Servlet threw java.lang.NullPointerException

Question

I am using netbeans 7.4 with hibernate 3.6.10 to develop a web application. I have surfed the net and read quite a number of site, I believe the error is caused by wrong configuration between hibernate and my servlet. As I am new to jsp, servlet and hibernate, I cannot figure out what have I did wrongly. Hope you guys can solve this problem.

Here comes the code. 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.java

package cart.hibernate;

public class PaymentMethod {
    private int paymentMethodId;
    private String paymentMethod;

    public PaymentMethod(){
    }

    public PaymentMethod(String method){
        this.paymentMethod = method;
    } 

    public int getPaymentMethodId() {
        return paymentMethodId;
    }

    public String getPaymentMethod(){
        return paymentMethod;
    }

    public void setPaymentMethodId(int id) {
        this.paymentMethodId = id;
    }

    public void setPaymentMethod(String method){
        this.paymentMethod = method;
    }  
}

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>

ManagePaymentMethod.java

package cart.hibernate; 

import java.util.List; 
import java.util.Iterator;  
import org.hibernate.HibernateException; 
import org.hibernate.Session; 
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class ManagePaymentMethod {

    private static SessionFactory factory;

    public Integer addPaymentMethod(String methodName) { 
        Session session = factory.openSession();  // Error occur here  <--
        Transaction tx = null;
        Integer paymentMethodId = null;

        try {
            tx = session.beginTransaction();
            PaymentMethod payMethod = new PaymentMethod(methodName);
            paymentMethodId = (Integer) session.save(payMethod);
            tx.commit();
        } catch (HibernateException e) {
            if (tx != null) {
                tx.rollback();
            }
            e.printStackTrace();
        } finally {
            session.close();
        }
        return paymentMethodId;
    }
}

addPaymentMethodServlet.java

package cart.hibernate;

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class addPaymentMethodServlet extends HttpServlet {
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();

        String method = request.getParameter("paymentMethod");

        try {
            ManagePaymentMethod manager = new ManagePaymentMethod();

            Integer paymentMethodId = manager.addPaymentMethod(method);
            // Receive from a jsp page and I have checked the value of method is correct

            out.print("..."); // html page

        } finally {
            out.close();
        }

    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    @Override
    public String getServletInfo() {
        return "Short description";
    }

}

When the servlet is called, exception is caught. The following is the error log

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)

I have tested the addPaymentMethod() by executing a main() method in the ManagePaymentMethod.java. The addPaymentMethod() run correctly. Moreover, the value that passed from jsp to addPaymentMethodServlet.java is correct.

If you have more details, please let me know.

When you post code snippets for an exception, bear in mind that we can't see the line numbers from your source-file.. so tell us which line threw the exception, already. You know, we don't. — Thomas W
– Thomas W, Commented Nov 22, 2013 at 11:29

Suresh Atta · Accepted Answer · 2013-11-22 11:13:40Z

2

in the line

Session session = factory.openSession();

facotory is null

You declared

  private static SessionFactory factory;

And never initialized and using in addPaymentMethod method.

answered Nov 22, 2013 at 11:13

Suresh Atta

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2 Comments

Biboo Chung Over a year ago

oh.. I have did it in the testing main method and I just forget to do this afterward !_! lol thank you

Suresh Atta Over a year ago

@BibooChung That's fine. But please don't big posts. It's really hard to trace the problem in it. Post the suspected areas. Glad to help :)

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