简单的Mybatis程序示例
1. 引入Mybatis组件
参考官网：https://mybatis.org/mybatis-3/zh/getting-started.html 下载mybatis组件：
在工程pom中引入：
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.2</version>
</dependency>
引入jdbc和junit依赖
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.32</version>
</dependency>
在项目工程resources路径下创建Mybatis基础配置文件mybatis-config.xml
内容如下：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306?useSSL=true&useUnicode=true&characterEncoding=UTF-8"/>
<property name="username" value="root"/>
<property name="password" value="123456"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper class="com.wcj.dao.UserMapper" />
</mappers>
</configuration>
(可选)项目工程resources路径下创建db.properties文件,用于配置数据库信息，也可直接写死到mybatis的配置文件中
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306?useSSL=true&useUnicode=true&characterEncoding=UTF-8
username=root
password=123456
2. Mybatis工具类
package com.wcj.utils;
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.InputStream;
public class MybatisUtil {
private static SqlSessionFactory sqlSessionFactory;
static {
try {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
} catch (Exception e) {
e.printStackTrace();
}
}
public SqlSession getConnect() {
return sqlSessionFactory.openSession();
}
}
3. Mapper文件(sql接口文件)
public interface UserMapper {
List<User> getUser();
User getUserById(int id);
int insertUser(User user);
int updateUser(User user);
int delUser(int id);
}
4. Mapper.xml文件(sql文件)
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.wcj.dao.UserMapper">
<select id="getUser" resultType="com.wcj.pojo.User">
select * from mybatis.user
</select>
<select id="getUserById" parameterType="int" resultType="com.wcj.pojo.User" >
select * from mybatis.user where id = #{id}
</select>
<insert id="insertUser" parameterType="com.wcj.pojo.User" >
insert into mybatis.user (`id`,`name`,`age`) values (#{id},#{name},#{age})
</insert>
<update id="updateUser" parameterType="com.wcj.pojo.User" >
update mybatis.user set `name` = #{name} where id = #{id}
</update>
<delete id="delUser" parameterType="int" >
delete from mybatis.user where id = #{id}
</delete>
</mapper>
5. Junit测试
public class Mytest {
@Test
public void test_getUser() {
SqlSession connect = MybatisUtil.getConnect();
UserMapper mapper = connect.getMapper(UserMapper.class);
List<User> users = mapper.getUser();
for (User user : users) {
System.out.println(user);
}
connect.close();
}
@Test
public void test_getUserById() {
SqlSession connect = MybatisUtil.getConnect();
UserMapper mapper = connect.getMapper(UserMapper.class);
User user = mapper.getUserById(1);
System.out.println(user);
connect.close();
}
@Test
public void test_insertUser() {
SqlSession connect = MybatisUtil.getConnect();
UserMapper mapper = connect.getMapper(UserMapper.class);
User user = new User(6, "大王", 35);
mapper.insertUser(user);
// 需要显示提交
connect.commit();
connect.close();
}
@Test
public void test_updateUser() {
SqlSession connect = MybatisUtil.getConnect();
UserMapper mapper = connect.getMapper(UserMapper.class);
User user = new User(5, "www", 18);
mapper.updateUser(user);
// 需要显示提交
connect.commit();
connect.close();
}
@Test
public void test_delUser() {
SqlSession connect = MybatisUtil.getConnect();
UserMapper mapper = connect.getMapper(UserMapper.class);
mapper.delUser(5);
// 需要显示提交
connect.commit();
connect.close();
}
}
截图：
常见错误和补充
1. xxxMapper.xml文件没有在mybatis配置文件mybatis-config.xml中注册：
解决办法：
在mybatis配置文件中注册对应的mapper.xml文件：
注意：
当使用class标签绑定mapper文件时，需要满足以下条件：
1.接口和对应的mapper文件必须同名
2.接口和对应的mapper文件必须在同一个包下
参考：https://mybatis.net.cn/configuration.html#mappers
2. mapper.xml绑定异常或者找不到mapper.xml文件
排查和解决办法：
1.排查mapper.xml的命名空间namespace是否和mapper接口文件的类名一致
2.排查mapper.xml的id和mapper接口文件中的方法名是否保持一致
3.查看mybatis配置文件中是否正确注册mapper.xml文件
4.排查maven打包导出mapper.xml是否正常
需要在pom文件中显示打包xml或者properties文件：
<build>
<resources>
<resource>
<directory>src/main/resources</directory>
<includes>
<include>**/*.xml</include>
<include>**/*.properties</include>
</includes>
<filtering>true</filtering>
</resource>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.xml</include>
<include>**/*.properties</include>
</includes>
<filtering>true</filtering>
</resource>
</resources>
</build>
增加以上代码后能正常出包：
3. 当对象属性或者表字段太多时，可以适当使用map来传递参数
示例如下：
int insertUser2(Map userMap);
<insert id="insertUser2" parameterType="map" >
insert into mybatis.user (`name`,`age`) values (#{mapName},#{mapAge})
</insert>
@Test
public void test_insertUser2() {
SqlSession connect = MybatisUtil.getConnect();
UserMapper mapper = connect.getMapper(UserMapper.class);
Map<String, String> map = new HashMap<>();
map.put("mapName", "map名字");
map.put("mapAge", "555");
mapper.insertUser2(map);
// 需要显示提交
connect.commit();
connect.close();
}
4. 模糊查询
List<User> getUser2(String key);
<select id="getUser2" resultType="com.wcj.pojo.User" parameterType="String">
select * from mybatis.user where name like #{key}
</select>
@Test
public void test_getUser2() {
SqlSession connect = MybatisUtil.getConnect();
UserMapper mapper = connect.getMapper(UserMapper.class);
List<User> users = mapper.getUser2("%王%");
for (User user : users) {
System.out.println(user);
}
connect.close();
}
