Hibernate示例程序中的java.lang.NullPointerException

Question

我尝试运行 hibernate 的示例应用程序，它在运行时给我一个错误:

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Exception in thread "main" java.lang.NullPointerException at transaction.rollback();

这是在 Main.java 中:

public class Main {

public static void main(String[] args) {
    Session session = HibernateUtil.getSessionFactory().openSession();
    Transaction transaction = null;
    try {
        transaction = session.beginTransaction();
        Address address = new Address("ABC", "Delhi", "TN", "110001");
        Student student = new Student("kumar", address);
        session.save(student);
        transaction.commit();
    } catch (HibernateException e) {
        transaction.rollback();
        e.printStackTrace();
    } finally {
        session.close();
    }

Answer 1

应该改变

transaction.rollback();

至

if (transaction != null) {
    transaction.rollback();
}

因为事务的赋值有可能抛出异常。

如果你想摆脱 Log4J 消息，你可以添加一个调用

BasicConfigurator.configure();

设置基本日志记录