Question

我想从数据库中搜索数据，当我按下搜索按钮时，会给我一些信息，如：

严重：servlet [dispatcherServlet]的Servlet.service（）与上下文有关 path [/ FirstSpring]抛出异常[请求处理失败;嵌套具有根本原因的异常是java.lang.NullPointerException] java.lang.NullPointerException at tw.idv.firstspring.dao.imp.StudentDAOImpl.search（StudentDAOImpl.java:19）在 tw.idv.firstspring.service.imp.StudentServiceImpl.search（StudentServiceImpl.java:37）在 tw.idv.firstspring.controller.StudentController.johnnySearch（StudentController.java:45） at sun.reflect.NativeMethodAccessorImpl.invoke0（Native Method）at sun.reflect.NativeMethodAccessorImpl.invoke（未知来源）at sun.reflect.DelegatingMethodAccessorImpl.invoke（未知来源）at java.lang.reflect.Method.invoke（未知来源）at org.springframework.web.method.support.InvocableHandlerMethod.invoke（InvocableHandlerMethod.java:219）在 org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest（InvocableHandlerMethod.java:132）在 org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle（ServletInvocableHandlerMethod.java:100）在 org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod（RequestMappingHandlerAdapter.java:604）在 org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal（RequestMappingHandlerAdapter.java:565）在 org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle（AbstractHandlerMethodAdapter.java:80）在 org.springframework.web.servlet.DispatcherServlet.doDispatch（DispatcherServlet.java:923）在 org.springframework.web.servlet.DispatcherServlet.doService（DispatcherServlet.java:852）在 org.springframework.web.servlet.FrameworkServlet.processRequest（FrameworkServlet.java:882）在 org.springframework.web.servlet.FrameworkServlet.doGet（FrameworkServlet.java:778）在javax.servlet.http.HttpServlet.service（HttpServlet.java:635）at javax.servlet.http.HttpServlet.service（HttpServlet.java:742）at at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:231）在 org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:166）在 org.apache.tomcat.websocket.server.WsFilter.doFilter（WsFilter.java:52）在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:193）在 org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:166）在 org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal（CharacterEncodingFilter.java:88）在 org.springframework.web.filter.OncePerRequestFilter.doFilter（OncePerRequestFilter.java:76）在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:193）在 org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:166）在 org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal（OpenSessionInViewFilter.java:198）在 org.springframework.web.filter.OncePerRequestFilter.doFilter（OncePerRequestFilter.java:76）在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:193）在 org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:166）在 org.apache.catalina.core.StandardWrapperValve.invoke（StandardWrapperValve.java:198）在 org.apache.catalina.core.StandardContextValve.invoke（StandardContextValve.java:96）在 org.apache.catalina.authenticator.AuthenticatorBase.invoke（AuthenticatorBase.java:504）在 org.apache.catalina.core.StandardHostValve.invoke（StandardHostValve.java:140）在 org.apache.catalina.valves.ErrorReportValve.invoke（ErrorReportValve.java:81）在 org.apache.catalina.valves.AbstractAccessLogValve.invoke（AbstractAccessLogValve.java:650）在 org.apache.catalina.core.StandardEngineValve.invoke（StandardEngineValve.java:87）在 org.apache.catalina.connector.CoyoteAdapter.service（CoyoteAdapter.java:342）在 org.apache.coyote.http11.Http11Processor.service（Http11Processor.java:803）在 org.apache.coyote.AbstractProcessorLight.process（AbstractProcessorLight.java:66）在 org.apache.coyote.AbstractProtocol $ ConnectionHandler.process（AbstractProtocol.java:790）在 org.apache.tomcat.util.net.NioEndpoint $ SocketProcessor.doRun（NioEndpoint.java:1459）在 org.apache.tomcat.util.net.SocketProcessorBase.run（SocketProcessorBase.java:49） at java.util.concurrent.ThreadPoolExecutor.runWorker（Unknown Source） at java.util.concurrent.ThreadPoolExecutor $ Worker.run（Unknown Source）在 org.apache.tomcat.util.threads.TaskThread $ WrappingRunnable.run（TaskThread.java:61）在java.lang.Thread.run（未知来源）

