界面差不多。然而,用户选择的值将被保存到Cookie(本页面将数据发送到CustomizedSearchEngines Servlet,由后者设置Cookie)。用户以后再访问同一页面时,即使浏览器是退出之后再启动,表单中也会自动填好上一次搜索所填写的内容。 注意该Servlet用到了ServletUtilities.java,其中getCookieValue前面已经介绍过,headWithTitle用于生成HTML页面的一部分。另外,这里也用到了前面已经说明的LongLiveCookie类,我们用它来创建作废期限很长的Cookie。 package hall; import java.io.*; import javax.servlet.*; import javax.servlet.http.*; import java.net.*; public class SearchEnginesFrontEnd extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { Cookie[] cookies = request.getCookies(); String searchString = ServletUtilities.getCookieValue(cookies, "searchString", "Java Programming"); String numResults = ServletUtilities.getCookieValue(cookies, "numResults", "10"); String searchEngine = ServletUtilities.getCookieValue(cookies, "searchEngine", "google"); response.setContentType("text/html"); PrintWriter out = response.getWriter(); String title = "Searching the Web"; out.println(ServletUtilities.headWithTitle(title) + "<BODY BGCOLOR=\"#FDF5E6\">\n" + "<H1 ALIGN=\"CENTER\">Searching the Web</H1>\n" + "\n" + "<FORM ACTION=\"/servlet/hall.CustomizedSearchEngines\">\n" + "<CENTER>\n" + "Search String:\n" + "<INPUT TYPE=\"TEXT\" NAME=\"searchString\"\n" + " VALUE=\"" + searchString + "\"><BR>\n" + "Results to Show Per Page:\n" + "<INPUT TYPE=\"TEXT\" NAME=\"numResults\"\n" + " VALUE=" + numResults + " SIZE=3><BR>\n" + "<INPUT TYPE=\"RADIO\" NAME=\"searchEngine\"\n" + " VALUE=\"google\"" + checked("google", searchEngine) + ">\n" + "Google |\n" + "<INPUT TYPE=\"RADIO\" NAME=\"searchEngine\"\n" + " VALUE=\"infoseek\"" + checked("infoseek", searchEngine) + ">\n" + "Infoseek |\n" + "<INPUT TYPE=\"RADIO\" NAME=\"searchEngine\"\n" + " VALUE=\"lycos\"" + checked("lycos", searchEngine) + ">\n" + "Lycos |\n" + "<INPUT TYPE=\"RADIO\" NAME=\"searchEngine\"\n" + " VALUE=\"hotbot\"" + checked("hotbot", searchEngine) + ">\n" + "HotBot\n" + "<BR>\n" + "<INPUT TYPE=\"SUBMIT\" VALUE=\"Search\">\n" + "</CENTER>\n" + "</FORM>\n" + "\n" + "</BODY>\n" + "</HTML>\n"); } private String checked(String name1, String name2) { if (name1.equals(name2)) return(" CHECKED"); else return(""); } } CustomizedSearchEngines.java 前面的SearchEnginesFrontEnd Servlet把数据发送到CustomizedSearchEngines Servlet。本例在许多方面与前面介绍HTTP状态代码时的例子相似,区别在于,本例除了要构造一个针对搜索引擎的URL并向用户发送一个重定向应答之外,还要发送保存用户数据的Cookies。 package hall; import java.io.*; import javax.servlet.*; import javax.servlet.http.*; import java.net.*; public class CustomizedSearchEngines extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String searchString = request.getParameter("searchString"); Cookie searchStringCookie = new LongLivedCookie("searchString", searchString); response.addCookie(searchStringCookie); searchString = URLEncoder.encode(searchString); String numResults = request.getParameter("numResults"); Cookie numResultsCookie = new LongLivedCookie("numResults", numResults); response.addCookie(numResultsCookie); String searchEngine = request.getParameter("searchEngine"); Cookie searchEngineCookie = new LongLivedCookie("searchEngine", searchEngine); response.addCookie(searchEngineCookie); SearchSpec[] commonSpecs = SearchSpec.getCommonSpecs(); for(int i=0; i<commonSpecs.length; i++) { SearchSpec searchSpec = commonSpecs[i]; if (searchSpec.getName().equals(searchEngine)) { String url = searchSpec.makeURL(searchString, numResults); response.sendRedirect(url); return; } } response.sendError(response.SC_NOT_FOUND, "No recognized search engine specified."); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } } |
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