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2022-1-19 MyBatis day1 简介

野见 2022-01-20 阅读 23
数据库sqljava

一、简介

MyBatis通过xml或注解的方式将执行的各种statement配置起来，并通过java对象和statement中的sql进行映射生成最终执行的sql语句，最后由mybatis框架执行sql并将结果映射成java对象并返回。

Mybatis没有将Java对象和数据库表关联起来，而是将Java方法和SQL语句关联。（需要手动创建对象，表，然后关联起来）
好处是可以充分利用数据库各种功能。

执行结果自动映射成对象，集合等。

二、一个helloworld

添加依赖：

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.17</version>
        </dependency>
    </dependencies>

resource中添加sql脚本：

/*
 Navicat Premium Data Transfer

 Source Server         : test
 Source Server Type    : MySQL
 Source Server Version : 80021
 Source Host           : localhost:3306
 Source Schema         : test

 Target Server Type    : MySQL
 Target Server Version : 80021
 File Encoding         : 65001

 Date: 19/01/2022 15:10:06
*/

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for account
-- ----------------------------
DROP TABLE IF EXISTS `account`;
CREATE TABLE `account`  (
                            `id` int NOT NULL AUTO_INCREMENT,
                            `username` varchar(30) CHARACTER SET gb2312 COLLATE gb2312_chinese_ci NULL DEFAULT NULL,
                            `money` int NULL DEFAULT NULL,
                            PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 2 CHARACTER SET = gb2312 COLLATE = gb2312_chinese_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of account
-- ----------------------------
INSERT INTO `account` VALUES (1, 'zhangsan', 500);
INSERT INTO `account` VALUES (2, 'lisi', 1500);

SET FOREIGN_KEY_CHECKS = 1;

目录如下：
在这里插入图片描述

新建model-Account

package org.kk.mybatis01.model;

/**
 * @program: mybatis01
 * @description:
 * @author: zjx
 * @create: 2022-01-19 15:11
 **/
public class Account {
    private Integer id;
    private String username;
    private Integer money;

    @Override
    public String toString() {
        return "Account{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", money=" + money +
                '}';
    }

    public Integer getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Integer getMoney() {
        return money;
    }

    public void setMoney(Integer money) {
        this.money = money;
    }
}

mapper：
Mapper是用来在MyBatis中定义SQL的XML配置文件，实际开发中经常需要用时Mapper，因此建议写成模版文件。

<?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">
<mapper namespace="#[[$namespace$]]#">
</mapper>

mapper包下创建：AccountMapper.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">
<mapper namespace="org.kk.mybatis01.mapper.AccountMapper">
    <select id="getAllAcount" resultType="org.kk.mybatis01.model.Account">
        select * from account;
    </select>
</mapper>

<mapper>下写的其实就是增删改查…

resources中还需要有MyBatis的配置（相当于是全局配置）：
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">
<configuration>
    <environments default="development">
<!-- 可以配置多个环境 生产环境、测试环境、开发环境       -->
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///test?serverTimezone=Asia/Shanghai"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="org/kk/mybatis01/mapper/AccountMapper.xml"/>
    </mappers>
</configuration>

进行使用：（Main函数）

package org.kk.mybatis01;

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 org.kk.mybatis01.model.Account;

import java.io.IOException;
import java.util.List;

/**
 * @program: mybatis01
 * @description:
 * @author: zjx
 * @create: 2022-01-19 21:31
 **/
public class Main {
    public static void main(String[] args) throws IOException {
        //加载主配置文件
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
        SqlSession sqlSession = factory.openSession(); //这个session其实就是创立的“连接”
        List<Account> list = sqlSession.selectList("org.kk.mybatis01.mapper.AccountMapper.getAllAccounts");
        for(Account account:list)
        {
            System.out.println("account="+account);
        }


        sqlSession.close();


    }
}

如果这样：
在这里插入图片描述
这是maven的一些问题…maven默认将配置文件放在resource下，而如果按下面的目录这样写，那么这个配置的xml在mapper下。

在这里插入图片描述
因此对pom.xml增加一个配置：

    <build>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.xml</include>
                </includes>
            </resource>
            <resource>
                <directory>src/main/resources</directory>
            </resource>
        </resources>
    </build>

三、SqlSessionFactory单例模式

SqlSessionFactory是一个connection对象

新建一个utils包，然后进行以下封装：

public class SqlSessionFactoryUtils {
    private static SqlSessionFactory SQLSESSIONFACTORY=null;
    public static SqlSessionFactory getInstance() {
        if(SQLSESSIONFACTORY==null) {
            try {
                SQLSESSIONFACTORY=new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        return SQLSESSIONFACTORY;
    }
}

那么就可以这样用：

public class Main {
    public static void main(String[] args){
        //加载主配置文件
        SqlSessionFactory factory = SqlSessionFactoryUtils.getInstance();
        SqlSession sqlSession = factory.openSession(); //这个session其实就是创立的“连接”
        List<Account> list = sqlSession.selectList("org.kk.mybatis01.mapper.AccountMapper.getAllAccounts");
        for(Account account:list)
        {
            System.out.println("account="+account);
        }


        sqlSession.close();
    }
}

四、使用Log4j查看MyBatis运行日志

添加依赖（3个）

        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <version>2.14.0</version>
        </dependency>


        <!-- https://mvnrepository.com/artifact/log4j/log4j -->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-api -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>2.0.0-alpha1</version>
        </dependency>

log4j.properties(resource下)

log4j.rootLogger=DEBUG,console,file

#控制台输出的相关设置
log4j.appender.console = org.apache.log4j.ConsoleAppender
log4j.appender.console.Target = System.out
log4j.appender.console.Threshold=DEBUG
log4j.appender.console.layout = org.apache.log4j.PatternLayout
#log4j.appender.console.layout.ConversionPattern=[%c]-%m%n
log4j.appender.console.layout.ConversionPattern=%5p [%t] - %m%n
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