这是我的控制者：

package tw.idv.firstspring.controller;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.servlet.ModelAndView;

import tw.idv.firstspring.bean.StudentBean;
import tw.idv.firstspring.service.StudentService;

@Controller
@RequestMapping("/Student")
public class StudentController {

    @Autowired
    private StudentService studentService;

    @RequestMapping("/addStudent")
    public  ModelAndView addStudent(StudentBean StudentBean) throws Exception {
        studentService.addStudent(StudentBean);
        ModelAndView modelAndView = new ModelAndView("FormCheckResultView");
        return modelAndView;
    }

    @RequestMapping("/updateStudent")
    public @ResponseBody String updateStudent(StudentBean StudentBean) throws Exception {
        studentService.updateStudent(StudentBean);
        return null;
    }

    @RequestMapping("/searchStudent")
    public @ResponseBody List<StudentBean> searchStudent(StudentBean StudentBean) throws Exception {
        List<StudentBean> sbList = studentService.search(StudentBean);
        return sbList;
    }


    @RequestMapping( value= "/johnnySearch",method = RequestMethod.GET)// Johnny do in yourself.
    public @ResponseBody ModelAndView johnnySearch(StudentBean StudentBean) throws Exception {

        List<StudentBean> stu=studentService.search(StudentBean);
        return new ModelAndView("index","studentList",stu);
    }
}

这是视图（index.jsp）

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core"  prefix="c"%> 

<%
String path = request.getContextPath(); 
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>

<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">

<base href="<%=basePath%>">

<title>student information</title>

</head>

<body>

    <table border="1" cellpadding="10" cellspacing="0">
        <tr>
            <th>學生姓名</th>
            <th>學號</th>
            <th>學制</th>
            <th>性别</th>
            <th>班級</th>
            <th>老師姓名</th>
            <th>聯絡電話</th>
            <th>聯絡地址</th>
            <th>日間部/夜間部</th>

        </tr>
        <c:forEach items="${studentList}" var="stu">
            <tr>
                <td>${stu.name}</td>
                <td>${stu.stuNo}</td>
                <td>${stu.type}</td>
                <td>${stu.gender}</td>
                <td>${stu.classStr}</td>
                <td>${stu.teacher}</td>
                <td>${stu.phone}</td>
                <td>${stu.address}</td>
                <td>${stu.status}</td>

            </tr>
        </c:forEach>
    </table>
</body>

</html>

这是serviceImp

    package tw.idv.firstspring.service.imp;

import java.util.ArrayList;
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import tw.idv.firstspring.bean.StudentBean;
import tw.idv.firstspring.dao.StudentDAO;
import tw.idv.firstspring.service.StudentService;
import tw.idv.firstspring.utils.BeanUtility;
import tw.idv.firstspring.vo.Student;

@Service
public class StudentServiceImpl implements StudentService {

    @Autowired
    private StudentDAO studentDAO;

    @Override
    public void addStudent(StudentBean StudentBean) {
        Student s = new Student();
        BeanUtility.copyProperties(StudentBean, s);
        studentDAO.insertOrUpdate(s);
    }

    @Override
    public void updateStudent(StudentBean StudentBean) {
        Student s = new Student();
        BeanUtility.copyProperties(StudentBean, s);
        studentDAO.insertOrUpdate(s);
    }

    @Override
    public List<StudentBean> search(StudentBean StudentBean) {
        List<Student> sList = studentDAO.search(StudentBean);
        List<StudentBean> sbList = new ArrayList<>();
        for (Student s : sList) {
            StudentBean sb = new StudentBean();
            sb.setStuNo(s.getStuNo());
            sb.setAddress(s.getAddress());
            sb.setClassStr(s.getClass_());
            sb.setGender(s.getGender());
            sb.setName(s.getName());
            sb.setPassword(s.getPassword());
            sb.setTeacher(s.getTeacher());
            sb.setType(s.getType());
            sb.setPhone(s.getPhone());
            sb.setStatus(s.getStatus());
        }
        return sbList;
    }

