Question

这对我来说很奇怪......

所以这......会抛出ClassCastException

MyStatus object = Main.getSession().get(MyStatus.class, 1);

但这不会......

Object object = Main.getSession().get(MyStatus.class, 1);

我也做了instanceof上面返回的Object。它显然是一个MyStatus对象，它具有从DB获得的所有正确数据。我的Main类由Intellij自动生成。

public class Main {
    private static final SessionFactory ourSessionFactory;

    static {
        try {
            Configuration configuration = new Configuration();
            configuration.configure();

            ourSessionFactory = configuration.buildSessionFactory();
        } catch (Throwable ex) {
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static Session getSession() throws HibernateException {
        return ourSessionFactory.openSession();
    }

    public static void main(final String[] args) throws Exception {
        final Session session = getSession();
        try {
            System.out.println("querying all the managed entities...");
            final Metamodel metamodel = session.getSessionFactory().getMetamodel();
            for (EntityType<?> entityType : metamodel.getEntities()) {
                final String entityName = entityType.getName();
                final Query query = session.createQuery("from " + entityName);
                System.out.println("executing: " + query.getQueryString());
                for (Object o : query.list()) {
                    System.out.println("  " + o);
                }
            }
        } finally {
            session.close();
        }
    }
}

这是我的hibernate.cfg.xml文件

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">org.postgresql.Driver</property>
        <property name="hibernate.connection.url">jdbc:postgresql://localhost:5432/testdb</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password">test</property>
        <property name="dialect">org.hibernate.dialect.H2Dialect</property>

        <mapping resource="/com/test/app/MyStatus.hbm.xml" class="com.test.app.models.MyStatus" />
    </session-factory>
</hibernate-configuration>

这里是Exception抛出的

javax.servlet.ServletException: java.lang.ClassCastException: com.test.MyStatus cannot be cast to com.test.MyStatus
    org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:489)
    org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:427)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:388)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:341)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:228)

Answer 1

1）如果您在同一个类（同名和包）上有ClassCastException，则意味着您正在处理不同的ClassLoaders。如果您打印MyStatus.class.getClassLoader()和object.getClass().getClassLoader()，您会看到它们是ClassLoader的不同实例。当您在Glassfish类路径和战争中拥有相同的类时，可能会发生这种情况。

2）另一个奇怪的事情是，MyStatus中com.test.app.models.MyStatus被hibernate.cfg.xml声明为com.test.MyStatus，但例外情况为ClassCastException。这是两个不同的类，但很可能与python3.4 lilac.py问题无关。

Answer 2

您是否尝试过投射结果？

MyStatus object = (MyStatus) Main.getSession().get(MyStatus.class, 1);

正如@tsolakp所说，错误很奇怪，似乎加载了两个包。

在Hibernate中调用getSession（）。get（）时得到ClassCastException

2 个答案: