sharding-jdbc结合mybatis实现分库分表功能

转自：https://www.cnblogs.com/zwt1990/p/6762135.html

自学知识以防丢失

首先在pom文件中引入需要的依赖

<dependency>
            <groupId>com.dangdanggroupId>
            <artifactId>sharding-jdbc-coreartifactId>
            <version>1.4.2version>
        dependency>
        <dependency>
            <groupId>com.dangdanggroupId>
            <artifactId>sharding-jdbc-config-springartifactId>
            <version>1.4.0version>
        dependency>

　　二、新建一个sharding-jdbc.xml文件，实现分库分表的配置

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:context="http://www.springframework.org/schema/context" 
    xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:rdb="http://www.dangdang.com/schema/ddframe/rdb"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
                        http://www.springframework.org/schema/beans/spring-beans.xsd 
                        http://www.springframework.org/schema/tx 
                        http://www.springframework.org/schema/tx/spring-tx.xsd
                        http://www.springframework.org/schema/context 
                        http://www.springframework.org/schema/context/spring-context.xsd
                        http://www.dangdang.com/schema/ddframe/rdb 
                        http://www.dangdang.com/schema/ddframe/rdb/rdb.xsd">
                
    <rdb:strategy id="tableShardingStrategy" sharding-columns="user_id" algorithm-class="com.meiren.member.common.sharding.MemberSingleKeyTableShardingAlgorithm"/>
    
    <rdb:data-source id="shardingDataSource">
        <rdb:sharding-rule data-sources="dataSource">
            <rdb:table-rules>
                <rdb:table-rule logic-table="member_index" actual-tables="member_index_tbl_${[0,1,2,3,4,5,6,7,8,9]}${0..9}"  table-strategy="tableShardingStrategy"/>
                <rdb:table-rule logic-table="member_details" actual-tables="member_details_tbl_${[0,1,2,3,4,5,6,7,8,9]}${0..9}"  table-strategy="tableShardingStrategy"/>
            rdb:table-rules>
        rdb:sharding-rule>
    rdb:data-source>
    
    <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="shardingDataSource" />
    bean>
beans>

　　这里我简单介绍下一些属性的含义，

　　   配置分表规则器  sharding-columns：分表规 则　

　　依赖的名（根据user_id取模分表），algorithm-class:分表规则的实现类 

　　data-sources="dataSource"> 这里填写关联数据源（多个数据源用逗号隔开）,

　　  logic-table：逻辑表名（mybatis中代替的表名）actual-tables：

　　数据库实际的表名，这里支持inline表达式，比如：member_index_tbl_${0..2}会解析成member_index_tbl_0，member_index_tbl_1，member_index_tbl_2；member_index_tbl_${[a,b,c]}会被解析成

　   member_index_tbl_a,member_index_tbl_b和member_index_tbl_c,两种表达式一起使用的时候，会采取笛卡尔积的方式：member_index_tbl_${[a,b]}${0..2}解析为member_index_tbl_a0,member_index_tbl_a1                                       member_index_tbl_a2,member_index_tbl_b0,member_index_tbl_b1,member_index_tbl_b2;table-strategy:前面定义的分表规则器；

     三、配置好改文件后，需要修改之前我们的spring-dataSource的几个地方，把sqlSessionFactory和transactionManager原来关联的dataSource统一修改为shardingDataSource（这一步作用就是把数据源全部托管给sharding去管理）

　　

　四、实现分表（分库）逻辑，我们的分表逻辑类需要实现SingleKeyTableShardingAlgorithm接口的三个方法doBetweenSharding、doEqualSharding、doInSharding

/**
 * 分表逻辑
 * @author zhangwentao
 *
 */
public class MemberSingleKeyTableShardingAlgorithm implements SingleKeyTableShardingAlgorithm {
    
    /**
     * sql between 规则
     */
    public Collection doBetweenSharding(Collection tableNames, ShardingValue shardingValue) {
        Collection result = new LinkedHashSet(tableNames.size());
        Range range = (Range) shardingValue.getValueRange();
        for (long i = range.lowerEndpoint(); i <= range.upperEndpoint(); i++) {
            Long modValue = i % 100;
            String modStr = modValue < 10 ? "0" + modValue : modValue.toString();
            for (String each : tableNames) {
                if (each.endsWith(modStr)) {
                    result.add(each);
                }
            }
        }
        return result;
    }

    /**
     * sql == 规则
     */
    public String doEqualSharding(Collection tableNames, ShardingValue shardingValue) {
        Long modValue = shardingValue.getValue() % 100;
        String modStr = modValue < 10 ? "0" + modValue : modValue.toString();
        for (String each : tableNames) {
            if (each.endsWith(modStr)) {
                return each;
            }
        }
        throw new IllegalArgumentException();
    }

    /**
     * sql in 规则
     */
    public Collection doInSharding(Collection tableNames, ShardingValue shardingValue) {

        Collection result = new LinkedHashSet(tableNames.size());
        for (long value : shardingValue.getValues()) {
            Long modValue = value % 100;
            String modStr = modValue < 10 ? "0" + modValue : modValue.toString();
            for (String tableName : tableNames) {
                if (tableName.endsWith(modStr)) {
                    result.add(tableName);
                }
            }
        }
        return result;
    }
    
}

五、以上四步，我们就完成了sharding-jdbc的搭建，我们可以写一个测试demo来检查我们的成果

<select id="getDetailsById" resultType="com.meiren.member.dataobject.MemberDetailsDO"
        parameterType="java.lang.Long">
        select user_id userId ,qq,email from member_details where     user_id =#{userId} limit 1
    select>

private  static  final  String SERVICE_PROVIDER_XML =  "/spring/member-service.xml" ;
      private  static  final  String BEAN_NAME =  "idcacheService" ;

      private  ClassPathXmlApplicationContext context =  null ;
      IdcacheServiceImpl bean =  null ;
      IdcacheDao idcacheDao;

      @Before
      public  void  before() {
          context=  new  ClassPathXmlApplicationContext(
                  new  String[] {SERVICE_PROVIDER_XML});
         idcacheDao=context.getBean( "IdcacheDao" , IdcacheDao. class );
      }

      @Test
      public  void  getAllCreditActionTest() {
       // int id = bean.insertIdcache();
          Long s=100l;
        MemberDetailsDO memberDetailsDO=idcacheDao.getDetailsById(s);
        System.out.println( "QQ---------------------" +memberDetailsDO.getQq());
      }

　　打印sql语句，输出结果：QQ-------------------------------------100，证明成功！

　　注意点：这次搭建过程中，我有碰到一个小坑，就是执行的时候会报错：，官方文档是有解决方案：引入   ，引入这行代码的时候，·必须要要把这边管理配配置文件的bean删除，换句话说，即Spring容器仅允许最多定义一个PropertyPlaceholderConfigurer(或)，其余的会被Spring忽略掉（当时搞了半天啊）