分库分表是解决关系数据库大表的一个很重要的方式，本文将详细讲解如何使用当当网开源的框架来实现分库分表的具体实现，本文是不可多得的详细讲解并亲自实践的Sharding-jdbc的文章，请大家收藏学习。

一：数据库分片方案

• 客户端代理： 分片逻辑在应用端，封装在jar包中，通过修改或者封装JDBC层来实现。 当当网的 Sharding-JDBC 、阿里的TDDL是两种比较常用的实现。
• 中间件代理： 在应用和数据中间加了一个代理层。分片逻辑统一维护在中间件服务中。 我们现在谈的 Mycat、360的Atlas、网易的DDB等等都是这种架构的实现

二：Sharding-JDBC

Sharding-JDBC: https://github.com/dangdangdotcom/sharding-jdbc

Sharding-JDBC是一个开源的适用于微服务的分布式数据访问基础类库，它始终以云原生的基础开发套件为目标。

Sharding-JDBC定位为轻量级java框架，使用客户端直连数据库，以jar包形式提供服务，未使用中间层，无需额外部署，无其他依赖，DBA也无需改变原有的运维方式，可理解为增强版的JDBC驱动，旧代码迁移成本几乎为零。

Sharding-JDBC完整的实现了分库分表，读写分离和分布式主键功能，并初步实现了柔性事务。从2016年开源至今，在经历了整体架构的数次精炼以及稳定性打磨后，如今它已积累了足够的底蕴，相信可以成为开发者选择技术组件时的一个参考。

1.分库分表

• SQL解析功能完善，支持聚合，分组，排序，LIMIT，TOP等查询，并且支持级联表以及笛卡尔积的表查询
• 支持内、外连接查询
• 分片策略灵活，可支持=，BETWEEN，IN等多维度分片，也可支持多分片键共用，以及自定义分片策略
• 基于Hint的强制分库分表路由

2.读写分离

• 一主多从的读写分离配置，可配合分库分表使用
• 基于Hint的强制主库路由

3.柔性事务

• 最大努力送达型事务
• TCC型事务(TBD)

4.分布式主键

• 统一的分布式基于时间序列的ID生成器

5.兼容性

• 可适用于任何基于java的ORM框架，如：JPA, Hibernate, Mybatis, Spring JDBC Template或直接使用JDBC
• 可基于任何第三方的数据库连接池，如：DBCP, C3P0, BoneCP, Druid等
• 理论上可支持任意实现JDBC规范的数据库。目前支持MySQL，Oracle，SQLServer和PostgreSQL

6.灵活多样的配置

• Java
• YAML
• Inline表达式
• Spring命名空间
• Spring boot starter

7.分布式治理能力 (2.0新功能)

• 配置集中化与动态化，可支持数据源、表与分片策略的动态切换(2.0.0.M1)
• 客户端的数据库治理，数据源失效自动切换(2.0.0.M2)
• 基于Open Tracing协议的APM信息输出(2.0.0.M3)

架构图

三：sharding-jdbc + jpa + druid集成

1. 数据库准备

<code>-- 在db0数据库上分别创建t_order_0、t_order_1表
USE db0;
DROP TABLE IF EXISTS t_order_0; 
CREATE TABLE t_order_0 ( 
order_id bigint(20) NOT NULL, 
user_id bigint(20) NOT NULL, 
PRIMARY KEY (order_id) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin; 
DROP TABLE IF EXISTS t_order_1; 
CREATE TABLE t_order_1 ( 
order_id bigint(20) NOT NULL, 
user_id bigint(20) NOT NULL, 
PRIMARY KEY (order_id) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin; 


-- 在db1数据库上分别创建t_order_0、t_order_1表
USE db1;
DROP TABLE IF EXISTS t_order_0; 
CREATE TABLE t_order_0 ( 
order_id bigint(20) NOT NULL, 
user_id bigint(20) NOT NULL, 
PRIMARY KEY (order_id) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin; 

DROP TABLE IF EXISTS t_order_1; 
CREATE TABLE t_order_1 ( 
order_id bigint(20) NOT NULL, 
user_id bigint(20) NOT NULL, 
PRIMARY KEY (order_id) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin; 
/<code>

2. 引入依赖

<code>
<project>         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelversion>4.0.0/<modelversion>

    <groupid>com.company/<groupid>
    <artifactid>sharding-jdbc/<artifactid>
    <version>0.0.1-SNAPSHOT/<version> 

