多数据源产生的场景

一般情况下，不会有多数据源这样的场景出现，但老项目或者特殊需求的项目，可能会有这样的场景

同一个应用需要访问两个数据库
不用数据库中间件的读写分离

注入数据源选择的时机

声明两个数据源实例，在getConnection的时候根据业务的不同，注入不同数据源的连接

环境准备

准备sql脚本，建立两个库，这里mysql为例


create database stu;
create database tech;
use stu;
create table student
(id varchar(50) not null comment '主键',name varchar(50) null comment '姓名',stu_no varchar(50) null comment '学号',constraint student_pk primary key (id)
);insert into student values ('1','张同学','111');
insert into student values ('2','李同学','222');
use tech;
create table teacher
(id varchar(50) not null comment '主键',name varchar(50) null comment '姓名',teach_no varchar(50) null comment '教师号',constraint teacher_pk primary key (id)
);insert into teacher values ('1','王老师','111');
insert into teacher values ('2','高老师','222');

实现DataSource方式实现多数据源

配置多数据源

server:port: 9000
spring:datasource:type: com.alibaba.druid.pool.DruidDataSourcedatasource1:url: jdbc:mysql://shilei.tech:3306/stu?useSSL=true&serverTimezone=Asia/Shanghaiusername: rootpassword: root123456driver-class-name: com.mysql.cj.jdbc.Driverdatasource2:url: jdbc:mysql://shilei.tech:3306/tech?useSSL=true&serverTimezone=Asia/Shanghaiusername: rootpassword: root123456driver-class-name: com.mysql.cj.jdbc.Driverdruid:initial-size: 5min-idle: 1max-active: 20mybatis-plus:mapper-locations: classpath:/mapper/*.xmltype-aliases-package: com.datasource.dynamicdatasource.model

添加数据源配置

package com.datasource.dynamicdatasource.config;import com.alibaba.druid.pool.DruidDataSource;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;import javax.sql.DataSource;/*** @author sl*/
@Configuration
public class DataSourceConfig {@Bean("dataSource1")@ConfigurationProperties(prefix = "spring.datasource.datasource1")public DataSource dataSource1(){DruidDataSource druidDataSource = new DruidDataSource();return druidDataSource;}@Bean("dataSource2")@ConfigurationProperties(prefix = "spring.datasource.datasource2")public DataSource dataSource2(){DruidDataSource druidDataSource = new DruidDataSource();return druidDataSource;}
}

实现DataSource多数据源

package com.datasource.dynamicdatasource.config;import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;import javax.annotation.Resource;
import javax.sql.DataSource;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.SQLFeatureNotSupportedException;
import java.util.logging.Logger;/*** @author sl* @Primary主要注入的bean*/
@Configuration
@Primary
public class DynamicDataSource implements DataSource {public static ThreadLocal<String> nameFlag = new ThreadLocal<>();@Resourceprivate DataSource dataSource1;@Resourceprivate DataSource dataSource2;@Overridepublic Connection getConnection() throws SQLException {if("student".equals(nameFlag.get())){return dataSource1.getConnection();}return dataSource2.getConnection();}@Overridepublic Connection getConnection(String username, String password) throws SQLException {return null;}@Overridepublic <T> T unwrap(Class<T> iface) throws SQLException {return null;}@Overridepublic boolean isWrapperFor(Class<?> iface) throws SQLException {return false;}@Overridepublic PrintWriter getLogWriter() throws SQLException {return null;}@Overridepublic void setLogWriter(PrintWriter out) throws SQLException {}@Overridepublic void setLoginTimeout(int seconds) throws SQLException {}@Overridepublic int getLoginTimeout() throws SQLException {return 0;}@Overridepublic Logger getParentLogger() throws SQLFeatureNotSupportedException {return null;}
}

