searchengines.java

Servlet与JSP核心编程第二版代码

package coreservlets;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.net.*;

/** Servlet that takes a search string and a search
 *  engine name, sending the query to
 *  that search engine. Illustrates manipulating
 *  the response status code. It sends a 302 response
 *  (via sendRedirect) if it gets a known search engine,
 *  and sends a 404 response (via sendError) otherwise.
 *  <P>
 *  Taken from Core Servlets and JavaServer Pages 2nd Edition
 *  from Prentice Hall and Sun Microsystems Press,
 *  http://www.coreservlets.com/.
 *  &copy; 2003 Marty Hall; may be freely used or adapted.
 */

public class SearchEngines extends HttpServlet {
  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
      throws ServletException, IOException {
    String searchString = request.getParameter("searchString");
    if ((searchString == null) ||
        (searchString.length() == 0)) {
      reportProblem(response, "Missing search string");
      return;
    }
    // The URLEncoder changes spaces to "+" signs and other
    // non-alphanumeric characters to "%XY", where XY is the
    // hex value of the ASCII (or ISO Latin-1) character.
    // Browsers always URL-encode form values, and the
    // getParameter method decodes automatically. But since
    // we're just passing this on to another server, we need to
    // re-encode it to avoid characters that are illegal in
    // URLs. Also note that JDK 1.4 introduced a two-argument
    // version of URLEncoder.encode and deprecated the one-arg
    // version. However, since version 2.3 of the servlet spec
    // mandates only the Java 2 Platform (JDK 1.2 or later),
    // we stick with the one-arg version for portability.
    searchString = URLEncoder.encode(searchString);
    
    String searchEngineName =
      request.getParameter("searchEngine");
    if ((searchEngineName == null) ||
        (searchEngineName.length() == 0)) {
      reportProblem(response, "Missing search engine name");
      return;
    }
    String searchURL =
      SearchUtilities.makeURL(searchEngineName, searchString);
    if (searchURL != null) {
      response.sendRedirect(searchURL);
    } else {
      reportProblem(response, "Unrecognized search engine");
    } 
  }

  private void reportProblem(HttpServletResponse response,
                             String message)
      throws IOException {
    response.sendError(response.SC_NOT_FOUND, message);
  }
}