编写一个Mybatis程序

一、搭建数据库

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,'马西莫','123456'),
(2,'张三','123456'),
(3,'李四','123890')

二、新建一个普通的maven项目

2.1、删除src目录

2.2、导入maven依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

<!-- 父工程-->
    <groupId>com.massimo</groupId>
    <artifactId>Mybatis</artifactId>
    <version>1.0-SNAPSHOT</version>

<!-- 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>4.11</version>
        </dependency>
    </dependencies>


</project>

2.3、创建一个子模块

2.4、编写mybatis的核心配置文件

在新建模块下的src/main/resource下新建一个mybatis-config.xml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&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="org/mybatis/example/BlogMapper.xml"/>
    </mappers>
</configuration>

2.5、编写mybatis工具类

package com.massimo.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;

//sqlSessionFactory  -->  sqlSession
public class MybatisUtils {

    private static SqlSessionFactory sqlSessionFactory;

    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();
    }

}

2.6、编写实体类

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

2.7、Dao接口

package com.massimo.dao;

import com.massimo.pojo.User;

import java.util.List;

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

2.8、接口实现类由原来的UserDaoImpl转变为一个Mapper配置文件，所以建立一个UserMapper.xml配置文件

<?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=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.massimo.dao.UserDao">
    <!--select查询语句-->
    <select id="getUserList" resultType="com.massimo.pojo.User">
        select * from mybatis.user
    </select>
</mapper>

2.9、junit测试

注意点一：org-apache.ibatis. binding. BindingException: Type interface com.kuang.dao.UserDao is not known to the MapperRegistry.

大概意思是这个UserDao接口，MapperRegistry不知道。

MapperRegistry是什么?
核心配置文件中注册mappers

每一个Mapper.xml都需要在Mybatis核心配置文件中注册！注册如下：

注意点二：

原因：maven由于他的约定大于配置，所以可以能遇到写的配置文件,无法被导出或者生效的问题。

解决方案:在pom.xml配置文件中添加如下：

<!-- 在build中配置resources，防止发生资源导出失败-->
    <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>

测试代码：

package com.massimo.dao;

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

import java.util.List;

public class UserDaoTest {
    @Test
    public void test(){
        //第一步：获得sqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserDao userDao= sqlSession.getMapper(UserDao.class);
        List<User> userList = userDao.getUserList();

        for (User user : userList) {
            System.out.println(user);
        }
        //关闭sqlSession
        sqlSession.close();
    }
}

效果：

PS：根据以上操作，如果还出现错误，那么就将xml中的注释都删除掉，试一下。

三、项目结构