java - HTTP状态500-请求处理失败。嵌套的异常是java.lang.NullPointerException

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What is a NullPointerException, and how do I fix it?
                                
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所以我没什么问题。我无法将信息添加到数据库，因为出现错误：

HTTP Status 500 - Request processing failed; nested exception is java.lang.NullPointerException

这是我的控制器：

package pl.edu.controller;

@Controller
public class StudentAdmissionController {

    @RequestMapping(value = "/admissionForm.html", method = RequestMethod.GET)
    public ModelAndView getAdmissionForm() {

        ModelAndView model = new ModelAndView("AdmissionForm");

        return model;
    }

    @RequestMapping(value = "/submitAdmissionForm.html", method = RequestMethod.POST)
    public ModelAndView submitAdmissionForm(@RequestParam("pojemnosc") float pojemnosc,
            @RequestParam("modelSamochodu") String modelSamochodu, @RequestParam("liczbaPasazerow") int liczbaPasazerow,
            @RequestParam("liczbaDrzwi") int liczbaDrzwi) {

        ModelAndView model = new ModelAndView("AdmissionSuccess");

        Silnik silnik = new Silnik();
        silnik.setPojemnosc(pojemnosc);
        silnik.setId(1);

        Samochod samochod = new Samochod();
        samochod.setSilnik(silnik);
        samochod.setLiczbaDrzwi(liczbaDrzwi);
        samochod.setLiczbaPasazerow(liczbaPasazerow);
        samochod.setModel(modelSamochodu);
        samochod.setLiczbaPoduszek(liczbaPasazerow * 2);
        samochod.setId(1);

        model.addObject("msg",
                "Details submited by you: Pojemnosc: " + silnik.getPojemnosc() + " Model: " + samochod.getModel()
                        + ", Liczba drzwi: " + samochod.getLiczbaDrzwi() + ", Liczba pasazerow: "
                        + samochod.getLiczbaPasazerow() + ", Liczba poduszek: " + samochod.getLiczbaPoduszek());

        SamochodDao samochodDao = new SamochodDao();
        samochodDao.dodaj(samochod);

        return model;
    }
}

我的SamochodDao课：

public class SamochodDao {
    private JdbcTemplate jdbcTemplate;

    @Autowired
    public void setDataSource(DataSource dataSource) {
        this.jdbcTemplate = new JdbcTemplate(dataSource);
    }

    @Transactional
    public void dodaj(final Samochod samochod) {
        final String engineQuery = "insert into silnik (pojemnosc) values (?)";
        KeyHolder keyHolder = new GeneratedKeyHolder();
        jdbcTemplate.update(new PreparedStatementCreator() {
            public PreparedStatement createPreparedStatement(Connection connection) throws SQLException {
                PreparedStatement ps = connection.prepareStatement(engineQuery, new String[] { "id" });
                ps.setFloat(1, samochod.getSilnik().getPojemnosc());
                return ps;
            }
        }, keyHolder);

        String carQuery = "insert into samochod (id, silnik,model,liczbaDrzwi,liczbaPasazerow,liczbaPoduszek) values (?,?,?,?,?,?)";
        Object[] inputs = new Object[] { keyHolder.getKey(), keyHolder.getKey(), samochod.getModel(),
                samochod.getLiczbaDrzwi(), samochod.getLiczbaPasazerow(), samochod.getLiczbaPoduszek() };
        jdbcTemplate.update(carQuery, inputs);
    }

    public void usun(int id) {
        String query = "DELETE FROM samochod WHERE id = ?";
        Object[] inputs = new Object[] { id };
        jdbcTemplate.update(query, inputs);
        query = "DELETE FROM silnik WHERE id = ?";
        jdbcTemplate.update(query, inputs);
    }

    @SuppressWarnings({ "rawtypes", "unchecked" })
    public List<Samochod> listuj() {
        String sql = "SELECT * FROM Silnik";
        List<Silnik> listaSilnikow = jdbcTemplate.query(sql, new BeanPropertyRowMapper(Silnik.class));
        List<Samochod> listaSamochodow = new ArrayList();

        for (Silnik silnik : listaSilnikow) {
            sql = "SELECT * FROM samochod WHERE id = ?";
            Samochod samochod = (Samochod) jdbcTemplate.queryForObject(sql, new Object[] { silnik.getId() },
                    new SamochodRowMapper());
            samochod.setSilnik(silnik);
            listaSamochodow.add(samochod);
        }
        return listaSamochodow;
    }
}

还有我的servlet.xml：

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:context="http://www.springframework.org/schema/context"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">

    <context:component-scan base-package="pl.edu" />
    <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix">
            <value>/WEB-INF/</value>
        </property>
        <property name="suffix">
            <value>.jsp</value>
        </property>
    </bean>

    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost:3306/spring" />
        <property name="username" value="root" />
        <property name="password" value="" />
    </bean>

</beans>

当我尝试向数据库添加新的“ Samochod”时出现错误：

HTTP Status 500 - Request processing failed; nested exception is java.lang.NullPointerException

type Exception report

message Request processing failed; nested exception is java.lang.NullPointerException

description The server encountered an internal error that prevented it from fulfilling this request.

exception

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:868)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

root cause

java.lang.NullPointerException
    pl.edu.dao.SamochodDao.dodaj(SamochodDao.java:26)
    pl.edu.controller.StudentAdmissionController.submitAdmissionForm(StudentAdmissionController.java:48)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:497)
    org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:175)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:446)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:434)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:868)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

也许有人知道我在做什么错？

@编辑

SamochodDao的第26行：

jdbcTemplate.update(new PreparedStatementCreator() {

@ edit2
顺便说一句。当我运行此代码作为测试时，它可以正常工作。这是我从正常应用中得到的豆：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
    http://www.springframework.org/schema/aop
    http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
    http://www.springframework.org/schema/tx
    http://www.springframework.org/schema/tx/spring-tx-2.5.xsd ">

    <aop:aspectj-autoproxy />

    <tx:annotation-driven transaction-manager="transactionManager" />

    <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="dataSource" />
    </bean>

    <bean id="Silnik" class="pl.edu.lab1.Silnik">
        <property name="pojemnosc" value="1.4"></property>
        <property name="id" value="1"></property>
    </bean>
    <bean id="Samochod" class="pl.edu.lab1.Samochod">
        <property name="silnik" ref="Silnik"></property>
        <property name="model" value="Audi"></property>
        <property name="liczbaPasazerow" value="2"></property>
        <property name="liczbaDrzwi" value="4"></property>
        <property name="liczbaPoduszek" value="2"></property>
        <property name="id" value="1"></property>
    </bean>
    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost:3306/spring" />
        <property name="username" value="root" />
        <property name="password" value="" />
    </bean>
    <bean id="SamochodDao" class="pl.edu.dao.SamochodDao">
        <property name="dataSource" ref="dataSource" />
    </bean>

</beans>

但是，当我将其更改为网络应用程序时，会出现错误。

最佳答案

看起来jdbcTemplate是nullValue，因为它是在控制器中创建的。
尝试在上下文中创建一次Dao实例，然后自动连接到控制器中。