sessionFactory 的 NullPointerException 使用 spring

Question

我已经面临这个问题好几天了，并且尝试了 - 在我看来 - 一切都可以找到解决这个问题的方法。我完全没有想法......

程序应该做什么的描述：它应该在输入用户名和密码后连接到数据库并检查输入的用户名/密码是否在该数据库中。由于 sessionFactory 的 NullPointer，他永远不会进入此检查。

堆栈跟踪：

java.lang.NullPointerException
at de.mail.HibernateUtil.getSession(HibernateUtil.java:37)
at de.mail.gui.LoginServlet.doPost(LoginServlet.java:56)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:462)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:562)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:395)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:250)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:166)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)

context.xml：

    <!-- Component Scans -->
<context:component-scan base-package="de.mail" use-default-filters="false">
    <context:include-filter type="annotation" expression="org.springframework.stereotype.Component" />
</context:component-scan>

<!-- Datenbank -->
<bean id="c3p0DataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource"
    destroy-method="close">
    <property name="driverClass" value="org.postgresql.Driver" />
    <property name="jdbcUrl"
        value="****" />
    <property name="maxPoolSize" value="1" />
    <property name="properties">
        <props>
            <prop key="user">postgres</prop>
            <prop key="password">****</prop>
            <prop key="characterEncoding">UTF-8</prop>
            <!-- Properties sind nur notwendig, wenn man mal SSL für die DB-Verbindung 
                braucht (auch in der properties entkommentieren) -->
            <!-- <prop key="ssl">${db.ssl}</prop> <prop key="sslfactory">${db.sslfactory}</prop> -->
        </props>
    </property>
</bean>
<alias name="c3p0DataSource" alias="dataSource" />

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

<bean id="transactionManager"
    class="org.springframework.orm.hibernate4.HibernateTransactionManager">
    <property name="sessionFactory" ref="sessionFactory" />
    <property name="nestedTransactionAllowed" value="true" />
</bean>

<!-- SessionFactory -->
<bean id="sessionFactory"
    class="org.springframework.orm.hibernate4.LocalSessionFactoryBean"
    destroy-method="destroy">
    <property name="dataSource" ref="dataSource" />
    <property name="packagesToScan">
    <property name="hibernateProperties">
        <props>
            <prop key="hibernate.dialect">org.hibernate.dialect.PostgreSQLDialect</prop>
            <prop key="hibernate.current_session_context_class">thread</prop>
            <prop key="hibernate.cache.provider_class">org.hibernate.cache.NoCacheProvider</prop>
            <prop key="hibernate.show_sql">true</prop>
            <prop key="hibernate.hbm2ddl.auto">update</prop>
        </props>
    </property>
    <property name="annotatedPackages">
        <list>
            <value>de.mail</value>
            <value>de.mail.data.dao</value>
            <value>de.mail.vo</value>
            <value>de.mail.gui</value>
        </list>
    </property>
    <property name="annotatedClasses">
        <list>
            <value>de.mail.data.vo.UserVO</value>
            <value>de.mail.data.vo.FilterVO</value>
            <value>de.mail.data.vo.ResultVO</value>
            <value>de.mail.data.dao.ActionDAO</value>
            <value>de.mail.HibernateUtil</value>
            <value>de.mail.FilterJob</value>
            <value>de.mail.gui.ActionServlet</value>
            <value>de.mail.gui.CreateServlet</value>
            <value>de.mail.gui.DeleteServlet</value>
            <value>de.mail.gui.EditServlet</value>
            <value>de.mail.gui.FormServlet</value>
            <value>de.mail.gui.InitServlet</value>
            <value>de.mail.gui.LoginServlet</value>
            <value>de.mail.gui.LogoutServlet</value>
            <value>de.mail.gui.RegistrationServlet</value>
        </list>
    </property>
</bean>

HibernateUtil：

public abstract class HibernateUtil extends HttpServlet{

private static final long serialVersionUID = -1850678939342717642L;

@Autowired
private SessionFactory sessionFactory;

/**
 * Gibt die derzeitige Session zurück
 * 
 * @return derzeitige Session
 * @throws HibernateException
 */
public Session getSession() {
    /*try {
        return sessionFactory.getCurrentSession();          
    } catch (Throwable e){
        System.out.println("---> " + e);

        return null;
    }*/
    return sessionFactory.getCurrentSession();
}

LoginServlet：

@Component
public class LoginServlet extends HibernateUtil {

/**
 * 
 */
private static final long serialVersionUID = -776218596462464850L;
private static final Log LOG = LogFactory.getLog(LoginServlet.class);
private static final int HEX_FF = 0xFF;

/**
 * Bearbeitet den Loginversuch<br />
 * Es werden die eingegebenen Daten ausgelesen. Aus dem Passwort wird ein Hash-Wert generiert, der mit dem Datenbankeintrag mit dem
 * passenden Usernamen verglichen wird. Stimmt alles &uumlberein wird auf die main.jsp weitergeleitet. Im Fehlerfall wird zur&uumlck auf
 * die login.jsp verwiesen.
 * 
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 * @param response der HttpResponse
 * @param request der HttpRequest
 * @throws ServletException ex
 * @throws IOException ex
 */
@Override
@Transactional(propagation = Propagation.REQUIRES_NEW)
protected void doPost(final HttpServletRequest request, final HttpServletResponse response) throws ServletException, IOException {

    if (!"Registrieren".equals(request.getParameter("register"))) {

        final Session session = getSession();

