之前写过一篇mybatis 使用经验小结 提到过多数据源的处理方式,虽然简单但是姿势不太优雅,今天介绍一些更美观的办法:
spring中有一个AbstractRoutingDataSource的抽象类可以很好的支持多数据源,我们只需要继续它即可。
package com.cnblogs.yjmyzz.utils;
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;
public class RoutingDataSource extends AbstractRoutingDataSource {
@Override
protected Object determineCurrentLookupKey() {
return DBContext.getDBKey();
}
}
很简单,就一个方法。其中DBContext的代码如下:
package com.cnblogs.yjmyzz.utils;
public class DBContext {
//define count of database and it must match with resources/properties/jdbc.properties
private static final int DB_COUNT = 2;
private static final ThreadLocal<String> tlDbKey = new ThreadLocal<String>();
public static String getDBKey() {
return tlDbKey.get();
}
public static void setDBKey(String dbKey) {
tlDbKey.set(dbKey);
}
public static String getDBKeyByUserId(int userId) {
int dbIndex = userId % DB_COUNT;
return "db_" + (++dbIndex);
}
}
主要利用了ThreadLocal这个类在每个线程中保持自己私有的变量。
这里我模拟了一个分库的场景:假设一个应用允许用户注册,但是用户数量太多,全都放在一个数据库里,记录过多,会导致数据库性能瓶颈,比较容易想到的办法,把用户的数据分散到多个数据库中保存(注:可能马上有同学会说了,分开存了,要查询所有用户怎么办?这确实是分库带来的一个弊端,但也有相应的解决方案,本文先不讨论这个,以免跑题)。
假设我们有二个数据库,里面的表结构完全相同,有一张表T_USER用于保存用户数据,问题来了,如果有N个用户要注册,id分别是1、2、3...,服务端接到参数后,怎么知道把这些数据分别插入到这二个库中,必然要有一个规则 ,比较简单的办法就是取模,所以上面的getDBKeyByUserId就是干这个的。
然后是jdbc的属性配置文件:
jdbc-driver=com.mysql.jdbc.Driver
jdbc-key-1=db_1
jdbc-url-1=jdbc:mysql://default:3306/db_1?useUnicode=true&characterEncoding=utf8
jdbc-user-1=test
jdbc-password-1=123456
jdbc-key-2=db_2
jdbc-url-2=jdbc:mysql://default:3306/db_2?useUnicode=true&characterEncoding=utf8
jdbc-user-2=test
jdbc-password-2=123456
接下来是spring的配置文件:
1 <?xml version="1.0" encoding="UTF-8"?>
2 <beans xmlns="http://www.springframework.org/schema/beans"
3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
4 xmlns:context="http://www.springframework.org/schema/context"
5 xsi:schemaLocation="http://www.springframework.org/schema/beans
6 http://www.springframework.org/schema/beans/spring-beans.xsd
7 http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
8
9
10 <context:annotation-config/>
11
12 <context:component-scan base-package="com.cnblogs.yjmyzz"/>
13
14 <bean id="propertiesFactoryBean"
15 class="org.springframework.beans.factory.config.PropertiesFactoryBean">
16 <property name="locations">
17 <list>
18 <value>classpath:properties/jdbc.properties</value>
19 </list>
20 </property>
21 </bean>
22
23 <context:property-placeholder properties-ref="propertiesFactoryBean" ignore-unresolvable="true"/>
24
25 <bean id="parentDataSource" class="com.alibaba.druid.pool.DruidDataSource" init-method="init"
26 destroy-method="close">
27 <property name="driverClassName" value="${jdbc-driver}"/>
28 <property name="url" value="${jdbc-url-1}"/>
29 <property name="username" value="${jdbc-user-1}"/>
30 <property name="password" value="${jdbc-password-1}"/>
31 <property name="filters" value="stat"/>
32 <property name="maxActive" value="20"/>
33 <property name="initialSize" value="1"/>
34 <property name="maxWait" value="60000"/>
35 <property name="minIdle" value="1"/>
36 <property name="timeBetweenEvictionRunsMillis" value="3000"/>
37 <property name="minEvictableIdleTimeMillis" value="300000"/>
38 <property name="validationQuery" value="SELECT 'x'"/>
39 <property name="testWhileIdle" value="true"/>
40 <property name="testOnBorrow" value="false"/>
41 <property name="testOnReturn" value="false"/>
42 <property name="poolPreparedStatements" value="true"/>
43 <property name="maxPoolPreparedStatementPerConnectionSize" value="20"/>
44 <property name="connectionInitSqls" value="set names utf8mb4;"/>
45 </bean>
46
47 <bean id="dataSource1" parent="parentDataSource">
48 <property name="url" value="${jdbc-url-1}"/>
49 <property name="username" value="${jdbc-user-1}"/>
