Mybatis进阶

时间：2021-05-15 20:21:08 阅读：25 评论：0 收藏：0 [点我收藏+]

Mybatis高级特性

内容	说明	重要程度
Mybatis日志管理	Mybatis日志管理配置	??
动态SQL处理	多条件查询下的SQL的动态执行过程	?????
Mybatis缓存机制	介绍mybatis一二级缓存作用与配置	?????
多表级联查询	配置mybatis多表级联查询	??
PageHelper插件	mybatis分页插件的使用办法	?????

1. Mybatis日志管理

1.1 什么是日志

日志文件是用于记录系统操作的记录文件或文件集合
日志保存历史数据，是诊断问题的以及理解系统活动的重要依据

1.2 SLF4j与Logback

								日志门面
	Simple Logging Facede For Java			Apache Commons-Logging
			(SLF4J)
								|
							   桥接
								|
							    \/
							   
							 实现日志
			log4j   logback   java.util.logging(jul) 	...

1.3logback

<!--logback maven依赖-->
<dependency>
    <groupId>ch.qos.logback</groupId>
    <artifactId>logback-classic</artifactId>
    <version>1.2.3</version>
</dependency>

<!--logback.xml-->
<?xml version="1.0" encoding="UTF-8" ?>
<configuration>
    <appender name="console" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>[%thread] %d{HH:mm:ss.SSS} %-5level %logger{36} - %msg%n</pattern>
        </encoder>
    </appender>
    <!--
        日志输出级别（优先级高到低）
        error:错误 - 系统的故障日志
        warn:警告 - 存在风险或使用不当的日志
        info:一般性消息
        debug:程序内部用于调试信息
        trace:程序运行的跟踪信息
    -->
    <root level="debug">
        <appender-ref ref="console"/>
    </root>
</configuration>

2.Mybatis动态SQL

2.1动态SQL

动态SQL是指根据参数数据动态组织SQL的技术

<select id="dynamicSQL" parameterType="java.util.Map" resultType="com.xiaofeng.mybatis.entity.Goods">
    select * from t_goods
    <where>
        <if test="categoryId!=null">
            and category_id=#{categoryId}
        </if>
        <if test="currentPrice!=null">
            and current_price&lt;#{currentPrice}
        </if>
    </where>
</select>

@Test
public void testDynamicSQL() throws  Exception{
    SqlSession session = null;
    try {
        session = MybatisUtils.openSession();
        //看这里
        Map param = new HashMap();
        param.put("currentPrice",500);
        param.put("categoryId",44);
        //查询条件
        List<Goods> list = session.selectList("goods.dynamicSQL", param);
        for (Goods g : list) {
            System.out.println(g.getTitle()+":"+g.getCategoryId() + ":" + g.getCurrentPrice());
        }
    } catch (Exception e) {
        throw  e;
    } finally {
        MybatisUtils.closeSession(session);
    }
}

3.MyBatis二级缓存

1.一级缓存默认开启，缓存范围SqlSession会话
2.二级缓存手动开启，属于范围Mapper Namespace

二级缓存运行规则

1.二级开启后默认所有查询操作均使用缓存
2.写操作commit提交时对该namespace缓存强制清空
3.配置useCache="false"可以不使用缓存
4.配置flushCache="true"代表强制清空缓存

//一级缓存测试
@Test
public void testLv1Cache() {
    SqlSession session = null;
    try {
        session = MybatisUtils.openSession();
        Goods goods = session.selectOne("goods.selectById", 739);
        Goods goods1 = session.selectOne("goods.selectById", 739);
        System.out.println(goods.getTitle());
        System.out.println(goods1.getTitle());
        System.out.println(goods.hashCode()+":"+goods1.hashCode());
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        MybatisUtils.closeSession(session);
    }
    try {
        session = MybatisUtils.openSession();
        Goods goods = session.selectOne("goods.selectById", 739);
        session.commit();//commit提交时对该namespace缓存强制清空
        Goods goods1 = session.selectOne("goods.selectById", 739);
        System.out.println(goods.getTitle());
        System.out.println(goods1.getTitle());
        System.out.println(goods.hashCode()+":"+goods1.hashCode());
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        MybatisUtils.closeSession(session);
    }
}
//二级缓存测试
@Test
public void testLv2Cache() {
    SqlSession session = null;
    try {
        session = MybatisUtils.openSession();
        Goods goods = session.selectOne("goods.selectById", 739);
        System.out.println(goods.getTitle());

