MyBatis是轻量级的数据库访问API,封装了JDBC操作,可以实现对实体对象的CRUD操作。
MyBatis体系结构主要组成部分:
配置文件:SqlMapConfig.xml 主配置文件
声明了数据库连接参数,引用了映射文件
映射文件: 每个实体一个映射文件
映射文件与 Mapper接口对应。
映射文件中:
每个Mapper接口中的方法,对应映射文件中的SQL语句。
使用步骤:
使用MyBatis
1 导入包
2 创建配置文件
3 创建实体和Mapper接口,已经映射文件
4 使用 工厂创建SqlSession
5 创建Mapper接口对象,执行接口方法
下面来详细介绍。
1),加载配置
两钟形式,一种是XML配置文件,另一种是JAVA代码的注解。
MyBatis将SQL的配置信息加载成为一个个的MappedStatement对象(包括了传入参数映射配置,执行的SQL语句,结果映射配置),并将其存储在内存中。
A)SqlMapConfig.xml
只有一个,用于配置数据库连接参数和框架参数。
Java代码
<?xml version="1.0" encoding="UTF-8" ?>
<!--这段代码不能掉,否则出现异常-->
<!DOCTYPE configuration PUBLIC "-//ibatis.apache.org//DTD Config 3.0//EN"
"http://ibatis.apache.org/dtd/ibatis-3-config.dtd">
<configuration>
<!--配置数据库连接 -->
<environments default="environment">
<environment id="environment">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver"
value="oracle.jdbc.OracleDriver" />
<property name="url"
value="jdbc:oracle:thin:@localhost:1521:XE" />
<property name="username" value="root" />
<property name="password" value="root" />
</dataSource>
</environment>
</environments>
<!-- 引入 Dept.xml 配置 -->
<mappers>
<mapper resource="com/lydia/entity/Dept.xml"/>
</mappers>
</configuration>
B) 实体类对应的映射文件
Dept.xml ,该配置文件是映射Dept.java实体类的
Java代码
<!-- Dept.xml 在com.lydia.entity 包中 -->
<!DOCTYPE mapper PUBLIC "-//ibatis.apache.org//DTD Mapper 3.0//EN"
"http://ibatis.apache.org/dtd/ibatis-3-mapper.dtd">
<!-- namespace 的值是 DeptMapper 接口
每个Mapper 接口对应一个配置文件 -->
<mapper
namespace="com.lydia.entity.DeptMapper"> <!--此处的DeptMapper是我们封装的接口-->
<insert id="addDept"
parameterType="com.lydia.entity.Dept">
<selectKey keyProperty="deptno"
order="BEFORE"
resultType="int">
select SEQ_T_DEPT.nextval
from DUAL
</selectKey>
insert into T_DEPT (deptno, dname,
loc) values
(#{deptno}, #{dname}, #{loc})
</insert>
<delete id="deleteDept"
parameterType="com.lydia.entity.Dept">
delete from T_DEPT
where deptno = #{deptno}
</delete>
<select id="findDeptById"
parameterType="java.lang.Integer"
resultType="com.lydia.entity.Dept">
select deptno,dname,loc
from T_DEPT where deptno=#{deptno}
</select>
<update id="updateDept"
parameterType="com.lydia.entity.Dept">
<!-- #{deptno} 读取参数的Bean属性 -->
update T_DEPT set dname=#{dname},
loc = #{loc} where deptno=#{deptno}
</update>
<!-- 注意resultType 的值是List中元素类型
结果集行映射的数据类型-->
<select id="findAllDept"
resultType="com.lydia.entity.Dept">
select deptno, dname, loc
from T_DEPT
</select>
<select id="findDeptByLoc"
parameterType="java.lang.String"
resultType="com.lydia.entity.Dept">
select deptno, dname, loc
from T_DEPT where loc=#{loc}
</select>
<select id="findAllDname"
parameterType="java.lang.String"
resultType="java.util.Map">
select dname from T_DEPT
where loc=#{loc}
</select>
</mapper>
注意:这里特别要注意主键ID的处理。
本案例中使用Oracle,那么要先创建序列 CREATE SEQUENCE SEQ_T_DEPT; 然后使用<select-key>..
