30个类手写Spring核心原理之动态数据源切换（8）

本文节选自《Spring 5核心原理》

阅读本文之前，请先阅读以下内容：

30个类手写Spring核心原理之自定义ORM（上）（6）

30个类手写Spring核心原理之自定义ORM（下）（7）

4 动态数据源切换的底层原理

这里简单介绍一下AbstractRoutingDataSource的基本原理。实现数据源切换的功能就是自定义一个类扩展AbstractRoutingDataSource抽象类，其实相当于数据源的路由中介，可以实现在项目运行时根据相应key值切换到对应的DataSource上。先看看AbstractRoutingDataSource类的源码：

 public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean { /*只列出部分代码*/ @Nullable private Map<Object, Object> targetDataSources; @Nullable private Object defaultTargetDataSource; private boolean lenientFallback = true; private DataSourceLookup dataSourceLookup = new JndiDataSourceLookup(); @Nullable private Map<Object, DataSource> resolvedDataSources; @Nullable private DataSource resolvedDefaultDataSource; ... public Connection getConnection() throws SQLException { return this.determineTargetDataSource().getConnection(); } public Connection getConnection(String username, String password) throws SQLException { return this.determineTargetDataSource().getConnection(username, password); } ... protected DataSource determineTargetDataSource() { Assert.notNull(this.resolvedDataSources, "DataSource router not initialized"); Object lookupKey = this.determineCurrentLookupKey(); DataSource dataSource = (DataSource)this.resolvedDataSources.get(lookupKey); if(dataSource == null && (this.lenientFallback || lookupKey == null)) { dataSource = this.resolvedDefaultDataSource; } if(dataSource == null) { throw new IllegalStateException("Cannot determine target DataSource for lookup key [" + lookupKey + "]"); } else { return dataSource; } } @Nullable protected abstract Object determineCurrentLookupKey(); } 

可以看出，AbstractRoutingDataSource类继承了AbstractDataSource类，并实现了InitializingBean。AbstractRoutingDataSource类的getConnection()方法调用了determineTargetDataSource()的该方法。这里重点看determineTargetDataSource()方法的代码，它使用了determineCurrentLookupKey()方法，它是AbstractRoutingDataSource类的抽象方法，也是实现数据源切换扩展的方法。该方法的返回值就是项目中所要用的DataSource的key值，得到该key值后就可以在resolvedDataSource中取出对应的DataSource，如果找不到key对应的DataSource就使用默认的数据源。 自定义类扩展AbstractRoutingDataSource类时要重写determineCurrentLookupKey()方法来实现数据源切换。

4.1 DynamicDataSource

DynamicDataSource类封装自定义数据源，继承原生Spring的AbstractRoutingDataSource类的数据源动态路由器。

 package javax.core.common.jdbc.datasource; import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource; /** * 动态数据源 */ public class DynamicDataSource extends AbstractRoutingDataSource { private DynamicDataSourceEntry dataSourceEntry; @Override protected Object determineCurrentLookupKey() { return this.dataSourceEntry.get(); } public void setDataSourceEntry(DynamicDataSourceEntry dataSourceEntry) { this.dataSourceEntry = dataSourceEntry; } public DynamicDataSourceEntry getDataSourceEntry(){ return this.dataSourceEntry; } } 

4.2 DynamicDataSourceEntry

DynamicDataSourceEntry类实现对数据源的操作功能，代码如下：

 package javax.core.common.jdbc.datasource; import org.aspectj.lang.JoinPoint; /** * 动态切换数据源 */ public class DynamicDataSourceEntry { //默认数据源 public final static String DEFAULT_SOURCE = null; private final static ThreadLocal<String> local = new ThreadLocal<String>(); /** * 清空数据源 */ public void clear() { local.remove(); } /** * 获取当前正在使用的数据源的名字 * * @return String */ public String get() { return local.get(); } /** * 还原指定切面的数据源 * * @param joinPoint */ public void restore(JoinPoint join) { local.set(DEFAULT_SOURCE); } /** * 还原当前切面的数据源 */ public void restore() { local.set(DEFAULT_SOURCE); } /** * 设置已知名字的数据源 * * @param dataSource */ public void set(String source) { local.set(source); } /** * 根据年份动态设置数据源 * @param year */ public void set(int year) { local.set("DB_" + year); } } 

5 运行效果演示

5.1 创建Member实体类

创建Member实体类代码如下：

 package com.tom.orm.demo.entity; import lombok.Data; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.Table; import java.io.Serializable; @Entity @Table(name="t_member") @Data public class Member implements Serializable { @Id private Long id; private String name; private String addr; private Integer age; @Override public String toString() { return "Member{" + "id=" + id + ", name='" + name + '\'' + ", addr='" + addr + '\'' + ", age=" + age + '}'; } } 

