mybatis 的mapper 实现

在项目里面，我们经常用到mybatis，多年前的hibernate已经慢慢被大家所抛弃。自从iteye被收购以后，好久没有写博客了，今年是要多写一些补一补。今天来聊一下mybatis的mapper实现。

   @Component

public interface ActivityMapper {
/**

• 添加奖品记录
• @param prizeEntity
• @return
  */
  int addGift(PrizeEntity prizeEntity);

/**
 * 添加预约记录
 * @param activityPrevueEntity
 * @return
 */
int addActivityPrevue(ActivityPrevueEntity activityPrevueEntity);

/**
 * 根据手机号和活动id获取该用户是否预约过
 * @param phone
 * @param activityId
 * @return
 */
int countPrevueByPhoneAndActivityId(@Param("phone")String phone, @Param("activityId")Integer activityId);

}

这是一个比较常见的mapper类的写法。在xml里面我们需要定义一个和方法名一样的id.

<?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="cn.vcinema.mapper.ActivityMapper">

<insert id="addGift" parameterType="cn.vcinema.model.PrizeEntity">
    insert into pumpkin_ius.activity_prize_record(user_id, activity_id, prize_code, create_time)
    values(#{userIdInt}, #{activityIdInt}, #{prizeCodeStr}, now())
</insert>

<insert id="addActivityPrevue" parameterType="cn.vcinema.model.ActivityPrevueEntity">
    insert into pumpkin_ius.activity_user_enroll(activity_id, user_id, user_phone, user_name, user_email, create_time)
    values(#{activityId}, #{userId}, #{userPhone}, #{userName}, #{userEmail}, now())
</insert>

<select id="countPrevueByPhoneAndActivityId" resultType="java.lang.Integer">
    select count(*) from pumpkin_ius.activity_user_enroll where user_phone = #{phone} and activity_id = #{activityId}
</select>

</mapper>

在serviceimpl里面，我们通过调用mapper就可以实现xml 的sql执行。

Gift gift = Lottery.lottery(giftList, defaultGift.get(0));
PrizeEntity prizeEntity = setPrizeValue(gift, user.getUserId(), activityId);
// 添加抽奖记录
activityMapper.addGift(prizeEntity);

需要给MyBatis提供Mapper接口和与之匹配的映射文件,就能够让MyBatis按照我们的需求执行到对应的SQL 这里的实现原理就动态代理

public class MapperProxy<T> implements InvocationHandler, Serializable {
private static final long serialVersionUID = -6424540398559729838L;
private final SqlSession sqlSession;
private final Class<T> mapperInterface;
private final Map<Method, MapperMethod> methodCache;

public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
    this.sqlSession = sqlSession;
    this.mapperInterface = mapperInterface;
    this.methodCache = methodCache;
}

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if(Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, args);
    } else {
        MapperMethod mapperMethod = this.cachedMapperMethod(method);
        return mapperMethod.execute(this.sqlSession, args);
    }
}

private MapperMethod cachedMapperMethod(Method method) {
    MapperMethod mapperMethod = (MapperMethod)this.methodCache.get(method);
    if(mapperMethod == null) {
        mapperMethod = new MapperMethod(this.mapperInterface, method, this.sqlSession.getConfiguration());
        this.methodCache.put(method, mapperMethod);
    }

    return mapperMethod;
}

}

在invoke方法中可以看到,如果我们调用的是Object中的方法,不做任何处理,直接调用,否则执行:
mapperMethod.execute(this.sqlSession, args);

这里是用jdk的动态代理来实现了自动调用。

在开发的时候，我们有时候不写xml ，通过注解的形式直接实现调用，查看例子。

@Component
public interface FeedbackMapper {
int insert(Feedback feedback);

/**
 * 添加用户意见反馈
 * @param userFeedback
 */
@Insert("  INSERT INTO `pumpkin_ius`.`user_feedback`(`phone`, `device`, `pc_device`, `pc_os`, `pc_channel`, `pc_ip`, `pc_platform`, `pc_version`, `pc_browser_name`, `pc_browser_version`, `play_feedback`, `program_feedback`, `other_feedback`) VALUES (#{phone},#{device},#{pc_device},#{pc_os},#{pc_channel},#{pc_ip},#{pc_platform},#{pc_version},#{pc_browser_name},#{pc_browser_version},#{play_feedback},#{program_feedback},#{other_feedback});")
void addUserFeedback(UserFeedback userFeedback);

}

当然，在SQL复杂的时候，还是写xml比较方便维护，看起来不那么难受。