mybatis_2第一个mybatis程序
2、第一个Mybatis程序
思路:搭建环境-->导入Mybatis-->编写代码-->测试!
2.1、搭建环境
搭建数据库
CREATE DATABASE `mybatis`;
USE `mybatis`;
CREATE TABLE `user`(
`id` INT(20) NOT NULL PRIMARY KEY,
`name` VARCHAR(30) DEFAULT NULL,
`pwd` VARCHAR(30) DEFAULT NULL
)ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO `user`(`id`,`name`,`pwd`) VALUES
(1,'loading','12345'),
(2,'直直','12345'),
(3,'卷卷','12345')
新建项目
-
新建一个普通的maven项目
-
删除src目录
-
导入maven依赖
<!--导入依赖-->
<dependencies>
<!--mysql驱动-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.47</version>
</dependency>
<!--mybatis-->
<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.2</version>
</dependency>
<!--junit-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
</dependencies>
2.2、创建一个模块
-
编写mybatis的核心配置文件
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <!--configuration核心配置文件--> <configuration> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=UTF-8"/> <property name="username" value="root"/> <property name="password" value="123456"/> </dataSource> </environment> </environments> </configuration>
-
编写mybatis工具类
//sqlSessionFactory --> sqlSession public class MybatisUtils { private static SqlSessionFactory sqlSessionFactory; static{ try { //使用Mybatis第一步:获取sqlSessionFactory对象 String resource = "mybatis-config.xml"; //读取mybatis-config.xml配置文件 InputStream inputStream = Resources.getResourceAsStream(resource); //获取资源并输出成流 //SqlSessionFactoryBuilder 则可以从 XML 配置文件或一个预先配置的 Configuration 实例来构建出 SqlSessionFactory 实例 //SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder(); //SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream); sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); } catch (IOException e) { e.printStackTrace(); } } //既然有了 SqlSessionFactory,顾名思义,我们就可以从中获得 SqlSession 的实例了。 // SqlSession 完全包含了面向数据库执行 SQL 命令所需的所有方法。 public static SqlSession getSqlSession(){ return sqlSessionFactory.openSession(); } }
2.3、编写代码
-
实体类
package com.kuang.pojo; //实体类 public class User { private int id; private String name; private String pwd; public User() { } public User(int id, String name, String pwd) { this.id = id; this.name = name; this.pwd = pwd; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getPwd() { return pwd; } public void setPwd(String pwd) { this.pwd = pwd; } @Override public String toString() { return "User{" + "id=" + id + ", name='" + name + '\'' + ", pwd='" + pwd + '\'' + '}'; } }
-
Dao接口
public interface UserDao { List<User> getUserList(); }
-
接口实现类由原来的UserDaoImpl转变为一个 Mapper配置文件.
<?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"> <!--namespace=绑定一个对应的Dao/Mapper接口--> <mapper namespace="com.kuang.dao.UserDao"> <!--select查询语句--> <select id="getUserList" resultType="com.loading.pojo.User"> select * from mybatis.user </select> </mapper>
2.4、测试
注意点:
org.apache.ibatis.binding.BindingException: Type interface com.kuang.dao.UserDao is not known to the MapperRegistry.
MapperRegistry是什么?
核心配置文件中注册 mappers
<!--每一个Mapper.XML都需要在Mybatis核心配置文件中注册!-->
<mappers>
<mapper resource="com/loading/dao/UserMapper.xml"/>
<!-- <mapper class="com.loading.dao.UserMapper"/>-->
</mappers>
-
junit测试
@Test public void test(){ //第一步:获得SqlSession对象 SqlSession sqlSession = MybatisUtils.getSqlSession(); //方式一:getMapper UserDao userDao = sqlSession.getMapper(UserDao.class); List<User> userList = userDao.getUserList(); for (User user : userList) { System.out.println(user); } //关闭SqlSession sqlSession.close(); }
你们可以能会遇到的问题:
- 配置文件没有注册
<!--每一个Mapper.XML都需要在Mybatis核心配置文件中注册!-->
<mappers>
<mapper resource="com/loading/dao/UserMapper.xml"/>
<!-- <mapper class="com.loading.dao.UserMapper"/>-->
</mappers>
- 绑定接口错误。
<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.loading.dao.UserDao">
<select id="getUserList" resultType="com.loading.pojo.User">
select * from mybatis.user;
</select>
</mapper>
- 方法名不对
public interface UserDao {
List<User> getUserList();
}
//接口和调接口方法的测试类对应
- 返回类型不对
//方式一:getMapper
//UserDao userDao = sqlSession.getMapper(UserDao.class);
//UserList<User> userList = userDao.getUserList();
List<User> userList = sqlSession.getMapper(UserDao.class).getUserList();
for (User user : userList) {
System.out.println(user);
}
- Maven导出资源问题
<!--配置资源过滤,防止我们的xml文件无法导出-->
<build>
<resources>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.xml</include>
<include>**/*.properties</include>
</includes>
</resource>
<resource>
<directory>src/main/resources</directory>
<includes>
<include>**/*.xml</include>
<include>**/*.properties</include>
</includes>
</resource>
</resources>
</build>
官方建议格式:
import com.loading.dao.UserDao;
import com.loading.pojo.User;
import com.loading.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class MyTest {
@Test
public void test(){
//第一步:获得SqlSession对象
SqlSession sqlSession = MybatisUtils.getSqlSession();
try {
//方式一:getMapper 建议使用
//UserDao userDao = sqlSession.getMapper(UserDao.class);
//UserList<User> userList = userDao.getUserList();
List<User> userList = sqlSession.getMapper(UserDao.class).getUserList();
//方式二:利用sqlsqlSession中的方法绑定对应的接口中的相应方法,不建议使用
//List<User> userList = sqlSession.selectList("com.loading.dao.UserDao.getUserList");
for (User user : userList) {
System.out.println(user);
}
}catch (Exception e){
e.printStackTrace();
}finally {
//关闭SqlSession
sqlSession.close();
}
}
}