[英]Null Pointer Exception on Session in Hibernate Java
我正在创建一个简单的应用程序,由于某种原因,我不断收到空指针异常。 我的猜测是,这与我的session.open是否与if语句有关? 我得到的错误是在finally块上,它说session.close();。
import java.util.*;
import javax.persistence.*;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
public class OrderTester {
private static SessionFactory sessionFactory;
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
Session session = null;
Transaction transaction = null;
System.out.println("Press 1 to log in or press 2 to sign up");
int n = scan.nextInt();
if (n == 1) {
Customer c = new Customer();
// c.logIn();
} else if (n == 2) {
try {
sessionFactory = HibernateUtil.getSessionFactory();
session = sessionFactory.openSession();
transaction = session.beginTransaction();
Customer c = new Customer();
Address a = new Address();
session.save(c);
session.save(a);
Scanner read = new Scanner(System.in);
System.out.println("Enter a username");
String userName = read.next();
c.setUsername(userName);
System.out.println("Enter a password");
String password = read.next();
c.setPassword(password);
System.out.println("Enter the street name");
String streetName = read.next();
a.setStreetName(streetName);
System.out.println("Enter city");
String city = read.next();
a.setCity(city);
System.out.println("Enter state");
String state = read.next();
a.setState(state);
System.out.println("Enter zipcode");
String zipcode = read.next();
a.setZipCode(zipcode);
read.close();
transaction.commit();
} catch (Exception ex) {
transaction.rollback();
System.out.println("Transaction is rolled back.");
} finally {
session.close();
sessionFactory.close();
}
}
}
}
错误:
Press 1 to log in or press 2 to sign up
2
Mar 05, 2016 4:51:44 PM org.hibernate.annotations.common.reflection.java.JavaReflectionManager <clinit>
INFO: HCANN000001: Hibernate Commons Annotations {4.0.5.Final}
Mar 05, 2016 4:51:44 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate Core {4.3.11.Final}
Mar 05, 2016 4:51:44 PM org.hibernate.cfg.Environment <clinit>
INFO: HHH000206: hibernate.properties not found
Mar 05, 2016 4:51:44 PM org.hibernate.cfg.Environment buildBytecodeProvider
INFO: HHH000021: Bytecode provider name : javassist
Mar 05, 2016 4:51:44 PM org.hibernate.cfg.Configuration configure
INFO: HHH000043: Configuring from resource: /hibernate.cfg.xml
Mar 05, 2016 4:51:44 PM org.hibernate.cfg.Configuration getConfigurationInputStream
INFO: HHH000040: Configuration resource: /hibernate.cfg.xml
Mar 05, 2016 4:51:45 PM org.hibernate.internal.util.xml.DTDEntityResolver resolveEntity
WARN: HHH000223: Recognized obsolete hibernate namespace http://hibernate.sourceforge.net/. Use namespace http://www.hibernate.org/dtd/ instead. Refer to Hibernate 3.6 Migration Guide!
Exception in thread "main" java.lang.NullPointerException
at Pizza.OrderTester.main(OrderTester.java:65)
该行上的NullPointerException
堆栈跟踪中没有其他内容仅表示session
为null。 据我所知,可能发生的唯一方法是session = sessionFactory.openSession();
分配从未执行-这意味着在sessionFactory.openSession()
或HibernateUtil.getSessionFactory()
中发生异常,该异常被finally
块中引发的更高版本的异常隐藏。
我希望,如果您在调试器中单步执行此代码,您将看到执行流从这两行之一跳到catch
块,然后在transaction.rollback()
上命中NullPointerException
(因为事务分配从未发生过)和跳转到finally
块,在此撞上另一个NullPointerException
并退出。
由于在try / catch块之外将session
和sessionFactory
都初始化为null
,所以永远不要假设在finally
子句中它们将不为null并直接调用close()
。 将其更改为以下内容:
} catch (Exception ex) {
if(transaction != null) {
try {
transaction.rollback();
} catch (Exception e) { // Log error }
}
ex.printStackTrace();
System.out.println("Transaction is rolled back.");
} finally {
if(session != null) {
try {
session.close();
} catch (Exception e) { // Log error }
}
if(sessionFactory != null) {
try {
sessionFactory.close();
} catch (Exception e) { // Log error }
}
}
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