spring:
  datasource:
    master:
      url: jdbc:mysql://localhost:3306/db_master
      username: root
      password: ******
      driver-class-name: com.mysql.cj.jdbc.Driver
      type: com.alibaba.druid.pool.DruidDataSource
    slave:
      url: jdbc:mysql://localhost:3306/db_slave
      username: root
      password: Hxy@950504
      driver-class-name: com.mysql.cj.jdbc.Driver
      type: com.alibaba.druid.pool.DruidDataSource
mybatis:
  mapper-locations: classpath:mapper/**/*.xml

@Configuration
public class DataSourceConfig {
    @Bean(name = "masterDataSource")
    @ConfigurationProperties("spring.datasource.master")
    public DataSource masterDataSource() {
        return DruidDataSourceBuilder.create().build();
    }
    @Bean(name = "slaveDataSource")
    @ConfigurationProperties("spring.datasource.slave")
    public DataSource slaveDataSource() {
        return DruidDataSourceBuilder.create().build();
    }
}

public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean {
    // map結構，用來保存所有的數(shù)據(jù)源
	@Nullable
	private Map<Object, Object> targetDataSources;
    // 默認的數(shù)據(jù)源
	@Nullable
	private Object defaultTargetDataSource;
	@Override
	public void afterPropertiesSet() {
		if (this.targetDataSources == null) {
			throw new IllegalArgumentException("Property 'targetDataSources' is required");
		}
		this.resolvedDataSources = CollectionUtils.newHashMap(this.targetDataSources.size());
		this.targetDataSources.forEach((key, value) -> {
			Object lookupKey = resolveSpecifiedLookupKey(key);
			DataSource dataSource = resolveSpecifiedDataSource(value);
			this.resolvedDataSources.put(lookupKey, dataSource);
		});
		if (this.defaultTargetDataSource != null) {
			this.resolvedDefaultDataSource = resolveSpecifiedDataSource(this.defaultTargetDataSource);
		}
	}
	@Override
	public Connection getConnection() throws SQLException {
		return determineTargetDataSource().getConnection();
	}
	/**
	 * getConnection()方法和determineTargetDataSource()方法定義了獲取數(shù)據(jù)庫連接，選擇數(shù)據(jù)源的核心邏輯
	 */
	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;
	}
	/**
	 * 根據(jù)key選擇數(shù)據(jù)源，但是哪個接口用那個key，由用戶自己決定，這就是模板方法模式
	 */
	@Nullable
	protected abstract Object determineCurrentLookupKey();
}

/**
 * 繼承spring提供的多數(shù)據(jù)源路由類，初始化默認數(shù)據(jù)源和實現(xiàn)選擇數(shù)據(jù)源的方法
 *
 * @author HXY
 */
public class DynamicDataSource extends AbstractRoutingDataSource {
    // 有參構造器，初始化所有的數(shù)據(jù)源和默認數(shù)據(jù)源
    public DynamicDataSource(DataSource defaultTargetDataSource, Map<Object, Object> allDataSource) {
        super.setDefaultTargetDataSource(defaultTargetDataSource);
        super.setTargetDataSources(allDataSource);
        super.afterPropertiesSet();
    }
    // 實現(xiàn)抽象方法，定義我們獲取K的邏輯
    @Override
    protected Object determineCurrentLookupKey() {
        return DataSourceContextHolder.getDataSource();
    }
}

public class DataSourceContextHolder {
    private static final ThreadLocal<String> CONTEXT_HOLDER = new ThreadLocal<>();
    public static void setDataSource(String dataSourceKey) {
        CONTEXT_HOLDER.set(dataSourceKey);
    }
    public static String getDataSource() {
        return CONTEXT_HOLDER.get();
    }
    public static void release() {
        CONTEXT_HOLDER.remove();
    }
}

@Configuration
public class DataSourceConfig {
    @Bean(name = "masterDataSource")
    @ConfigurationProperties("spring.datasource.master")
    public DataSource masterDataSource() {
        return DruidDataSourceBuilder.create().build();
    }
    @Bean(name = "slaveDataSource")
    @ConfigurationProperties("spring.datasource.slave")
    public DataSource slaveDataSource() {
        return DruidDataSourceBuilder.create().build();
    }
    // DynamicDataSource要交給spring管理
    @Primary  // 一定要寫，讓DynamicDataSource被容器優(yōu)先選擇
    @Bean
    public DynamicDataSource dynamicDataSource(@Qualifier("masterDataSource") DataSource masterDataSource,
                                        @Qualifier("slaveDataSource") DataSource slaveDataSource) {
        // 所有數(shù)據(jù)源放到一個map中，交給動態(tài)數(shù)據(jù)源管理
        Map<Object, Object> targetDataSources = new HashMap<>(2);
        targetDataSources.put(DataSourceEnum.MASTER.name(), masterDataSource);
        targetDataSources.put(DataSourceEnum.SLAVE.name(), slaveDataSource);
        // 默認數(shù)據(jù)源、所有數(shù)據(jù)源
        return new DynamicDataSource(masterDataSource, targetDataSources);
    }
}

/**
 * 自定義注解用來選擇數(shù)據(jù)源
 *
 * @author HXY
 * @since 1.0.0
 */
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface DataSource {
    DataSourceEnum key() default DataSourceEnum.MASTER;
}

public enum DataSourceEnum {
    MASTER,
    SLAVE,
    ;
}

@Aspect
@Component
public class DynamicDataSourceAspect {
    // 用環(huán)繞通知攔截標記了DataSource注解的方法，方法執(zhí)行前選擇數(shù)據(jù)源，然后執(zhí)行原來的方法，最后返回結果
    @Around("@annotation(dataSource)")
    public Object selectDataSource(ProceedingJoinPoint joinPoint, DataSource dataSource) throws Throwable {
        try {
            String selectKey = dataSource.key().name();
            DataSourceContextHolder.setDataSource(selectKey);
            return joinPoint.proceed();
        } finally {
            // 請求處理完成后一定要及時釋放ThreadLocal數(shù)據(jù)，否則會引起內(nèi)存泄漏
            DataSourceContextHolder.release();
        }
    }
}