我的第一个MyBatis程序

下文笔者讲述我的第一个MyBatis程序的编写示例分享,如下所示

MyBatis简介

MyBatis是一款优秀的持久层框架
   用来简化Dao层
   简化繁琐JDBC

传统JDBC写法

package com.java265.test;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class TestJDBC {
    public static void main(String[] args) throws Exception{
        String url = "jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf8&useSSL=false";
        String username = "root";
        String password = "123456";

        //加载驱动
        Class.forName("com.mysql.jdbc.Driver");

        //连接数据库
        Connection connection = DriverManager.getConnection(url, username, password);

        //获得操作对象
        Statement statement = connection.createStatement();

        //编写sql
        String sql = "SELECT * from `users`";
        ResultSet resultSet = statement.executeQuery(sql);

        while (resultSet.next()){
            System.out.println("id="+resultSet.getObject("id"));
            System.out.println("name="+resultSet.getObject("name"));
            System.out.println("password="+resultSet.getObject("password"));
            System.out.println("email="+resultSet.getObject("email"));
            System.out.println("birthday="+resultSet.getObject("birthday"));
        }

        //释放资源
        resultSet.close();
        statement.close();
        connection.close();

    }
}

使用mybatis的效果

<?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Mapper接口，
     id为接口中方法名，
	 resultType为返回值的实体类型位置
-->
<mapper namespace="com.java265.dao.UserDao">
    <select id="getUserlist" resultType="com.java265.pojo.User">
        select * from mybatis.user
    </select>

</mapper>

我的第一个mybatis程序(使用maven)

1.搭建测试数据库

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,'编程之外','123456'),
(2,'张三','123456'),
(3,'李四','123890')

2.IDEA构建空项目(不适用模板)

pom.xml导入以下依赖

<!--导入依赖-->
    <dependencies>
        <!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <!--mybatis-->
        <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>
            <!--<scope>test</scope>-->
        </dependency>
    </dependencies>

在resources目录下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">
<!--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=false&useUnicode=true&characterEncoding=UTF8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

</configuration>

编写mybatis工具类MyBatisUtils

package com.java265.utils;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.InputStream;

public class MybatisUtils {

    private static SqlSessionFactory sqlSessionFactory;

    static {

        try {
            //获取SQLSession对象
            String resource = "mybatis-config.xml";
            InputStream in = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);

        } catch (IOException e) {
            e.printStackTrace();
        
        }

    }

    //获取SQLSession
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

编写实体类User

package com.java265.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 + '\'' +
                '}';
    }
}

编写dao层
先写接口UserDao
注意现在不用接口实现类
将UserDaoImpl转换为UserMapper.xml

UserDao

public interface UserDao {
    List<User> getUserList();
}

UserMapper.xml

<?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Mapper接口，id为接口中方法名，resultType为返回值的实体类型位置-->
<mapper namespace="com.java265.dao.UserDao">
    <select id="getUserList" resultType="com.java265.pojo.User">
        select * from mybatis.user
    </select>

</mapper>

在核心配置文件mybatis-config.xml中编写映射

映射

 <mappers>
        <mapper resource="com/kuang/dao/UserMapper.xml"/>
 </mappers>

修改后的mybatis-config.xml信息

<?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">
<!--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=false&useUnicode=true&characterEncoding=UTF8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>


    <mappers>
        <mapper resource="com/java265/dao/UserMapper.xml"/>
    </mappers>

</configuration>

注意事项:
  当你的UserMapper.xml在Dao目录下
   需要在pom.xml加上一些内容
    防止资源导出失败
   当你的UserMapper.xml在resources目录下

pom.xml文件修改

 <!--在build中配置resources，来防止我们资源导出失败的问题-->
    <build>

        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>false</filtering>
            </resource>
        </resources>

    </build>

单元测试

package com.java265.dao;

import com.java265.pojo.User;
import com.java265.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserMapperTest {

    @Test
    public void test() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        List<User> userList = mapper.getUserList();

        for (User user : userList){
            System.out.println(user);
        }
    }
}