MyBatis进阶--接口代理方式实现Dao 和动态SQL
2021/5/24 2:25:39
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MyBatis接口代理方式实现Dao层
接口代理方式-实现规则
传统方式实现Dao层，我们既要写接口。还要写实现类。而MyBatis框架可以帮助我们省略写Dao层接口实现类的步骤。程序员只需要编写接口，由MyBatis框架根据接口的定义来创
1该接口的动态代理对象。
实现规则：
1.映射配置文件中的名称空间必须和Dao层接口的全类名相同
2.映射配置文件中的增删改查标签的id属性必须和Dao层接口的方法名相同
3.映射配置文件中的增删改查标签的paramrterType属性必须和Dao层接口方法的参数相同
4.映射配置文件中的增删改查标签的resultType属性必须和Dao层接口方法的返回值相同
接口代理方式-代码实现
1.删除mapper层接口的实现类
2.修改映射配置文件
3.修改service层接口的实现类，采用接口代理方式实现功能
删除mapper层接口的实现类
修改映射配置文件
package com.itheima.service.impl;
import com.itheima.bean.Student;
import com.itheima.mapper.StudentMapper;
import com.itheima.service.StudentService;
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.InputStream;
import java.util.List;
/*
业务层实现类
*/
public class StudentServiceImpl implements StudentService {
@Override
public List<Student> selectAll() {
List<Student> list = null;
SqlSession sqlSession = null;
InputStream is = null;
try{
//1.加载核心配置文件
is = Resources.getResourceAsStream("MyBatisConfig.xml");
//2.获取SqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
//3.通过工厂对象获取SqlSession对象
sqlSession = sqlSessionFactory.openSession(true);
//4.获取StudentMapper接口的实现类对象
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); // StudentMapper mapper = new StudentMapperImpl();
//5.通过实现类对象调用方法，接收结果
list = mapper.selectAll();
} catch (Exception e) {
} finally {
//6.释放资源
if(sqlSession != null) {
sqlSession.close();
}
if(is != null) {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//7.返回结果
return list;
}
@Override
public Student selectById(Integer id) {
Student stu = null;
SqlSession sqlSession = null;
InputStream is = null;
try{
//1.加载核心配置文件
is = Resources.getResourceAsStream("MyBatisConfig.xml");
//2.获取SqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
//3.通过工厂对象获取SqlSession对象
sqlSession = sqlSessionFactory.openSession(true);
//4.获取StudentMapper接口的实现类对象
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); // StudentMapper mapper = new StudentMapperImpl();
//5.通过实现类对象调用方法，接收结果
stu = mapper.selectById(id);
} catch (Exception e) {
} finally {
//6.释放资源
if(sqlSession != null) {
sqlSession.close();
}
if(is != null) {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//7.返回结果
return stu;
}
@Override
public Integer insert(Student stu) {
Integer result = null;
SqlSession sqlSession = null;
InputStream is = null;
try{
//1.加载核心配置文件
is = Resources.getResourceAsStream("MyBatisConfig.xml");
//2.获取SqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
//3.通过工厂对象获取SqlSession对象
sqlSession = sqlSessionFactory.openSession(true);
//4.获取StudentMapper接口的实现类对象
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); // StudentMapper mapper = new StudentMapperImpl();
//5.通过实现类对象调用方法，接收结果
result = mapper.insert(stu);
} catch (Exception e) {
} finally {
//6.释放资源
if(sqlSession != null) {
sqlSession.close();
}
if(is != null) {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//7.返回结果
return result;
}
@Override
public Integer update(Student stu) {
Integer result = null;
SqlSession sqlSession = null;
InputStream is = null;
try{
//1.加载核心配置文件
is = Resources.getResourceAsStream("MyBatisConfig.xml");
//2.获取SqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
//3.通过工厂对象获取SqlSession对象
sqlSession = sqlSessionFactory.openSession(true);
//4.获取StudentMapper接口的实现类对象
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); // StudentMapper mapper = new StudentMapperImpl();
//5.通过实现类对象调用方法，接收结果
result = mapper.update(stu);
} catch (Exception e) {
} finally {
//6.释放资源
if(sqlSession != null) {
sqlSession.close();
}
if(is != null) {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//7.返回结果
return result;
}
@Override
public Integer delete(Integer id) {
Integer result = null;
SqlSession sqlSession = null;
InputStream is = null;
try{
//1.加载核心配置文件
is = Resources.getResourceAsStream("MyBatisConfig.xml");
//2.获取SqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
//3.通过工厂对象获取SqlSession对象
sqlSession = sqlSessionFactory.openSession(true);
//4.获取StudentMapper接口的实现类对象
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); // StudentMapper mapper = new StudentMapperImpl();
//5.通过实现类对象调用方法，接收结果
result = mapper.delete(id);
