Mybatis-01(创建一个Mybatis程序)
------------恢复内容开始------------
创建一个Mybatis项目:
①导入依赖包:
<dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.47</version> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.5.2</version> </dependency> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> </dependency> </dependencies>
②编写配置文件mybatis-config.xml
<?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="admin"/> </dataSource> </environment> </environments> </configuration>
③编写实体类。set,get,tostring,有参无参构造函数
package pojo; public class User { private int id; private String name; private String pwd; }
④编写dao接口
public interface UserDao { List<User> getUserList(); }
⑤编写UserMapper.xml当中放在dao目录下。
<?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"> <mapper namespace="dao.UserDao"> <select id="getUserList" resultType="pojo.User"> select * from mybatis.user </select> </mapper>
namespace绑定一个对应的dao接口,select中的id绑定接口中的方法名 resultType对应返回类型。
⑥测试,测试前需要明白,maven是约定大于配置的,他只识别resources下的xml文件,而本文是写在了main/java/dao目录下,是识别不了的,所以需要在pom.xml(父工程以及子工程)中添加以下代码:
<build> <resources> <resource> <directory>src/main/resources</directory> <includes> <include>**/*.properties</include> <include>**/*.xml</include> </includes> <filtering>true</filtering> </resource> <resource> <directory>src/main/java</directory> <includes> <include>**/*.properties</include> <include>**/*.xml</include> </includes> <filtering>true</filtering> </resource> </resources> </build>
⑦然后你发现你编写的UserMapper.xml,只是编写了,并没有与这个项目联系起来,这时候需要在mybatis-config.xml中添加映射代码:(这个里面目录之间用"/" 而不是".")
<mappers> <mapper resource="dao/UserMapper.xml"/> </mappers>
还有其他两个办法,一个是把使用class文件绑定注册,另一个是用使用扫描包进行注入绑定,这两个问题比较多,不建议用,如果硬要用注意两个注意点:
- 接口和他的Mapper配置文件必须同名!本文中的接口用的是UserDao,配置文件时UserMapper.xml就不行,必须是一样的名字。比如都用UserMapper。
- 接口和他的Mapper配置文件必须在同一个包下!
⑧编写测试类:
@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(); }
注意,增删改的话,要提交事务。
即close()前面加一段代码:
sqlSession.commit();
------------恢复内容结束------------