5.2 创建Order实体类

创建Order实体类代码如下：

 package com.tom.orm.demo.entity; import lombok.Data; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.Table; import java.io.Serializable; @Entity @Table(name="t_order") @Data public class Order implements Serializable { private Long id; @Column(name="mid") private Long memberId; private String detail; private Long createTime; private String createTimeFmt; @Override public String toString() { return "Order{" + "id=" + id + ", memberId=" + memberId + ", detail='" + detail + '\'' + ", createTime=" + createTime + ", createTimeFmt='" + createTimeFmt + '\'' + '}'; } } 

5.3 创建MemberDao

创建MemberDao代码如下：

 package com.tom.orm.demo.dao; import com.tom.orm.demo.entity.Member; import com.tom.orm.framework.BaseDaoSupport; import com.tom.orm.framework.QueryRule; import org.springframework.stereotype.Repository; import javax.annotation.Resource; import javax.sql.DataSource; import java.util.List; @Repository public class MemberDao extends BaseDaoSupport<Member,Long> { @Override protected String getPKColumn() { return "id"; } @Resource(name="dataSource") public void setDataSource(DataSource dataSource){ super.setDataSourceReadOnly(dataSource); super.setDataSourceWrite(dataSource); } public List<Member> selectAll() throws Exception{ QueryRule queryRule = QueryRule.getInstance(); queryRule.andLike("name","Tom%"); return super.select(queryRule); } } 

5.4 创建OrderDao

创建OrderDao代码如下：

 package com.tom.orm.demo.dao; import com.tom.orm.demo.entity.Order; import com.tom.orm.framework.BaseDaoSupport; import org.springframework.stereotype.Repository; import javax.annotation.Resource; import javax.core.common.jdbc.datasource.DynamicDataSource; import javax.sql.DataSource; import java.text.SimpleDateFormat; import java.util.Date; @Repository public class OrderDao extends BaseDaoSupport<Order, Long> { private SimpleDateFormat yearFormat = new SimpleDateFormat("yyyy"); private SimpleDateFormat fullDataFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); private DynamicDataSource dataSource; @Override protected String getPKColumn() {return "id";} @Resource(name="dynamicDataSource") public void setDataSource(DataSource dataSource) { this.dataSource = (DynamicDataSource)dataSource; this.setDataSourceReadOnly(dataSource); this.setDataSourceWrite(dataSource); } /** * @throws Exception * */ public boolean insertOne(Order order) throws Exception{ //约定优于配置 Date date = null; if(order.getCreateTime() == null){ date = new Date(); order.setCreateTime(date.getTime()); }else { date = new Date(order.getCreateTime()); } Integer dbRouter = Integer.valueOf(yearFormat.format(date)); System.out.println("自动分配到【DB_" + dbRouter + "】数据源"); this.dataSource.getDataSourceEntry().set(dbRouter); order.setCreateTimeFmt(fullDataFormat.format(date)); Long orderId = super.insertAndReturnId(order); order.setId(orderId); return orderId > 0; } } 

5.5 修改db.properties文件

修改db.properties文件代码如下：

 #sysbase database mysql config #mysql.jdbc.driverClassName=com.mysql.jdbc.Driver #mysql.jdbc.url=jdbc:mysql://127.0.0.1:3306/gp-vip-spring-db-demo?characterEncoding=UTF-8&rewriteBatchedStatements=true #mysql.jdbc.username=root #mysql.jdbc.password=123456 db2018.mysql.jdbc.driverClassName=com.mysql.jdbc.Driver db2018.mysql.jdbc.url=jdbc:mysql://127.0.0.1:3306/gp-vip-spring-db-2018?characterEncoding=UTF-8&rewriteBatchedStatements=true db2018.mysql.jdbc.username=root db2018.mysql.jdbc.password=123456 db2019.mysql.jdbc.driverClassName=com.mysql.jdbc.Driver db2019.mysql.jdbc.url=jdbc:mysql://127.0.0.1:3306/gp-vip-spring-db-2019?characterEncoding=UTF-8&rewriteBatchedStatements=true db2019.mysql.jdbc.username=root db2019.mysql.jdbc.password=123456 #alibaba druid config dbPool.initialSize=1 dbPool.minIdle=1 dbPool.maxActive=200 dbPool.maxWait=60000 dbPool.timeBetweenEvictionRunsMillis=60000 dbPool.minEvictableIdleTimeMillis=300000 dbPool.validationQuery=SELECT 'x' dbPool.testWhileIdle=true dbPool.testOnBorrow=false dbPool.testOnReturn=false dbPool.poolPreparedStatements=false dbPool.maxPoolPreparedStatementPerConnectionSize=20 dbPool.filters=stat,log4j,wall 

