1.新建Java项目,引入jar包,mybatis的jar包和mysql的jar包,添加到buildPath库里
mybatis-3.3.0.jar mysql-connector-java-5.1.23-bin.jar
2.建立数据库users,建立表user(id,userName,userPwd)
3.编写实体类User.java
package javastudy;
public class User {
private int id;
private String userName;
private String userPwd;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public String getUserPwd() {
return userPwd;
}
public void setUserPwd(String userPwd) {
this.userPwd = userPwd;
}
@Override
public String toString() {
return "User [id=" + id + ", userName=" + userName + ", userPwd=" + userPwd + "]";
}
}
4.在实体类所在包下,编写userMapper.xml文件,用xml实现映射器
<?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="javastudy.UserMapper">
<select id="selectUser" resultType="javastudy.User">
select * from User where id = #{id}
</select>
</mapper>
这里我们只是使用了select语句。根据id查询相应的字段。
5.在mybatis中xml分为两类。一类是基础配置文件mybatis-cfg.xml,通常只有一个,主要是配置一些最基础的上下文参数和运行环境;另一类是映射文件,它可以配置映射关系,SQL,参数等信息。在src目录下建立mybatis-cfg.xml配置文件如下。
<?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>
<properties resource="db.properties"></properties>
<!-- 对事务的管理和连接池的配置 -->
<environments default="development">
<environment id="users">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="${db.driver}" />
<property name="url" value="${db.url}" />
<property name="username" value="${db.username}"/>
<property name="password" value="${db.password}" />
</dataSource>
</environment>
</environments>
<!-- mapping 文件路径配置 -->
<mappers>
<mapper resource="javastudy/userMapper.xml"/>
</mappers>
</configuration>
注意mapper路径这里容易出错:正确为 <mapper resource="javastudy/userMapper.xml"/>
如果通过右键复制文件名很容易导致错误::<mapper resource=" /MyBatisTest/src/javastudy/userMapper.xml"/>
因为刚开始学,花了大半天的时间网上找才解决这个问题。
这里值得注意的是environment的id="users",后面在MyBatisUtis中SqlSessionFactoryBuilder().build(InputStream,String environment)中会用到。
6.在src目录下建立数据库的properties文件,我们可以配置多个键值放在一个properties中,将数据库连接信息写入单独的properties文件方便日后维护和修改。
db.properties代码如下:
db.driver=com.mysql.jdbc.Driver
db.url=jdbc:mysql://localhost:3306/users
db.username=root
db.password=12345678
7.编写MyBatis的工具类,通过SqlSessionFactoryBuilder来构建SqlSessionFactory。代码如下
package utility;
import java.io.IOException;
import java.io.InputStream;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
public class MyBatisUtils {
public static SqlSession openSession() throws IOException
{
String resource = "mybatis-config.xml";
InputStream in = Resources.getResourceAsStream(resource);
SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(in,"users");
return sessionFactory.openSession();
}
}
8.到这里基本构建好了,接下来我们通过JUnit来测试我们写的代码(注意在方法前添加@Test)。新建一个MyTest.java类
package test;
import java.io.IOException;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import javastudy.User;
import utility.MyBatisUtils;
public class MyTest {
@Test
public void testSelect() throws IOException {
SqlSession session=MyBatisUtils.openSession();
//确定sql语句,参考userMapper.xml定义
String statement="javastudy.UserMapper.selectUser";
User user=session.selectOne(statement,1);//返回一条记录,返回一条对象
System.out.println(user);
session.close();
}
}
程序打印结果为: User [id=1, userName=张三, userPwd=12345678]