Question

mybatis做简单的查询怎么总是报空指针

<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mxl.bean.TeacherMapper">
<select id="getTeacher" parameterType="int" resultType="Teacher">
select t_id,t_name from teacher where t_id= #{tid}
</select>
</mapper>

@Test
public void testTeacher(){
SqlSession session = MybatisUtil.getSesssion();
String statem = "com.mxl.bean.TeacherMapper.getTeacher";
Teacher t = session.selectOne(statem,1);
System.out.println(t.toString());
}
控制台输出
DEBUG 11-15 23:39:50,392 ==> Preparing: select t_id,t_name from teacher where t_id= ? (BaseJdbcLogger.java:139)
DEBUG 11-15 23:39:50,435 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:139)
DEBUG 11-15 23:39:50,458 <== Total: 1 (BaseJdbcLogger.java:139)
sql语句在数据库里可以执行

Answer 1

根据DEBUG 11-15 23:39:50,458 <== Total: 1 (BaseJdbcLogger.java:139)
可以看到有查询到结果的，只是赋值时候没对应

resultType="Teacher" 这里的Teacher路径前缀加上，就像com.mxl.bean.TeacherMapper

除非你在前面有定义了别名

Answer 2

哪个语句报空null异常的。。。。。。。

追问

Teacher t = session.selectOne(statem,1);
返回对象为空，打印的sql语句在数据库里面能查出来

追答

那就是说明session未创建好

去这里面 MybatisUtil.getSesssion(); 找原因

追问

问题是我测试其它类都没问题