第一个MyBatis程序

声明

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参考文章链接

(3条消息) 【狂神说】Mybatis学习笔记（全）_黑心白莲的博客-CSDN博客_狂神说mybatis笔记

(3条消息) 狂神说 | Mybatis完整版笔记_小七rrrrr的博客-CSDN博客_狂神说mybatis笔记

第一个Mybatis程序

思路：搭建环境–>导入Mybatis–>编写代码–>测试

1 搭建环境

搭建数据库

CREATE DATABASE `mybatis` IF NOT EXISTS;

USE `mybatis`;

CREATE TABLE `users`(
	`id` INT(20) NOT NULL PRIMARY KEY,
	`name` VARCHAR(30) DEFAULT NULL,
	`pwd` VARCHAR(30) DEFAULT NULL
)ENGINE=INNODB DEFAULT CHARSET=utf8;

INSERT INTO `users`(`id`,`name`,`pwd`) VALUES
(1,'xy','123456'),
(2,'xyz','123456'),
(3,'xyzz','123456')

新建项目

新建一个普通maven项目
删除src目录

导入maven依赖

<!--import dependencies-->
<dependencies>
    <!--mysql driver-->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.47</version>
    </dependency>
    <!--mybatis-->
    <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.6</version>
    </dependency>
    <!--junit-->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
</dependencies>

2 创建一个模块

编写mybatis的核心配置文件

<?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>
    <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&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="xy680501*"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="org/mybatis/example/BlogMapper.xml"/>
    </mappers>
</configuration>

编写mybatis工具类

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.InputStream;

public class MyBatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static {
        try {
            //使用Mybaties第一步：获取sqlSessionFactory对象
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (Exception 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。你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句。
    public static SqlSession getSqlSession(){
//        SqlSession sqlSession =  sqlSessionFactory.openSession();
//        return sqlSession;

        return sqlSessionFactory.openSession();
    }
}

3 编写代码

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 String getName() {
        return name;
    }

    public String getPwd() {
        return pwd;
    }

    public void setId(int id) {
        this.id = id;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }
}

Dao接口

import com.xy.pojo.User;

import java.util.List;

public interface UseDao {
    //可以避免JDBC代码和手动设置参数
    List<User> getUserList();
}

接口实现类

由原来的UserDaoImpl.java代码转变成一个Mapper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="xy.dao.UserDao">
    <!--select查询语句-->
    <!--id相当于重写方法的名字们这里是重写方法，当实现一个接口的时候以前是需要重写方法的-->
    <!--resultType时返回类型-->
    <select id="getUserList" resultType="xy.pojo.User">
        select * from mybatis.users
    </select>
</mapper>

4 测试

方法一

主要是为了获得SqlSession对象

junit测试(以后测试程序结构都像下图一样，测试与上边的架构保持一致)

package com.xy.dao;

import com.xy.pojo.User;
import com.xy.utils.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserDaoTest {
        @Test
        public void test(){
            //第一步获取SqlSession对象
            SqlSession sqlSession = MyBatisUtils.getSqlSession();
            //方式一：执行sql getMapper
            UserDao userDao = sqlSession.getMapper(UserDao.class);//这里是反射，实现了一个接口，并且创建了实现类的实例
            List<User> userList = userDao.getUserList();
            for (User user : userList){
                System.out.println(user);
            }

            sqlSession.close();
        }
}

在测试的过程中可能遇到的问题：

没有注册mapper：org.apache.ibatis.binding.BindingException: Type interface com.kuang.dao.UserDao is not known to the MapperRegistry.

解决方法为在mybatis的核心配置文件里面添加注册

xml文件找到不到：java.io.IOException: Could not find resource com/xy/dao/UserMapper.xml

这是个导包问题，解决方法为在pom.xml中配置resources防止资源到处失败的问题

<!--在pom.xml的<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/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

方法名错误
返回类型不对
Maven导出资源问题

方法二(不推荐)

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

import java.util.List;

public class UserDaoTest {
    @Test
    public void test(){
        //第一步获取SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //方式一：执行sql getMapper
        try {
            UserDao userDao = sqlSession.getMapper(UserDao.class);
            List<User> userList = userDao.getUserList();
            for (User user : userList){
                System.out.println(user);
            }
            //方式二：不推荐使用
            //List<User> userList1 = sqlSession.selectList("com.xy.dao.UserDao.getUserList");
            //for (User user : userList1){
                //System.out.println(user);
            //}
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            sqlSession.close();
        }
       
    }
}