-简单类型
-对象
-对象集合
-HashMap
<注意resultType与resultMap不能同时使用>
resultType要求用于数据库中字段名与javaBean中属性名一致的情况下使用
字段与属性名不一致情况下使用resultMap，本篇使用的全部为resultType
1.输出类型为简单类型
studentMapper.xml
<!-- 输出类型：简单类型-->
<select id="selectSimple" resultType="int">
select count (1) from student
</select>
StudentMapper.java
package com.bb.mapper;
import com.bb.entity.Student;
import org.apache.ibatis.annotations.Select;
import java.util.HashMap;
public interface StudentMapper {
/*
* 1。方法名和StudentMapper.xml文件中标签的id值一致
* 2。方法输入参数与StudentMapper.xml文件中标签的parameterType一致
* 3。返回值与StudentMapper.xml文件中标签的resultType一致
*
*/
int selectSimple();
}
TestMybatis.java
package com.bb.service;
import com.bb.entity.Address;
import com.bb.entity.Student;
import com.bb.mapper.StudentMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.Reader;
import java.util.HashMap;
public class TestMybatis {
//输出类型：简单类型
public static void queryCount() throws IOException {
Reader resourceAsReader = Resources.getResourceAsReader("conf.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsReader);
SqlSession sqlSession = sqlSessionFactory.openSession();
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
int count = mapper.selectSimple();
System.out.println(count);
}
public static void main(String[] args) throws IOException {
// queryStudentById();
// queryStudentByParams(1,"bb");
// queryStudentByParams2(1,"bb");
// queryWithResultMap();
// queryStudentWithClasses();
queryCount();
}
}
结果输出：
2
2.输出参数为对象
之前均有用到，此处不表
3.输出参数为对象集合,resultType为对象类名
studentMapper.xml
<!-- 输出类型:对象集合-->
<select id="selectObjects" resultType="Student">
select * from student
</select>
StudentMapper.java，返回值类型为List<Student>
public interface StudentMapper {
List<Student> selectObjects();
}
Student.java 重写toString()方法
@Override
public String toString() {
return "Student{" +
"id=" + id +
", name='" + name + '\'' +
", age=" + age +
", address=" + address +
'}';
}
TestMybatis.java
public class TestMybatis {
//输出类型：对象集合
public static void queryStudents() throws IOException {
Reader resourceAsReader = Resources.getResourceAsReader("conf.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsReader);
SqlSession sqlSession = sqlSessionFactory.openSession();
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
List<Student> students = mapper.selectObjects();
System.out.println(students);
}
public static void main(String[] args) throws IOException {
queryStudents();
}
}
输出结果：
[Student{id=1, name='bb', age=11, address=null}, Student{id=2, name='ss', age=22, address=null}]
4.输出为HashMap,与对象无关？？？
studentMapper.xml
<!-- 输出类型：HashMap-->
<select id="selectHashMap" resultType="HashMap">
select id as id_hashmapKEY,name as name_hashmapKEY,age as age_hashmapKEY from student
</select>
StudentMapper.java
public interface StudentMapper {
List<HashMap<String,Object>> selectHashMap();
}
TestMybatis.java
//输出类型：HashMap
public static void queryStudentsByHashMap() throws IOException {
Reader resourceAsReader = Resources.getResourceAsReader("conf.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsReader);
SqlSession sqlSession = sqlSessionFactory.openSession();
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
List<HashMap<String, Object>> hashMaps = mapper.selectHashMap();
System.out.println(hashMaps);
}
输出结果：
[{age_hashmapKEY=11, name_hashmapKEY=bb, id_hashmapKEY=1}, {age_hashmapKEY=22, name_hashmapKEY=ss, id_hashmapKEY=2}]
- 输出类型：HashMap 使用@MapKey
studentMapper.xml
<!-- 输出类型：HashMap 使用@MapKey -->
<select id="selectHashMaps" resultType="HashMap">
select id,name,age from student
</select>
StudentMapper.java接口：
public interface StudentMapper {
//出类型：HashMap 使用@MapKey,输出格式为 @MapKey的值={...}
//本例为 id={Student}
@MapKey("id")
HashMap<Integer,Student> selectHashMaps();
}
TestMybatis.java
//输出类型：HashMap 使用@MapKey
public static void queryStudentsByHashMaps() throws IOException {
Reader resourceAsReader = Resources.getResourceAsReader("conf.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsReader);
SqlSession sqlSession = sqlSessionFactory.openSession();
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
HashMap<Integer, Student> hashMaps = mapper.selectHashMaps();
System.out.println("返回的全部值："+hashMaps);
System.out.println("根据MapKey的值获取单独一个map集合："+hashMaps.get(1));
//hashMaps.get(1)虽然是一个Student对象，但是sql的返回值是map集合，无法获得一个真是的 Student对象
//直接使用Student对象会报错：HashMap cannot be cast to com.bb.entity.Student
//Student student = hashMaps.get(1);
//System.out.println(student);
//所以要将单独的一个map集合转变为json对象，通过json对象的getString()方法获取map集合中具体字段的值
JSONObject json = (JSONObject)JSON.toJSON(hashMaps.get(1));
System.out.println("转为json对象后的值："+json);
String name = json.getString("name");
System.out.println("json对象中name的值（MapKey中id为1的值的map集合中name的值）："+name);
}
输出结果：
返回的全部值：{1={name=bb, id=1, age=11}, 2={name=ss, id=2, age=22}, 3={name=cc, id=3, age=33}, 5={name=dd, id=5, age=44}, 6={name=ee, id=6, age=55}}
根据MapKey的值获取单独一个map集合：{name=bb, id=1, age=11}
转为json对象后的值：{"name":"bb","age":11,"id":1}
json对象中name的值（MapKey中id为1的值的map集合中name的值）：bb