    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        MybatisUtils.closeSession(session);
    }
    try {
        session = MybatisUtils.openSession();
        Goods goods = session.selectOne("goods.selectById", 739);
        System.out.println(goods.getTitle());
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        MybatisUtils.closeSession(session);
    }
}

<!-- 开启了二级缓存-->
<!-- 
	eviction是缓存的清除策略，当缓存对象数量达到上限后，自动触发对应算法对缓存对象清除
		1.LRU - 最近最久未使用：移除最长时间不被使用的对象
			o1 o2 o3 o4 ... o512
			14 99 83  1 ...  893
		2.FIFO - 先进先出：按对象进入缓存的顺序来移除它们
		3.SOFT - 软引用： 移除基于垃圾收集器状态和软引用规则的对象(jvm)
		4.WEAK - 弱引用：更积极的移除基于垃圾收集器状态和弱引用规则的对象（jvm）
		5.LFU - 最近最少使用：移除最近访问频率最低的对象
	flushInterval 代表间隔多长时间自动清空缓存，单位毫秒，600000毫秒=10分钟
	size  缓存存储上限，用于保存对象或集合（1个集合算1个对象）的数量上限
	readOnly 设置为true，代表返回只读缓存，每次从缓存取出放入是缓存对象本身，这种执行效率较高
			设置为false，代表每次取出的是缓存对象的“副本”，每一次取出的对象都是不同的，这种安全性较高
-->
<cache eviction="LRU" flushInterval="600000" size="512" readOnly="true"/>

4.多表级联查询

4.1OneToMany对象关联查询

<!--goods.xml-->
    <!--
        resultMap可用于说明一对多或者多对一的映射逻辑
        id是resultMap属性引用的标志
        type是指向One的实体（Goods）
    -->
    <resultMap id="rmGoods1" type="com.xiaofeng.mybatis.entity.Goods">
        <!--映射goods对象的主键到goods_id字段-->
        <id column="goods_id" property="goodsId"></id>
        <!--
           collection的含义是，
           在select * from t_goods limit 0,10 得到结果后，对所有Goods对象遍历得到goods_id字段值，并代入到goodsDetail命名空间的selectByGoodsId的SQL中进行查询，将得到的“商品详情”集合赋值给goodsDetail List 对象
        -->
        <collection property="goodsDetails" select="goodsDetail.selectByGoodsId" column="goods_id"/>
    </resultMap>
    <select id="selectOneToMany" resultMap="rmGoods1">
    	select * from t_goods limit 0 ,1
	</select>

<!--goods_detail.xml-->
<mapper namespace="goodsDetail">
    <select id="selectByGoodsId" resultType="com.xiaofeng.mybatis.entity.GoodsDetail" parameterType="Integer">
        select * from  t_goods_detail where goods_id=#{value}
    </select>
</mapper>

@Test
public void testOneToMany() {
    SqlSession session = null;
    try {
        session = MybatisUtils.openSession();
        //看这里
       List<Goods>  list = session.selectList("goods.selectOneToMany");
       for(Goods g:list){
           System.out.println(g.getTitle());
       }

    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        MybatisUtils.closeSession(session);
    }

}

//Goods实体类
public class Goods {
    private Integer goodsId;
    private String  title;
    private String  subTitle;
    private Float originalCost;
    private Float currentPrice;
    private Float  discount;
    private Integer isFreeDelivery;
    private Integer categoryId;
    private List<GoodsDetail> goodsDetails; //GoodsDetail

    public List<GoodsDetail> getGoodsDetails() {
        return goodsDetails;
    }

    public void setGoodsDetails(List<GoodsDetail> goodsDetails) {
        this.goodsDetails = goodsDetails;
    }

    public Integer getGoodsId() {
        return goodsId;
    }

    public void setGoodsId(Integer goodsId) {
        this.goodsId = goodsId;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getSubTitle() {
        return subTitle;
    }

    public void setSubTitle(String subTitle) {
        this.subTitle = subTitle;
    }

