IntelliJ IDEA下Mybatis和Maven入门示例

青旅半醒 2023-06-25 06:29 3阅读 0赞

## 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 ##

1.  新建一个Maven工程，可以不用骨架。
2.  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>
        
        <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>

1.  给学生表写一个实体类，学生表如下图：  
    ![在这里插入图片描述][20191226221313884.png]  
    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 + '\'' +
                    '}';
        }
    }

1.  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);
    }

1.  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>

1.  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：  
    ![在这里插入图片描述][20191226222009266.png]  
    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>

1.  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();
    
        }
    }

1.  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 - %m\n
    
    # 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 - %m\n

## 三、总结 ##

1.  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。
2.  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。
3.  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）
4.  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）。
5.  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。

[20191226221313884.png]: https://img-blog.csdnimg.cn/20191226221313884.png
[20191226222009266.png]: https://img-blog.csdnimg.cn/20191226222009266.png