        // Generiert einen HashWert aus dem eingegebenen Passwort
        try {
            final byte[] pwBytes = request.getParameter("password").getBytes();
            final MessageDigest algorithm = MessageDigest.getInstance("MD5");
            algorithm.reset();
            algorithm.update(pwBytes);
            final byte[] messageDigest = algorithm.digest();

            final StringBuffer hexString = new StringBuffer();

            for (byte digest : messageDigest) {
                hexString.append(Integer.toHexString(HEX_FF & digest));
            }

            final LoginDAO dao = new LoginDAO();
            final List<UserVO> list = dao.checkLogin(request, session);

            final UserVO userVO = list.get(0);

            if (userVO.getPassword().equals(hexString.toString())) {

                request.getSession().setAttribute("userid", userVO.getId());
                final RequestDispatcher dispatcher = request.getRequestDispatcher("main.jsp");
                dispatcher.forward(request, response);

            } else {

                final RequestDispatcher dispatcher = request.getRequestDispatcher("login.jsp");
                dispatcher.forward(request, response);
            }

        } catch (NoSuchAlgorithmException nsax) {
            LOG.debug("Keine MessageDigestSpi fuer den entsprechenden Alogrithmus gefunden");

        } catch (NullPointerException npx) {
            final RequestDispatcher dispatcher = request.getRequestDispatcher("login.jsp");
            dispatcher.forward(request, response);

        } catch (IndexOutOfBoundsException ioobx) {
            final RequestDispatcher dispatcher = request.getRequestDispatcher("login.jsp");
            dispatcher.forward(request, response);
        }
    } else {
        final RequestDispatcher dispatcher = request.getRequestDispatcher("register.jsp");
        dispatcher.forward(request, response);
    }
}

/**
 * Tut nix besonders. Leiet an die doPost-Methode weiter
 * 
 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
 * @param response der HttpResponse
 * @param request der HttpRequest
 * @throws ServletException ex
 * @throws IOException ex
 */
@Override
protected void doGet(final HttpServletRequest request, final HttpServletResponse response) throws ServletException, IOException {
    doPost(request, response);
}

我真的不明白这里的错误。我检查了每个文件，尤其是缺少内容的 spring 上下文，但实际上什么也没找到。我认为错误是由非常简单的事情引起的。对我来说 - 我对 spring 和 hibernate 很陌生 - 不想发现错误。

Answer 1

您的LoginServlet 有一个@Component 注释，这将使它成为一个spring 托管bean，但是您的web.xml 中可能还有一个servlet 声明。您现在有 2 个 servlet 实例，一个由 spring 管理（非常无用，因为它没有在其他地方使用）和一个由 web 容器管理的实例，它与@Autowired 没有任何关系。

要解决您的问题，请使用依赖项查找而不是尝试进行依赖项注入。为此，请使用 servlet 的 init 方法并简单地删除 HibernateUtil 类以及 @Component 注释。

public class LoginServlet extends HttpServlet {

    private SessionFactory sessionFactory;

    public void init() {
        ApplicationContext ctx = WebApplicationContext.getApplicationContext(getServletContext());
        sessionFactory = ctx.getBean(SessionFactory.class);
    }

    protected Session getSession() {
        return sessionFactory.getCurrentSession();
    }
    …
}

您的@Transactional 永远不会工作，因为bean 不是弹簧管理的，注释基本上什么都不做。您可以通过将 doPost 方法包装在 TransactionTemplate 中来解决此问题。

<bean id="txTemplate"  class="TransactionTemplate">
    <constructor-arg ref="transactionManager" />
</bean>

然后在您的 init 方法中为它添加一个查找

public class LoginServlet extends HttpServlet {

    private TransactionTemplate txTemplate;

    public void init() {
        ApplicationContext ctx = WebApplicationContext.getApplicationContext(getServletContext());
        …
        txTemplate = ctx.getBean(TransactionTemplate.class);
    }

将您原来的 doPost 方法重命名为 doPostInternal 并可选择将其命名为 private 并添加以下 doPost 方法`

protected void doPost(final HttpServletRequest request, final HttpServletResponse response) throws ServletException, IOException {
    txTemplate.execute(new TransactionCallbackWithoutResult() {
        public void doInTransactionWithoutResult(TransactionStatus status) {
            doPostInternal(request,response);
        }
    });
}

最后你的休眠配置也有缺陷，因为你在搞乱hibernate.current_session_context_class。使用 spring 时，除非您使用 JTA，否则您应该单独保留此属性。查看您的配置，您并没有删除该属性的设置，当前设置破坏了与休眠的正确弹簧集成。

我强烈建议你看看你的整体架构，因为你当前的设计是有缺陷的恕我直言。你有一个依赖于 web 层的 dao 层（它依赖于HttpServletRequest）。您正在尝试将弹簧插入非基于弹簧的应用程序中（您可以按照上述方式进行工作，但使用弹簧更容易）。将代码移动到Controller 并制作正确的LoginDao 将改善您的整体架构。它还将使测试变得更容易（不再有 Web 依赖项）。

Answer 2

尝试为 HibernateUtil 编写以下代码

import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.SessionFactory;


    public class HibernateUtil {

        private static final SessionFactory sessionFactory;

        static {
            try {
                // Create the SessionFactory from standard (hibernate.cfg.xml) 
                // config file.
                sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
            } catch (Throwable ex) {
                // Log the exception. 
                System.err.println("Initial SessionFactory creation failed." + ex);
                throw new ExceptionInInitializerError(ex);
            }
        }

        public static SessionFactory getSessionFactory() {
            return sessionFactory;
        }
    }

下面的代码将指导你如何使用上面的类

HibernateUtil hu= new HibernateUtil();
SessionFactory sessionFactory =hu.getSessionFactory();
Session session = sessionFactory.openSession();
Query q = session.createQuery ("from UserM where userid='"+lf.getUser()+"' and userpass='"+lf.getPassword()+"'");

Answer 3

尝试使用“c3p0DataSource”引用 SessionFactory bean 而不是使用别名。