    public Float getOriginalCost() {
        return originalCost;
    }

    public void setOriginalCost(Float originalCost) {
        this.originalCost = originalCost;
    }

    public Float getCurrentPrice() {
        return currentPrice;
    }

    public void setCurrentPrice(Float currentPrice) {
        this.currentPrice = currentPrice;
    }

    public Float getDiscount() {
        return discount;
    }

    public void setDiscount(Float discount) {
        this.discount = discount;
    }

    public Integer getIsFreeDelivery() {
        return isFreeDelivery;
    }

    public void setIsFreeDelivery(Integer isFreeDelivery) {
        this.isFreeDelivery = isFreeDelivery;
    }

    public Integer getCategoryId() {
        return categoryId;
    }

    public void setCategoryId(Integer categoryId) {
        this.categoryId = categoryId;
    }

    
}

//GoodsDetail实体类
public class GoodsDetail {
    private Integer gdId;
    private Integer goodsId;
    private String gdPicUrl;
    private Integer gdOrder;

    public Integer getGdId() {
        return gdId;
    }

    public void setGdId(Integer gdId) {
        this.gdId = gdId;
    }

    public Integer getGoodsId() {
        return goodsId;
    }

    public void setGoodsId(Integer goodsId) {
        this.goodsId = goodsId;
    }

    public String getGdPicUrl() {
        return gdPicUrl;
    }

    public void setGdPicUrl(String gdPicUrl) {
        this.gdPicUrl = gdPicUrl;
    }

    public Integer getGdOrder() {
        return gdOrder;
    }

    public void setGdOrder(Integer gdOrder) {
        this.gdOrder = gdOrder;
    }
}

4.2ManyToOne对象关联查询

<!--goods_detail.xml-->
<resultMap id="rmGoodsDetail" type="com.xiaofeng.mybatis.entity.GoodsDetail">
    <id column="gd_id" property="gdId"></id>
    <result column="goods_id" property="goodsId"></result>
    <association property="goods" select="goods.selectById" column="goods_id"></association>
</resultMap>
<select id="selectManyToOne"  resultMap="rmGoodsDetail">
    select * from t_goods_detail limit 0,20
</select>

<!--goods.xml-->
<select id="selectById" parameterType="Integer" resultType="com.xiaofeng.mybatis.entity.Goods">
    select * from t_goods where goods_id=#{value}
</select>

@Test
public void testManyToOne() {
    SqlSession session = null;
    try {
        session = MybatisUtils.openSession();
        //看这里
        List<GoodsDetail>  list = session.selectList("goodsDetail.selectManyToOne");
        for(GoodsDetail gd:list){
            System.out.println(gd.getGdPicUrl()+":"+gd.getGoods().getTitle());
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        MybatisUtils.closeSession(session);
    }

}

//GoodsDetail实体类
public class GoodsDetail {
    private Integer gdId;
    private Integer goodsId;
    private String gdPicUrl;
    private Integer gdOrder;
    private Goods goods; //Goods实体

    public Goods getGoods() {
        return goods;
    }

    public void setGoods(Goods goods) {
        this.goods = goods;
    }

    public Integer getGdId() {
        return gdId;
    }

    public void setGdId(Integer gdId) {
        this.gdId = gdId;
    }

    public Integer getGoodsId() {
        return goodsId;
    }

    public void setGoodsId(Integer goodsId) {
        this.goodsId = goodsId;
    }

    public String getGdPicUrl() {
        return gdPicUrl;
    }

    public void setGdPicUrl(String gdPicUrl) {
        this.gdPicUrl = gdPicUrl;
    }

    public Integer getGdOrder() {
        return gdOrder;
    }

    public void setGdOrder(Integer gdOrder) {
        this.gdOrder = gdOrder;
    }
}

