Mybatis学习笔记(一) 安装与使用

Mybaits是什么？

它是一款优秀的持久层框架，避免了几乎所有的JDBC代码和手动设置参数和获取结果集的工作。

什么是数据持久化

持久化就是程序的数据由瞬时状态转化为持久状态的过程；

内存:断电则失，属于瞬时状态

数据库，io文件：属于持久状态

第一个程序

• 创建数据库
• 创建maven项目
• 导入依赖
• 创建配置文件
• 创建工具类
• 创建实体映射类
• 创建接口类
• 创建Mapper配置文件
• 建立映射
• 创建测试类

创建数据库

使用ideal自带的数据库管理工具，注意下方serverTimezone的设置

 

整个项目的文件组织结构

创建maven项目

• 删除src目录
• 在父pom配置依赖，子模块就不需要再配置依赖了

导入依赖

• 注意<build>选项是为了让maven项目可以找到我们的mapper.xml，否则maven默认只会到resource目录下找资源文件
• 父pom内容如下

<?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>

    <groupId>org.example</groupId>
    <artifactId>mybaitsLearning</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>mybaits01</module>
    </modules>

    <build>
       <resources>
           <resource>
               <directory> src/main/resources</directory>
               <includes>
                   <include>**/*.properties</include>
                   <include>**/*.xml</include>
               </includes>
               <filtering>false</filtering>
           </resource>
           <resource>
               <directory> src/main/java</directory>
               <includes>
                   <include>**/*.properties</include>
                   <include>**/*.xml</include>
               </includes>
               <filtering>true</filtering>
           </resource>
       </resources>
    </build>
    <dependencies>
        <!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.46</version>
        </dependency>
        <!-- mybaits -->
        <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>
        </dependency>

    </dependencies>
</project>

创建配置文件

<?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>
    <!--you can set different environment-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                 <!--数据库驱动 -->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <!--连接地址，注意需要保持选项否则中文会乱码 -->
                <property name="url" value="jdbc:mysql://localhost:3306/mybait?useUnicode=true&amp;characterEncoding=UTF-8"/>
                <!--用户名 --> 
                <property name="username" value="root"/>
                <!--密码--> 
                <property name="password" value="asdf1234ASDF."/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/hjc/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

创建工具类

数据库连接通过工厂方法创建，没必要每次创建，因此通过工具类获取

public class MyBatisUtils {
    private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
    private static SqlSessionFactory sqlSessionFactory;
    static{
        try {
            Reader reader = Resources.getResourceAsReader("mybatis.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (IOException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
    private MyBatisUtils() {}
    public static SqlSession getSqlSession(){
        SqlSession sqlSession = threadLocal.get();
        if(sqlSession == null){
            sqlSession = sqlSessionFactory.openSession();
            threadLocal.set(sqlSession);
        }
        return sqlSession;
    }
    
    public static void closeSqlSession(){
        SqlSession sqlSession = threadLocal.get();
        if(sqlSession != null){
            sqlSession.close();
            threadLocal.remove();
        }
    }
    
}

 

创建实体映射类

• 包括有参和无参构造器
• set/get方法

package com.hjc.POJO;

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 + '\'' +
                '}';
    }
}

创建接口类

package com.hjc.mapper;

import com.hjc.POJO.User;

import java.util.List;

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

创建Mapper.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">
<!-- 接口所在类-->
<mapper namespace="com.hjc.mapper.UserMapper">
<!-- 对应的方法-->
    <select id="getUserList" resultType="com.hjc.POJO.User">
    select * from mybait.user
  </select>
</mapper>

建立映射

在总配置文件下添加，总配置文件的内容上面已给出全部

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

创建测试类

package com.hjc.mapper;

import com.hjc.util.MybaitsUtils;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.junit.Test;

public class UserMapperTest {
    @Test
    public void test(){

        SqlSession session = MyBatisUtils.getSqlSession()

       UserMapper mapper = session.getMapper(UserMapper.class); mapper.getUserList().stream().forEach(i->{System.out.println(i);}); } }

可能存在问题

认真检查上述配置，以下问题都可解决

• 配置文件没有注册
• 绑定接口错误
• 方法名错误
• 返回类型错误
• maven生成target，资源找不到