mybatis入门

前言：什么是Mybatis？

它是一款半自动的ORM持久层框架，具有较高的SQL灵活性，支持高级映射(一对一，一对多)，动态SQL，延迟加载和缓存等特性，但它的数据库无关性较低它是一款半自动的ORM持久层框架，具有较高的SQL灵活性，支持高级映射(一对一，一对多)，动态SQL，延迟加载和缓存等特性，但它的数据库无关性较低

一、搭建mybatis框架环境

1、创建maven工程

首先我们在学习mybatis之前先创建一个基础的maven项目

右击项目名——>new——>module

选择maven项目——>选择jdk版本——>选择webapp

输入项目名

选择好maven项目的文件位置——>点击添加按钮——>配置好参数

2、导入相关pom依赖

创建好maven项目之后我们还需修改一下，我们可以去看一下小编的另外一篇文章，我们可以修改一下在这里小编就不在重复写了。接下来我们导入Mybatis 的相关pom依赖

POM依赖：


<properties>
        <maven.compiler.source>1.8maven.compiler.source>
        <maven.compiler.target>1.8maven.compiler.target>
    properties>
 
    <dependencies>
        
        <dependency>
            <groupId>junitgroupId>
            <artifactId>junitartifactId>
            <version>4.12version>
            <scope>testscope>
        dependency>
 
        
        <dependency>
            <groupId>javax.servletgroupId>
            <artifactId>javax.servlet-apiartifactId>
            <version>4.0.0version>
            <scope>providedscope>
        dependency>
 
        
        <dependency>
            <groupId>org.mybatisgroupId>
            <artifactId>mybatisartifactId>
            <version>3.4.5version>
        dependency>
 
        
        <dependency>
            <groupId>mysqlgroupId>
            <artifactId>mysql-connector-javaartifactId>
            <version>5.1.44version>
        dependency>
 
        
        
        
        
        <dependency>
            <groupId>org.apache.logging.log4jgroupId>
            <artifactId>log4j-coreartifactId>
            <version>2.9.1version>
        dependency>
        <dependency>
            <groupId>org.apache.logging.log4jgroupId>
            <artifactId>log4j-apiartifactId>
            <version>2.9.1version>
        dependency>
        
        <dependency>
            <groupId>org.apache.logging.log4jgroupId>
            <artifactId>log4j-webartifactId>
            <version>2.9.1version>
        dependency>
dependencies>
 
 
 <build>
        <resources>
            
            <resource>
                <directory>src/main/javadirectory>
                <includes>
                    <include>**/*.xmlinclude>
                includes>
            resource>
            
            <resource>
                <directory>src/main/resourcesdirectory>
                <includes>
                    <include>jdbc.propertiesinclude>
                    <include>*.xmlinclude>
                includes>
            resource>
        resources>
 
        <plugins>
            <plugin>
                <groupId>org.mybatis.generatorgroupId>
                <artifactId>mybatis-generator-maven-pluginartifactId>
                <version>1.3.2version>
                <dependencies>
                    
                    <dependency>
                        <groupId>mysqlgroupId>
                        <artifactId>mysql-connector-javaartifactId>
                        <version>5.1.44version>
                    dependency>
                dependencies>
                <configuration>
                    <overwrite>trueoverwrite>
                configuration>
            plugin>
        plugins>
 
    build>

然后我们知道Mybatis是一款有关于数据库的框架，所以我们还需要导入关于数据库连接的配置文件：

jdbc.properties：


jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis_ssm?useUnicode=true&characterEncoding=UTF-8
jdbc.username=root
jdbc.password=123456

修改web.xml文件


web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >
 
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
 
         version="3.1">web-app>

3、Mybatis相关插件安装

配置好pom依赖之后我们继续学习mybatis的环境搭建，接下来我们需要安装几款插件

①        Free mybatis plugin

②        Mybatis generator

③        mybatis tools

④        maven helper

4、Mybatis.cfg.xml配置

众所周知，一款框架必定有自己的配置文件，Mybatis也是一样有配置文件

Mybatis.cfg.xml


configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    
    <properties resource="jdbc.properties"/>
 
    <settings>
        <setting name="logImpl" value="LOG4J2"/>
    settings>
 
    
    <typeAliases>
        
    typeAliases>
 
 
    
    <environments default="development">
        <environment id="development">
            
            <transactionManager type="jdbc"/>
 
            
            
            
            
            <dataSource type="POOLED">
                <property name="driver"
                          value="${jdbc.driver}"/>
                <property name="url"
                          value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            dataSource>
        environment>
    environments>
 
    <mappers>
        <mapper resource="com/javaxl/mapper/BookMapper.xml"/>
    mappers>
configuration>

二、基于ssm逆向工程的使用（IDEA）

1、安装Mybatis generator插件

这个插件我们刚才已经安装好了

2、配置generatorConfig.xml

generatorConfig.xml：


generatorConfiguration PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
        "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd" >
<generatorConfiguration>
    
    <properties resource="jdbc.properties"/>
 
    
    <classPathEntry location="D:\\mvn-repository\\mysql\\mysql-connector-java\\5.1.44\\mysql-connector-java-5.1.44.jar"/>
 
    
    <context id="infoGuardian">
        
        <commentGenerator>
            <property name="suppressAllComments" value="true"/>
            <property name="suppressDate" value="true"/> 
        commentGenerator>
 
        
        <jdbcConnection driverClass="${jdbc.driver}"
                        connectionURL="${jdbc.url}" userId="${jdbc.username}" password="${jdbc.password}"/>
 