    <packaging>jar/<packaging>

    <name>sharding-jdbc/<name>
    <description>Demo project for Spring Boot/<description>

    <parent>
        <groupid>org.springframework.boot/<groupid>
        <artifactid>spring-boot-starter-parent/<artifactid>
        <version>2.0.3.RELEASE/<version>
        <relativepath> 
    /<parent>

    <properties>
        <project.build.sourceencoding>UTF-8/<project.build.sourceencoding>
        <project.reporting.outputencoding>UTF-8/<project.reporting.outputencoding>
        <java.version>1.8/<java.version>
    /<properties>

    <dependencies>
        <dependency>
            <groupid>mysql/<groupid>
            <artifactid>mysql-connector-java/<artifactid>
            <version>5.1.41/<version>
        /<dependency>

        <dependency>
            <groupid>com.alibaba/<groupid>
            <artifactid>druid/<artifactid>
            <version>1.1.10/<version>
        /<dependency>

        <dependency>
            <groupid>org.springframework.boot/<groupid>
            <artifactid>spring-boot-starter-data-jpa/<artifactid>
        /<dependency>

        <dependency>
            <groupid>com.dangdang/<groupid>
            <artifactid>sharding-jdbc-core/<artifactid>
            <version>1.5.4/<version>
        /<dependency>
        <dependency>
            <groupid>org.springframework.boot/<groupid>
            <artifactid>spring-boot-starter-web/<artifactid>
        /<dependency>

        <dependency>
            <groupid>org.projectlombok/<groupid>
            <artifactid>lombok/<artifactid> 

            <optional>true/<optional>
        /<dependency>
        <dependency>
            <groupid>org.springframework.boot/<groupid>
            <artifactid>spring-boot-starter-test/<artifactid>
            <scope>test/<scope>
        /<dependency>
    /<dependencies>

    <build>
        <plugins>
            <plugin>
                <groupid>org.springframework.boot/<groupid>
                <artifactid>spring-boot-maven-plugin/<artifactid>
            /<plugin>
        /<plugins>
    /<build>
/<project>
/<code>

注意mysql-connector-java的版本不要太高了

3. application.yml

<code>spring:
  jpa:
    database: mysql
    show-sql: true
    hibernate:
      ddl-auto: none
/<code>

注意：hibernate.ddl-auto=none 是因为分表就会有多个表，例如torder0、torder1等，而ORM只能映射成一个，所以关闭自动的ddl语句。

4. domain

<code>@Entity
@Table(name = "t_order")
@Data
public class Order {
    @Id
    private Long orderId;

    private Long userId;
}
/<code> 

注意：orderId上使用@Id注解并没有使用@GeneratedValue(strategy = GenerationType.AUTO)的主键生成策略，原因是分表必须要保证所有表的主键id不重复，如果使用mysql的自动生成，那么id就会重复，这里的id一般要使用分布式主键id来通过代码来生成。

5. Repository

<code>import com.company.shardingjdbc.domain.Order;
import org.springframework.data.repository.CrudRepository;

public interface OrderRepository extends CrudRepository<order> {
}
/<order>/<code>

6. Controller

<code>import com.company.shardingjdbc.domain.Order;
import com.company.shardingjdbc.repository.OrderRepository;
import com.dangdang.ddframe.rdb.sharding.keygen.KeyGenerator;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/order")
public class OrderController {

    @Autowired
    private OrderRepository orderRepository;

    @Autowired
    private KeyGenerator keyGenerator;

    @RequestMapping("/create")
    public Object add() {
        for (int i = 0; i < 10; i++) {
            Order order = new Order();
            order.setUserId((long) i);
            order.setOrderId((long) i);
            orderRepository.save(order);
        }
        for (int i = 10; i < 20; i++) {
            Order order = new Order();
            order.setUserId((long) i + 1); 

            order.setOrderId((long) i);
            orderRepository.save(order);
        }

//        for (int i = 0; i < 30; i++) {
//            Order order = new Order();
//            order.setOrderId(keyGenerator.generateKey().longValue());
//            order.setUserId(keyGenerator.generateKey().longValue());
//            orderRepository.save(order);
//        }

        return "success";
    }

    @RequestMapping("query")
    private Object queryAll() {
        return orderRepository.findAll();
    }
}
/<code>

