请尽量使用准确的文字描述作为标题
（甚至只是简单的错误信息-- What are the error messages?）
若新帖再無恰当标题，可能会被刪除
原來的标题： 新手请教
我按照书上例子写了一个Servlet小程序,编译通过.运行就抛出空指针错误,请大家帮忙看看.
ServletUtilities.java:
package myjava;
import javax.servlet.http.Cookie;
public class ServletUtilities {
public static final String DOCTYPE = "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0 Transitional//EN\">";
public static String headWithTitle(String title) {
return (DOCTYPE + "\n" + "<html>\n" + "<head><title>" + title + "</title></head>\n");
}
public static String getCookieValue(Cookie[] cookies, String cookieName,String defaultValue) {
for (int i = 0; i < cookies.length; i++) {
Cookie cookie = cookies[i];
if (cookieName.equals(cookie.getName())) {
return (cookie.getValue());
}
}
return (defaultValue);
}
}
}
SearchEnginesFrontEnd.java:
package myjava;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.net.*;
/**
* Servlet implementation class for Servlet: SearchEnginesFrontEnd
*
*/
public class SearchEnginesFrontEnd extends javax.servlet.http.HttpServlet implements javax.servlet.Servlet {
public SearchEnginesFrontEnd() {
super();
}
protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
// TODO Auto-generated method stub
Cookie[] cookies=req.getCookies();
String searchString=ServletUtilities.getCookieValue(cookies,"searchString","Java Programming"); //出错的地方
//String searchString="null"; //如果用这句替换上面一句的话,就正常
res.setContentType("text/html");
PrintWriter out=res.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=CustomizedSearchEngines>\n"
+"<center>\n"+"Search String:\n"
+"<input type=text name=searchString value="+searchString+"><br>\n"
+"<input type=radio name=searchEngine value=google>Google\n"
+"<input type=radio name=searchEngine value=baidu>Baidu\n"
+"<input type=radio name=searchEngine value=hotbot>Hotbot\n"
+"<input type=radio name=searchEngine value=yahoo>Yahoo<br>\n"
+"<input type=submit value=search><br>\n"
+"</center>\n"+"</form>\n"+"</body>\n"+"</html>\n");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request,response);
}
}
我的工具是sdk1.5+eclipse+tomcat
Print this page
