背景：主从架构下，数据库的读写分离

1. 依赖

    <dependencies>
        <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>
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.5.3</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.2.16</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.29</version>
        </dependency>
    </dependencies>

2.配置数据源

spring:
  datasource:
    druid:
      type: com.alibaba.druid.pool.DruidDataSource
      master:
        url: jdbc:mysql://127.0.0.1:3307/user1?useUnicode=true&characterEncoding=utf8&useSSL=false
        username: root
        password: root
        driver-class-name: com.mysql.cj.jdbc.Driver
      slave1:
        enabled: true
        url: jdbc:mysql://127.0.0.1:3308/user1?useUnicode=true&characterEncoding=utf8&useSSL=false
        username: root
        password: root
        driver-class-name: com.mysql.cj.jdbc.Driver
      otmstariff:
        enabled: false
        url: jdbc:mysql://127.0.0.1:3306/user1?useUnicode=true&characterEncoding=utf8&useSSL=false
        username: root
        password: root
        driver-class-name: com.mysql.cj.jdbc.Driver

3. 注册数据源

1）创建一个数据源枚举类

public enum DataSourceType {
    /**
     * 主库
     */
    MASTER,

    /**
     * 从库
     */
    SLAVE1,

    SLAVE2
}

2）我们切换数据库所需要的bean全部交给spring容器中

@Configuration
public class DynamicDataSourceConfig {

    @Bean
    @Qualifier("masterDataSource")
    @ConfigurationProperties("spring.datasource.druid.master")
    public DataSource masterDataSource() {
        return DruidDataSourceBuilder.create().build();
    }

    @Qualifier("slave1DataSource")
    @Bean
    @ConfigurationProperties("spring.datasource.druid.slave1")
    // 根据配置文件enabled属性，判断该配置是否生效
    @ConditionalOnProperty(prefix = "spring.datasource.druid.slave1", name = "enabled", havingValue = "true")
    public DataSource slave1DataSource() {
        return DruidDataSourceBuilder.create().build();
    }

    @Qualifier("slave2DataSource")
    @Bean
    @ConfigurationProperties("spring.datasource.druid.slave2")
    @ConditionalOnProperty(prefix = "spring.datasource.druid.slave2", name = "enabled", havingValue = "true")
    public DataSource slave2DataSource() {
        return DruidDataSourceBuilder.create().build();
    }



    @Bean(name = "dynamicDataSource")
    @Primary
    public DynamicDataSource dataSource(DataSource masterDataSource) {
        Map<Object, Object> targetDataSources = new HashMap<>();
        targetDataSources.put(DataSourceType.MASTER.name(), masterDataSource);
        setDataSource(targetDataSources, DataSourceType.SLAVE1.name(), "slave1DataSource");
        setDataSource(targetDataSources, DataSourceType.SLAVE2.name(), "slave2DataSource");
        DynamicDataSource dynamicDataSource = new DynamicDataSource();
        dynamicDataSource.setTargetDataSources(targetDataSources);
        dynamicDataSource.setDefaultTargetDataSource(masterDataSource);
        return dynamicDataSource;
    }

    /**
     * 设置数据源
     *
     * @param targetDataSources 备选数据源集合
     * @param sourceName 数据源名称
     * @param beanName bean名称
     */
    public void setDataSource(Map<Object, Object> targetDataSources, String sourceName, String beanName)
    {
        try
        {
            DataSource dataSource = SpringUtils.getBean(beanName);
            targetDataSources.put(sourceName, dataSource);
        }
        catch (Exception e)
        {
        }
    }


}

4.切换数据源

public class DynamicDataSourceContextHolder {
    // 线程安全
    private static final ThreadLocal<String> CONTEXT_HOLDER = new ThreadLocal<>();
	/**
     * 设置数据源变量
     * @param dataSourceEnum 数据源变量
     */
    public static void setDataSourceType(String type) {
        CONTEXT_HOLDER.set(type);
    }
	/**
     * 获取数据源变量
     * @return 数据源变量
     */
    public static String getDataSourceType() {
        return CONTEXT_HOLDER.get();
    }
	/**
     * 清理数据源
     * @return 数据源变量
     */
    public static void clearDataSourceType() {
        CONTEXT_HOLDER.remove();
    }
}

5.设置数据源

新建DynamicDataSource类继承AbstractRoutingDataSource类，并实现determineCurrentLookupKey方法，该方法是指定当前默认数据源的方法，该类是实现动态切换数据源的关键

public class DynamicDataSource extends AbstractRoutingDataSource {

    @Override
    protected Object determineCurrentLookupKey() {
        return DynamicDataSourceContextHolder.getDataSourceType();
    }
}

6. 自定义多数据源切换注解

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface DataSource {
    DataSourceType value() default DataSourceType.MASTER;
}

7. AOP拦截器的实现

@Slf4j
@Aspect
@Component
public class DataSourceAspect {

    @Pointcut("@annotation(com.example.datasourceprimordialdemo2.datasource.annotation.DataSource)")
    public void doPointCut() {
    }

    @Around("doPointCut()")
    public Object around(ProceedingJoinPoint pointcut) throws Throwable {
        MethodSignature signature = (MethodSignature) pointcut.getSignature();
        Method method = signature.getMethod();
        DataSource dataSource = method.getAnnotation(DataSource.class);
        if (Objects.nonNull(dataSource)) {
            DynamicDataSourceContextHolder.setDataSourceType(dataSource.value().name());
        }
        try {
            return pointcut.proceed();
        } finally {
            // 销毁数据源 在执行方法之后
            DynamicDataSourceContextHolder.clearDataSourceType();
        }
    }
}

8. 启动类修改

@SpringBootApplication(exclude = DataSourceAutoConfiguration.class)

9. 使用

此处为了测试，直接放在controller使用

    @GetMapping("/0")
    @DataSource(DataSourceType.MASTER)
    public ResponseEntity<List<User>> query() {
        return ResponseEntity.ok(this.userService.query());
    }

    @GetMapping("/1")
    @DataSource(DataSourceType.SLAVE1)
    public ResponseEntity<List<User>> query2() {
        return ResponseEntity.ok(this.userService.query());
    }

    @GetMapping("/2")
    @DataSource(DataSourceType.SLAVE2)
    public ResponseEntity<List<User>> query3() {
        return ResponseEntity.ok(this.userService.query());
    }

为了区分数据不一样，数据库未做主从同步

master的数据

slave1的数据

slave2的数据

5.用postman进行测试

获取master的数据

获取slave1的数据

获取slave2的数据

完成～～～ 源码: gitee github

注： 为什么配置了三个数据源，是为了展示我在做的过程中遇到的一个问题

1. 刚开始我是按照网上查到的方式注册数据源

2. 这样做，在全部数据源都注入的时候没有问题，当我在配置中心停掉其中一个数据源时就会出现问题

3)问题(在masterDataSource添加@Primary又会出现其他的错误)

Parameter 1 of method dataSource in com.example.datasourceprimordialdemo2.datasource.config.DynamicDataSourceConfig required a single bean, but 2 were found:
	- masterDataSource: defined by method 'masterDataSource' in class path resource [com/example/datasourceprimordialdemo2/datasource/config/DynamicDataSourceConfig.class]
	- slave2DataSource: defined by method 'slave2DataSource' in class path resource [com/example/datasourceprimordialdemo2/datasource/config/DynamicDataSourceConfig.class]
Action:
Consider marking one of the beans as @Primary, updating the consumer to accept multiple beans, or using @Qualifier to identify the bean that should be consumed

4.解决办法（此方式只针对我代码的解决办法，可能会有其他问题导致 此报错，请再寻找其他方法）

5. 大佬们如果有其他方式请在评论区告知，万分感谢

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