7. Configuration

<code>package com.company.shardingjdbc.configuration;

import com.alibaba.druid.pool.DruidDataSource;
import com.company.shardingjdbc.common.ModuleDatabaseShardingAlgorithm;
import com.company.shardingjdbc.common.ModuleTableShardingAlgorithm;
import com.dangdang.ddframe.rdb.sharding.api.ShardingDataSourceFactory;
import com.dangdang.ddframe.rdb.sharding.api.rule.DataSourceRule;
import com.dangdang.ddframe.rdb.sharding.api.rule.ShardingRule;
import com.dangdang.ddframe.rdb.sharding.api.rule.TableRule;
import com.dangdang.ddframe.rdb.sharding.api.strategy.database.DatabaseShardingStrategy;
import com.dangdang.ddframe.rdb.sharding.api.strategy.table.TableShardingStrategy;
import com.dangdang.ddframe.rdb.sharding.keygen.DefaultKeyGenerator;
import com.dangdang.ddframe.rdb.sharding.keygen.KeyGenerator;
import com.mysql.jdbc.Driver;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.sql.DataSource;
import java.sql.SQLException;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;


@Configuration
public class DataSourceConfiguration {
    @Bean 

    public DataSource getDataSource() throws SQLException {
        return buildDataSource();
    }

    private DataSource buildDataSource() throws SQLException {
        // 设置分库映射
        Map<string> dataSourceMap = new HashMap<>(2);
        // 添加两个数据库db0,db1到map里
        dataSourceMap.put("db0", createDataSource("db0"));
        dataSourceMap.put("db1", createDataSource("db1"));
        // 设置默认db为db0，也就是为那些没有配置分库分表策略的指定的默认库
        // 如果只有一个库，也就是不需要分库的话，map里只放一个映射就行了，只有一个库时不需要指定默认库，但2个及以上时必须指定默认库，否则那些没有配置策略的表将无法操作数据
        DataSourceRule dataSourceRule = new DataSourceRule(dataSourceMap, "db0");

        // 设置分表映射，将t_order_0和t_order_1两个实际的表映射到t_order逻辑表
        // 0和1两个表是真实的表，t_order是个虚拟不存在的表，只是供使用。如查询所有数据就是select * from t_order就能查完0和1表的
        TableRule orderTableRule = TableRule.builder("t_order")
                .actualTables(Arrays.asList("t_order_0", "t_order_1"))
                .dataSourceRule(dataSourceRule)
                .build();

        // 具体分库分表策略，按什么规则来分
        ShardingRule shardingRule = ShardingRule.builder()
                .dataSourceRule(dataSourceRule)
                .tableRules(Arrays.asList(orderTableRule))
                .databaseShardingStrategy(new DatabaseShardingStrategy("user_id", new ModuleDatabaseShardingAlgorithm()))
                .tableShardingStrategy(new TableShardingStrategy("order_id", new ModuleTableShardingAlgorithm())).build();

        DataSource dataSource = ShardingDataSourceFactory.createDataSource(shardingRule);
 

        return dataSource;
    }

    private static DataSource createDataSource(final String dataSourceName) {
        // 使用druid连接数据库
        DruidDataSource result = new DruidDataSource();
        result.setDriverClassName(Driver.class.getName());
        result.setUrl(String.format("jdbc:mysql://localhost:3306/%s", dataSourceName));
        result.setUsername("root");
        result.setPassword("root123");
        return result;
    }

    @Bean
    public KeyGenerator keyGenerator() {
        return new DefaultKeyGenerator();
    }
}
/<string>/<code>

ModuleDatabaseShardingAlgorithm

<code>package com.company.shardingjdbc.common;

import com.dangdang.ddframe.rdb.sharding.api.ShardingValue;
import com.dangdang.ddframe.rdb.sharding.api.strategy.database.SingleKeyDatabaseShardingAlgorithm;
import com.google.common.collect.Range;

import java.util.Collection;
import java.util.LinkedHashSet;

/**
 * 单键数据库分片算法.
 *
 * 支持单键和多键策略
 * 

 *     
单键 SingleKeyDatabaseShardingAlgorithm

 *     
多键 MultipleKeysDatabaseShardingAlgorithm

 * 

 *
 * 支持的分片策略 

 * 

 *     
 = doEqualSharding 例如 where order_id = 1 

 *     
 IN doInSharding 例如 where order_id in (1, 2)

