编写一个Mybatis程序

        思路：搭建环境 --> 导入Mybatis --> 编写代码 --> 测试

搭建环境

    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,'小明','123456'),
(2,'张三','123456'),
(3,'李四','123456');

    新建项目

1. 新建一个普通的maven项目

2. 删除src目录（作为父工程）

3. 在pom.xml文件下导入maven依赖

    <dependencies>
        <dependency>
            <groupId>mysqlgroupId>
            <artifactId>mysql-connector-javaartifactId>
            <version>5.1.47version>
        dependency>
 
        <dependency>
            <groupId>org.mybatisgroupId>
            <artifactId>mybatisartifactId>
            <version>3.5.7version>
        dependency>
 
        <dependency>
            <groupId>junitgroupId>
            <artifactId>junitartifactId>
            <version>4.12version>
        dependency>
    dependencies>

创建一个模板

        编写mybatis的核心配置文件（mybatis-config.xml）

"1.0" encoding="UTF-8" ?>
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&useUnicode=true&characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            dataSource>
        environment>
    environments>
    
    
    <mappers>
        <mapper resource="com/yuan/dao/UserMapper.xml"/>
    mappers>
configuration>

        在java.com.xxx.utils层下编写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.IOException;
import java.io.InputStream;
 
//sqlSessionFactory --> sqlSession
public class MybatisUtils {
 
    private static SqlSessionFactory sqlSessionFactory;
 
    static {
        //获取sqlSessionFactory对象
        String resource = "mybatis-config.xml";
        try {
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 
    //既然有了SqlSessionFactory，顾名思义，我们就可以从中获得SqlSession的实例了
    //SqlSession 完全包含了面向数据库执行SQL命令所需的所有方法
 
    public static SqlSession getSqlSession(){
        //SqlSession sqlSession = sqlSessionFactory.openSession();
        return sqlSessionFactory.openSession();
    }
 
}

编写代码

        在java.com.xxx.pojo层下编写实体类（以User为例）

public class User {
    private  int id;
    private String name;
    private String pwd;
 
    public User(int id) {
        this.id = id;
    }
 
    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 + '\'' +
                '}';
    }
}

       在 java.com.xxx.dao下编写UserMapper（即Dao接口）

import java.util.List;
import java.util.Map;
 
public interface UserMapper {
    //获取全部用户
    List getUserList();
}

        在 java.com.xxx.dao编写接口实现类UserMapper.xml（由原来的UserDaoImpl转为一个Mapper配置文件）

"1.0" encoding="UTF-8" ?>
mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.yuan.dao.UserMapper">
 
    
    <select id="getUserList" resultType="com.yuan.pojo.User">
        select id, name, pwd from `user`
    select>
mapper>

测试

        修改pom.xml文件

"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">
    <parent>
        <artifactId>Mybatis-StudyartifactId>
        <groupId>com.yuangroupId>
        <version>1.0-SNAPSHOTversion>
    parent>
    <modelVersion>4.0.0modelVersion>
 
    <artifactId>mybatis-01artifactId>
 
    <properties>
        <maven.compiler.source>8maven.compiler.source>
        <maven.compiler.target>8maven.compiler.target>
    properties>
 
    
    <build>
        <resources>
            <resource>
                <directory>src/main/resourcesdirectory>
                <includes>
                    <include>**/*.propertiesinclude>
                    <include>**/*.xmlinclude>
                includes>
                <filtering>falsefiltering>
            resource>
            <resource>
                <directory>src/main/javadirectory>
                <includes>
                    <include>**/*.propertiesinclude>
                    <include>**/*.xmlinclude>
                includes>
                <filtering>falsefiltering>
            resource>
        resources>
    build>
 
project>

        在test.java.com.xxx.dao下编写UserDaoTest

import com.yuan.pojo.User;
import com.yuan.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();
 
        try{
            //方式一：getMapper
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            List userList = userMapper .getUserList();
 
            //方式二：
//        List userList = sqlSession.selectList("com.yuan.dao.UserDao.getUserList");
 
            for(User user : userList){
                System.out.println(user);
            }
 
        }catch(Exception e){
            e.printStackTrace();
        }finally {
            //关闭SqlSession
            sqlSession.close();
        }
    }
}

目录

  在创建Mybatis中可能会出现的错误

• 配置文件没有注册
• 绑定接口错误
• 方法名不对
• 返回类型不对
• Maven导出资源问题