//Goods实体类
public class Goods {
    private Integer goodsId;
    private String  title;
    private String  subTitle;
    private Float originalCost;
    private Float currentPrice;
    private Float  discount;
    private Integer isFreeDelivery;
    private Integer categoryId;
    private List<GoodsDetail> goodsDetails;

    public List<GoodsDetail> getGoodsDetails() {
        return goodsDetails;
    }

    public void setGoodsDetails(List<GoodsDetail> goodsDetails) {
        this.goodsDetails = goodsDetails;
    }

    public Integer getGoodsId() {
        return goodsId;
    }

    public void setGoodsId(Integer goodsId) {
        this.goodsId = goodsId;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getSubTitle() {
        return subTitle;
    }

    public void setSubTitle(String subTitle) {
        this.subTitle = subTitle;
    }

    public Float getOriginalCost() {
        return originalCost;
    }

    public void setOriginalCost(Float originalCost) {
        this.originalCost = originalCost;
    }

    public Float getCurrentPrice() {
        return currentPrice;
    }

    public void setCurrentPrice(Float currentPrice) {
        this.currentPrice = currentPrice;
    }

    public Float getDiscount() {
        return discount;
    }

    public void setDiscount(Float discount) {
        this.discount = discount;
    }

    public Integer getIsFreeDelivery() {
        return isFreeDelivery;
    }

    public void setIsFreeDelivery(Integer isFreeDelivery) {
        this.isFreeDelivery = isFreeDelivery;
    }

    public Integer getCategoryId() {
        return categoryId;
    }

    public void setCategoryId(Integer categoryId) {
        this.categoryId = categoryId;
    }


}

5. PageHelper分页插件

5.1 分页查询的麻烦事

1. 当前页数据查询 - select * from tab limit 0 , 10
2. 总记录数查询 - select count（*） from tab
3. 程序计算总页数、上一页页码、下一页页码

5.2 PageHelper使用流程

1.maven引入PageHelper与jsqlparser
2.mybatis-config.xml增加Plugin配置
3.代码中使用PageHelper.startPage()自动分页

<!--maven pom.xml-->
<!--pageHelper分页插件-->
<dependency>
    <groupId>com.github.pagehelper</groupId>
    <artifactId>pagehelper</artifactId>
    <version>5.1.10</version>
</dependency>
<!--sql 解析工具-->
<dependency>
    <groupId>com.github.jsqlparser</groupId>
    <artifactId>jsqlparser</artifactId>
    <version>2.0</version>
</dependency>

<!--mybatis-config.xml-->
<!--启用PageHelper分页插件-->
<plugins>
    <plugin interceptor="com.github.pagehelper.PageInterceptor">
        <!--设置数据库类型-->
        <property name="helperDialect" value="mysql"/>
        <!--分页合理化-->
        <property name="reasonable" value="true"/>
    </plugin>
</plugins>

/**
 * PageHelper分页查询
 */
@Test
public void testSelectPage() {
    SqlSession session = null;
    try {
        session = MybatisUtils.openSession();
        //startPage方法会自动将下一次查询进行分页
        PageHelper.startPage(2,10);
        Page<Goods> page=(Page) session.selectList("goods.selectPage");
        System.out.println("总页数："+page.getPages());
        System.out.println("总记录数："+page.getTotal());
        System.out.println("开始行号："+page.getStartRow());
        System.out.println("结束行号："+page.getEndRow());
        System.out.println("当前页码："+page.getPageNum());
        List<Goods> data=page.getResult();//当前页数据
        for(Goods g:data){
            System.out.println(g.getTitle());
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        MybatisUtils.closeSession(session);
    }
}

5.3 不同数据库的分页实现原理

5.3.1 MySQL分页

select * from table limit 10,20;

5.3.2 Oracle分页

select t3.* from(
	select t2.*,rownum as row_num from(
		select * from table order by id asc 
	) t2 
	where rownum<=20
) t3
where t2.row_num>11;

5.3.3 SQL Server 2000 分页

select top 3 * from table
where
	id not in 
	(select top 15 id from table)

5.3.4 SQL Server 2012+ 分页

select * from table order by id 
	offset 4 rows fetch next 5 rows only

6. MyBatis整合C3P0连接池

<!--maven pox.xml-->
<!--c3p0连接池-->
<dependency>
    <groupId>com.mchange</groupId>
    <artifactId>c3p0</artifactId>
    <version>0.9.5.4</version>
</dependency>

import com.mchange.v2.c3p0.ComboPooledDataSource;
import org.apache.ibatis.datasource.unpooled.UnpooledDataSourceFactory;

/**
 * C3P0与Mybatis兼容使用的数据源工厂类
 */
public class C3P0DataSource extends UnpooledDataSourceFactory {
    public C3P0DataSource(){
        this.dataSource=new ComboPooledDataSource();
    }