        
        <javaTypeResolver>
            
            <property name="forceBigDecimals" value="false"/>
        javaTypeResolver>
 
        
        
        
        <javaModelGenerator targetPackage="com.zq.model"
                            targetProject="src/main/java">
            
            <property name="enableSubPackages" value="false"/>
            
            <property name="constructorBased" value="true"/>
            
            <property name="trimStrings" value="false"/>
            
            <property name="immutable" value="false"/>
        javaModelGenerator>
 
        
        <sqlMapGenerator targetPackage="com.zq.mapper"
                         targetProject="src/main/java">
            
            <property name="enableSubPackages" value="false"/>
        sqlMapGenerator>
 
        
        
        
        
        <javaClientGenerator targetPackage="com.zq.mapper"
                             targetProject="src/main/java" type="XMLMAPPER">
            
            <property name="enableSubPackages" value="false"/>
        javaClientGenerator>
 
        
        
        
        
        
        
        
        
        
        
        
        
        
 
        <table schema="" tableName="t_mvc_Book" domainObjectName="Book"
               enableCountByExample="false" enableDeleteByExample="false"
               enableSelectByExample="false" enableUpdateByExample="false">
            
            
            
            
        table>
 
        <table schema="" tableName="t_oa_permission" domainObjectName="Permission"
               enableCountByExample="false" enableDeleteByExample="false"
               enableSelectByExample="false" enableUpdateByExample="false">
            
            
            
            
        table>
 
    context>
generatorConfiguration>

总结一下修改的位置：

1.1 修改5.1.44的jar的路径

1.2 修改实体类生成的地址

1.3 修改SQL对应的配置文件的生成地址

1.4修改Dao层代码地址

1.5指定需要生成增删改查代码对应的表

3、配置maven运行generator命令

我们再在pom文件中右键

然后我们就可以看到它将帮我们自定创建好了实体类和方法了

三、Mybatis增删改查案例

插叙：面试题：SQLSession的作用

sqlsession的作用:

1.sqlsession可以拿到mapper对象

2.作为缓存使用，一级缓存，默认会开启的缓存、

3.出于对性能的考虑，会采用二级缓存，二级缓存需要手动开启

创建一个util包和一个SessionUtil类


package com.zq.util;
 
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 
/**
 * @author张强
 * @site www.zq.com
 * @create  2022-08-11 1:32
 */
public class SessionUtil {
    private static SqlSessionFactory sessionFactory;
    private static ThreadLocal threadLocal = new ThreadLocal();
    static {
        sessionFactory = new SqlSessionFactoryBuilder().build(SessionUtil.class.getResourceAsStream("/mybatis.cfg.xml"));
    }
 
    public static SqlSession openSession() {
        SqlSession session = threadLocal.get();
        if (null == session) {
            session = sessionFactory.openSession();
            threadLocal.set(session);
        }
        return session;
    }
 
    public static void main(String[] args) {
        SqlSession session = openSession();
        System.out.println(session.getConnection());
        session.close();
    }
}

创建biz层BookBiz：


package com.zq.biz;
 
import com.zq.model.Book;
 
/**
 * @author张强
 * @site www.zq.com
 * @create  2022-08-11 1:35
 */
public interface BookBiz {
 
    int deleteByPrimaryKey(Integer bid);
 
    Book selectByPrimaryKey(Integer bid);
 
}

用bookbizimpl实现bookbiz


package com.zq.biz.impl;
 
import com.zq.biz.BookBiz;
import com.zq.mapper.BookMapper;
import com.zq.model.Book;
 
/**
 * @author张强
 * @site www.zq.com
 * @create  2022-08-11 1:38
 */
public class BookBizImpl implements BookBiz {
    private BookMapper bookMapper;
 
    public BookMapper getBookMapper() {
        return bookMapper;
    }
 
    public void setBookMapper(BookMapper bookMapper) {
        this.bookMapper = bookMapper;
    }
 
 
    @Override
    public int deleteByPrimaryKey(Integer bid) {
        return bookMapper.deleteByPrimaryKey(bid);
    }
 
    @Override
    public Book selectByPrimaryKey(Integer bid) {
        return bookMapper.selectByPrimaryKey(bid);
    }
}

以及它的测试类BookBizImplTest


package com.zq.biz.impl;
 
import com.zq.mapper.BookMapper;
import com.zq.util.SessionUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
 
/**
 * @author张强
 * @site www.zq.com
 * @create  2022-08-11 1:41
 */
public class BookBizImplTest {
    private BookBizImpl bookBiz = new BookBizImpl();
    SqlSession sqlSession;
 
    @Before
    public void setUp() throws Exception {
        System.out.println("初始换方法。。。");
        //工具类中获取session对象
        sqlSession = SessionUtil.openSession();
        //从session对象中获取mapper对象
        BookMapper mapper = sqlSession.getMapper(BookMapper.class);
        bookBiz.setBookMapper(mapper);
    }
 
    @After
    public void tearDown() throws Exception {
        System.out.println("方法测试结束。。");
    }
 
    @Test
    public void deleteByPrimaryKey() {
    }
 
    @Test
    public void selectByPrimaryKey() {
 
        System.out.println("测试的业务方法。。。");
        //System.out.println(bookBiz.getBookMapper());
        System.out.println(bookBiz.selectByPrimaryKey(44));
    }
 
}

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原文地址：https://blog.csdn.net/weixin_66110079/article/details/126276724