} catch (Exception e) {
} finally {
//6.释放资源
if(sqlSession != null) {
sqlSession.close();
}
if(is != null) {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//7.返回结果
return result;
}
}
修改service层接口的实现类，采用接口代理方式实现功能
接口代理方式-源码分析
分析动态代理对象如何生成的？
通过动态代理开发的模式，我们只需要编写一个接口，不写实现类，我们通过getMapper()方法最终获取到
org.apache.ibatis.binding.MapperProxy代理对象，然后执行功能，而这个代理对象正是MyBatis使用了JDK的动态代理技术，帮助我们生成了代理实现类对象。从而可以进行相关持久化操作。
分析方法是如何执行的？
动态代理的实现类对象再执行方法的时候最终调用了maperMethod.execute()方法，这个方法中通过switch语句根据操作类型来判断是新增，修改，删除，查询操作，最后一步回到了MMyBatis最原生的SqlSession方式来执行增删改查。
接口代理方式小结
接口代理方式可以让我们只编写接口即可，而实现类对象由MyBatis生成。
实现规则：
1.映射配置文件中的名称空间必须和Dao层接口的全类名相同
2.映射配置文件中的增删改查标签的id属性必须和Dao层接口的方法名相同
3.映射配置文件中的增删改查标签的paramrterType属性必须和Dao层接口方法的参数相同
4.映射配置文件中的增删改查标签的resultType属性必须和Dao层接口方法的返回值相同
获取动态代理对象
SqlSession功能类中的getMapper()方法
删除mapper中的实现类 ，保留接口
在StudentMapper.xml中修改 <mapper namespace="com.itheima.mapper.StudentMapper">
更改service包下 StudentServiceImpl文件
package com.itheima.service.impl;
import com.itheima.bean.Student;
import com.itheima.mapper.StudentMapper;
import com.itheima.service.StudentService;
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.InputStream;
import java.util.List;
/*
业务层实现类
*/
public class StudentServiceImpl implements StudentService {
@Override
public List<Student> selectAll() {
List<Student> list = null;
SqlSession sqlSession = null;
InputStream is = null;
try{
//1.加载核心配置文件
is = Resources.getResourceAsStream("MyBatisConfig.xml");
//2.获取SqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
//3.通过工厂对象获取SqlSession对象
sqlSession = sqlSessionFactory.openSession(true);
//4.获取StudentMapper接口的实现类对象
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); // StudentMapper mapper = new StudentMapperImpl();
//5.通过实现类对象调用方法，接收结果
list = mapper.selectAll();
} catch (Exception e) {
} finally {
//6.释放资源
if(sqlSession != null) {
sqlSession.close();
}
if(is != null) {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//7.返回结果
return list;
}
@Override
public Student selectById(Integer id) {
Student stu = null;
SqlSession sqlSession = null;
InputStream is = null;
try{
//1.加载核心配置文件
is = Resources.getResourceAsStream("MyBatisConfig.xml");
//2.获取SqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
//3.通过工厂对象获取SqlSession对象
sqlSession = sqlSessionFactory.openSession(true);
//4.获取StudentMapper接口的实现类对象
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); // StudentMapper mapper = new StudentMapperImpl();
//5.通过实现类对象调用方法，接收结果
stu = mapper.selectById(id);
} catch (Exception e) {
} finally {
//6.释放资源
if(sqlSession != null) {
sqlSession.close();
}
if(is != null) {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//7.返回结果
return stu;
}
@Override
public Integer insert(Student stu) {
Integer result = null;
SqlSession sqlSession = null;
InputStream is = null;
try{
//1.加载核心配置文件
is = Resources.getResourceAsStream("MyBatisConfig.xml");
//2.获取SqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
//3.通过工厂对象获取SqlSession对象
sqlSession = sqlSessionFactory.openSession(true);
//4.获取StudentMapper接口的实现类对象
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); // StudentMapper mapper = new StudentMapperImpl();
//5.通过实现类对象调用方法，接收结果
result = mapper.insert(stu);
} catch (Exception e) {
} finally {
//6.释放资源
if(sqlSession != null) {
sqlSession.close();
}
if(is != null) {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//7.返回结果
return result;
}
@Override
public Integer update(Student stu) {
Integer result = null;
SqlSession sqlSession = null;
InputStream is = null;
try{
//1.加载核心配置文件
is = Resources.getResourceAsStream("MyBatisConfig.xml");
//2.获取SqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
//3.通过工厂对象获取SqlSession对象
sqlSession = sqlSessionFactory.openSession(true);
//4.获取StudentMapper接口的实现类对象
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); // StudentMapper mapper = new StudentMapperImpl();
//5.通过实现类对象调用方法，接收结果
result = mapper.update(stu);
} catch (Exception e) {
} finally {
//6.释放资源
if(sqlSession != null) {
sqlSession.close();
}
if(is != null) {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//7.返回结果
return result;
}
@Override
public Integer delete(Integer id) {
Integer result = null;
