Spring多数据源配置

Spring多数据源配置原理

Spring的多数据源配置主要靠是AbstractRoutingDataSource类，该类中有个抽象方法用来获取数据源的名称,建立一个Java类来实现获取数据源名称的方法

• AbstractRoutingDataSource获取数据源名称的方法

protected DataSource determineTargetDataSource() {
		Assert.notNull(this.resolvedDataSources, "DataSource router not initialized");
		//获取数据源名称
		Object lookupKey = determineCurrentLookupKey();
		//经过相应的数据源名称来获取相应的数据源
		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;
	}
	
protected abstract Object determineCurrentLookupKey();

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存在多线程的安全性问题，将数据源名称变量存到本地线程里面，获取数据源名称时能够直接从本地线程中获取

/**
 * 保存数据源名称的类
 */

public class DatabaseContextHolder {

	private static final ThreadLocal<String> contextHolder = new ThreadLocal<String>();

	public static void setCustomerType(String customerType) {
		contextHolder.set(customerType);
	}

	public static String getCustomerType() {
		return contextHolder.get();
	}

	public static void clearCustomerType() {
		contextHolder.remove();
	}
}

/**
 * 获取数据源名称的类
 */
public class DynamicDataSource extends AbstractRoutingDataSource {

	@Override
	protected Object determineCurrentLookupKey() {
		return DatabaseContextHolder.getCustomerType();
	}
}

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切换数据源的时候,能够选择配置AOP去切换数据源，也能够手动通DatabaseContextHolder.setCustomerType(dataSourceName)去切换数据源

• xml配置文件

<!--数据源1-->
<bean id="dataSourcev14" class="org.apache.commons.dbcp2.BasicDataSource" destroy-method="close">
		<property name="driverClassName" value="${jdbc.v14.driverClassName}"/>
		<property name="url" value="${jdbc.v14.url}"/>
		<property name="username" value="${jdbc.v14.username}"/>
		<property name="password" value="${jdbc.v14.password}"/>
	</bean>
<!--数据源2-->
	<bean id="dataSourcev11" class="org.apache.commons.dbcp2.BasicDataSource" destroy-method="close">
		<property name="driverClassName" value="${jdbc.v11.driverClassName}"/>
		<property name="url" value="${jdbc.v11.url}"/>
		<property name="username" value="${jdbc.v11.username}"/>
		<property name="password" value="${jdbc.v11.password}"/>
	</bean>

<!--动态数据源引用-->
	<bean id="dynamicDataSource" class="cn.com.egova.source.DynamicDataSource">
		<property name="targetDataSources">
			<map key-type="java.lang.String">
				<entry key="dataSourcev11" value-ref="dataSourcev11"></entry>
				<entry key="dataSourcev14" value-ref="dataSourcev14"></entry>
			</map>
		</property>
		<property name="defaultTargetDataSource" ref="dataSourcev14">
		</property>
	</bean>
<!--Spring Jdbc引用-->
<bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
	    <property name="dataSource" ref="dynamicDataSource"/>
	</bean>
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Spring动态数据库切换原理

• 查询数据库记录时手动切换数据源

<!--手动切换数据源-->
DatabaseContextHolder.setCustomerType("dataSourcev11");
<!--查询相应的数据库记录-->
int count2 = jdbcTemplate.queryForObject("select count(*) from to_stat_info",Integer.class);
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• jdbcTemplate类查询源码

<!--通过层层的封装以后到了execute方法-->
public <T> T execute(StatementCallback<T> action) throws DataAccessException {
		Assert.notNull(action, "Callback object must not be null");

        <!--获取数据源链接方法-->
		Connection con = DataSourceUtils.getConnection(getDataSource());
		Statement stmt = null;
		try {
			Connection conToUse = con;
			if (this.nativeJdbcExtractor != null &&
					this.nativeJdbcExtractor.isNativeConnectionNecessaryForNativeStatements()) {
				conToUse = this.nativeJdbcExtractor.getNativeConnection(con);
			}
			stmt = conToUse.createStatement();
			applyStatementSettings(stmt);
			Statement stmtToUse = stmt;
			if (this.nativeJdbcExtractor != null) {
				stmtToUse = this.nativeJdbcExtractor.getNativeStatement(stmt);
			}
			T result = action.doInStatement(stmtToUse);
			handleWarnings(stmt);
			return result;
		}
		catch (SQLException ex) {
			// Release Connection early, to avoid potential connection pool deadlock
			// in the case when the exception translator hasn't been initialized yet. JdbcUtils.closeStatement(stmt); stmt = null; DataSourceUtils.releaseConnection(con, getDataSource()); con = null; throw getExceptionTranslator().translate("StatementCallback", getSql(action), ex); } finally { JdbcUtils.closeStatement(stmt); DataSourceUtils.releaseConnection(con, getDataSource()); } } 复制代码

• DataSourceUtils类中getConnection方法

public static Connection getConnection(DataSource dataSource) throws CannotGetJdbcConnectionException {
		try {
			return doGetConnection(dataSource);
		}
		catch (SQLException ex) {
			throw new CannotGetJdbcConnectionException("Could not get JDBC Connection", ex);
		}
	}
	
public static Connection doGetConnection(DataSource dataSource) throws SQLException {
		Assert.notNull(dataSource, "No DataSource specified");
        //首先查看事务管理器里面是否有Connection链接
		ConnectionHolder conHolder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);
		if (conHolder != null && (conHolder.hasConnection() || conHolder.isSynchronizedWithTransaction())) {
			conHolder.requested();
			if (!conHolder.hasConnection()) {
				logger.debug("Fetching resumed JDBC Connection from DataSource");
				conHolder.setConnection(dataSource.getConnection());
			}
			return conHolder.getConnection();
		}
		logger.debug("Fetching JDBC Connection from DataSource");
		//从数据源中获取链接，实现AbstractRoutingDataSource类中方法（由于配置文件中dataSource实现类是DynamicDataSource继承了AbstractRoutingDataSource抽象类）
		Connection con = dataSource.getConnection();

		if (TransactionSynchronizationManager.isSynchronizationActive()) {
			logger.debug("Registering transaction synchronization for JDBC Connection");
			ConnectionHolder holderToUse = conHolder;
			if (holderToUse == null) {
				holderToUse = new ConnectionHolder(con);
			}
			else {
				holderToUse.setConnection(con);
			}
			holderToUse.requested();
			TransactionSynchronizationManager.registerSynchronization(
					new ConnectionSynchronization(holderToUse, dataSource));
			holderToUse.setSynchronizedWithTransaction(true);
			if (holderToUse != conHolder) {
				TransactionSynchronizationManager.bindResource(dataSource, holderToUse);
			}
		}

		return con;
	}
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• AbstractRoutingDataSource类中获取数据源Connection链接方法

public Connection getConnection() throws SQLException {
		return determineTargetDataSource().getConnection();
	}

//determineTargetDataSource方法
protected DataSource determineTargetDataSource() {
		Assert.notNull(this.resolvedDataSources, "DataSource router not initialized");
		//刚才建立的DynamicDataSource，实现AbstractRoutingDataSource抽象方法获取数据源名称
		Object lookupKey = determineCurrentLookupKey();
		//经过数据源名称来获取相应的数据源
		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;
	}
//getConnection方法
public Connection getConnection() throws SQLException {
		return determineTargetDataSource().getConnection();
	}

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注意

实现动态数据源时，要注意一下aop的事务配置，由于aop的管理器会在方法执前先注入数据源，后面doGetConnection中获取链接时会直接从事务管理器里面获取，这样就会致使数据源切换失败