5.6 修改application-db.xml文件

修改application-db.xml文件代码如下：

 <bean id="datasourcePool" abstract="true" class="com.alibaba.druid.pool.DruidDataSource" init-method="init" destroy-method="close"> <property name="initialSize" value="${dbPool.initialSize}" /> <property name="minIdle" value="${dbPool.minIdle}" /> <property name="maxActive" value="${dbPool.maxActive}" /> <property name="maxWait" value="${dbPool.maxWait}" /> <property name="timeBetweenEvictionRunsMillis" value="${dbPool.timeBetweenEvictionRunsMillis}" /> <property name="minEvictableIdleTimeMillis" value="${dbPool.minEvictableIdleTimeMillis}" /> <property name="validationQuery" value="${dbPool.validationQuery}" /> <property name="testWhileIdle" value="${dbPool.testWhileIdle}" /> <property name="testOnBorrow" value="${dbPool.testOnBorrow}" /> <property name="testOnReturn" value="${dbPool.testOnReturn}" /> <property name="poolPreparedStatements" value="${dbPool.poolPreparedStatements}" /> <property name="maxPoolPreparedStatementPerConnectionSize" value="${dbPool.maxPoolPreparedStatementPerConnectionSize}" /> <property name="filters" value="${dbPool.filters}" /> </bean> <bean id="dataSource" parent="datasourcePool"> <property name="driverClassName" value="${db2019.mysql.jdbc.driverClassName}" /> <property name="url" value="${db2019.mysql.jdbc.url}" /> <property name="username" value="${db2019.mysql.jdbc.username}" /> <property name="password" value="${db2019.mysql.jdbc.password}" /> </bean> <bean id="dataSource2018" parent="datasourcePool"> <property name="driverClassName" value="${db2018.mysql.jdbc.driverClassName}" /> <property name="url" value="${db2018.mysql.jdbc.url}" /> <property name="username" value="${db2018.mysql.jdbc.username}" /> <property name="password" value="${db2018.mysql.jdbc.password}" /> </bean> <bean id="dynamicDataSourceEntry" class="javax.core.common.jdbc.datasource.DynamicDataSourceEntry" /> <bean id="dynamicDataSource" class="javax.core.common.jdbc.datasource.DynamicDataSource" > <property name="dataSourceEntry" ref="dynamicDataSourceEntry"></property> <property name="targetDataSources"> <map> <entry key="DB_2019" value-ref="dataSource"></entry> <entry key="DB_2018" value-ref="dataSource2018"></entry> </map> </property> <property name="defaultTargetDataSource" ref="dataSource" /> </bean> 

5.7 编写测试用例

编写测试用例代码如下：

 package com.tom.orm.test; import com.tom.orm.demo.dao.MemberDao; import com.tom.orm.demo.dao.OrderDao; import com.tom.orm.demo.entity.Member; import com.tom.orm.demo.entity.Order; import org.junit.Ignore; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.test.context.ContextConfiguration; import org.springframework.test.context.junit4.SpringJUnit4ClassRunner; import java.text.SimpleDateFormat; import java.util.Arrays; import java.util.Date; import java.util.List; @ContextConfiguration(locations = {"classpath:application-context.xml"}) @RunWith(SpringJUnit4ClassRunner.class) public class OrmTest { private SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMddHHmmdd"); @Autowired private MemberDao memberDao; @Autowired private OrderDao orderDao; @Test public void testSelectAllForMember(){ try { List<Member> result = memberDao.selectAll(); System.out.println(Arrays.toString(result.toArray())); } catch (Exception e) { e.printStackTrace(); } } @Test @Ignore public void testInsertMember(){ try { for (int age = 25; age < 35; age++) { Member member = new Member(); member.setAge(age); member.setName("Tom"); member.setAddr("Hunan Changsha"); memberDao.insert(member); } }catch (Exception e){ e.printStackTrace(); } } @Test // @Ignore public void testInsertOrder(){ try { Order order = new Order(); order.setMemberId(1L); order.setDetail("历史订单"); Date date = sdf.parse("20180201123456"); order.setCreateTime(date.getTime()); orderDao.insertOne(order); }catch (Exception e){ e.printStackTrace(); } } } 

所谓ORM就是，对象关系映射，Object Relation Mapping，市面上ORM框架也非常多，比如Hibernate、Spring JDBC、MyBatis、JPA，它们都有对象关系管理的机制比如一对多、多对多、一对一关系。以上思路仅供参考，有兴趣的小伙伴可以参考本文提供的思想，约定优于配置，先制定顶层接口，参数返回值全部统一，比如：

 //List<?> Page<?> select(QueryRule queryRule) //Int delete(T entity) entity中的ID不能为空，如果ID为空，其他条件不能为空，都为空不予执行 //ReturnId insert(T entity) 只要entity不等于null //Int update(T entity) entity中的ID不能为空，如果ID为空，其他条件不能为空，都为空不予执行 

然后在此基础上进行扩展，基于Spring JDBC封装一套，基于Redis封装一套，基于MongoDB封装一套，基于ElasticSearch封装一套，基于Hive封装一套，基于HBase封装一套。本文完整地演示了自研ORM框架的原理，以及数据源动态切换的基本原理，并且了解了Spring JdbcTemplate的API应用。希望通过本章的学习，“小伙伴们”在日常工作中能够有更好的解决问题的思路，提高工作效率。

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