 *     
 BETWEEN doBetweenSharding 例如 where order_id between 1 and 2 

 * 

 *
 * @author mengday
 */
public class ModuleDatabaseShardingAlgorithm implements SingleKeyDatabaseShardingAlgorithm<long> {

    /**
     * 分片策略 相等=
     * @param availableTargetNames 可用的目标名字(这里指数据名db0、db1)
     * @param shardingValue 分片值[logicTableName="t_order" 逻辑表名, columnName="user_id" 分片的列名, value="20" 分片的列名对应的值(user_id=20)]
     * @return
     */
    @Override
    public String doEqualSharding(Collection<string> availableTargetNames, ShardingValue<long> shardingValue) {
        for (String each : availableTargetNames) {
            if (each.endsWith(shardingValue.getValue() % 2 + "")) {
                return each;
            }
        }
        throw new IllegalArgumentException();
    }

    @Override
    public Collection<string> doInSharding(Collection<string> availableTargetNames, ShardingValue<long> shardingValue) {
        Collection<string> result = new LinkedHashSet<>(availableTargetNames.size());
        for (Long value : shardingValue.getValues()) {
            for (String tableName : availableTargetNames) {
                if (tableName.endsWith(value % 2 + "")) {
                    result.add(tableName);
                }
            }
        }
        return result;
    } 


    @Override
    public Collection<string> doBetweenSharding(Collection<string> availableTargetNames,
                                                ShardingValue<long> shardingValue) {
        Collection<string> result = new LinkedHashSet<>(availableTargetNames.size());
        Range<long> range = shardingValue.getValueRange();
        for (Long i = range.lowerEndpoint(); i <= range.upperEndpoint(); i++) {
            for (String each : availableTargetNames) {
                if (each.endsWith(i % 2 + "")) {
                    result.add(each);
                }
            }
        }
        return result;
    }
}
/<long>/<string>/<long>/<string>/<string>/<string>/<long>/<string>/<string>/<long>/<string>/<long>/<code>

<code>package com.company.shardingjdbc.common;

import com.dangdang.ddframe.rdb.sharding.api.ShardingValue;
import com.dangdang.ddframe.rdb.sharding.api.strategy.table.SingleKeyTableShardingAlgorithm;
import com.google.common.collect.Range;

import java.util.Collection;
import java.util.LinkedHashSet;

public final class ModuleTableShardingAlgorithm implements SingleKeyTableShardingAlgorithm<long> {

    /**
     * doEqualSharding =
     * @param tableNames 实际物理表名
     * @param shardingValue [logicTableName="t_order", columnName="order_id", value=20]
     * 
     *  select * from t_order from t_order where order_id = 11
     *          └── SELECT *  FROM t_order_1 WHERE order_id = 11
     *  select * from t_order from t_order where order_id = 44
     *          └── SELECT *  FROM t_order_0 WHERE order_id = 44
     */
     *  select * from t_order from t_order where order_id = 11
     *          └── SELECT *  FROM t_order_1 WHERE order_id = 11
     *  select * from t_order from t_order where order_id = 44
     *          └── SELECT *  FROM t_order_0 WHERE order_id = 44
     */
    public String doEqualSharding(final Collection<string> tableNames, final ShardingValue<long> shardingValue) {
        for (String each : tableNames) {
            if (each.endsWith(shardingValue.getValue() % 2 + "")) {
                return each;
            }
        } 