SqlSession sqlSession = null;
InputStream is = null;
try{
//1.加载核心配置文件
is = Resources.getResourceAsStream("MyBatisConfig.xml");
//2.获取SqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
//3.通过工厂对象获取SqlSession对象
sqlSession = sqlSessionFactory.openSession(true);
//4.获取StudentMapper接口的实现类对象
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); // StudentMapper mapper = new StudentMapperImpl();
//5.通过实现类对象调用方法，接收结果
result = mapper.delete(id);
} catch (Exception e) {
} finally {
//6.释放资源
if(sqlSession != null) {
sqlSession.close();
}
if(is != null) {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//7.返回结果
return result;
}
}
创建dynamic下测试类Test01
package com.itheima.dynamic;
import com.itheima.bean.Student;
import com.itheima.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 org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
public class Test01 {
@Test
public void selectCondition() throws Exception {
InputStream is = Resources.getResourceAsStream("MyBatisConfig.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
SqlSession sqlSession = sqlSessionFactory.openSession(true);
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
Student stu=new Student();
stu.setId(2);
stu.setName("李四");
//stu.setAge(23);
List<Student> list = mapper.selectCondition(stu);
for (Student student:list){
System.out.println(student);
}
sqlSession.close();
is.close();
}
@Test
public void selectByIds() throws Exception {
InputStream is = Resources.getResourceAsStream("MyBatisConfig.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
SqlSession sqlSession = sqlSessionFactory.openSession(true);
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
List<Integer> ids=new ArrayList<>();
ids.add(1);
ids.add(2);
List<Student> list = mapper.selectByIds(ids);
for (Student student:list){
System.out.println(student);
}
sqlSession.close();
is.close();
}
}
MyBatis映射配置文件-----动态sql
动态SQL介绍
MyBatis映射配置文件中，前面我们的SQL都是比较简单的，有些时候业务逻辑复杂时，我们的SQL就时动态变化的，此时在前面学习的SQL就不能满足要求了。
多条件查询
id：3 name：王五 age：25
select * from Student where id=#{id} and name=#{name} and age=#{age}
id：3 name：王五
select * from Student where id=#{id} and name=#{name}
动态sql标签
<where>:条件标签。如果有动态条件，则使用该标签代替where关键字。
<if>:条件判断标签
<if test="条件判断">
查询条件拼接
</if>
<foreach>:循环遍历标签。适用于多个参数或者的关系。
<foreach collection="" open="" close="" item="" separator="">
获取参数
</foreach>
属性：
collection：参数容器类型，（list-集合，array-数组）。
open：开始的sql语句
close：结束额sql语句
item：参数变量名
separator：分隔符
Sql片段抽取
我们可以将一些重复的SQL语句进行抽取，以达到复用的效果
<sql>: 抽取SQL语句标签
<sql id ="片段唯一标识" >抽取的SQL语句</sql>
<include>:引入SQL片段标签
<include refid="片段唯一标识" />
StudentMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!--MyBatis的DTD约束-->
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--
mapper:核心根标签
namespace属性：名称空间
-->
<mapper namespace="com.itheima.mapper.StudentMapper">
<sql id="select">Select * FROM Student</sql>
<!--
select:查询功能的标签
id属性:唯一标识
resultType属性：指定结果映射对象的类型
parameterType：指定参数映射对象类型
-->
<select id="selectAll" resultType="student">
<include refid="select"/>
</select>
<select id="selectById" resultType="student" parameterType="int">
<include refid="select"/> where id = #{id}
</select>
<insert id="insert" parameterType="student">
Insert into Student values(#{id},#{name},#{age})
</insert>
<update id="update" parameterType="student">
update Student set name =#{name},age=#{age} where id=#{id}
</update>
<delete id="delete" parameterType="int">
delete from Student where id=#{id}
</delete>
<select id="selectCondition" resultType="student" parameterType="student">
<include refid="select"/>
<where>
<if test="id!=null">
id=#{id}
</if>
<if test="name!=null">
and name=#{name}
</if>
<if test="age!=null">
and age=#{age}
</if>
</where>
</select>
<select id="selectByIds" resultType="student" parameterType="list">
<include refid="select"/>
<where>
<foreach collection="list" open="id in (" close=")" item="id" separator=",">
#{id}
</foreach>
</where>
</select>
</mapper>
动态SQL小结
动态SQL指的就是SQL语句可以根据条件或者参数的不同进行动态的变化
<where>:条件标签
<if>:里面有个test标签可以帮我们进行判断
<foreach>:循环遍历的标签 collection="list" open="id in (" close=")" item="id" separator=","
<sql>:抽取SQL片段的标签
<include>:引入SQL片段的标签
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