}

studentBean

package tw.idv.firstspring.bean;

public class StudentBean {

    private String stuNo;
    private String name;
    private String gender;
    private String type;
    private String classStr;
    private String teacher;
    private String phone;
    private String address;
    private String password;
    private String status;

    public String getStuNo() {
        return stuNo;
    }

    public void setStuNo(String stuNo) {
        this.stuNo = stuNo;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getClassStr() {
        return classStr;
    }

    public void setClassStr(String classStr) {
        this.classStr = classStr;
    }

    public String getTeacher() {
        return teacher;
    }

    public void setTeacher(String teacher) {
        this.teacher = teacher;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getStatus() {
        return status;
    }

    public void setStatus(String status) {
        this.status = status;
    }

}

studentDAOImp

package tw.idv.firstspring.dao.imp;

import java.util.List;

import org.hibernate.criterion.DetachedCriteria;
import org.hibernate.criterion.Restrictions;
import org.springframework.stereotype.Repository;

import tw.idv.firstspring.bean.StudentBean;
import tw.idv.firstspring.dao.StudentDAO;
import tw.idv.firstspring.vo.Student;

@Repository
public class StudentDAOImpl extends BaseDAOImpl<Student> implements StudentDAO {

    @Override
    public List<Student> search(StudentBean studentBean) {
        DetachedCriteria detachedCriteria = DetachedCriteria.forClass(Student.class);
        if (!studentBean.getAddress().equals("") && studentBean.getAddress() != null) {
            detachedCriteria.add(Restrictions.eq("address", studentBean.getAddress()));
        }
        if (!studentBean.getName().equals("") && studentBean.getName() != null) {
            detachedCriteria.add(Restrictions.eq("name", studentBean.getName()));
        }
        if (!studentBean.getPhone().equals("") && studentBean.getPhone() != null) {
            detachedCriteria.add(Restrictions.eq("phone", studentBean.getPhone()));
        }
        if (!studentBean.getStuNo().equals("") && studentBean.getStuNo() != null) {
            detachedCriteria.add(Restrictions.eq("stuNo", studentBean.getStuNo()));
        }
        if (!studentBean.getGender().equals("") && studentBean.getGender() != null) {
            detachedCriteria.add(Restrictions.eq("gender", studentBean.getGender()));
        }
        if (!studentBean.getType().equals("") && studentBean.getType() != null) {
            detachedCriteria.add(Restrictions.eq("type", studentBean.getType()));
        }
        if (!studentBean.getClassStr().equals("") && studentBean.getClassStr() != null) {
            detachedCriteria.add(Restrictions.eq("class", studentBean.getClassStr()));
        }
        if (!studentBean.getTeacher().equals("") && studentBean.getTeacher() != null) {
            detachedCriteria.add(Restrictions.eq("teacher", studentBean.getTeacher()));
        }
        if (!studentBean.getPassword().equals("") && studentBean.getPassword() != null) {
            detachedCriteria.add(Restrictions.eq("password", studentBean.getPassword()));
        }
        if (!studentBean.getStatus().equals("") && studentBean.getStatus() != null) {
            detachedCriteria.add(Restrictions.eq("status", studentBean.getStatus()));
        }
        return this.getHibernateTemplate().findByCriteria(detachedCriteria);
    }

}

Answer 1

StudentDaoImpl在第一行抛出一个空指针异常（NPE）。 19：

if (!studentBean.getAddress().equals("") && studentBean.getAddress() != null) {

studentBean或studentBean.getAddress（）在这里都为null，因此是异常。从逻辑上讲，您需要在search（StudentBean studentBean）方法中重写所有条件以避免NPE。例如：

if (studentBean!= null && !"".equals(studentBean.getAddress()) {

此外，验证一旦studentBean不为null。事实上，如果它为null，则不需要执行所有这些代码（并且您可以在搜索方法的开头抛出异常）并且您的条件将缩短为：

if (!"".equals(studentBean.getAddress()) {

java.lang.NullPointerException ---当我尝试使用hibernate / SpringMVC

1 个答案: