java - 在 JSP 中编写 Hibernate 查询会给出 java.lang.NullPointerException

Question

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>WebSLCM</display-name>
  <welcome-file-list>
    <welcome-file>/WEB-INF/resources/jsp/index.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>spring-dispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>/WEB-INF/dispatcher-servlet.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>spring-dispatcher</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
  <error-page>
    <error-code>404</error-code>
    <location>/WEB-INF/resources/jsp/404.jsp</location>
  </error-page>
</web-app>

dispatcher-servlet.xml

<?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:context="http://www.springframework.org/schema/context"
        xmlns:tx="http://www.springframework.org/schema/tx" xmlns:mvc="http://www.springframework.org/schema/mvc"
        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/context 
             http://www.springframework.org/schema/context/spring-context.xsd 
             http://www.springframework.org/schema/mvc
             http://www.springframework.org/schema/mvc/spring-mvc.xsd
             http://www.springframework.org/schema/tx 
             http://www.springframework.org/schema/tx/spring-tx.xsd
             http://www.springframework.org/schema/aop 
             http://www.springframework.org/schema/aop/spring-aop.xsd">

    <mvc:annotation-driven />
    <!-- <mvc:default-servlet-handler/> -->
    <mvc:resources mapping="/resources/**" location="WEB-INF/resources/" />
    <context:component-scan base-package="com.slv.controller" />

    <!-- JDBC Properties -->
    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost:3306/webslcm" />
        <property name="username" value="root" />
        <property name="password" value="root" />
    </bean>

    <!-- Accounts -->
    <bean id="accountsDaoImpl" class="com.slv.daoimpl.AccountsDaoImpl">
        <property name="sessionFactory" ref="sessionFactory" />
    </bean>

    <!-- Hibernate Session properties -->
    <bean id="sessionFactory"
        class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="packagesToScan" value="com.slv.model" />
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>
                <prop key="hibernate.show_sql">true</prop>
                <prop key="hibernate.hbm2ddl.auto">update</prop>
            </props>
        </property>
    </bean>

    <!-- ViewResolver Spring Will redirecting -->
    <bean
        class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/resources/jsp/" />
        <property name="suffix" value=".jsp" />
    </bean>

Jsp 页面:

<%!
    @Autowired
    public AccountsDaoImpl accountsDaoImpl;
%>
<% 
    List<Object[]> list =  accountsDaoImpl.getSQLObjectValues("SELECT examId, examName FROM examtypes", session);
%>

当我在 JSP 中运行上述代码时，我得到了 java.lang.NullPointerException 异常。

无法解决，我是否错过了任何重要的事情？我应该对我的代码进行哪些更改才能正常工作？

AccountsDaoImpl.java

public class AccountsDaoImpl implements AccountsDao{

@Autowired
    public SessionFactory sessionFactory;

public SessionFactory getSessionFactory() {
    return sessionFactory;
}

public void setSessionFactory(SessionFactory sessionFactory) {
    this.sessionFactory = sessionFactory;
}

@Override
    public List<Object[]> getSQLObjectValues(String sqlQuery, HttpSession session2) {
        Session session=sessionFactory.openSession(); // Here im getting the below exception 
        session.beginTransaction();
        try{
            Query query = session.createSQLQuery(sqlQuery);
            List<Object[]> list=query.list();
            return list;
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            session.close();sessionFactory.close();
        }
        return null;
    }
}

异常:

java.lang.NullPointerException
    at com.slv.daoimpl.AccountsDaoImpl.getSQLObjectValues(AccountsDaoImpl.java:384)
    at org.apache.jsp.WEB_002dINF.resources.jsp.reUsableReport_jsp._jspService(reUsableReport_jsp.java:179)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:749)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:487)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:412)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:339)
    at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:168)
    at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1244)
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

Answer 1

您没有使用 Spring 上下文为您生成 bean，基本上忽略了所有 Spring 配置。你可以从JSP中的应用程序内容中查找bean，但是在JSP中编写应用程序代码总是一个坏主意!所以我不会给出更详细的答案，不要拍自己故意在脚上。在 servlet 中 Autowiring bean，并通过 JSP 中的请求调用它。

servlet 中的 Autowiring

您可以使用 SpringBeanAutowiringSupport 工具类来注入(inject)您的 spring bean:

public class MyServlet implements HttpServlet {

    @Autowired
    private MyBean myBean;

    public void init(ServletConfig config) {
        super.init(config);
        SpringBeanAutowiringSupport.processInjectionBasedOnServletContext(this);
    }
}