MyBatis工程搭建&MyBatis实现Mapper配置查询

一、MyMyBatis工程搭建

新建Maven项目：mybatis-demo

准备数据源

 1 # 删除mybatis_demo数据库
 2 drop database if exists mybatis_demo;
 3
 4 # 创建mybatis_demo数据库
 5 create database mybatis_demo;
 6
 7 # 使用mybatis_demo数据库
 8 use mybatis_demo;
 9
10 # 创建account表
11 create table user (
12     id int auto_increment primary key,
13     username varchar(20),
14     age int,
15     score int
16 );
17
18 # 新增数据
19 insert into user (id, username, age, score) values
20 (1,'peter', 18, 100), (2,'pedro', 24, 200),
21 (3,'jerry', 28, 500), (4,'mike', 12, 300),
22 (5,'tom', 27, 1000);

连接数据库

1 <dependencies>
2     <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
3     <dependency>
4         <groupId>mysql</groupId>
5         <artifactId>mysql-connector-java</artifactId>
6         <version>8.0.23</version>
7     </dependency>
8 </dependencies>

代码结构图：

代码编写：

JDBCDemo.java

 1 import java.sql.Connection;
 2 import java.sql.DriverManager;
 3 import java.sql.PreparedStatement;
 4 import java.sql.ResultSet;
 5
 6 public class JDBCDemo {
 7     public static void main(String[] args) throws Exception {
 8         //1.注册驱动
 9         Class.forName("com.mysql.cj.jdbc.Driver");
10         //2.获取连接
11         Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mybatis_demo", "root", "root");
12         //3.获取Statement对象
13         PreparedStatement preparedStatement = connection.prepareStatement("select * from user WHERE id = ?");
14         preparedStatement.setInt(1, 1);
15         //4.执行SQL语句返回结果集
16         ResultSet resultSet = preparedStatement.executeQuery();
17         //5.遍历结果集
18         while (resultSet.next()) {
19             System.out.println("username: " + resultSet.getString("username"));
20             System.out.println("age: " + resultSet.getString("age"));
21         }
22         //6.释放资源
23         resultSet.close();
24         preparedStatement.close();
25         connection.close();
26     }
27 }

执行结果：

引入MyBatis依赖

 1 <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
 2 <dependency>
 3     <groupId>org.mybatis</groupId>
 4     <artifactId>mybatis</artifactId>
 5     <version>3.5.6</version>
 6 </dependency>
 7 <!-- https://mvnrepository.com/artifact/ch.qos.logback/logback-classic -->
 8 <dependency>
 9     <groupId>ch.qos.logback</groupId>
10     <artifactId>logback-classic</artifactId>
11     <version>1.3.0-alpha5</version>
12     <scope>test</scope>
13 </dependency>

删除JDBC连接：JDBCDemo.java

新建文件：StartNoXml.java

 1 import org.apache.ibatis.datasource.pooled.PooledDataSource;
 2 import org.apache.ibatis.mapping.Environment;
 3 import org.apache.ibatis.session.Configuration;
 4 import org.apache.ibatis.session.SqlSession;
 5 import org.apache.ibatis.session.SqlSessionFactory;
 6 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 7 import org.apache.ibatis.transaction.jdbc.JdbcTransactionFactory;
 8
 9 import java.sql.PreparedStatement;
10 import java.sql.ResultSet;
11 import java.sql.SQLException;
12
13 @SuppressWarnings({"SqlResolve", "SqlNoDataSourceInspection", "Duplicates"})
14 public class StartNoXml {
15     public static void main(String[] args) throws SQLException {
16         // 准备jdbc事务类
17         JdbcTransactionFactory jdbcTransactionFactory = new JdbcTransactionFactory();
18         // 配置数据源
19         PooledDataSource dataSource = new PooledDataSource(
20                 "com.mysql.cj.jdbc.Driver",
21                 "jdbc:mysql://localhost:3306/mybatis_demo?useSSL=false",
22                 "root",
23                 "root");
24         // 配置环境，向环境中指定环境id、事务和数据源
25         Environment environment = new Environment.Builder("development")
26                 .transactionFactory(jdbcTransactionFactory)
27                 .dataSource(dataSource).build();
28         // 新建 MyBatis 配置类
29         Configuration configuration = new Configuration(environment);
30         // 得到 SqlSessionFactory 核心类
31         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
32         // 开始一个 sql 会话
33         SqlSession session = sqlSessionFactory.openSession();
34         // 得到 sql 连接并运行 sql 语句
35         PreparedStatement preStatement = session
36                 .getConnection()
37                 .prepareStatement("SELECT * FROM user WHERE id = ?");
38         preStatement.setInt(1, 1);
39         ResultSet result = preStatement.executeQuery();
40         // 验证结果
41         while (result.next()) {
42             System.out.println("username: " + result.getString("username"));
43             System.out.println("age: " + result.getString("age"));
44         }
45         // 关闭会话
46         session.close();
47     }
48 }