50 <property name="password" value="${jdbc-password-1}"/>
51 </bean>
52
53 <bean id="dataSource2" parent="parentDataSource">
54 <property name="url" value="${jdbc-url-2}"/>
55 <property name="username" value="${jdbc-user-2}"/>
56 <property name="password" value="${jdbc-password-2}"/>
57 </bean>
58
59 <!-- config switch routing db -->
60 <bean id="dataSource" class="com.cnblogs.yjmyzz.utils.RoutingDataSource">
61 <property name="targetDataSources">
62 <map key-type="java.lang.String">
63 <entry key="${jdbc-key-1}" value-ref="dataSource1"/>
64 <entry key="${jdbc-key-2}" value-ref="dataSource2"/>
65 </map>
66 </property>
67 </bean>
68
69 <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
70 <property name="configLocation" value="classpath:mybatis-config.xml"></property>
71 <property name="dataSource" ref="dataSource"/>
72 <property name="mapperLocations">
73 <array>
74 <value>classpath:mybatis/*.xml</value>
75 </array>
76 </property>
77 </bean>
78
79 <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
80 <property name="basePackage" value="com.cnblogs.yjmyzz.mapper"/>
81 </bean>
82
83 </beans>
关键的是parentDataSource,dataSource1,dataSource2,dataSource这几个bean的配置,一看就懂。
服务端的核心代码:
package com.cnblogs.yjmyzz.service.impl;
import com.cnblogs.yjmyzz.entity.UserEntity;
import com.cnblogs.yjmyzz.mapper.UserEntityMapper;
import com.cnblogs.yjmyzz.service.UserService;
import com.cnblogs.yjmyzz.utils.DBContext;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
/**
* Created by yangjunming on 2/15/16.
* author: yangjunming@huijiame.com
*/
@Service("userService")
public class UserServiceImpl implements UserService {
@Autowired
UserEntityMapper userEntityMapper;
@Override
public void addUser(UserEntity userEntity) {
//switch db
DBContext.setDBKey(DBContext.getDBKeyByUserId(userEntity.getUserId()));
userEntityMapper.insertSelective(userEntity);
}
@Override
public UserEntity getUser(int userId) {
//switch db
DBContext.setDBKey(DBContext.getDBKeyByUserId(userId));
return userEntityMapper.selectByPrimaryKey(userId);
}
}
注意:25,32行在调用mybatis操作数据库前,先根据需要切换到不同的数据库,然后再操作。
运行完成后,可以看下db_1,db_2这二个数据库,确认数据是否已经分散存储到每个库中:
如果不喜欢在代码里手动切换db,也可以用注解的方式自动切换,比如:我们又增加了一个db_main
jdbc-driver=com.mysql.jdbc.Driver
jdbc-key-1=db_1
jdbc-url-1=jdbc:mysql://default:3306/db_1?useUnicode=true&characterEncoding=utf8
jdbc-user-1=test
jdbc-password-1=123456
jdbc-key-2=db_2
jdbc-url-2=jdbc:mysql://default:3306/db_2?useUnicode=true&characterEncoding=utf8
jdbc-user-2=test
jdbc-password-2=123456
jdbc-key-main=db_main
jdbc-url-main=jdbc:mysql://default:3306/db_main?useUnicode=true&characterEncoding=utf8
jdbc-user-main=test
jdbc-password-main=123456
然后在spring配置文件里,要做些调整:
1 <bean id="parentDataSource" class="com.alibaba.druid.pool.DruidDataSource" init-method="init"
2 destroy-method="close">
3 <property name="driverClassName" value="${jdbc-driver}"/>
4 <property name="url" value="${jdbc-url-1}"/>
5 <property name="username" value="${jdbc-user-1}"/>
6 <property name="password" value="${jdbc-password-1}"/>
7 <property name="filters" value="stat"/>
8 <property name="maxActive" value="20"/>
9 <property name="initialSize" value="1"/>
10 <property name="maxWait" value="60000"/>
11 <property name="minIdle" value="1"/>
12 <property name="timeBetweenEvictionRunsMillis" value="3000"/>
13 <property name="minEvictableIdleTimeMillis" value="300000"/>
14 <property name="validationQuery" value="SELECT 'x'"/>
15 <property name="testWhileIdle" value="true"/>
16 <property name="testOnBorrow" value="false"/>
17 <property name="testOnReturn" value="false"/>
18 <property name="poolPreparedStatements" value="true"/>
19 <property name="maxPoolPreparedStatementPerConnectionSize" value="20"/>
20 <property name="connectionInitSqls" value="set names utf8mb4;"/>
21 </bean>
