AOP动态数据源切换实现主从读写分离

痛定思痛。 2023-06-30 15:57 8阅读 0赞

## 前言 ##

MySQL 主从可以更好的减少数据库压力，今天搞了一个小demo，只读接口让他去从库查，用注解方式实现。代码上传至码云：  
[https://gitee.com/yunup/some-examples][https_gitee.com_yunup_some-examples]

## 环境信息 ##

Java 版本 1.8  
SpringBoot 版本 2.2.3.RELEASE  
MySQL主库 test  
           从库 test2

## 编写配置文件 ##

spring:
      datasource:
        url: "jdbc:mysql://localhost:3306/test\?useUnicode=true&characterEncoding=utf-8&useAffectedRows=true\&allowMultiQueries=true&useSSL=false&serverTimezone=Asia/Shanghai"
        username: root
        password: root
        driver-class-name: com.mysql.cj.jdbc.Driver
        type: com.zaxxer.hikari.HikariDataSource
        hikari:
          minimumIdle: 0
          maximum-pool-size: 20
          idle-timeout: 180000
          
    dynamic-data-source:
      enabled: true
      slave:
        url: "jdbc:mysql://localhost:3306/test2\?useUnicode=true&characterEncoding=utf-8&useAffectedRows=true\&allowMultiQueries=true&useSSL=false&serverTimezone=Asia/Shanghai"
        username: root
        password: root

## 动态数据源类 ##

创建 DynamicDataSource 类，继承自 AbstractRoutingDataSource ，用于判断使用哪个数据源

public class DynamicDataSource extends AbstractRoutingDataSource { 
    
      private static final ThreadLocal<DataSourceType> dataSourceTypeThreadLocal = new ThreadLocal<>();
    
      public static void removeDataSourceType() { 
        dataSourceTypeThreadLocal.remove();
      }
    
      public static void setDataSourceType(DataSourceType dataSourceType) { 
        if (dataSourceTypeThreadLocal.get() == null) { 
          dataSourceTypeThreadLocal.set(dataSourceType);
        }
      }
    
      @Override
      protected Object determineCurrentLookupKey() { 
        return dataSourceTypeThreadLocal.get() == null ? DataSourceType.Master : dataSourceTypeThreadLocal.get();
      }
    }

## 多数据源配置 ##

首先，配置多个数据源，配置文件中 dynamic-data-source的enabled为true，表示开启动态数据源，则注入主数据源和从数据源：

@Bean({ "masterDataSource"})
      @ConditionalOnProperty(name = { "dynamic-data-source.enabled"}, havingValue = "true")
      public DataSource masterDataSource() throws CloneNotSupportedException { 
        this.log.info("init masterDataSource...");
        // 此处省略设置参数的代码
        return new HikariDataSource(properties);
      }
    
      @Bean({ "slaverDataSource"})
      @ConditionalOnProperty(name = { "dynamic-data-source.enabled"}, havingValue = "true")
      public DataSource slaverDataSource() throws CloneNotSupportedException { 
        this.log.info("init slaverDataSource...");
        // 此处省略设置参数的代码
        return new HikariDataSource(properties);
      }
    
      @Bean
      @Primary
      @DependsOn({ "masterDataSource", "slaverDataSource"})
      @ConditionalOnProperty(name = { "dynamic-data-source.enabled"}, havingValue = "true")
      public DynamicDataSource dataSource(DataSource masterDataSource, DataSource slaverDataSource) { 
        this.log.info("init dynamicDataSource...");
        DynamicDataSource source = new DynamicDataSource();
        Map<Object, Object> map = new HashMap<>();
        map.put(DataSourceType.Master, masterDataSource);
        map.put(DataSourceType.Slave, slaverDataSource);
        source.setTargetDataSources(map);
        source.setDefaultTargetDataSource(masterDataSource);
        return source;
      }

## 创建注解类 ##

创建两个注解类，如果是查询接口，接口上就标注 DBReadOnly，让他去查询从库

@Target({ ElementType.TYPE, ElementType.METHOD})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface DBReadOnly { 
    
    }
    
    @Target({ ElementType.TYPE, ElementType.METHOD})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface DBWriteable { 
      
    }

## 编写切面代码 ##

@Aspect
    @Component
    @ConditionalOnProperty(name = { "dynamic-data-source.enabled"}, havingValue = "true")
    public class DataSourceAspect { 
    
      @Around("@annotation(annotation)")
      public Object processDBReadOnly(ProceedingJoinPoint joinPoint, DBReadOnly annotation) { 
        DynamicDataSource.setDataSourceType(DataSourceType.Slave);
        Object var3 = null;
        try { 
          var3 = joinPoint.proceed();
        } catch (Throwable throwable) { 
          throwable.printStackTrace();
        } finally { 
          DynamicDataSource.removeDataSourceType();
        }
        return var3;
      }
    
      @Around("@annotation(annotation)")
      public Object processDBWriteable(ProceedingJoinPoint joinPoint, DBWriteable annotation) { 
        DynamicDataSource.setDataSourceType(DataSourceType.Master);
        Object var3 = null;
        try { 
          var3 = joinPoint.proceed();
        } catch (Throwable throwable) { 
          throwable.printStackTrace();
        } finally { 
          DynamicDataSource.removeDataSourceType();
        }
        return var3;
      }
    }

## 测试效果 ##

在控制器上对于两个请求进行标注，findAll 请求去查 test（主） 数据库，findAllSecond 去查 test2（从） 数据库。

@GetMapping("/findAll")
      @DBWriteable
      public List<Users> findAll() { 
        List<Users> users = usersService.findAll();
        return users;
      }
    
      @GetMapping("/findAllSecond")
      @DBReadOnly
      public List<Users> findAllSecond() { 
        List<Users> users = usersService.findAll();
        return users;
      }

findAll 结果：\[\{“userId”:1,“userName”:“张三”\},\{“userId”:2,“userName”:“李四”\},\{“userId”:3,“userName”:“王五”\}\]  
findAllSecond 结果： \[\{“userId”:1,“userName”:“Lucy”\},\{“userId”:2,“userName”:“Dick”\},\{“userId”:3,“userName”:“Angel”\}\]

编码中，遇到了循环依赖的问题，可见：[https://blog.csdn.net/K\_Tang/article/details/83117354][https_blog.csdn.net_K_Tang_article_details_83117354]

[https_gitee.com_yunup_some-examples]: https://gitee.com/yunup/some-examples
[https_blog.csdn.net_K_Tang_article_details_83117354]: https://blog.csdn.net/K_Tang/article/details/83117354