IntelliJ IDEA下Mybatis和Maven入门示例

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我是靠谱客的博主哭泣草莓，最近开发中收集的这篇文章主要介绍IntelliJ IDEA下Mybatis和Maven入门示例，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

一、前言

Mybatis和Maven配置起来其实挺麻烦的，很容易忘记，所以记录一下配置的过程。Mybatis作为一个持久层的框架，是用来和数据库打交道的。这里以MySQL数据库为例，对用户user表进行增删改查。

二、步骤

新建一个Maven工程，可以不用骨架。
先配置一下Maven工程的pom.xml，相当与传统的“导入jar包”，代码如下：

<?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>cug</groupId>
    <artifactId>MybatisCRUD</artifactId>
    <version>1.0-SNAPSHOT</version>
    <!--我是分界线，上面的内容是自动生成的，下面的才是手动增加的-->
    <packaging>jar</packaging>
    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.5</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.26</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>

</project>

给学生表写一个实体类，学生表如下图：

实体类的代码如下：

package domain;

import java.util.Date;

/**
 * @author laoyingyong
 * @date: 2019-12-26 19:29
 */
public class User
{
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;

    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 Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + ''' +
                ", birthday=" + birthday +
                ", sex='" + sex + ''' +
                ", address='" + address + ''' +
                '}';
    }
}

写一个UserDao接口，代码如下：

package dao;

import domain.User;

import java.util.List;

/**
 * @author laoyingyong
 * @date: 2019-12-26 19:42
 */
public interface UserDao {
    /**
     * 查询所有用户
     * @return
     */
    List<User> findAll();

    /**
     * 保存方法
     * @param user
     */
    void saveUser(User user);

    /**
     * 更新方法
     * @param user
     */
    void updateUser(User user);

    /**
     * 删除方法
     * @param userId
     */
    void deleteUser(Integer userId);
}

新建一个Mybatis的配置文件SqlMapCofig.xml，代码如下：

<?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="mysql">
        <environment id="mysql">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"></property>
                <property name="url" value="jdbc:mysql://localhost:3306/test?characterEncoding=utf8"></property>
                <property name="username" value="root"></property>
                <property name="password" value=""></property>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="dao/UserDao.xml"></mapper>
    </mappers>
</configuration>

新建一个映射配置文件UserDao.xml，注意UserDao.xml
存放的位置，要放在dao目录下，和接口的一样。整个项目的结构如下图所示：

UserDao.xml的具体内容如下：

<?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="dao.UserDao">
    <select id="findAll" resultType="domain.User">
        select * from user;
    </select>

    <insert id="saveUser" parameterType="domain.User">
        insert into user (username,birthday,sex,address)values(#{username},#{birthday},#{sex},#{address});
    </insert>


    <update id="updateUser" parameterType="domain.User">
        update user set username=#{username},birthday=#{birthday},sex=#{sex},address=#{address} where id=#{id};
    </update>

    <delete id="deleteUser" parameterType="java.lang.Integer">
        delete from user where id=#{uid};/*uid只是占位符*/
    </delete>
    
</mapper>

因为用到了单元测试，测试类的代码如下：

package test;

import dao.UserDao;
import domain.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.Test;

import java.io.InputStream;
import java.util.Date;
import java.util.List;

/**
 * @author laoyingyong
 * @date: 2019-12-26 19:49
 */
public class MybatisTest {
    @Test
    public void testFindAll() throws Exception
    {
        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
        SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(in);
        SqlSession sqlSession = factory.openSession();
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List<User> list = userDao.findAll();
        for (User user : list) {
            System.out.println(user);

        }
        sqlSession.close();
        in.close();
    }

    @Test
    public void testSaveUser() throws Exception
    {
        User user=new User();
        user.setUsername("鲁班");
        user.setBirthday(new Date());
        user.setAddress("峡谷");
        user.setSex("男");

        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
        SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(in);
        SqlSession sqlSession = factory.openSession();
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        userDao.saveUser(user);

        sqlSession.commit();

        sqlSession.close();
        in.close();
    }

    @Test
    public void testUpdateUser() throws Exception
    {
        User user=new User();
        user.setId(50);
        user.setUsername("小鲁班");
        user.setBirthday(new Date());
        user.setAddress("王者峡谷");
        user.setSex("男");

        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
        SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(in);
        SqlSession sqlSession = factory.openSession();
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        userDao.updateUser(user);

        sqlSession.commit();

        sqlSession.close();
        in.close();
    }
    @Test
    public void testDeleteUser() throws Exception
    {
        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
        SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(in);
        SqlSession sqlSession = factory.openSession();
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        userDao.deleteUser(50);

        sqlSession.commit();

        sqlSession.close();
        in.close();

    }
}

再给出日志log4j的配置log4j.properties，代码如下：

# Set root category priority to INFO and its only appender to CONSOLE.
#log4j.rootCategory=INFO, CONSOLE            debug   info   warn error fatal
log4j.rootCategory=debug, CONSOLE, LOGFILE

# Set the enterprise logger category to FATAL and its only appender to CONSOLE.
log4j.logger.org.apache.axis.enterprise=FATAL, CONSOLE

# CONSOLE is set to be a ConsoleAppender using a PatternLayout.
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %mn

# LOGFILE is set to be a File appender using a PatternLayout.
log4j.appender.LOGFILE=org.apache.log4j.FileAppender
log4j.appender.LOGFILE.File=d:axis.log
log4j.appender.LOGFILE.Append=true
log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.LOGFILE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %mn

三、总结

当然最后的单元测试有很多代码都是重复的，为了省事我也就没有进行共性代码的抽取，直接复制粘贴，更加节省时间。
其实UserDao.xml这个配置文件也有替代者，就是使用注解的方式去配置，这里就不说明如何使用注解配置了。
与之前学的JdbcTemplate相比，采用Mybatis框架可以少写很多的逻辑代码，缺点就是入门者很不适应xml配置，感觉比较麻烦，难以记住配置的流程和一些细节方面的东西。（JdbcTemplate不能说是框架，它只是Spring框架下的一个工具类）
最好让实体类的属性名和数据库中的列名保持一致，否则会引起不必要的麻烦。（虽说实体类的属性名和数据库表中的列名不可以不相同，但配置xml时会很麻烦，要多写很多东西）。
上面的UserDao接口我并没有写对应的实现类，但Mybatis同样也支持写Dao的实现类，但是最好不写，因为增加了很多代码。使用框架就是为了简化开发，还写实现类的话，也是自找麻烦。