第一个Mybatis程序
思路:搭建环境 --> 导入MyBatis --> 编写代码 --> 测试
1、搭建环境
新建项目
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创建一个普通的maven项目
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删除src目录 (就可以把此工程当做父工程了,然后创建子工程)
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导入maven依赖
<!--导入依赖--> <dependencies> <!--mysqlq驱动--> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.12</version> </dependency> <!--mybatis--> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.5.4</version> </dependency> <!--junit--> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> </dependency> </dependencies>
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创建一个Module模块
2、创建一个模块
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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/db_mybatis?userSSL=false&useUnicode=true&characterEncoding=UTF-8"/> <property name="username" value="root"/> <property name="password" value="123456"/> </dataSource> </environment> </environments> </configuration>
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编写mybatis工具类
java">//sqlSessionFactory --> sqlSession public class MybatisUtils { static SqlSessionFactory sqlSessionFactory = null; static { try { //使用Mybatis第一步 :获取sqlSessionFactory对象 String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); } catch (IOException e) { e.printStackTrace(); } } //既然有了 SqlSessionFactory,顾名思义,我们可以从中获得 SqlSession 的实例. // SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。 public static SqlSession getSqlSession(){ return sqlSessionFactory.openSession(); } }
3、代码编写
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pojo实体类,实现构造方法,set/get方法,toString方法
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Dao/Mapper接口
java">public interface UserDao { public List<User> getUserList(); }
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接口实现(Mapper.xml配置文件),由原来的UserDaoImpl转变为一个Mapper配置文件,相当于原来的的UserDaoImpl
<?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=绑定一个指定的Dao/Mapper接口--> <mapper namespace="com.kuang.dao.UserDao"> <select id="getUserList" resultType="com.hhb.pojo.User"> select * from users </select> </mapper>
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开始测试
注意点,常见错误:
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,在resource中的mybatis-config.xml文件中配置注册UserMapper.xml
<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/db_mybatis?userSSL=false&useUnicode=true&characterEncoding=UTF-8"/> <property name="username" value="root"/> <property name="password" value="123456"/> </dataSource> </environment> </environments> <!-- 每一个Mapper.xml 都需要在Mybatis核心配置文件中注册 --> <mappers> <mapper resource="com/hhb/dao/UserMapper.xml"/> </mappers> </configuration>
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junit测试代码
java">@Test public void test(){ //1.获取SqlSession对象 SqlSession sqlSession = MybatisUtils.getSqlSession(); //2.执行SQL // 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(); }
可能会遇到的问题:
- 配置文件没有注册
- 绑定接口错误
- 方法名不对
- 返回类型不对
- Maven导出资源问题