使用面向切面编程 + ThreadLocal + 自定义注解完成动态数据源切换

动态数据源切换可以通过AOP（面向切面编程）和ThreadLocal来实现。其中，ThreadLocal是Java中的一个线程级别的变量，可以在同一个线程中共享数据。自定义注解可以用来标记需要切换数据源的方法。

实现步骤如下：

1. 定义数据源切换注解

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface DataSource {
    String value() default "primary";
}

2. 定义数据源切换切面

@Aspect
@Component
public class DataSourceAspect {
 
    @Pointcut("@annotation(com.example.demo.annotation.DataSource)")
    public void dataSourcePointCut() {
    }
 
    @Before("dataSourcePointCut()")
    public void before(JoinPoint joinPoint) {
        MethodSignature signature = (MethodSignature) joinPoint.getSignature();
        DataSource dataSource = signature.getMethod().getAnnotation(DataSource.class);
        if (dataSource != null) {
            DynamicDataSourceContextHolder.setDataSource(dataSource.value());
        } else {
            DynamicDataSourceContextHolder.setDataSource("primary");
        }
    }
 
    @After("dataSourcePointCut()")
    public void after(JoinPoint joinPoint) {
        DynamicDataSourceContextHolder.clearDataSource();
    }
}

3. 定义ThreadLocal存储数据源信息

public class DynamicDataSourceContextHolder {
 
    private static final ThreadLocal<String> contextHolder = new ThreadLocal<>();
 
    public static void setDataSource(String dataSource) {
        contextHolder.set(dataSource);
    }
 
    public static String getDataSource() {
        return contextHolder.get();
    }
 
    public static void clearDataSource() {
        contextHolder.remove();
    }
}

4. 在数据源配置文件中定义多个数据源

@Configuration
public class DataSourceConfig {
 
    @Bean
    @ConfigurationProperties("datasource.primary")
    public DataSource primaryDataSource() {
        return DataSourceBuilder.create().build();
    }
 
    @Bean
    @ConfigurationProperties("datasource.secondary")
    public DataSource secondaryDataSource() {
        return DataSourceBuilder.create().build();
    }
 
    @Bean
    @Primary
    public DynamicDataSource dataSource() {
        DynamicDataSource dynamicDataSource = new DynamicDataSource();
        Map<Object, Object> dataSourceMap = new HashMap<>(2);
        dataSourceMap.put("primary", primaryDataSource());
        dataSourceMap.put("secondary", secondaryDataSource());
        dynamicDataSource.setTargetDataSources(dataSourceMap);
        dynamicDataSource.setDefaultTargetDataSource(primaryDataSource());
        return dynamicDataSource;
    }
}

5. 在需要切换数据源的方法上添加@DataSource注解

@Service
public class UserServiceImpl implements UserService {
 
    @Autowired
    private UserMapper userMapper;
 
    @Override
    @DataSource("primary")
    public List<User> listPrimaryUsers() {
        return userMapper.listUsers();
    }
 
    @Override
    @DataSource("secondary")
    public List<User> listSecondaryUsers() {
        return userMapper.listUsers();
    }
}

这样，在调用listPrimaryUsers和listSecondaryUsers方法时，就会自动切换到对应的数据源。