执行结果：

配置文件：mybatis-config.xml

 1 <?xml version="1.0" encoding="UTF-8" ?>
 2 <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
 3 <configuration>
 4     <!-- 环境变量 -->
 5     <environments default="development">
 6         <environment id="development">
 7             <!-- 事务管理器 -->
 8             <transactionManager type="JDBC"/>
 9             <!-- 数据源 -->
10             <dataSource type="POOLED">
11                 <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
12                 <property name="url" value="jdbc:mysql://localhost:3306/mybatis_demo?useSSL=false"/>
13                 <property name="username" value="root"/>
14                 <property name="password" value="123456"/>
15             </dataSource>
16         </environment>
17     </environments>
18     <!-- mapper配置 -->
19     <mappers>
20         <mapper class="mapper.UserMapper"/>
21     </mappers>
22 </configuration>

修改StartNoXml.java类名：StartWithXml.java

 1 import org.apache.ibatis.datasource.pooled.PooledDataSource;
 2 import org.apache.ibatis.io.Resources;
 3 import org.apache.ibatis.mapping.Environment;
 4 import org.apache.ibatis.session.Configuration;
 5 import org.apache.ibatis.session.SqlSession;
 6 import org.apache.ibatis.session.SqlSessionFactory;
 7 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 8 import org.apache.ibatis.transaction.jdbc.JdbcTransactionFactory;
 9
10 import java.io.IOException;
11 import java.io.InputStream;
12 import java.sql.PreparedStatement;
13 import java.sql.ResultSet;
14 import java.sql.SQLException;
15
16 @SuppressWarnings({"SqlResolve", "SqlNoDataSourceInspection", "Duplicates"})
17 public class StartWithXml {
18     public static void main(String[] args) throws SQLException, IOException {
19         // 读取配置文件
20         InputStream configuration = Resources.getResourceAsStream("mybatis-config.xml");
21         // 得到 SqlSessionFactory 核心类
22         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
23         // 开始一个 sql 会话
24         SqlSession session = sqlSessionFactory.openSession();
25         // 得到 sql 连接并运行 sql 语句
26         PreparedStatement preStatement = session
27                 .getConnection()
28                 .prepareStatement("SELECT * FROM user WHERE id = ?");
29         preStatement.setInt(1, 1);
30         ResultSet result = preStatement.executeQuery();
31         // 验证结果
32         while (result.next()) {
33             System.out.println("username: " + result.getString("username"));
34             System.out.println("age: " + result.getString("age"));
35         }
36         // 关闭会话
37         session.close();
38     }
39 }

执行结果：

二、MyBatis实现Mapper配置查询

注解方式使用Mapper

代码编写：

在mybatis-config.xml配置文件中加入mapper配置

1 <!-- mapper配置 -->
2 <mappers>
3     <mapper class="mapper.UserMapper"/>
4 </mappers>

新建mapper包，新建一个UserMapper.java类

UserMapper.java

 1 package mapper;
 2
 3 import entity.User;
 4 import org.apache.ibatis.annotations.Select;
 5
 6 public interface UserMapper {
 7     /**
 8      * 通过用户id查询用户名称
 9      *
10      * @param id 用户id
11      * @return 用户名称
12      */
13     //通过#{**}的方式来查询
14     @Select("SELECT username FROM user WHERE id = #{id}")
15     String selectUsernameById(Integer id);
16     /**
17      * 通过用户id查询用户年龄
18      *
19      * @param id 用户id
20      * @return 用户年龄
21      */
22     Integer selectUserAgeById(Integer id);
23
24     /**
25      * 通过用户id查询用户信息
26      *
27      * @param id
28      * @return
29      */
30     User selectUserById(Integer id);
31
32 }

UserTest.java

 1 import entity.User;
 2 import mapper.UserMapper;
 3 import org.apache.ibatis.io.Resources;
 4 import org.apache.ibatis.session.SqlSession;
 5 import org.apache.ibatis.session.SqlSessionFactory;
 6 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 7
 8 import java.io.IOException;
 9 import java.io.InputStream;
10 import java.sql.SQLException;
11
12 @SuppressWarnings({"SqlResolve", "SqlNoDataSourceInspection", "Duplicates"})
13 public class UserTest {
14     public static void main(String[] args) throws IOException, SQLException {
15         // 读取配置文件
16         InputStream configuration = Resources.getResourceAsStream("mybatis-config.xml");
17         // 得到 SqlSessionFactory 核心类
18         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
19         // 开始一个 sql 会话
20         SqlSession session = sqlSessionFactory.openSession();
21         // 得到 mapper
22         UserMapper mapper = session.getMapper(UserMapper.class);
23         // 调用注解的SQL
24         String username = mapper.selectUsernameById(1);
25         System.out.println("username: " + username);
26         // 调用XML的SQL
27         Integer age = mapper.selectUserAgeById(1);
28         System.out.println("age: " + age);
29
30         // 调用通过用户id查询用户信息的方法
31         User user = mapper.selectUserById(1);
32         System.out.println(user);
33         // 关闭会话
34         session.close();
35     }
36 }

执行结果：