java.lang.NullPointerException

2009-03-24 09:57:30 127 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

C/C++_五大常规算法_分治算法分治法一个装有 16 枚硬币的袋子，16 枚硬币中有一个是伪造的，伪造的硬币和普通硬币从表面上看不出有任何差别，但是那个伪造的硬币比真的硬币要轻。现有给你一台天平，请你在尽可能最短的时间内找出那枚伪造的硬币。常规思维：每次从待比较的硬币中取两枚进行计较，如果天平平衡（相等）就继续取剩下的硬币进行比较继续以上过程，直到找到硬币。强者思维: 我们先将 16 枚硬币分为左右两个部分，各为 8 个硬币，分别称重，必然会有一半轻一半重，而我们要的就是轻的那组,重的舍去。接下来我们继续对轻的进行五五分阅读详情

LoginAction调用DAO时出现空指针异常，代码如下：

package com.hotel.struts.action;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.apache.log4j.Logger;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.action.ActionMessage;
import org.apache.struts.action.ActionMessages;
import org.apache.struts.actions.DispatchAction;

import com.hotel.hibernate.dao.OperatorDAO;
import com.hotel.struts.form.LoginForm;
import com.hotel.struts.util.Constants;

public class LoginAction extends DispatchAction {

protected OperatorDAO operatorDAO ;

Logger log = Logger.getLogger(this.getClass());

public OperatorDAO getOperatorDAO() {
return operatorDAO;
}

public void setOperatorDAO(OperatorDAO operatorDAO) {
this.operatorDAO = operatorDAO;
}

public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response)
throws Exception {

ActionMessages messages = new ActionMessages();
ActionForward forward = new ActionForward();
LoginForm loginForm = (LoginForm) form;

// try {
// get parameters
String oid = loginForm.getOid();

// invalidate the original session if exists
HttpSession session = request.getSession(false);
if (session != null) {
session.invalidate();
}

// create a new session for the user
session = request.getSession(true);

// login
boolean isValid = valid(request, loginForm);
if (isValid) {

session.setAttribute(Constants.OPERATOR_KEY, oid);

log.info("Operator " + oid + " login.");
} else {
messages.add(ActionMessages.GLOBAL_MESSAGE, new ActionMessage(
"login.message.failed"));
}

// } catch (Exception e) {
// messages.add(ActionMessages.GLOBAL_MESSAGE, new ActionMessage(
// "register.message.failed"));
// }

// If a message is required, save the specified key(s)
// into the request for use by the <struts:errors> tag.

if (!messages.isEmpty()) {
saveErrors(request, messages);
request.setAttribute("loginFormBean", loginForm);
forward = mapping.findForward(Constants.FAILURE_KEY);
} else {
forward = mapping.findForward(Constants.SUCCESS_KEY);
}

// Finish with
return (forward);
}

private boolean valid(HttpServletRequest request, LoginForm loginForm) {
if (getOperatorDAO().isValid(loginForm.getOid(),
loginForm.getOpwd())) {
return true;
} else {
return false;
}
}

}

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