在我的服务方法中自动装配dao类时引发Null指针异常

Question

我有两个服务，其中一个是触发邮件的邮件服务，我正在使用Quartz Scheduler来调度作业，因此当我尝试自动连接dao类（将所有数据库记录都检索到邮件服务）时，它会抛出一个错误。空指针异常。我在其他服务中调用相同的dao方法，并且可以正常工作。谁能给我解决办法

@Service("mailService")
public class MailServiceImpl implements MailService{

    static Logger logger = Logger.getLogger(MailServiceImpl.class);

    @Autowired
    ReleaseScheduleDaoImpl releaseScheduleDao ;

    @Override
    public void sendEmail(String from, String to, String subject, String content){
        //PropertyConfigurator.configure("log4j.properties");
        System.out.println("Inside sendEmail()");
        Security.addProvider(new com.sun.net.ssl.internal.ssl.Provider());
        try {
            Properties props = new Properties();
            props.setProperty("mail.transport.protocol", "smtp");
            props.setProperty("mail.host", "smtp.gmail.com");
            props.put("mail.smtp.auth", "true");
            props.put("mail.smtp.port", "465");
            props.put("mail.debug", "true");
            props.put("mail.smtp.socketFactory.port", "465");
            props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
            props.put("mail.smtp.socketFactory.fallback", "false");
            props.setProperty("mail.smtp.quitwait", "false");

            Session session = Session.getDefaultInstance(props,
                    new javax.mail.Authenticator() {
                        protected PasswordAuthentication getPasswordAuthentication() {
                            return new PasswordAuthentication(
                                "sureshnambiar.c@gmail.com", "Ammaammus");
                        }
                    });

            session.setDebug(true);
            Transport transport = session.getTransport();
            InternetAddress addressFrom = new InternetAddress(from);
            MimeMessage message = new MimeMessage(session);
            message.setSender(addressFrom);
            message.setSubject(subject);
            message.setContent(content, "text/plain");
            message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
            transport.connect();
            transport.send(message);
            transport.close();

        }catch (MessagingException mex){
            logger.error(mex.getMessage());
        }

    }

    // here I am thrown with an null pointer exception
    @Override
    public List<ReleaseScheduleFieldName> getAllReleaseScheduleFieldName() {
        return releaseScheduleDao.getAllReleaseScheduleFieldName();
    }
}


// my quartz scheduler execute method
public class ReleaseMailScheduler extends QuartzJobBean {

    MailServiceImpl mailService = new MailServiceImpl();

    @Override
    protected void executeInternal(JobExecutionContext jobExecutionContext) throws JobExecutionException {
        System.out.println("inside execute");
        try {
            List<ReleaseScheduleFieldName> fieldList = mailService.getAllReleaseScheduleFieldName();
            System.out.println("fieldList " + fieldList);
            mailService.sendEmail("sureshnambiar.c@gmail.com", "sureshnambiar.c@gmail.com", "test Plain", "this is a test");
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}

//my dao class
@Override
public List<ReleaseScheduleFieldName> getAllReleaseScheduleFieldName() {
    session = this.sessionFactory.openSession();
    List<ReleaseScheduleFieldName> fieldNames= new ArrayList<>();
    try {
        String sql = "from ReleaseScheduleFieldName rf ORDER BY rf.fieldNameId";
        fieldNames = (List<ReleaseScheduleFieldName>) session.createQuery(sql).list();
    }catch(Exception e){
        logger.error(e.getMessage());
    }finally {
        session.close();
    }
    return fieldNames;
}

以下是我得到的例外情况

java.lang.NullPointerException
at com.cerner.release.Service.MailServiceImpl.getAllReleaseScheduleFieldName(MailServiceImpl.java:72)
at com.cerner.release.Scheduler.ReleaseMailScheduler.executeInternal(ReleaseMailScheduler.java:18)
at org.springframework.scheduling.quartz.QuartzJobBean.execute(QuartzJobBean.java:75)
at org.quartz.core.JobRunShell.run(JobRunShell.java:202)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:573)