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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