Java tutorial
/** * Copyright 2014 devacfr<christophefriederich@mac.com> * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.cfr.capsicum.datasource; import java.sql.Connection; import java.sql.SQLException; import java.sql.Statement; import javax.sql.DataSource; import org.apache.cayenne.BaseContext; import org.apache.cayenne.ObjectContext; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.jdbc.CannotGetJdbcConnectionException; import org.springframework.jdbc.datasource.ConnectionHolder; import org.springframework.jdbc.datasource.ConnectionProxy; import org.springframework.jdbc.datasource.DataSourceTransactionManager; import org.springframework.jdbc.datasource.DelegatingDataSource; import org.springframework.jdbc.datasource.SmartDataSource; import org.springframework.jdbc.datasource.TransactionAwareDataSourceProxy; import org.springframework.transaction.TransactionDefinition; import org.springframework.transaction.support.TransactionSynchronizationAdapter; import org.springframework.transaction.support.TransactionSynchronizationManager; import org.springframework.util.Assert; /** * Helper class that provides static methods for obtaining JDBC Connections from * a {@link javax.sql.DataSource}. Includes special support for Spring-managed * transactional Connections, e.g. managed by {@link DataSourceTransactionManager} * or {@link org.springframework.transaction.jta.JtaTransactionManager}. * * <p>Used internally by Spring's {@link org.springframework.jdbc.core.JdbcTemplate}, * Spring's JDBC operation objects and the JDBC {@link DataSourceTransactionManager}. * Can also be used directly in application code. * * @author Rod Johnson * @author Juergen Hoeller * @see #getConnection * @see #releaseConnection * @see DataSourceTransactionManager * @see org.springframework.transaction.jta.JtaTransactionManager * @see org.springframework.transaction.support.TransactionSynchronizationManager */ public abstract class DataSourceUtils { /** * Order value for TransactionSynchronization objects that clean up * JDBC Connections. */ public static final int CONNECTION_SYNCHRONIZATION_ORDER = 1000; private static final Logger logger = LoggerFactory.getLogger(DataSourceUtils.class); /** * Obtain a Connection from the given DataSource. Translates SQLExceptions into * the Spring hierarchy of unchecked generic data access exceptions, simplifying * calling code and making any exception that is thrown more meaningful. * <p>Is aware of a corresponding Connection bound to the current thread, for example * when using {@link DataSourceTransactionManager}. Will bind a Connection to the * thread if transaction synchronization is active, e.g. when running within a * {@link org.springframework.transaction.jta.JtaTransactionManager JTA} transaction). * @param dataSource the DataSource to obtain Connections from * @return a JDBC Connection from the given DataSource * @throws org.springframework.jdbc.CannotGetJdbcConnectionException * if the attempt to get a Connection failed * @see #releaseConnection */ public static Connection getConnection(DataSource dataSource) throws CannotGetJdbcConnectionException { try { return doGetConnection(dataSource); } catch (SQLException ex) { throw new CannotGetJdbcConnectionException("Could not get JDBC Connection", ex); } } /** * Actually obtain a JDBC Connection from the given DataSource. * Same as {@link #getConnection}, but throwing the original SQLException. * <p>Is aware of a corresponding Connection bound to the current thread, for example * when using {@link DataSourceTransactionManager}. Will bind a Connection to the thread * if transaction synchronization is active (e.g. if in a JTA transaction). * <p>Directly accessed by {@link TransactionAwareDataSourceProxy}. * @param dataSource the DataSource to obtain Connections from * @return a JDBC Connection from the given DataSource * @throws SQLException if thrown by JDBC methods * @see #doReleaseConnection */ public static Connection doGetConnection(DataSource dataSource) throws SQLException { Assert.notNull(dataSource, "No DataSource specified"); CayenneConnectionHolder conHolder = (CayenneConnectionHolder) 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(); } // Else we either got no holder or an empty thread-bound holder here. logger.debug("Fetching JDBC Connection from DataSource"); Connection con = dataSource.getConnection(); if (TransactionSynchronizationManager.isSynchronizationActive()) { logger.debug("Registering transaction synchronization for JDBC Connection"); // Use same Connection for further JDBC actions within the transaction. // Thread-bound object will get removed by synchronization at transaction completion. CayenneConnectionHolder holderToUse = conHolder; if (holderToUse == null) { ObjectContext context = BaseContext.getThreadObjectContext(); holderToUse = new CayenneConnectionHolder(con, context); } else { holderToUse.setConnection(con); } holderToUse.requested(); TransactionSynchronizationManager .registerSynchronization(new ConnectionSynchronization(holderToUse, dataSource)); holderToUse.setSynchronizedWithTransaction(true); if (holderToUse != conHolder) { TransactionSynchronizationManager.bindResource(dataSource, holderToUse); } } return con; } /** * Prepare the given Connection with the given transaction semantics. * @param con the Connection to prepare * @param definition the transaction definition to apply * @return the previous isolation level, if any * @throws SQLException if thrown by JDBC methods * @see #resetConnectionAfterTransaction */ public static Integer