mybatis 使用经验小结

一、多数据源问题

主要思路是把dataSource、sqlSesstionFactory、MapperScannerConfigurer在配置中区分开，各Mapper对应的包名、类名区分开

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:tx="http://www.springframework.org/schema/tx" xmlns:jdbc="http://www.springframework.org/schema/jdbc"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="
     http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd
     http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
     http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-3.0.xsd
     http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
     http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.0.xsd"
       default-autowire="byName">

    <bean id="dataSource1" class="org.h2.jdbcx.JdbcConnectionPool"
          destroy-method="dispose">
        <constructor-arg>
            <bean class="org.h2.jdbcx.JdbcDataSource">
                <property name="URL" value="jdbc:h2:r:/h2db/awbprint/a"/>
                <property name="user" value="sa"/>
                <property name="password" value="sa"/>
            </bean>
        </constructor-arg>
    </bean>


    <bean id="dataSource2" class="org.h2.jdbcx.JdbcConnectionPool"
          destroy-method="dispose">
        <constructor-arg>
            <bean class="org.h2.jdbcx.JdbcDataSource">
                <property name="URL" value="jdbc:h2:r:/h2db/awbprint/b"/>
                <property name="user" value="sa"/>
                <property name="password" value="sa"/>
            </bean>
        </constructor-arg>
    </bean>

    <bean id="sqlSessionFactory1" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource1"/>
        <property name="configLocation" value="classpath:mybatis-config.xml"></property>
        <property name="typeAliasesPackage" value="awbprint.mybatis.entity"></property>
        <property name="mapperLocations" value="classpath:mybatis/a/**/*.xml"></property>
    </bean>

    <bean id="sqlSessionFactory2" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource2"/>
        <property name="configLocation" value="classpath:mybatis-config.xml"></property>
        <property name="typeAliasesPackage" value="awbprint.mybatis.entity"></property>
        <property name="mapperLocations" value="classpath:mybatis/b/**/*.xml"></property>
    </bean>

    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory1"></property>
        <property name="basePackage" value="awbprint.mybatis.mapper.a"/>
    </bean>

    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory2"></property>
        <property name="basePackage" value="awbprint.mybatis.mapper.b"/>
    </bean>


</beans>

上面的配置，一个连h2的a数据库，一个连h2的b数据库，至于事务管理器，大家可参考这个思路，建二个，各管各的。

项目中mapper接口及映射文件均用包名区分开，如下图：

二、如何使用Map做为参数及动态条件生成

    <resultMap id="BaseResultMap" type="awbprint.mybatis.entity.PrintLayout">
        <id column="D_RECID" property="recid" jdbcType="DECIMAL"/>
        <result column="D_USER_NAME" property="userName" jdbcType="VARCHAR"/>
        <result column="D_NAME" property="name" jdbcType="VARCHAR"/>
        <result column="D_TYPE" property="type" jdbcType="VARCHAR"/>
        ...
       
    </resultMap>

   <sql id="Base_Column_List">
        D_RECID, D_USER_NAME, D_NAME, D_TYPE, ...
    </sql>

    <select id="select" resultMap="BaseResultMap"
            parameterType="java.util.Map">
        select
        <include refid="Base_Column_List"/>
        from T_PRINT_LAYOUT
        where D_USER_NAME = #{userName,jdbcType=VARCHAR} and D_TYPE = #{awbType,jdbcType=VARCHAR}
        <if test="recId != null">
            and D_RECID = #{recId,jdbcType=DECIMAL}
        </if>
        <if test="ids != null">
            or D_RECID in
            <foreach item="item" index="index" collection="ids"
                     open="(" separator="," close=")">
                #{item}
            </foreach>
        </if>

    </select>

14-31演示了如何使用Map做为参数，动态传入查询条件，及List参数生成in(...)条件

java端代码示例：

        PrintLayoutMapper mapper = context.getBean(PrintLayoutMapper.class);
        
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("userName", "ADMIN");
        map.put("awbType", "CARGOLABEL_MU");
        map.put("recId", 1);
        
        List<Integer> ids = new ArrayList<Integer>();
        ids.add(0, 1);
        ids.add(0, 2);
        ids.add(0, 3);
        
        map.put("ids", ids);

        List<?> list = mapper.select(map);

其实PrintLayoutMapper接口的定义为：

public interface PrintLayoutMapper {    
    ...
    
