Spring Mybatis PageHelper 设置使用

PageHelper是一个Mybatis的分页插件, 负责将已经写好的sql语句, 进行分页加工.

设置

现在使用的是PageHelper 5.0 版本 :

在build.gradle先引用jar包:

// https://mvnrepository.com/artifact/com.github.pagehelper/pagehelper
compile group: 'com.github.pagehelper', name: 'pagehelper', version: '5.0.0'

然后在mybatis的config文件中增加配置项, 我的config文件是 mybatis_general_config.xml:
注意里面的顺序非常重要一定要放在正确的位置

<?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>
    <!-- 引用db.properties配置文件 -->
    <!--<properties resource="config/mybatis/jdbc-mysql.properties"/>-->
    <properties resource="config/mybatis/jdbc-mssql.properties"/>



    <plugins>
        <!-- PageHelper4.1.1 -->
        <plugin interceptor="com.github.pagehelper.PageInterceptor">
            <property name="helperDialect" value="sqlserver"/>
            <property name="offsetAsPageNum" value="false"/>
            <property name="rowBoundsWithCount" value="false"/>
            <property name="pageSizeZero" value="true"/>
            <property name="reasonable" value="false"/>
            <property name="supportMethodsArguments" value="true"/>
            <property name="returnPageInfo" value="none"/>
        </plugin>
    </plugins>

    <!--
        development : 开发模式
        work : 工作模式
    -->
    <environments default="mssql_dev">
        <!--<environment id="development">-->
            <!--<transactionManager type="JDBC"/>-->
            <!--&lt;!&ndash; 配置数据库连接信息 &ndash;&gt;-->
            <!--<dataSource type="POOLED">-->
                <!--<property name="driver" value="${jdbc.driverClassName}"/>-->
                <!--<property name="url" value="${jdbc.url}"/>-->
                <!--<property name="username" value="${jdbc.user}"/>-->
                <!--<property name="password" value="${jdbc.pass}"/>-->
            <!--</dataSource>-->
        <!--</environment>-->
        <environment id="mssql_dev">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driverClassName}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>



    <mappers>
        <!--&lt;!&ndash; 注册userMapper.xml文件，-->
        <!--userMapper.xml位于me.gacl.mapping这个包下，所以resource写成me/gacl/mapping/userMapper.xml&ndash;&gt;-->
        <!--<mapper resource="resources/mapper/studentMapper.xml"/>-->
        <!--<mapper class="lyb.anno_mapper.StudentMapper"/>-->
        <!--<mapper class="lyb.mapper.StudentMapper"/>-->
        <!--<mapper resource="resources/mapper/classesMapper.xml"/>-->
        <!--<mapper resource="mybatis_mapper/StudentMapper.xml"/>-->
        <!--<mapper resource="mybatis_mapper/PosInReportMapper.xml"/>-->
        <mapper class="lyb.mapper.PosInReportMapper"/>
        <mapper class="lyb.mapper.SalesOutReportMapper"/>
        <mapper class="lyb.mapper.TransVouchMapper"/>
        <mapper class="lyb.mapper.CurrentStockMapper"/>
        <mapper class="lyb.mapper.Wcc_User_Customer_ConnMapper"/>
    </mappers>

</configuration>

**这里有个坑 : **

 <plugin interceptor="com.github.pagehelper.PageInterceptor">

这里的4.X版本的interceptor是PageHelper, 但是5.0版本后改成了PageInterceptor
如果设置的不对会报错.

有关具体设置详见:
https://pagehelper.github.io/docs/howtouse/

<!--
    plugins在配置文件中的位置必须符合要求，否则会报错，顺序如下:
    properties?, settings?,
    typeAliases?, typeHandlers?,
    objectFactory?,objectWrapperFactory?,
    plugins?,
    environments?, databaseIdProvider?, mappers?
-->
<plugins>
    <!-- com.github.pagehelper为PageHelper类所在包名 -->
    <plugin interceptor="com.github.pagehelper.PageInterceptor">
        <!-- 使用下面的方式配置参数，后面会有所有的参数介绍 -->
        <property name="param1" value="value1"/>
	</plugin>
</plugins>

如果顺序放置的不对, 也会出现不能初始化sqlSessionFactory的错误

代码里的使用方法 :

直接加上一个PageHelper的静态方法

PageHelper.startPage(2,10);
List<CurrentStockReport> reportList = mapper.getReport(params.getCustomer_code(),
        params.getRegion_name(),
        params.getInv_class_code(),
        params.getInvcode(),
        params.getBarcode());

仅有PageHelper.startPage(int pageNum, int pageSize) 后面的一个查询是会分页的, 我在这里使用的对应的mapper中的查询语句是:

SELECT
  CurrentStock.AutoID,
  Customer.cCusName,
  DistrictClass.cDCName,
  Customer.cCusCode,
  CurrentStock.cWhCode,
  CurrentStock.iQuantity as stock,
  CurrentStock.cBatch,
  Inventory.cInvStd,
  Inventory.cInvName,
  Inventory.cInvAddCode
FROM CurrentStock
  INNER JOIN Customer ON SUBSTRING(CurrentStock.cWhCode, 1, 6) = Customer.cCusCode
  INNER JOIN DistrictClass ON customer.cdccode = DistrictClass.cdccode
  INNER JOIN Inventory ON Inventory.cInvCode = CurrentStock.cInvCode;

而由plugin产生的sql语句是 :

SELECT TOP 10
  cCusName,
  AutoID,
  cDCName,
  cWhCode,
  stock,
  cBatch,
  cInvStd,
  cInvName,
  cInvAddCode
FROM (SELECT
        ROW_NUMBER()
        OVER (
          ORDER BY RAND() ) PAGE_ROW_NUMBER,
        cCusName,
        AutoID,
        cDCName,
        cWhCode,
        stock,
        cBatch,
        cInvStd,
        cInvName,
        cInvAddCode
      FROM (SELECT
              Customer.cCusName,
              CurrentStock.AutoID,
              DistrictClass.cDCName,
              CurrentStock.cWhCode,
              CurrentStock.iQuantity AS stock,
              CurrentStock.cBatch,
              Inventory.cInvStd,
              Inventory.cInvName,
              Inventory.cInvAddCode
            FROM CurrentStock
              LEFT OUTER JOIN Customer ON SUBSTRING(CurrentStock.cWhCode, 1, 6) = Customer.cCusCode
              LEFT OUTER JOIN DistrictClass ON customer.cdccode = DistrictClass.cdccode
              LEFT OUTER JOIN Inventory ON Inventory.cInvCode = CurrentStock.cInvCode
            WHERE (Customer.cCusCode = '100001')) AS PAGE_TABLE_ALIAS) AS PAGE_TABLE_ALIAS
WHERE PAGE_ROW_NUMBER > 10
ORDER BY PAGE_ROW_NUMBER

这里可以看出, 本质上对于我们自己的sql插件做的事就是在外面套了一层select, 其中增加了一个column作为排序的依据.
关键在于这一句:
ROW_NUMBER() OVER (ORDER BY RAND())
ROW_NUMBER() 函数就是根据OVER之中的条件, 不断给出一个从1开始自增1的序列, 如果条件正确就一直生成.
这里通过RAND() 生成随机数, 来进行生成ROW_NUMBER(), 然后再在外面套一层SELECT作为选择分页的条件, 如PAGE_ROW_NUMBER > x 就是根据从某一页开始取, TOP y就是取多少个. 这些都是根据刚才的调用 **PageHelper.startPage(int pageNum, int pageSize) ** 计算得到的.

所以可以对任意的sql语句来进行构建分页, 以后可以看下这个插件源码.