prepareConnectionForTransaction(Connection con, TransactionDefinition definition) throws SQLException { Assert.notNull(con, "No Connection specified"); // Set read-only flag. if (definition != null && definition.isReadOnly()) { try { if (logger.isDebugEnabled()) { logger.debug("Setting JDBC Connection [" + con + "] read-only"); } con.setReadOnly(true); } catch (Throwable ex) { // SQLException or UnsupportedOperationException // -> ignore, it's just a hint anyway. logger.debug("Could not set JDBC Connection read-only", ex); } } // Apply specific isolation level, if any. Integer previousIsolationLevel = null; if (definition != null && definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) { if (logger.isDebugEnabled()) { logger.debug("Changing isolation level of JDBC Connection [" + con + "] to " + definition.getIsolationLevel()); } previousIsolationLevel = new Integer(con.getTransactionIsolation()); con.setTransactionIsolation(definition.getIsolationLevel()); } return previousIsolationLevel; } /** * Reset the given Connection after a transaction, * regarding read-only flag and isolation level. * @param con the Connection to reset * @param previousIsolationLevel the isolation level to restore, if any * @see #prepareConnectionForTransaction */ public static void resetConnectionAfterTransaction(Connection con, Integer previousIsolationLevel) { Assert.notNull(con, "No Connection specified"); try { // Reset transaction isolation to previous value, if changed for the transaction. if (previousIsolationLevel != null) { if (logger.isDebugEnabled()) { logger.debug("Resetting isolation level of JDBC Connection [" + con + "] to " + previousIsolationLevel); } con.setTransactionIsolation(previousIsolationLevel.intValue()); } // Reset read-only flag. if (con.isReadOnly()) { if (logger.isDebugEnabled()) { logger.debug("Resetting read-only flag of JDBC Connection [" + con + "]"); } con.setReadOnly(false); } } catch (Throwable ex) { logger.debug("Could not reset JDBC Connection after transaction", ex); } } /** * Determine whether the given JDBC Connection is transactional, that is, * bound to the current thread by Spring's transaction facilities. * @param con the Connection to check * @param dataSource the DataSource that the Connection was obtained from * (may be <code>null</code>) * @return whether the Connection is transactional */ public static boolean isConnectionTransactional(Connection con, DataSource dataSource) { if (dataSource == null) { return false; } CayenneConnectionHolder conHolder = (CayenneConnectionHolder) TransactionSynchronizationManager .getResource(dataSource); return conHolder != null && connectionEquals(conHolder, con); } /** * Apply the current transaction timeout, if any, * to the given JDBC Statement object. * @param stmt the JDBC Statement object * @param dataSource the DataSource that the Connection was obtained from * @throws SQLException if thrown by JDBC methods * @see java.sql.Statement#setQueryTimeout */ public static void applyTransactionTimeout(Statement stmt, DataSource dataSource) throws SQLException { applyTimeout(stmt, dataSource, 0); } /** * Apply the specified timeout - overridden by the current transaction timeout, * if any - to the given JDBC Statement object. * @param stmt the JDBC Statement object * @param dataSource the DataSource that the Connection was obtained from * @param timeout the timeout to apply (or 0 for no timeout outside of a transaction) * @throws SQLException if thrown by JDBC methods * @see java.sql.Statement#setQueryTimeout */ public static void applyTimeout(Statement stmt, DataSource dataSource, int timeout) throws SQLException { Assert.notNull(stmt, "No Statement specified"); Assert.notNull(dataSource, "No DataSource specified"); ConnectionHolder holder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource); if (holder != null && holder.hasTimeout()) { // Remaining transaction timeout overrides specified value. stmt.setQueryTimeout(holder.getTimeToLiveInSeconds()); } else if (timeout > 0) { // No current transaction timeout -> apply specified value. stmt.setQueryTimeout(timeout); } } /** * Close the given Connection, obtained from the given DataSource, * if it is not managed externally (that is, not bound to the thread). * @param con the Connection to close if necessary * (if this is <code>null</code>, the call will be ignored) * @param dataSource the DataSource that the Connection was obtained from * (may be <code>null</code>) * @see #getConnection */ public static void releaseConnection(Connection con, DataSource dataSource) { try { doReleaseConnection(con, dataSource); } catch (SQLException ex) { logger.debug("Could not close JDBC Connection", ex); } catch (Throwable ex) { logger.debug("Unexpected exception on closing JDBC Connection", ex); } } /** * Actually close the given Connection, obtained from the given DataSource. * Same as {@link #releaseConnection}, but throwing the original SQLException. * <p>Directly accessed by {@link TransactionAwareDataSourceProxy}. * @param con the Connection to close if necessary * (if this is <code>null</code>, the call will be ignored) * @param dataSource the DataSource that the Connection was obtained from * (may be <code>null</code>) * @throws SQLException if thrown by JDBC methods * @see #doGetConnection */ public static void doReleaseConnection(Connection con, DataSource dataSource) throws SQLException { if (con == null) { return; } if (dataSource != null) { CayenneConnectionHolder conHolder = (CayenneConnectionHolder) TransactionSynchronizationManager .getResource(dataSource); if (conHolder != null && connectionEquals(conHolder, con)) { // It's the transactional Connection: Don't close it. conHolder.released(); return; } } // Leave the Connection open only if the DataSource is our // special SmartDataSoruce and it wants the Connection left open. if (!