测试多数据源

package com.datasource.dynamicdatasource.controller;import com.datasource.dynamicdatasource.config.DynamicDataSource;
import com.datasource.dynamicdatasource.model.Student;
import com.datasource.dynamicdatasource.model.Teacher;
import com.datasource.dynamicdatasource.service.StudentService;
import com.datasource.dynamicdatasource.service.TeacherService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;import java.util.List;/*** @author sl*/
@RestController
public class TestDataSourceController {@Autowiredprivate StudentService studentService;@Autowiredprivate TeacherService teacherService;@GetMapping("/stu")public String getStu(){DynamicDataSource.nameFlag.set("student");List<Student> allStudent = studentService.findAllStudent();return allStudent.toString();}@GetMapping("/tech")public String getTech(){DynamicDataSource.nameFlag.set("teacher");List<Teacher> allTeacher = teacherService.findAllTeacher();return allTeacher.toString();}
}

效果如下所示

此实现方式的弊端

实现DataSource接口我们本质上只使用了一个方法，就是getConnection()这个无参的方法，其他方法，当内部调用时可能会导致错误，我们不可能实现所有的方法，所以我们继承AbstractRoutingDataSource抽象类

继承AbstractRoutingDataSource实现多数据源

AbstractRoutingDataSource的结构

可以看到AbstractRoutingDataSource继承自DataSource，提供了一些实现方法

AbstractRoutingDataSource的重要属性

targetDataSources 所有数据源 (需指定)

defaultTargetDataSource 默认数据源(需指定)

resolvedDataSources= targetDataSources 负责最终切换的数据源map 等于 tagetDataSources

继承AbstractRoutingDataSource实现多数据源

package com.datasource.dynamicdatasource.config;import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;import javax.annotation.Resource;
import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;/*** @author sl* @Primary主要注入的bean*/
@Configuration
@Primary
public class DynamicDataSource extends AbstractRoutingDataSource {public static ThreadLocal<String> nameFlag = new ThreadLocal<>();@Resourceprivate DataSource dataSource1;@Resourceprivate DataSource dataSource2;@Overrideprotected Object determineCurrentLookupKey() {// 返回当前数据源的标识return nameFlag.get();}@Overridepublic void afterPropertiesSet() {// 为targetDataSources 初始化所有数据源Map<Object,Object> targetDataSources=new HashMap<>();targetDataSources.put("student",dataSource1);targetDataSources.put("teacher",dataSource2);super.setTargetDataSources(targetDataSources);// 设置默认数据源super.setDefaultTargetDataSource(dataSource1);// 循环给resolvedDataSources，也就是最终数据源mapsuper.afterPropertiesSet();}
}

determineCurrentLookupKey的作用

看一段源码，就是通过determineCurrentLookupKey获取数据源的key，然后去resolvedDataSources中取数据源，resolvedDataSources数据源其实就是targetDataSources

	protected DataSource determineTargetDataSource() {Assert.notNull(this.resolvedDataSources, "DataSource router not initialized");Object lookupKey = determineCurrentLookupKey();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 + "]");}return dataSource;}

测试多数据源

package com.datasource.dynamicdatasource.controller;import com.datasource.dynamicdatasource.config.DynamicDataSource;
import com.datasource.dynamicdatasource.model.Student;
import com.datasource.dynamicdatasource.model.Teacher;
import com.datasource.dynamicdatasource.service.StudentService;
import com.datasource.dynamicdatasource.service.TeacherService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;import java.util.List;/*** @author sl*/
@RestController
public class TestDataSourceController {@Autowiredprivate StudentService studentService;@Autowiredprivate TeacherService teacherService;@GetMapping("/stu")public String getStu(){// 默认数据源就是studentList<Student> allStudent = studentService.findAllStudent();return allStudent.toString();}@GetMapping("/tech")public String getTech(){DynamicDataSource.nameFlag.set("teacher");List<Teacher> allTeacher = teacherService.findAllTeacher();return allTeacher.toString();}
}

