MyBatis 逆向工程

一、Mybatis Generator:

1）简称 MBG，是一个专门为 MyBatis 框架使用者定制的代码生成器，可以快速的根据表生成对应的映射文件、接口，以及 Bean 类，支持基本的增删改查，以及 QBC 风格的条件查询。但是表连接、存储过程等复杂 sql 的定义需要我们手工编写

2）官方文档地址

3）官方工程地址

二、MBG 使用步骤-使用 maven 构造

1）引入插件

        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.6</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis.generator</groupId>
            <artifactId>mybatis-generator-core</artifactId>
            <version>1.3.7</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.12</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <!-- mybatis 逆向工程 -->
            <plugin>
                <groupId>org.mybatis.generator</groupId>
                <artifactId>mybatis-generator-maven-plugin</artifactId>
                <version>1.3.7</version>
                <configuration>
                    <verbose>true</verbose>
                    <overwrite>true</overwrite>
                </configuration>
                <dependencies>
                    <dependency>
                        <groupId>mysql</groupId>
                        <artifactId>mysql-connector-java</artifactId>
                        <version>8.0.12</version>
                    </dependency>
                </dependencies>
            </plugin>
        </plugins>
    </build>      

2）编写 MBG 的配置文件，指定生成策略==【注意文件名称：必须为generatorConfig.xml】==

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE generatorConfiguration
        PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
        "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">

<generatorConfiguration>
    <!--
    <classPathEntry
    location="C:\Users\YoYo\.m2\repository\mysql\mysql-connector-java\8.0.12\mysql-connector-java-8.0.12.jar"/>
    -->

    <context id="DB2Tables" targetRuntime="MyBatis3Simple">
        <!--取消注释-->
        <commentGenerator>
            <property name="suppressAllComments" value="true"/>
        </commentGenerator>

        <!--配置数据库连接-->
        <jdbcConnection driverClass="com.mysql.cj.jdbc.Driver"
                        connectionURL="jdbc:mysql:///ssmcrud?serverTimezone=GMT&amp;allowMultiQueries=true"
                        userId="root"
                        password="root">
        </jdbcConnection>

        <javaTypeResolver>
            <property name="forceBigDecimals" value="false"/>
        </javaTypeResolver>

        <!--java 模型生成：指定 javabean 生成的位置-->
        <javaModelGenerator
                targetPackage="info.yingying.crud.bean"
                targetProject=".\src\main\java">
            <property name="enableSubPackages" value="true"/>
            <property name="trimStrings" value="true"/>
        </javaModelGenerator>

        <!--指定 sql 映射文件的位置-->
        <sqlMapGenerator
                targetPackage="mybatis.mapper"
                targetProject=".\src\main\resources">
            <property name="enableSubPackages" value="true"/>
        </sqlMapGenerator>

        <!--指定 dao 接口的位置-->
        <javaClientGenerator type="XMLMAPPER"
                             targetPackage="info.yingying.crud.dao"
                             targetProject=".\src\main\java">
            <property name="enableSubPackages" value="true"/>
        </javaClientGenerator>

        <!--指定每个表的生成策略-->
        <!--加上 schema 指定特定的数据库-->
        <table schema="ssmcrud" tableName="employee" domainObjectName="Employee"/>
        <table schema="ssmcrud" tableName="department" domainObjectName="Department"/>

    </context>
</generatorConfiguration>

也可在配置文件中指定数据库 jar 包，这是第二种方式

3）运行 maven 插件

4）测试

① 准备 db.properties

driver=com.mysql.jdbc.Driver
url=jdbc:mysql:///ssmcrud?serverTimezone=GMT&allowMultiQueries=true
user=root
password=root

② 准备 mybatis 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>
    <properties resource="db.properties"/>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${user}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <package name="info.yingying.crud.dao"/>
    </mappers>
</configuration>

③ 准备测试代码

String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory =
    new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = sqlSessionFactory.openSession(true);

注：有兴趣的同学可以去学习 MyBatis Plus

Mybatis-PageHelper

1）导入依赖

<dependency>
    <groupId>com.github.pagehelper</groupId>
    <artifactId>pagehelper</artifactId>
    <version>5.1.7</version>
</dependency>

2）在 mybatis 核心配置文件中配置插件

<plugins>
    <!-- com.github.pagehelper 为 PageHelper 类所在包名 -->
    <plugin interceptor="com.github.pagehelper.PageInterceptor">
    </plugin>
</plugins>

3）测试

Page<Object> page = PageHelper.startPage(1, 10);// 紧跟着的查询会被分页
List<Employee> employees = employeeMapper.selectByExample(null);
for (Employee employee : employees) {
    System.out.println(employee);
}