Spring数据库连接与Threadlocal

╰半橙微兮° 2023-01-02 04:19 58阅读 0赞

**目录**

关键类：

数据库连接放入Threadlocal：

从ThreadLocal取数据库连接：

--------------------

# 关键类： #

TransactionSynchronizationManager

# 数据库连接放入Threadlocal： #

TransactionInterceptor.invoke(MethodInvocation invocation)---》TransactionStatusorg.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(@NullableTransactionDefinition definition) throws TransactionException\---》

void org.springframework.jdbc.datasource.DataSourceTransactionManager.doBegin(Object transaction, TransactionDefinition definition)

@Override
    	protected void doBegin(Object transaction, TransactionDefinition definition) {
    		DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
    		Connection con = null;
    
    		try {
    			if (!txObject.hasConnectionHolder() ||
    					txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
    				Connection newCon = obtainDataSource().getConnection();
    				if (logger.isDebugEnabled()) {
    					logger.debug("Acquired Connection [" + newCon + "] for JDBC transaction");
    				}
    				txObject.setConnectionHolder(new ConnectionHolder(newCon), true);
    			}
    
    			txObject.getConnectionHolder().setSynchronizedWithTransaction(true);
    			con = txObject.getConnectionHolder().getConnection();
    
    			Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
    			txObject.setPreviousIsolationLevel(previousIsolationLevel);
    			txObject.setReadOnly(definition.isReadOnly());
    
    			// Switch to manual commit if necessary. This is very expensive in some JDBC drivers,
    			// so we don't want to do it unnecessarily (for example if we've explicitly
    			// configured the connection pool to set it already).
    			if (con.getAutoCommit()) {
    				txObject.setMustRestoreAutoCommit(true);
    				if (logger.isDebugEnabled()) {
    					logger.debug("Switching JDBC Connection [" + con + "] to manual commit");
    				}
    				con.setAutoCommit(false);
    			}
    
    			prepareTransactionalConnection(con, definition);
    			txObject.getConnectionHolder().setTransactionActive(true);
    
    			int timeout = determineTimeout(definition);
    			if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
    				txObject.getConnectionHolder().setTimeoutInSeconds(timeout);
    			}
    
    			// Bind the connection holder to the thread.
                //绑定数据库连接到线程
    			if (txObject.isNewConnectionHolder()) {
    				TransactionSynchronizationManager.bindResource(obtainDataSource(), txObject.getConnectionHolder());
    			}
    		}
    
    		catch (Throwable ex) {
    			if (txObject.isNewConnectionHolder()) {
    				DataSourceUtils.releaseConnection(con, obtainDataSource());
    				txObject.setConnectionHolder(null, false);
    			}
    			throw new CannotCreateTransactionException("Could not open JDBC Connection for transaction", ex);
    		}
    	}

void org.springframework.transaction.support.TransactionSynchronizationManager.bindResource(Object key, Object value) throws IllegalStateException：

public static void bindResource(Object key, Object value) throws IllegalStateException {
    		Object actualKey = TransactionSynchronizationUtils.unwrapResourceIfNecessary(key);
    		Assert.notNull(value, "Value must not be null");
    		Map<Object, Object> map = resources.get();
    		// set ThreadLocal Map if none found
    		if (map == null) {
    			map = new HashMap<>();
    			resources.set(map);
    		}
    		Object oldValue = map.put(actualKey, value);
    		// Transparently suppress a ResourceHolder that was marked as void...
    		if (oldValue instanceof ResourceHolder && ((ResourceHolder) oldValue).isVoid()) {
    			oldValue = null;
    		}
    		if (oldValue != null) {
    			throw new IllegalStateException("Already value [" + oldValue + "] for key [" +
    					actualKey + "] bound to thread [" + Thread.currentThread().getName() + "]");
    		}
    		if (logger.isTraceEnabled()) {
    			logger.trace("Bound value [" + value + "] for key [" + actualKey + "] to thread [" +
    					Thread.currentThread().getName() + "]");
    		}
    	}

resources是一个ThreadLocal变量：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NodWl4dWUyNA_size_16_color_FFFFFF_t_70][]

# 从ThreadLocal取数据库连接： #

取连接时，是调用了TransactionSynchronizationManager.getResource(Object key),下图是调用到该方法的一些类：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NodWl4dWUyNA_size_16_color_FFFFFF_t_70 1][]

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NodWl4dWUyNA_size_16_color_FFFFFF_t_70 1]: /images/20221120/5e5e6332a96149e4a0ccebee3fd0de00.png