    List<PrintLayout> select(Map<String, Object> map);
}

最终生成的SQL语句为：

select D_RECID, D_USER_NAME, D_NAME, D_TYPE, ... from T_PRINT_LAYOUT where D_USER_NAME = ? and D_TYPE = ? and D_RECID = ? or D_RECID in ( ? , ? , ? )

三、兼容不同的数据库

<insert id="insert">
 <selectKey keyProperty="id" resultType="int" order="BEFORE">
 <if test="_databaseId == 'oracle'">
 select seq_users.nextval from dual
 </if>
 <if test="_databaseId == 'db2'">
 select nextval for seq_users from sysibm.sysdummy1"
 </if>
 </selectKey>
 insert into users values (#{id}, #{name})
</insert>

这是官方文档上的示例，演示了如何兼容oracle与db2这二种不同的数据库，来获取序列的下一个值

四、加强版的分支、选择判断

<select id="findActiveBlogLike"
 resultType="Blog">
 SELECT * FROM BLOG WHERE state = ‘ACTIVE’
 <choose>
 <when test="title != null">
 AND title like #{title}
 </when>
 <when test="author != null and author.name != null">
 AND author_name like #{author.name}
 </when>
 <otherwise>
 AND featured = 1
 </otherwise>
 </choose>
</select>

这也是官方文档上的示例，因为<if>...</if>并没对应的<else>标签，所以要达到<if>...<else>...</else> </if>的效果，得借助<choose>、<when>、<otherwise>组合使用。

五、避免Where 空条件的尴尬

<select id="findActiveBlogLike" resultType="Blog">
 SELECT * FROM BLOG
 WHERE
 <if test="state != null">
 state = #{state}
 </if> 
</select>

如果state参数为空时，最终生成SQL语句为 

 SELECT * FROM BLOG
 WHERE

执行会出错，当然，你可以在where 后加一个1=1，改成

<select id="findActiveBlogLike" resultType="Blog">
 SELECT * FROM BLOG
 WHERE 1=1
 <if test="state != null">
 and state = #{state}
 </if> 
</select>

但是这个做法不太“环保”（毕竟引入了一个垃圾条件），其实只要改成<where>...</where>即可

<select id="findActiveBlogLike" resultType="Blog">
 SELECT * FROM BLOG
 <where>
     <if test="state != null">
         and state = #{state}
     </if>
 </where> 
</select>

六、$与#的区别

 select * from T_PRINT_LAYOUT where  D_RECID = ${recId}

最后生成的SQL为：

select * from T_PRINT_LAYOUT where  D_RECID = 1

即：直接将参数值替换到了原来${recId}的位置，相当于硬拼SQL

 select * from T_PRINT_LAYOUT where  D_RECID = #{recid,jdbcType=DECIMAL}

最后生成的SQL为：

select * from T_PRINT_LAYOUT where  D_RECID = ?

即：#{...}被识别为一个SQL参数

七、大量数据的批量insert

大量数据(条数>10000)做insert时，如果按常规方式，每条insert into table(...) values(...);来提交，速度巨慢。改善性能的思路是多条insert批量提交。

oracle环境中，有一种批量insert的小技巧，原理是 insert into ... select from ...，套在mybatis上，变形为：

INSERT INTO T_TEST
  (ID, COL_A, COL_B)
  SELECT SEQ_TEST.NEXTVAL, A.*
    FROM (
              SELECT 'A1', 'B1' FROM DUAL
    UNION ALL SELECT 'A2', 'B2' FROM DUAL
    UNION ALL SELECT 'A3', 'B3' FROM DUAL
    UNION ALL SELECT 'A4', 'B4' FROM DUAL
    UNION ALL SELECT 'A5', 'B5' FROM DUAL
    UNION ALL SELECT 'A6', 'B6' FROM DUAL
    ) A

中间的部分非常有规律，可以用foreach标签生成，参考下面的片段：

<insert id="insertBatch2" parameterType="ctas.entity.SharkFlt">
    <selectKey keyProperty="recId" order="BEFORE" resultType="Long">
      select SEQ_CTAS_SHARK_FLT.nextval as recId from dual
    </selectKey>
    insert into CTAS_SHARK_FLT (<include refid="Base_Column_List"/>) SELECT SEQ_TEST.NEXTVAL, A.*
    FROM (
    <foreach collection="list" item="item" index="index" open="" close="" separator="union all">
      select #{item.awbType,jdbcType=VARCHAR}, #{item.awbPre,jdbcType=VARCHAR},... from dual
    </foreach>
    ) A
  </insert>

