标签：style blog http io ar color os sp java
自我总结，欢迎拍砖！
目的：在需要返回int，long等基础类型数据的情况下，尽量在mybatis的Mapper中用基础类型的包装类。
原因：当查询的字段为空值时，mybatis会返回null，用基础类型接收则会出现异常，但是用包装类就把这个问题规避了。
一.读数据环境准备：
创建student表（无主键）：
create table student(id int,name varchar(20),idCard bigint,classNo varchar(10));
insert into student set id=1,name=‘007‘;
insert into studetn set name =‘911911‘;
二.代码：
StudentMapper.xml
<?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.core.mapper.StudentMapper">
<select id="getStudent" resultType="com.core.entity.Student">
select id,name,idCard,classNo from student where id = #{id}
</select>
<select id="getIdCard" resultType="Long">
select idCard from student where id = #{id}
</select>
<select id="getId" resultType="Integer">
select id from student where name = #{name}
</select>
</mapper>
StudentMapper.java
package com.core.mapper; import org.apache.ibatis.annotations.Param; import com.core.entity.Student; public interface StudentMapper { public Student getStudent(@Param("id") int id); public Long getIdCard(@Param("id") int id); public Integer getId(@Param("name") String name); }
测试类StudentTest
package com.core.test; import org.apache.ibatis.session.SqlSession; import org.junit.Test; import com.core.common.SessionFactory; import com.core.entity.Student; import com.core.mapper.StudentMapper; public class StudentTest { public static void main(String[] args) { SqlSession session =SessionFactory.getSqlSession(); try { StudentMapper mapper = session.getMapper(StudentMapper.class); Student blog = mapper.getStudent(1); System.out.println(blog.getName()); } finally { session.close(); } } //通过ID获取IdCard @Test public void TestGetIdCard(){ SqlSession session =SessionFactory.getSqlSession(); try { StudentMapper mapper = session.getMapper(StudentMapper.class); Long idCard = mapper.getIdCard(1); } finally { session.close(); } } //通过name获取Id @Test public void TestGetIdByName(){ SqlSession session =SessionFactory.getSqlSession(); try { StudentMapper mapper = session.getMapper(StudentMapper.class); Integer id = mapper.getId("911911"); } finally { session.close(); } } }
3.分析：
1.若StudentMapper.java和StudentMapper.xml中getIdCard的返回值类型为long类型，此时传递的参数id为1，查询idCard的记录为null，long 类型无法接受null值，所以会报异常，若均如上方的代码中改成包装类Long，则可以接受null值。
2.若StudentMapper.java和StudentMapper.xml中getId的返回值类型为int类型，此时传递的参数name为‘911911‘，查询id的记录为null，int 类型无法接受null值，所以会报异常，若均如上方的代码中改成包装类Integer，则可以接受null值。
总结：在需要返回int，long等基础类型数据的情况下，尽量在mybatis的Mapper中用基础类型的包装类。
PS:在Mapper.java中尽量用@Param这种参数传递方式和Mapper.xml对相对应。这样就不用在Mapper.xml中配置属性parameterType了
问题描述：
标签：style blog http io ar color os sp java
原文地址：http://www.cnblogs.com/xxyfhjl/p/4157988.html
