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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