        throw new IllegalArgumentException();
    }

    /**
     *  select * from t_order from t_order where order_id in (11,44)
     *          ├── SELECT *  FROM t_order_0 WHERE order_id IN (11,44)
     *          └── SELECT *  FROM t_order_1 WHERE order_id IN (11,44)
     *  select * from t_order from t_order where order_id in (11,13,15)
     *          └── SELECT *  FROM t_order_1 WHERE order_id IN (11,13,15)
     *  select * from t_order from t_order where order_id in (22,24,26)
     *          └──SELECT *  FROM t_order_0 WHERE order_id IN (22,24,26)
     */
    public Collection<string> doInSharding(final Collection<string> tableNames, final ShardingValue<long> shardingValue) {
        Collection<string> result = new LinkedHashSet<>(tableNames.size());
        for (Long value : shardingValue.getValues()) {
            for (String tableName : tableNames) {
                if (tableName.endsWith(value % 2 + "")) {
                    result.add(tableName);
                }
            }
        }
        return result;
    }
    /**
     *  select * from t_order from t_order where order_id between 10 and 20
     *          ├── SELECT *  FROM t_order_0 WHERE order_id BETWEEN 10 AND 20
     *          └── SELECT *  FROM t_order_1 WHERE order_id BETWEEN 10 AND 20
     */
    public Collection<string> doBetweenSharding(final Collection<string> tableNames, final ShardingValue<long> shardingValue) {
        Collection<string> result = new LinkedHashSet<>(tableNames.size());
        Range<long> range = shardingValue.getValueRange();
        for (Long i = range.lowerEndpoint(); i <= range.upperEndpoint(); i++) {
            for (String each : tableNames) {
                if (each.endsWith(i % 2 + "")) {
                    result.add(each);
                }
            }
        }
        return result;
    }
}
/<long>/<string>/<long>/<string>/<string>/<string>/<long>/<string>/<string>/<long>/<string>/<long>/<code>

8. localhost:8080/order/create

db0 ├── torder0 userid为偶数 orderid为偶数 ├── torder1 userid为偶数 orderid为奇数 db1 ├── torder0 userid为奇数 orderid为偶数 ├── torder1 userid为奇数 orderid为奇数

四：sharding-jdbc + mybatis + druid集成

此示例是在jap原有的集成上集成mybatis

1. 引入mybatis依赖

<code><dependency>
    <groupid>org.mybatis.spring.boot/<groupid>
    <artifactid>mybatis-spring-boot-starter/<artifactid>
    <version>1.3.2/<version>
/<dependency>
/<code>

2. 在Application上添加注解@MapperScan

<code>@MapperScan("com.company.shardingjdbc.mapper")
@SpringBootApplication
public class ShardingJdbcApplication {

    public static void main(String[] args) {
        SpringApplication.run(ShardingJdbcApplication.class, args);
    }
}
/<code>

3. application.yml

<code># Mybatis 配置
mybatis:
  typeAliasesPackage: com.company.shardingjdbc.domain
  mapperLocations: classpath:mapper/*.xml
  configuration.map-underscore-to-camel-case: true

# 打印mybatis中的sql语句和结果集
logging:
  level.com.company.shardingjdbc.mapper: TRACE
/<code>

4. OrderMapper

<code>import org.apache.ibatis.annotations.Param;

import java.util.List;
 

public interface OrderMapper {

    void insert(Order order);

    List<order> queryById(@Param("orderIdList") List<long> orderIdList);
}
/<long>/<order>/<code>

5. OrderMapper.xml

<code>

<mapper>
    <select>
        SELECT * FROM t_order WHERE order_id IN
        <foreach>
            #{orderId}
        /<foreach>
    /<select>

    <insert>
        INSERT INTO t_order (order_id, user_id) VALUES (#{orderId}, #{userId})
    /<insert>
/<mapper>
/<code>

6. OrderController

<code>import com.dangdang.ddframe.rdb.sharding.keygen.KeyGenerator;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

@RestController
@RequestMapping("/order")
public class OrderController {

    @Autowired
    private OrderMapper orderMapper;

    @RequestMapping("/insert")
    public Object insert() {
        for (int i = 20; i < 30; i++) {
            Order order = new Order();
            order.setUserId((long) i); 

            order.setOrderId((long) i);
            orderMapper.insert(order);
        }
        for (int i = 30; i < 40; i++) {
            Order order = new Order();
            order.setUserId((long) i + 1);
            order.setOrderId((long) i);
            orderMapper.insert(order);
        }

        return "success";
    }

    @RequestMapping("queryById")
    public List<order> queryById(String orderIds) {
        List<string> strings = Arrays.asList(orderIds.split(","));
        List<long> orderIdList = strings.stream().map(item -> Long.parseLong(item)).collect(Collectors.toList());
        return orderMapper.queryById(orderIdList);
    }
}
/<long>/<string>/<order>/<code>

7. 插入数据

localhost:8080/order/insert

• ModuleDatabaseShardingAlgorithm: 先根据分片键user_id及值来确定要操作的数据库是db0还是db1
• ModuleTableShardingAlgorithm: 再根据分片键orderid及值来确定要操作的数据库对应的表是torder0还是torder_1
• 当数据库名和表名都确定了就可以操作数据库了

localhost:8080/order/queryById?orderIds=20,31,30,21

五：源码

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