即使这样，也不能直接run，oracle中一次执行的sql语句长度是有限制的，如果最后拼出来的sql字符串过长，会导致执行失败，所以java端还要做一个分段处理，参考下面的处理:

        List<SharkFlt> data = new ArrayList<SharkFlt>();
        for (TSharkFlt f : sharkFlts) {
            data.add(getSharkFlt(f));
        }

        System.out.println(data.size());

        long beginTime = System.currentTimeMillis();
        System.out.println("开始插入...");
        SqlSessionFactory sqlSessionFactory = ctx.getBean(SqlSessionFactory.class);
        SqlSession session = null;
        try {
            session = sqlSessionFactory.openSession(ExecutorType.BATCH, false);
            int a = 2000;//每次提交2000条
            int loop = (int) Math.ceil(data.size() / (double) a);

            List<SharkFlt> tempList = new ArrayList<SharkFlt>(a);
            int start, stop;
            for (int i = 0; i < loop; i++) {
                tempList.clear();
                start = i * a;
                stop = Math.min(i * a + a - 1, data.size() - 1);
                System.out.println("range:" + start + " - " + stop);
                for (int j = start; j <= stop; j++) {
                    tempList.add(data.get(j));
                }
                session.insert("ctas.importer.writer.mybatis.mappper.SharkFltMapper.insertBatch2", tempList);
                session.commit();
                session.clearCache();
                System.out.println("已经插入" + (stop + 1) + " 条");
            }
        } catch (Exception e) {
            e.printStackTrace();
            session.rollback();
        } finally {
            if (session != null) {
                session.close();
            }
        }
        long endTime = System.currentTimeMillis();
        System.out.println("插入完成，耗时 " + (endTime - beginTime) + " 毫秒！");

13,27-29这几行是关键，这一段逻辑会经常使用，为了重用，可以封装一下：

    /**
     * 批量提交数据
     * @param sqlSessionFactory
     * @param mybatisSQLId SQL语句在Mapper XML文件中的ID
     * @param commitCountEveryTime 每次提交的记录数
     * @param list 要提交的数据列表
     * @param logger 日志记录器
     */
    private <T> void batchCommit(SqlSessionFactory sqlSessionFactory, String mybatisSQLId, int commitCountEveryTime, List<T> list, Logger logger) {
        SqlSession session = null;
        try {
            session = sqlSessionFactory.openSession(ExecutorType.BATCH, false);
            int commitCount = (int) Math.ceil(list.size() / (double) commitCountEveryTime);
            List<T> tempList = new ArrayList<T>(commitCountEveryTime);
            int start, stop;
            Long startTime = System.currentTimeMillis();
            for (int i = 0; i < commitCount; i++) {
                tempList.clear();
                start = i * commitCountEveryTime;
                stop = Math.min(i * commitCountEveryTime + commitCountEveryTime - 1, list.size() - 1);
                for (int j = start; j <= stop; j++) {
                    tempList.add(list.get(j));
                }
                session.insert(mybatisSQLId, tempList);
                session.commit();
                session.clearCache();
            }
            Long endTime = System.currentTimeMillis();
            logger.debug("batchCommit耗时：" + (endTime - startTime) + "毫秒");
        } catch (Exception e) {
            logger.error("batchCommit error!", e);
            e.printStackTrace();
            session.rollback();
        } finally {
            if (session != null) {
                session.close();
            }
        }
    }

对应的，如果是批量update，也是类似的思路，只不过要注意一点：oracle环境中，多条语句提交的sql语句为

begin

　　update xxx set xxx =xxx ;

　　update xxx set xxx =xxx;

end;

用mytais拼的时候，参考下面的写法：

  <update id="updateBatch" parameterType="java.util.List">
    <foreach collection="list" item="item" index="index" open="begin" close="end;" >
      update xxx set x=#{item.x,jdbcType=VARCHAR} where x =#{item.x,jdbcType=VARCHAR};
    </foreach>
  </update>

关于批量提交的性能，Oracle环境下，我大概测试了一下：

insert into ... select xxx

  union all select yyy

  union all select zzz;

最快，其次是

begin

  insert into ... values  ...;

  insert into ... values ...;

end;

