Servlet抛出了java.lang.NullPointerException

我正在使用netbeans 7.4和hibernate 3.6.10开发一个web应用程序。 我上网浏览了很多网站，我相信错误是由hibernate和我的servlet之间的错误配置造成的。由于我不熟悉jsp、servlet和hibernate，我无法找出我做错了什么。希望你们能解决这个问题

代码来了。 hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
  <session-factory>
    <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
    <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/webasgdvd?zeroDateTimeBehavior=convertToNull</property>
    <property name="hibernate.connection.username">root</property>
    <mapping class="cart.hibernate.PaymentMethod" package="cart.hibernate" resource="cart/hibernate/PaymentMethod.hbm.xml"/>
  </session-factory>
</hibernate-configuration>

PaymentMethod.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="cart.hibernate.PaymentMethod" table="payment_method">
        <meta attribute="class-description">
            This class contains the payment method detail. 
        </meta>
        <id name="paymentMethodId" type="int" column="payment_method_id">
            <generator class="native"/>
        </id>
        <property name="PaymentMethod" column="payment_method" type="string"/>
    </class>
</hibernate-mapping>

调用servlet时，捕获异常。下面是错误日志

Nov 22, 2013 6:55:22 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [addPaymentMethodServlet] in context with path [/eShop] threw exception
java.lang.NullPointerException
    at cart.hibernate.ManagePaymentMethod.addPaymentMethod(ManagePaymentMethod.java:93)
    at cart.hibernate.addPaymentMethodServlet.processRequest(addPaymentMethodServlet.java:46)
    at cart.hibernate.addPaymentMethodServlet.doPost(addPaymentMethodServlet.java:90)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    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.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    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:100)
    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:1041)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    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)

通过在ManagePaymentMethod.java中执行

main（）

方法，我已经测试了

addPaymentMethod（）

。

addPaymentMethod（）

运行正常。 此外，从jsp传递到

addPaymentMethodServlet.java

的值是正确的

如果您有更多详细信息，请让我知道。

在线

Session session = factory.openSession();

传真机为

null

你宣布

  private static SessionFactory factory;

---

切勿初始化并在

addPaymentMethod

方法中使用。

当您发布异常代码片段时，请记住，我们无法看到源文件中的行号。。那么告诉我们哪一行已经抛出了异常。你知道，我们没有。。我已经在测试主方法中进行了测试，但我只是忘记了在之后进行此操作！哈哈，谢谢you@BibooChung那很好。但请不要发大帖子。很难找出其中的问题。张贴可疑区域。很乐意帮忙：）

Nov 22, 2013 6:55:22 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [addPaymentMethodServlet] in context with path [/eShop] threw exception
java.lang.NullPointerException
    at cart.hibernate.ManagePaymentMethod.addPaymentMethod(ManagePaymentMethod.java:93)
    at cart.hibernate.addPaymentMethodServlet.processRequest(addPaymentMethodServlet.java:46)
    at cart.hibernate.addPaymentMethodServlet.doPost(addPaymentMethodServlet.java:90)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    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.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    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:100)
    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:1041)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    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)

Session session = factory.openSession();

  private static SessionFactory factory;