一个简单的MyBatis项目

1、log4j.properties,我们把它设为debug级别，以便于调试。生产环境可以设为INFO,本项目放在src下面：

# Global logging configuration
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

2、Role.java,一个pojo(plain ordinary java object)，用于映射：

package com.ssm.pojo;

/**
 * Created by czz on 2019/7/23.
 */
public class Role {
    private Long id;
    private String roleName;
    private String note;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getRoleName() {
        return roleName;
    }

    public void setRoleName(String roleName) {
        this.roleName = roleName;
    }

    public String getNote() {
        return note;
    }

    public void setNote(String note) {
        this.note = note;
    }

    @Override
    public String toString() {
        return "Role{" +
                "id=" + id +
                ", roleName='" + roleName + '\'' +
                ", note='" + note + '\'' +
                '}';
    }
}

3、用XML方式构建映射器，它包含一个接口和一个XML。其中，RoleMapper.java：

package com.ssm.mapper;

import com.ssm.pojo.Role;

import java.util.List;

/**
 * Created by czz on 2019/7/23.
 */
public interface RoleMapper {
    int insertRole(Role role);
    int deleteRole(Long id);
    int updateRole(Role role);
    Role getRole(Long id);
    List<Role> findRoles(String roleName);
}

4、xml构建中的xml

<?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="com.ssm.mapper.RoleMapper">

    <insert id="insertRole" parameterType="role">
        INSERT INTO t_role(role_name,note) VALUES (#{role_name},#{note})
    </insert>

    <delete id="deleteRole" parameterType="long">
        DELETE FROM t_role WHERE id = #{id}
    </delete>

    <update id="updateRole" parameterType="role">
        UPDATE t_role SET role_name = #{roleName},note = #{note} WHERE id = #{id}
    </update>

    <select id="getRole" parameterType="long" resultType="role">
        SELECT id ,role_name roleName,note FROM t_role WHERE id = #{id}
    </select>

    <select id="findRoles" parameterType="long" resultType="com.ssm.pojo.Role">
        SELECT id ,role_name roleName,note FROM t_role WHERE role_name LIKE concat('%',#{roleName},'%')
    </select>
</mapper>

5、mybatis-config.xml用于构建SqlSessionFactory,代码清单如下：

<?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>
    <!-- 全局setting配置，根据需要添加 -->

    <!-- 配置别名 -->
    <typeAliases>
        <typeAlias type="com.ssm.pojo.Role" alias="role"/>
    </typeAliases>
    <!-- 配置数据库环境 -->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/ssm?useUnicode=true&amp;characterEncoding=utf8&amp;serverTimezone=UTC"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <package name="com.ssm.mapper"/>
    </mappers>
</configuration>

6、由于SqlSessionFactory应该采用单例模式，所以这里采用单例模式，利用SqlSessionFactoryBuilder来构建它：

package com.ssm.utils;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

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

/**
 * Created by czz on 2019/7/24.
 */
public class SqlSessionFactoryUtils {
    private final static Class<SqlSessionFactoryUtils> LOCK = SqlSessionFactoryUtils.class;
    private static SqlSessionFactory sqlSessionFactory = null;
    //防止其他代码通过new的方式创建它
    private SqlSessionFactoryUtils(){

    }

    public static SqlSessionFactory getSqlSessionFactory(){
        // 加锁是为了防止多线程中多次实例化，以保证其唯一性
        synchronized (LOCK){
            if (sqlSessionFactory != null){
                return sqlSessionFactory;
            }
            String resource = "mybatis-config.xml";
            InputStream inputStream;
            try {
                inputStream = Resources.getResourceAsStream(resource);
                sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            }catch (IOException e){
                e.printStackTrace();
                return null;
            }
            return sqlSessionFactory;
        }
    }
}

7、运行代码：

package com.ssm.chapter3.main;

import com.ssm.mapper.RoleMapper;
import com.ssm.pojo.Role;
import com.ssm.utils.SqlSessionFactoryUtils;
import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;

/**
 * Created by czz on 2019/7/24.
 */
public class Chapter3Main {
    public static void main(String[] args) {
        Logger log = Logger.getLogger(Chapter3Main.class);
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.getSqlSessionFactory().openSession();
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
            Role role = roleMapper.getRole(1L);
            log.info(role.getRoleName());
        }finally {
            if (sqlSession!=null){
                sqlSession.close();
            }
        }
    }
}

8、jar包下载：
(1)mybatis 3.5.2（当前最新版）
官网
百度云 :提取码：xnjz
(2)数据库驱动包（mysql）:
百度云 :提取码：c963

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