如果是MySQL 或者 DB2,主键ID是自动增长的,可以如下设置:
Java代码
<!-- 自增类型(MySql SqlServer DB2 Derby)-->
<insert id="addDept" useGeneratedKeys="true"
keyProperty="deptno"
parameterType="com.tarean.entity.Dept">
insert into T_DEPT(dname, loc)
values (#{dname},#{loc})
</insert>
2),SQL解析
当API接口层接收到调用请求时,会接收到传入SQL的ID和传入对象(可以是Map,JavaBean,基本数据类型))。MyBatis会根据SQL 的ID找到对应的MappedStatement,然后根据传入参数对象对MappedStatement进行解析。解析后可以得到最终要执行的SQL和 参数。
3),结果映射
将操作数据库的结果按照映射的配置进行转换。可以转换成HashMap,JavaBean或者基本数据类型,并最终将结果返回。
创建DeptMapper.java接口,该接口中封装了Dept.xml中指定的SQL方法。
Java代码
/**
* Mapper接口,类似于Dao,但是语法有限定
* 不能有重载
* Mapper 定义实体Dept对象的CRUD操作
*该类中的方法名必须和Dept.xml中SQL的id一致
*/
Java代码
public interface DeptMapper {
void addDept(Dept dept);
void deleteDept(Dept dept);
void updateDept(Dept dept);
Dept findDeptById(Integer deptno);
List<Dept> findAllDept();
List<Dept> findDeptByLoc(String loc);
List<Map<String, Object>> findAllDname(
String loc);
}
MyBatis框架中设计到的几个API
SqlSessionFactoryBuilder
--该对象负责根据MyBatis配置文件SqlMapConfig.xml构建SqlSessionFactory实例
SqlSessionFactory
--每一个MyBatis的应用程序都以一个SqlSessionFactory对象为核心。该对象负责创建SqlSession对象实例。
SqlSession
--该对象包含了所有执行SQL操作的方法,用于执行已映射的SQL语句
TestCass.java类负责调用MyBatis中的基本API来操作数据库。
Java代码
package com.lydia.test;
import java.io.Reader;
import java.sql.Connection;
import java.util.List;
import java.util.Map;
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 org.junit.Test;
import com.lydia.entity.Dept;
import com.lydia.entity.DeptMapper;
public class TestCase {
// @Test
public void testSqlSession() throws Exception {
String cfg = "SqlMapConfig.xml";
Reader reader = Resources.getResourceAsReader(cfg);
//创建builder对象
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(reader);
//创建session
SqlSession session = factory.openSession();
Connection conn = session.getConnection();
System.out.println(conn);
System.out.println(conn.getMetaData().getDatabaseProductName());
conn.close();
session.close();
}
@Test
public void testAddDept() throws Exception {
String cfg = "SqlMapConfig.xml";
Reader reader = Resources.getResourceAsReader(cfg);
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(reader);
SqlSession session = factory.openSession();
// +++++++++++++++++++++++++++++++++++++++
// 通过Mapper映射器去执行SQL
// DeptMapper mapper =
// session.getMapper(DeptMapper.class);
// Dept dept = new Dept("C++","武汉");
// mapper.addDept(dept);
// System.out.println(dept);
// +++++++++++++++++++++++++++++++++++++++
// 通过session去执行SQL
Dept dept = new Dept("C++", "武汉");
session.insert("addDept", dept);
// +++++++++++++++++++++++++++++++++++++++
session.commit();
session.close();
}
// @Test
public void testDelete() throws Exception {
String cfg = "SqlMapConfig.xml";
Reader reader = Resources.getResourceAsReader(cfg);
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(reader);
SqlSession session = factory.openSession();
DeptMapper mapper = session.getMapper(DeptMapper.class);
Dept dept = mapper.findDeptById(2);
mapper.deleteDept(dept);
System.out.println(dept);
Dept d = mapper.findDeptById(2);
System.out.println(d);
session.commit();
session.close();
}
@Test
public void testFindAll() throws Exception {
String cfg = "SqlMapConfig.xml";
Reader reader = Resources.getResourceAsReader(cfg);
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(reader);
SqlSession session = factory.openSession();
DeptMapper mapper = session.getMapper(DeptMapper.class);
List<Dept> list = mapper.findAllDept();
for (Dept dept : list) {
System.out.println(dept);
}
session.close();
}
// @Test
public void testUpdate() throws Exception {
String cfg = "SqlMapConfig.xml";
Reader reader = Resources.getResourceAsReader(cfg);
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(reader);
SqlSession session = factory.openSession();
DeptMapper mapper = session.getMapper(DeptMapper.class);
Dept d = mapper.findDeptById(4);
d.setDname("PHP");
d.setLoc("苏州桥");
mapper.updateDept(d);
List<Dept> list = mapper.findAllDept();
for (Dept dept : list) {
System.out.println(dept);
}
session.commit();
session.close();
}
// @Test
public void testMap() throws Exception {
String cfg = "SqlMapConfig.xml";
Reader reader = Resources.getResourceAsReader(cfg);
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(reader);
SqlSession session = factory.openSession();
DeptMapper mapper = session.getMapper(DeptMapper.class);
List<Map<String, Object>> list = mapper.findAllDname("苏州桥");
System.out.println(list);
session.close();
}
@Test
public void testPage() throws Exception {
String cfg = "SqlMapConfig.xml";
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
Reader reader = Resources.getResourceAsReader(cfg);
SqlSessionFactory factory = builder.build(reader);
SqlSession session = factory.openSession();
//+++++++++++++++++++++++++++++++++++++
RowBounds bounds = new RowBounds(0, 2);
//此处用的selectList(arg1,arg2,arg3); 中间arg2参数不要掉
List<Dept> list = session.selectList("findAllDept",null, bounds);
for (Dept dept : list) {
System.out.println(dept);
}
session.commit();
session.close();
//+++++++++++++++++++++++++++++++++++++
}
}
注意:上面调用CRUD的操作方法也可以使用以下的代替
Java代码
String cfg = "SqlMapConfig.xml";
Reader reader =
Resources.getResourceAsReader(cfg);
SqlSessionFactoryBuilder builder=
new SqlSessionFactoryBuilder();
SqlSessionFactory factory =
builder.build(reader);
SqlSession session =
factory.openSession();
Dept dept = new Dept("C++","武汉");
session.insert("addDept", dept);
session.commit();
session.close();
ResultMap映射定义:
在Dept.xml中定义<select>操作时,如果查询结果字段名和javaBean属性不一致,需要使用<resultMap>元素显示指定映射关系。例如Dept.java中的属性是 no,name,loc,那么应该如下配置:
Java代码
<select id ="findAll2" resultMap="deptMap">
select DEPTNO,DNAME,LOC from DEPT
</select>
<resultMap id = "deptMap" type="com.lydia.Dept">
<result property="no" column="deptno"/>
<result property="name" column="dname"/>
<result property="loc" column="loc"/>
</resultMap>
代码目录结构如下: