最近忙于项目已经好久几天没写博客了，前2篇文章我给大家介绍了搭建基础springMvc+mybatis的maven工程，这个简单框架已经可以对付一般的小型项目。但是我们实际项目中会碰到很多复杂的场景，比如数据量很大的情况下如何保证性能。今天我就给大家介绍数据库分库分表的优化，本文介绍mybatis结合当当网的sharding-jdbc分库分表技术（原理这里不做介绍）
首先在pom文件中引入需要的依赖
<dependency> <groupId>com.dangdang</groupId> <artifactId>sharding-jdbc-core</artifactId> <version>1.4.2</version> </dependency> <dependency> <groupId>com.dangdang</groupId> <artifactId>sharding-jdbc-config-spring</artifactId> <version>1.4.0</version> </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，
<rdb:strategy id="tableShardingStrategy" sharding-columns="user_id" algorithm-class="com.meiren.member.common.sharding.MemberSingleKeyTableShardingAlgorithm"/> 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
<rdb:sharding-rule data-sources="dataSource"> 这里填写关联数据源（多个数据源用逗号隔开）,
<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"/> 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<Long> { /** * sql between 规则 */ public Collection<String> doBetweenSharding(Collection<String> tableNames, ShardingValue<Long> shardingValue) { Collection<String> result = new LinkedHashSet<String>(tableNames.size()); Range<Long> range = (Range<Long>) 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<String> tableNames, ShardingValue<Long> 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<String> doInSharding(Collection<String> tableNames, ShardingValue<Long> shardingValue) { Collection<String> result = new LinkedHashSet<String>(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>
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | 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 <context:property-placeholder location="classpath:/member_service.properties" ignore-unresolvable="true" /> ，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<context:property-placeholder/>)，其余的会被Spring忽略掉（当时搞了半天啊）
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