}

  <!-- mybatis-config.xml -->
<environment id="dev">
    <!--采用JDBC方式对数据库事务进行commit/rollback-->
    <transactionManager type="JDBC"></transactionManager>
    <!--采用C3P0连接池方式管理数据库连接-->
    <dataSource type="com.xiaofeng.mybatis.datasource.C3P0DataSource">
        <property name="driverClass" value="com.mysql.cj.jdbc.Driver"/>
        <property name="jdbcUrl"
                  value="jdbc:mysql://localhost:3306/babytun?useSSL=false&amp;useUnicode=true&amp;characterEncoding=UTF-8&amp;serverTimezone=Asia/Shanghai&amp;allowPublicKeyRetrieval=true"/>
        <property name="user" value="root"/>
        <property name="password" value="root"/>
        <property name="initialPoolSize" value="5"/>
        <property name="maxPoolSize" value="20"/>
        <property name="minPoolSize" value="5"/>
    </dataSource>
</environment>

7. MyBatis批处理

7.1 批量插入数据

 <!--
	批量插入数据的局限：
		1.无法获得插入数据的id
		2.批量生成的SQL太长，可能会被服务器拒绝
-->
 <!--
	insert into table
	value("a","a1","a2"),("b","b1","b2")
-->
<insert id="batchInsert" parameterType="java.util.List">
    INSERT INTO babytun.t_goods( title, sub_title, original_cost, current_price, discount, is_free_delivery, category_id)
    VALUES
    <foreach collection="list" item="item" index="index" separator=",">
        (#{item.title},#{item.subTitle},#{item.originalCost},#{item.currentPrice},#{item.discount},#{item.isFreeDelivery},#{item.categoryId})
    </foreach>
</insert>

  /**
   * 批量插入数据
   * @throws Exception
   */
@Test
public void testBatchInsert() throws Exception {
    SqlSession session = null;
    try {
        long st=new Date().getTime();//开始时间
        session = MybatisUtils.openSession();
        //看这里
        List list=new ArrayList();
        for(int i=0;i<1000;i++){
            Goods goods=new Goods();
            goods.setTitle("批量插入测试数据");
            goods.setSubTitle("批量插入测试子标题");
            goods.setOriginalCost(100f);
            goods.setCurrentPrice(100f);
            goods.setDiscount(1f);
            goods.setIsFreeDelivery(1);
            goods.setCategoryId(43);
            //insert()方法返回值代表本次成功插入的记录总数
            list.add(goods);
        }
        int num = session.insert("goods.batchInsert", list);
        session.commit();//提交事务数据
        long et=new Date().getTime();//结束时间
        System.out.println("执行时间："+(et-st)+"毫秒");

    } catch (Exception e) {
        if (session!=null){
            session.rollback();
        }
        throw e;
    } finally {
        MybatisUtils.closeSession(session);
    }
}

7.2 批量删除数据

<delete id="batchDelete" parameterType="java.util.List">
    delete from t_goods where goods_id in
    <foreach collection="list" index="index" item="item" open="(" close=")" separator=",">
        #{item}
    </foreach>
</delete>

/**
 * 批量删除数据
 * @throws Exception
 */
@Test
public void testBatchDelete() throws Exception {
    SqlSession session = null;
    try {
        long st=new Date().getTime();//开始时间
        session = MybatisUtils.openSession();
        List list=new ArrayList();
        for(int i=12684;i<13683;i++){
            list.add(i);
        }
        int num = session.insert("goods.batchDelete", list);
        session.commit();//提交事务数据
        long et=new Date().getTime();//结束时间
        System.out.println("执行时间："+(et-st)+"毫秒");

    } catch (Exception e) {
        if (session!=null){
            session.rollback();
        }
        throw e;
    } finally {
        MybatisUtils.closeSession(session);
    }
}

8.MyBatis注解开发

8.1 Mybatis常用注解

注解	对应XML	说明
@Insert	< insert >	新增SQL
@Update	< update>	更新SQL
@Delete	< delete>	删除SQL
@Select	< select >	查询SQL
@Param	- -	参数映射
@Results	< resultMap >	结果映射
@Result	< id >< result >	字段映射

