mybatis下opening session时空指针异常

先看错误信息

Exception in thread "main" org.apache.ibatis.exceptions.PersistenceException: 
### Error opening session.  Cause: java.lang.NullPointerException
### Cause: java.lang.NullPointerException
	at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:23)
	at org.apache.ibatis.session.defaults.DefaultSqlSessionFactory.openSessionFromDataSource(DefaultSqlSessionFactory.java:88)
	at org.apache.ibatis.session.defaults.DefaultSqlSessionFactory.openSession(DefaultSqlSessionFactory.java:43)
	at com.swj.util.DbUtil.openSession(DbUtil.java:30)
	at com.swj.test.Test.main(Test.java:13)
Caused by: java.lang.NullPointerException
	at org.apache.ibatis.session.defaults.DefaultSqlSessionFactory.openSessionFromDataSource(DefaultSqlSessionFactory.java:83)
	... 3 more

先找到错误的信息是在factory.openSession()这里，以为是factory没有拿到，输出了下factory发现是有对象存在的，

就很奇怪。- -应该是哪里配置错了 看下配置文件 和获取SqlSession的地方

package com.swj.util;

import java.io.IOException;
import java.io.Reader;
import java.nio.charset.Charset;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class DbUtil {
	private static SqlSessionFactory factory;
	
	private DbUtil(){}
	
	static{
		try {
			Resources.setCharset(Charset.forName("utf-8"));
			Reader reader = Resources.getResourceAsReader("mybatis.xml");
			factory = new SqlSessionFactoryBuilder().build(reader,"oracle");
		} catch (IOException e) {
			e.printStackTrace();
		}catch(Exception e){
			e.printStackTrace();
		}
	}
	
	public static SqlSession openSession(){
		return factory.openSession();
	}
	
	public static void close(SqlSession session){
		if(session!=null){
			session.close();
		}
	}
}

找了半天- -发现是在配置文件里的环境名字是database，而获取factory时传入的环境是oracle，开始以为是用的什么数据库传的就是数据库的名称- -