22
23 <bean id="dataSource1" parent="parentDataSource">
24 <property name="url" value="${jdbc-url-1}"/>
25 <property name="username" value="${jdbc-user-1}"/>
26 <property name="password" value="${jdbc-password-1}"/>
27 </bean>
28
29 <bean id="dataSource2" parent="parentDataSource">
30 <property name="url" value="${jdbc-url-2}"/>
31 <property name="username" value="${jdbc-user-2}"/>
32 <property name="password" value="${jdbc-password-2}"/>
33 </bean>
34
35 <bean id="dataSourceMain" parent="parentDataSource">
36 <property name="url" value="${jdbc-url-main}"/>
37 <property name="username" value="${jdbc-user-main}"/>
38 <property name="password" value="${jdbc-password-main}"/>
39 </bean>
40
41 <!-- method 1: config switch routing db -->
42 <bean id="dataSource" class="com.cnblogs.yjmyzz.utils.RoutingDataSource">
43 <property name="targetDataSources">
44 <map key-type="java.lang.String">
45 <entry key="${jdbc-key-1}" value-ref="dataSource1"/>
46 <entry key="${jdbc-key-2}" value-ref="dataSource2"/>
47 <entry key="${jdbc-key-main}" value-ref="dataSourceMain"/>
48 </map>
49 </property>
50 </bean>
51
52 <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
53 <property name="configLocation" value="classpath:mybatis-config.xml"></property>
54 <property name="dataSource" ref="dataSource"/>
55 <property name="mapperLocations">
56 <array>
57 <value>classpath:mybatis/*.xml</value>
58 </array>
59 </property>
60 </bean>
61
62 <bean id="userScannerConfigurer" class="org.mybatis.spring.mapper.MapperScannerConfigurer">
63 <property name="basePackage" value="com.cnblogs.yjmyzz.mapper.user"/>
64 <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>
65 </bean>
66
67 <!-- method 2: config annotation auto switch-->
68 <bean id="sqlSessionFactoryMain" class="org.mybatis.spring.SqlSessionFactoryBean">
69 <property name="configLocation" value="classpath:mybatis-config.xml"></property>
70 <property name="dataSource" ref="dataSourceMain"/>
71 <property name="mapperLocations">
72 <array>
73 <value>classpath:mybatis/*.xml</value>
74 </array>
75 </property>
76 </bean>
77
78 <bean id="orderScannerConfigurer" class="org.mybatis.spring.mapper.MapperScannerConfigurer">
79 <property name="basePackage" value="com.cnblogs.yjmyzz.mapper.order"/>
80 <property name="sqlSessionFactoryBeanName" value="sqlSessionFactoryMain"/>
81 </bean>
注意:67-81行,主要是增加了一个单独的sqlSessionFactoryMain,然后将一个新的MapperScannerConfigurer关联到它。
新库里对应表的Mapper类可以这么写:
@Resource(name = "orderScannerConfigurer")
public interface OrderEntityMapper extends Mapper<OrderEntity> {
}
注解里name对应的值,必须与刚才spring文件里新增的MapperScannerConfigurer对应。
这样,服务层就可以省去手动切换的代码了,即:
public class UserServiceImpl implements UserService {
@Autowired
UserEntityMapper userEntityMapper;
@Autowired
OrderEntityMapper orderEntityMapper;
@Override
public void addUser(UserEntity userEntity) {
//switch db
DBContext.setDBKey(DBContext.getDBKeyByUserId(userEntity.getUserId()));
userEntityMapper.insertSelective(userEntity);
}
@Override
public UserEntity getUser(int userId) {
//switch db
DBContext.setDBKey(DBContext.getDBKeyByUserId(userId));
return userEntityMapper.selectByPrimaryKey(userId);
}
@Override
public void addOrder(OrderEntity orderEntity) {
//since orderEntityMapper can auto switch db by annotation
//so we don't need to switch db manually
orderEntityMapper.insertSelective(orderEntity);
}
@Override
public OrderEntity getOrder(int orderId) {
//since orderEntityMapper can auto switch db by annotation
//so we don't need to switch db manually
return orderEntityMapper.selectByPrimaryKey(orderId);
}
}
上述二种方式可以共存在同一个项目中,个人建议:如果分库的表结构相同,且表数量较多,第1种手动切换的方式比较适合,这样mapper类不用重复建多个,如果分库的表结构完全不同,第2种比较合适,因为表结构不同,mapper肯定也不同,所以mapper多个是无法避免的,这时候就宁可加点配置,代码中就不用手动切换,可以省事点。
最后,在github上放了一份示例代码,供有需要的同学下载。