8.2 查询 @Select

   <!--mybatis-config.xml-->
<mappers>
        <!--两者二选一即可-->
        <mapper class="com.xiaofeng.mybatis.dao.GoodsDAO"/>
<!--   <package name="com.xiaofeng.mybatis.dao"/>-->
    </mappers>

//goodsDAO.class 这个名千万不要写成goodsDao  一定要写成xxxDAO
import com.xiaofeng.mybatis.entity.Goods;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface GoodsDAO {
    @Select("select * from t_goods where current_price between #{min} and #{max} order by current_price limit 0,#{limt}")
    public List<Goods> selectByPriceRange(@Param("min") Float min, @Param("max") Float max, @Param("limt")Integer limt);
}

@Test
public void testSelectByPriceRange() throws Exception {
    SqlSession session = null;
    try {
        session = MybatisUtils.openSession();
        //看这里
        GoodsDAO goodsDAO= session.getMapper(GoodsDAO.class);
        List<Goods> list=goodsDAO.selectByPriceRange(100f,500f,20);
        System.out.println(list.size());

    } catch (Exception e) {
        throw  e;
    } finally {
        MybatisUtils.closeSession(session);
    }
}

8.3 新增 @Insert

import com.xiaofeng.mybatis.entity.Goods;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.SelectKey;

import java.util.List;

public interface GoodsDAO {
    @Insert("INSERT INTO t_goods(title, sub_title, original_cost, current_price, discount, is_free_delivery, category_id) VALUES (#{title},#{subTitle},#{originalCost},#{currentPrice},#{discount},#{isFreeDelivery},#{categoryId})")
    @SelectKey(statement = "select last_insert_id()", before = false, keyProperty = "goodsId", resultType = Integer.class)
    public int insert(Goods goods);
}

@Test
public void testInsert() throws Exception {
    SqlSession session = null;
    try {
        session = MybatisUtils.openSession();
        //看这里
        Goods goods = new Goods();
        goods.setTitle("测试数据");
        goods.setSubTitle("测试子标题");
        goods.setOriginalCost(300f);
        goods.setCurrentPrice(200f);
        goods.setDiscount(0.7f);
        goods.setIsFreeDelivery(0);
        goods.setCategoryId(44);
        GoodsDAO goodsDAO= session.getMapper(GoodsDAO.class);
         //insert()方法返回值代表本次成功插入的记录总数
        int num=goodsDAO.insert(goods);
        session.commit();//提交事务数据
        System.out.println(goods.getGoodsId());

    } catch (Exception e) {
        if (session != null) {
            session.rollback();//回滚事务
        }
        throw  e;
    } finally {
        MybatisUtils.closeSession(session);
    }
}

8.4 结果映射 @Results

//GoodsDAO.java
import com.xiaofeng.mybatis.dto.GoodsDTO;
import com.xiaofeng.mybatis.entity.Goods;
import org.apache.ibatis.annotations.*;

import java.util.List;

public interface GoodsDAO {
    @Select("select * from t_goods")
    //<resultMap>
    @Results({
            //<id>
            @Result(column = "goods_id", property = "goodsId", id = true),
            //<result>
            @Result(column = "title", property = "title"),
            @Result(column = "current_price", property = "currentPrice")
    })
    public List<GoodsDTO> selectAll();
}

@Test
public  void testSelectAll() throws Exception{
    SqlSession session = null;
    try {
        session = MybatisUtils.openSession();
		//看这里
        GoodsDAO goodsDAO= session.getMapper(GoodsDAO.class);
        List<GoodsDTO> list=goodsDAO.selectAll();
        System.out.println(list.size());

    } catch (Exception e) {

        throw  e;
    } finally {
        MybatisUtils.closeSession(session);
    }
}

//GoodsDTO.java
//Data Transfer Object 数据传输对象
public class GoodsDTO {
    private Integer goodsId;
    private String title;
    private Float currentPrice;

    public Integer getGoodsId() {
        return goodsId;
    }

    public void setGoodsId(Integer goodsId) {
        this.goodsId = goodsId;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public Float getCurrentPrice() {
        return currentPrice;
    }

    public void setCurrentPrice(Float currentPrice) {
        this.currentPrice = currentPrice;
    }
}

Mybatis进阶

原文：https://www.cnblogs.com/xiaofengrong/p/14771950.html

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