hibernate 空指针异常问题

Question

package com.yuqidi.mapping;

import java.util.Iterator;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;

public class mappingTest {
private static SessionFactory sessionFactory;

@BeforeClass
public static void beforeClass() {
new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);
sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
}
@AfterClass
public static void afterClass() {
sessionFactory.close();
}

@Test
public void testSaveGroup() {
User u1 = new User();
u1.setName("u1");
User u2 = new User();
u2.setName("u2");
Group g = new Group();
g.setName("g1");
g.getUsers().add(u1);
g.getUsers().add(u2);
u1.setGroup(g);
u2.setGroup(g);
Session s = sessionFactory.getCurrentSession();
s.beginTransaction();

s.save(g);
s.getTransaction().commit();

}

@Test
public void testGetGroup(){
testSaveGroup();
Session s = sessionFactory.getCurrentSession();

s.beginTransaction();
Group g=(Group)s.get(Group.class, 0);
System.out.println(g.getName());
s.getTransaction().commit();

}
@Test
public void testSchemaExport() {
new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);
}

public static void main(String[] args) {

beforeClass();

}
}

用Junit 测试时会报空指针异常；去掉System.out.println(g.getName());可以通过测试，情各位指教

Answer 1

1.0 打开的你的数据库 去表 Group 看一下！ID 的值
2.0 把ID 放到这个位置

[quote]Group g=(Group)s.get(Group.class, [color=red]数据库里面的ID[/color]);
System.out.println(g.getName()); [/quote]

然后运行就OK了！