当然最慢是逐条insert提交，最后谈下Spring与mybatis集成后，AOP事务管理 对 批量提交的影响 ，通常情况下，我们会这样配置AOP事务管理：

    <tx:advice id="txAdvice" transaction-manager="transactionManager">
        <tx:attributes>
            <tx:method name="do*" read-only="false" rollback-for="java.lang.Exception"/>
            <tx:method name="*" propagation="SUPPORTS" read-only="true"/>
        </tx:attributes>
    </tx:advice>

    <aop:config>
        <aop:pointcut id="pc" expression="execution(* ctas.service.*.*(..))"/>
        <aop:advisor pointcut-ref="pc" advice-ref="txAdvice"/>
    </aop:config>

这样，ctas.service（及子包）下的所有方法都被拦截，而且只有do开头的方法，具有可写的事务（即：能insert/update/delete记录），而其它方法是只读事务（即：只能select数据），但是我们前面谈到的批量提交操作，都是写代码手动提交的，不需要spring管理，所以配置中需要将某些方法排除，可以约定self开头的方法，由开发者自己管理事务，不需要spring代为管理，上面的配置要改成：

    <aop:config>
        <aop:pointcut id="pc" expression="execution(* ctas.service.*.*(..)) and !execution(* ctas.service.*.self*(..)))"/>
        <aop:advisor pointcut-ref="pc" advice-ref="txAdvice"/>
    </aop:config>

 通过 and !execution(...) 将self开头的方法排除就可以了，前面的批量操作代码写到selfXXX方法中。

关于批量提交，还有一种情况：父子表的批量插入。思路还是一样的，但是SQL的写法有点区别，原理参考下面的语句(Oracle环境)

DECLARE
  BASE_ID   INTEGER;
  DETAIL_ID INTEGER;
BEGIN
  --第1组记录
  SELECT SEQ_T_BASE.NEXTVAL INTO BASE_ID FROM DUAL;
  INSERT INTO T_BASE (ID, FEE) VALUES (BASE_ID, ?);
  
  SELECT SEQ_T_DETAIL.NEXTVAL INTO DETAIL_ID FROM DUAL;
  INSERT INTO T_DETAIL (ID, BASE_ID, FEE) VALUES (DETAIL_ID, BASE_ID, ?);
  SELECT SEQ_T_DETAIL.NEXTVAL INTO DETAIL_ID FROM DUAL;
  INSERT INTO T_DETAIL (ID, BASE_ID, FEE) VALUES (DETAIL_ID, BASE_ID, ?);
  
  --第2组记录
  SELECT SEQ_T_BASE.NEXTVAL INTO BASE_ID FROM DUAL;
  INSERT INTO T_BASE (ID, FEE) VALUES (BASE_ID, ?);
  
  SELECT SEQ_T_DETAIL.NEXTVAL INTO DETAIL_ID FROM DUAL;
  INSERT INTO T_DETAIL (ID, BASE_ID, FEE) VALUES (DETAIL_ID, BASE_ID, ?);
  SELECT SEQ_T_DETAIL.NEXTVAL INTO DETAIL_ID FROM DUAL;
  INSERT INTO T_DETAIL (ID, BASE_ID, FEE) VALUES (DETAIL_ID, BASE_ID, ?);
  
  --...
END;

xml映射文件中的写法：

    <insert id="insertBatch" parameterType="java.util.List">
        DECLARE
        base_id INTEGER ;
        detail_id INTEGER ;
        <foreach collection="list" item="item" index="index" open="begin" close="end;">
            select seq_t_base.nextval into base_id from dual;
            insert into t_base(id, fee) values(base_id, #{item.baseEntity.fee,jdbcType=DECIMAL});
            <foreach collection="item.details" item="detail" index="index">
                select seq_t_detail.nextval into detail_id from dual;
                insert into t_detail(id, base_id, fee) values(detail_id,base_id,#{detail.fee,jdbcType=DECIMAL});
            </foreach>
        </foreach>
    </insert>

 List中的Dto定义

public class BaseDetailDto {

    private TBase baseEntity;

    private List<TDetail> details;

    public TBase getBaseEntity() {
        return baseEntity;
    }

    public void setBaseEntity(TBase baseEntity) {
        this.baseEntity = baseEntity;
    }


    public List<TDetail> getDetails() {
        return details;
    }

    public void setDetails(List<TDetail> details) {
        this.details = details;
    }
}