Mybatis逆向工程实现自动生成Mapper（DAO）层与POJO（Entity，Bean）层

什么是逆向工程

Mybatis需要程序员自己编写SQL语句，mybatis官网提供逆向工程，可以针对单表自动生成mybatis执行所有需要代码（mapper.java,mapper.xml,po）

企业实际开发中，常用的逆向工程方式：

         数据库表来生产Java代码，

         企业开发中，是先对数据库进行设计，也就是编码之前数据库已经有了。

实现步骤如下：

首先：建立一个Maven项目

目录结构如下：

先进行配置pom.xml

<?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>hyx.revorse</groupId>
    <artifactId>revorse-project</artifactId>
    <version>1.0-SNAPSHOT</version>



    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <junit.version>4.12</junit.version>
        <mybatis.version>3.4.4</mybatis.version>
        <mysql.version>5.1.34</mysql.version>
        <log4j.version>1.2.17</log4j.version>
        <fastjson.version>1.2.35</fastjson.version>
        <slf4j.version>1.7.25</slf4j.version>
    </properties>

    <dependencies>
        <!-- mybatis核心包 -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>${mybatis.version}</version>
        </dependency>
        <!--mysql包-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>${mysql.version}</version>
        </dependency>

        <!-- 日志文件管理包 -->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>${log4j.version}</version>
        </dependency>

        <!-- 格式化对象，方便输出日志 -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>${fastjson.version}</version>
        </dependency>


        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>${slf4j.version}</version>
        </dependency>

        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>${slf4j.version}</version>
        </dependency>

        <!--测试包-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>RELEASE</version>
            <scope>compile</scope>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>RELEASE</version>
            <scope>compile</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.mybatis.generator</groupId>
                <artifactId>mybatis-generator-maven-plugin</artifactId>
                <version>1.3.5</version>
                <configuration>
                    <verbose>true</verbose>
                    <overwrite>true</overwrite>
                </configuration>
            </plugin>
        </plugins>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.xml</include>
                </includes>
            </resource>
        </resources>
    </build>

</project>

建立generatorConfig.xml配置文件

<?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>
    <!-- （1）配置mysql 驱动jar包路径.用了绝对路径 -->
    <classPathEntry location="E:\Linux\repository-big\repository\mysql\mysql-connector-java\5.1.38\mysql-connector-java-5.1.38.jar" />

    <context id="scm_mysql_tables" targetRuntime="MyBatis3">
        <!-- 防止生成的代码中有很多注释，加入下面的配置控制 -->
        <commentGenerator>
            <property name="suppressAllComments" value="true" />
            <property name="suppressDate" value="true" />
        </commentGenerator>

        <!-- （2）数据库连接 -->
        <jdbcConnection driverClass="com.mysql.jdbc.Driver"
        connectionURL="jdbc:mysql://localhost:3306/mybatis01?characterEncoding=UTF-8"
                        userId="root"
                        password="123">
        </jdbcConnection>

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

        <!-- （3）数据表对应的model层  -->
        <javaModelGenerator targetPackage="com.hd.po"
                            targetProject="src\main\java">
            <property name="enableSubPackages" value="true" />
            <property name="trimStrings" value="true" />
        </javaModelGenerator>

        <!-- (4)sql mapper 映射配置文件 -->
        <sqlMapGenerator targetPackage="com.hd.mapper"
                         targetProject="src\main\java">
            <property name="enableSubPackages" value="true" />
        </sqlMapGenerator>

        <!-- (5)mybatis3中的mapper接口 -->
        <javaClientGenerator type="XMLMAPPER"
                             targetPackage="com.hd.mapper"
                             targetProject="src\main\java">
            <property name="enableSubPackages" value="true" />
        </javaClientGenerator>

        <!-- (5)数据表进行生成操作 schema:相当于库名; tableName:表名;
            domainObjectName:对应的DO
        -->
        <table schema="mybatis" tableName="user" domainObjectName="User"
               enableCountByExample="false" enableUpdateByExample="false"
               enableDeleteByExample="false" enableSelectByExample="false"
               selectByExampleQueryId="false">
        </table>
        <table schema="mybatis" tableName="orders" domainObjectName="Orders"
               enableCountByExample="false" enableUpdateByExample="false"
               enableDeleteByExample="false" enableSelectByExample="false"
               selectByExampleQueryId="false">
        </table>

    </context>
</generatorConfiguration>

开始生成实体类与DAO层

生成成功如下图所示，查看Mapper.interface接口可以看到很多增删改查的方法

开始测试：.

先进行配置sqlMapconfig.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>

    <settings>
        <setting name="lazyLoadingEnabled" value="true"/>
        <setting name="aggressiveLazyLoading" value="false"/>
    </settings>

    <typeAliases>
        <package name="com.hd.po"></package>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"></property>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis01"></property>
                <property name="username" value="root"></property>
                <property name="password" value="123"></property>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <!--<mapper resource="com/huadian/c_dao_mapper/mapper/OrdersMapper.xml"></mapper>-->
        <package name="com.hd.mapper"></package>
    </mappers>

</configuration>

配置日志输出配置文件

# Global logging configuration
#在开发环境下日志级别设置为debug，生产环境下设置成info或error
log4j.rootLogger=debug, stdout
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n

测试代码：

package com.hd.test;

import com.hd.mapper.UserMapper;
import com.hd.po.User;
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.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;


public class Demo01 {
    private SqlSessionFactory sqlSessionFactory;

    @Before
    public void fun0() throws IOException {

        InputStream inputStream = Resources.getResourceAsStream( "sqlMapconfig.xml" );
        //通过配置创建会话工厂
        sqlSessionFactory = new SqlSessionFactoryBuilder().build( inputStream );

    }

    @Test
    public void fun1(){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.selectByPrimaryKey(1);

        System.out.println(user);
    }
}

输出结果，User类没有toString方法，所以输出时是一个对象

新手还是要多去练习如何写相应Mapper.interface接口中在Mapper.xml文件中实现的方法