spring动态数据源切换

AbstractRoutingDataSource

1、原理

• 可在程序中动态设置数据源
• 给子类提供获取当前数据源名称实现，保证一个线程一个连接
• 对外提供getConnection方法，选取对应的数据源获取连接

2、使用

• 1.创建DataSourceContextHolder类，内置ThreadLocal，提供设置datasourceName和移除的方法

• 2.继承AbstractRoutingDataSource类，实现determineCurrentLookupKey方法，调用DataSourceContextHolder方法

• 3.所需切换数据源处，注入AbstractRoutingDataSource实现类，调用此三个方法重设数据源
  this.dynamicDataSource.setDefaultTargetDataSource(defaultDataSource);
  this.dynamicDataSource.setTargetDataSources(targetDataSources);
  this.dynamicDataSource.afterPropertiesSet();

• 4.重设数据源后，DataSourceContextHolder中设置新的datasourceName

• 5.后续此线程获取数据库连接即为刚才设置的。

3、源码

	// 根据当前设置的数据源，返回相应的连接
	@Override
	public Connection getConnection() throws SQLException {
		return determineTargetDataSource().getConnection();
	}

        // 由继承类实现，可定义DataSourceContextHolder类，
	// 使用ThreadLocal保存唯一的数据源名称，使得每个请求线程保有自己本次的数据源
	@Nullable
	protected abstract Object determineCurrentLookupKey();

	// 根据实现的determineCurrentLookupKey方法，动态从resolvedDataSources获取当前数据源
	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;
	}

	// 设置当前数据源
	public void setTargetDataSources(Map<Object, Object> targetDataSources) {
		this.targetDataSources = targetDataSources;
	}

	// 设置默认数据源即主数据源
	public void setDefaultTargetDataSource(Object defaultTargetDataSource) {
		this.defaultTargetDataSource = defaultTargetDataSource;
	}

	// 将设置的数据源放入resolvedDataSources、resolvedDefaultDataSource
	@Override
	public void afterPropertiesSet() {
		if (this.targetDataSources == null) {
			throw new IllegalArgumentException("Property 'targetDataSources' is required");
		}
		this.resolvedDataSources = new HashMap<>(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);
		}
	}