(dataSource instanceof SmartDataSource) || ((SmartDataSource) dataSource).shouldClose(con)) { logger.debug("Returning JDBC Connection to DataSource"); con.close(); } } /** * Determine whether the given two Connections are equal, asking the target * Connection in case of a proxy. Used to detect equality even if the * user passed in a raw target Connection while the held one is a proxy. * @param conHolder the ConnectionHolder for the held Connection (potentially a proxy) * @param passedInCon the Connection passed-in by the user * (potentially a target Connection without proxy) * @return whether the given Connections are equal * @see #getTargetConnection */ private static boolean connectionEquals(CayenneConnectionHolder conHolder, Connection passedInCon) { if (!conHolder.hasConnection()) { return false; } Connection heldCon = conHolder.getConnection(); // Explicitly check for identity too: for Connection handles that do not implement // "equals" properly, such as the ones Commons DBCP exposes). return heldCon == passedInCon || heldCon.equals(passedInCon) || getTargetConnection(heldCon).equals(passedInCon); } /** * Return the innermost target Connection of the given Connection. If the given * Connection is a proxy, it will be unwrapped until a non-proxy Connection is * found. Otherwise, the passed-in Connection will be returned as-is. * @param con the Connection proxy to unwrap * @return the innermost target Connection, or the passed-in one if no proxy * @see ConnectionProxy#getTargetConnection() */ public static Connection getTargetConnection(Connection con) { Connection conToUse = con; while (conToUse instanceof ConnectionProxy) { conToUse = ((ConnectionProxy) conToUse).getTargetConnection(); } return conToUse; } /** * Determine the connection synchronization order to use for the given * DataSource. Decreased for every level of nesting that a DataSource * has, checked through the level of DelegatingDataSource nesting. * @param dataSource the DataSource to check * @return the connection synchronization order to use * @see #CONNECTION_SYNCHRONIZATION_ORDER */ private static int getConnectionSynchronizationOrder(DataSource dataSource) { int order = CONNECTION_SYNCHRONIZATION_ORDER; DataSource currDs = dataSource; while (currDs instanceof DelegatingDataSource) { order--; currDs = ((DelegatingDataSource) currDs).getTargetDataSource(); } return order; } /** * Callback for resource cleanup at the end of a non-native JDBC transaction * (e.g. when participating in a JtaTransactionManager transaction). * @see org.springframework.transaction.jta.JtaTransactionManager */ private static class ConnectionSynchronization extends TransactionSynchronizationAdapter { private final CayenneConnectionHolder connectionHolder; private final DataSource dataSource; private final int order; private boolean holderActive = true; public ConnectionSynchronization(CayenneConnectionHolder connectionHolder, DataSource dataSource) { this.connectionHolder = connectionHolder; this.dataSource = dataSource; this.order = getConnectionSynchronizationOrder(dataSource); } @Override public int getOrder() { return this.order; } @Override public void suspend() { if (this.holderActive) { TransactionSynchronizationManager.unbindResource(this.dataSource); if (this.connectionHolder.hasConnection() && !this.connectionHolder.isOpen()) { // Release Connection on suspend if the application doesn't keep // a handle to it anymore. We will fetch a fresh Connection if the // application accesses the ConnectionHolder again after resume, // assuming that it will participate in the same transaction. releaseConnection(this.connectionHolder.getConnection(), this.dataSource); this.connectionHolder.setConnection(null); } } } @Override public void resume() { if (this.holderActive) { TransactionSynchronizationManager.bindResource(this.dataSource, this.connectionHolder); } } @Override public void beforeCompletion() { // Release Connection early if the holder is not open anymore // (that is, not used by another resource like a Hibernate Session // that has its own cleanup via transaction synchronization), // to avoid issues with strict JTA implementations that expect // the close call before transaction completion. if (!this.connectionHolder.isOpen()) { TransactionSynchronizationManager.unbindResource(this.dataSource); this.holderActive = false; if (this.connectionHolder.hasConnection()) { releaseConnection(this.connectionHolder.getConnection(), this.dataSource); } } } @Override public void afterCompletion(int status) { // If we haven't closed the Connection in beforeCompletion, // close it now. The holder might have been used for other // cleanup in the meantime, for example by a Hibernate Session. if (this.holderActive) { // The thread-bound ConnectionHolder might not be available anymore, // since afterCompletion might get called from a different thread. TransactionSynchronizationManager.unbindResourceIfPossible(this.dataSource); this.holderActive = false; if (this.connectionHolder.hasConnection()) { releaseConnection(this.connectionHolder.getConnection(), this.dataSource); // Reset the ConnectionHolder: It might remain bound to the thread. this.connectionHolder.setConnection(null); } } this.connectionHolder.reset(); } } }