AOP自定义注解方式+AbstractRoutingDataSource实现多数据源

数据源的切换还是使用AbstractRoutingDataSource，只不过切换方式采用aop拦截自定义注解切换数据源，这种方式也是mybatis-plus多数据源插件所采用的方式

自定义注解

package com.datasource.dynamicdatasource.annotation;import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;/*** @author sl*/
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface MyDataSource {String value() default "student";
}

配置切面

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-aop</artifactId>
</dependency>

package com.datasource.dynamicdatasource.aspect;import com.datasource.dynamicdatasource.annotation.MyDataSource;
import com.datasource.dynamicdatasource.config.DynamicDataSource;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
import org.aspectj.lang.reflect.MethodSignature;
import org.springframework.stereotype.Component;import java.lang.reflect.Method;/*** @author sl*@Aspect 标识是一个切面*/
@Aspect
@Component
public class DatasourceAspect {/*** 切点规则*/@Pointcut("@annotation(com.datasource.dynamicdatasource.annotation.MyDataSource)")public void pointcut() {}@Before("pointcut()")public void dataSourceAspect(JoinPoint joinPoint){// 获取方法Method method = ((MethodSignature) joinPoint.getSignature()).getMethod();// 判断方法中是否添加了注解if(method.isAnnotationPresent(MyDataSource.class)){// 获取方法上的注解MyDataSource annotation = method.getAnnotation(MyDataSource.class);String value = annotation.value();//  设置数据源DynamicDataSource.nameFlag.set(value);}}
}

测试自定义注解切换数据源

    @GetMapping("/tech")@MyDataSource("teacher")public String getTech(){List<Teacher> allTeacher = teacherService.findAllTeacher();return allTeacher.toString();}

dynamic-datasource多数据源组件实现多数据源

官方文档及搭建指南地址：多数据源 | MyBatis-Plus

引入依赖

<dependency><groupId>com.baomidou</groupId><artifactId>dynamic-datasource-spring-boot-starter</artifactId><version>3.6.1</version>
</dependency>

配置数据源

server:port: 9000
spring:datasource:type: com.alibaba.druid.pool.DruidDataSourcedynamic:#设置默认的数据源或者数据源组,默认值即为masterprimary: master#严格匹配数据源,默认false. true未匹配到指定数据源时抛异常,false使用默认数据源strict: falsedatasource:master:url: jdbc:mysql://shilei.tech:3306/stu?useSSL=true&serverTimezone=Asia/Shanghaiusername: rootpassword: root123456driver-class-name: com.mysql.cj.jdbc.Driverteacher:url: jdbc:mysql://shilei.tech:3306/tech?useSSL=true&serverTimezone=Asia/Shanghaiusername: rootpassword: root123456driver-class-name: com.mysql.cj.jdbc.Driverdruid:initial-size: 5min-idle: 1max-active: 20mybatis-plus:mapper-locations: classpath:/mapper/*.xmltype-aliases-package: com.datasource.dynamicdatasource.model

测试数据源切换

数据源切换使用@DS注解，不使用此注解，使用默认数据源，方法上使用>类上使用

package com.datasource.dynamicdatasource.controller;import com.baomidou.dynamic.datasource.annotation.DS;
import com.datasource.dynamicdatasource.model.Student;
import com.datasource.dynamicdatasource.model.Teacher;
import com.datasource.dynamicdatasource.service.StudentService;
import com.datasource.dynamicdatasource.service.TeacherService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;import java.util.List;/*** @author sl*/
@RestController
public class TestDataSourceController {@Autowiredprivate StudentService studentService;@Autowiredprivate TeacherService teacherService;@GetMapping("/stu")public String getStu(){List<Student> allStudent = studentService.findAllStudent();return allStudent.toString();}@GetMapping("/tech")@DS("teacher")public String getTech(){List<Teacher> allTeacher = teacherService.findAllTeacher();return allTeacher.toString();}
}