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.lang.reflect.InvocationHandler; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.lang.reflect.Proxy; import java.sql.Connection; import java.sql.SQLException; import java.sql.Statement; import javax.sql.DataSource; import org.springframework.jdbc.datasource.ConnectionProxy; import org.springframework.jdbc.datasource.DataSourceTransactionManager; import org.springframework.jdbc.datasource.DelegatingDataSource; import org.springframework.jdbc.datasource.LazyConnectionDataSourceProxy; import org.springframework.jdbc.datasource.UserCredentialsDataSourceAdapter; import org.springframework.transaction.support.TransactionSynchronizationManager; import org.springframework.util.Assert; /** * Proxy for a target JDBC {@link javax.sql.DataSource}, adding awareness of * Spring-managed transactions. Similar to a transactional JNDI DataSource * as provided by a J2EE server. * * <p>Data access code that should remain unaware of Spring's data access support * can work with this proxy to seamlessly participate in Spring-managed transactions. * Note that the transaction manager, for example {@link DataSourceTransactionManager}, * still needs to work with the underlying DataSource, <i>not</i> with this proxy. * * <p><b>Make sure that TransactionAwareDataSourceProxy is the outermost DataSource * of a chain of DataSource proxies/adapters.</b> TransactionAwareDataSourceProxy * can delegate either directly to the target connection pool or to some * intermediary proxy/adapter like {@link LazyConnectionDataSourceProxy} or * {@link UserCredentialsDataSourceAdapter}. * * <p>Delegates to {@link DataSourceUtils} for automatically participating in * thread-bound transactions, for example managed by {@link DataSourceTransactionManager}. * <code>getConnection</code> calls and <code>close</code> calls on returned Connections * will behave properly within a transaction, i.e. always operate on the transactional * Connection. If not within a transaction, normal DataSource behavior applies. * * <p>This proxy allows data access code to work with the plain JDBC API and still * participate in Spring-managed transactions, similar to JDBC code in a J2EE/JTA * environment. However, if possible, use Spring's DataSourceUtils, JdbcTemplate or * JDBC operation objects to get transaction participation even without a proxy for * the target DataSource, avoiding the need to define such a proxy in the first place. * * <p>As a further effect, using a transaction-aware DataSource will apply remaining * transaction timeouts to all created JDBC (Prepared/Callable)Statement. This means * that all operations performed through standard JDBC will automatically participate * in Spring-managed transaction timeouts. * * <p><b>NOTE:</b> This DataSource proxy needs to return wrapped Connections * (which implement the {@link ConnectionProxy} interface) in order to handle * close calls properly. Therefore, the returned Connections cannot be cast * to a native JDBC Connection type like OracleConnection or to a connection * pool implementation type. Use a corresponding * {@link org.springframework.jdbc.support.nativejdbc.NativeJdbcExtractor} * to retrieve the native JDBC Connection. * * @author Juergen Hoeller * @since 1.1 * @see javax.sql.DataSource#getConnection() * @see java.sql.Connection#close() * @see DataSourceUtils#doGetConnection * @see DataSourceUtils#applyTransactionTimeout * @see DataSourceUtils#doReleaseConnection */ public class TransactionAwareDataSourceProxy extends DelegatingDataSource { private boolean reobtainTransactionalConnections = false; /** * Create a new TransactionAwareDataSourceProxy. * @see #setTargetDataSource */ public TransactionAwareDataSourceProxy() { } /** * Create a new TransactionAwareDataSourceProxy. * @param targetDataSource the target DataSource */ public TransactionAwareDataSourceProxy(DataSource targetDataSource) { super(targetDataSource); } /** * Specify whether to reobtain the target Connection for each operation * performed within a transaction. * <p>The default is "false". Specify "true" to reobtain transactional * Connections for every call on the Connection proxy; this is advisable * on JBoss if you hold on to a Connection handle across transaction boundaries. * <p>The effect of this setting is similar to the * "hibernate.connection.release_mode" value "after_statement". */ public void setReobtainTransactionalConnections(boolean reobtainTransactionalConnections) { this.reobtainTransactionalConnections = reobtainTransactionalConnections; } /** * Delegates to DataSourceUtils for automatically participating in Spring-managed * transactions. Throws the original SQLException, if any. * <p>The returned Connection handle implements the ConnectionProxy interface, * allowing to retrieve the underlying target Connection. * @return a transactional Connection if any, a new one else * @see DataSourceUtils#doGetConnection * @see ConnectionProxy#getTargetConnection */ @Override public Connection getConnection() throws SQLException { DataSource ds = getTargetDataSource(); Assert.state(ds != null, "'targetDataSource' is required"); return getTransactionAwareConnectionProxy(ds); } /** * Wraps the given Connection with a proxy that delegates every method call to it * but delegates <code>close()</code> calls to DataSourceUtils. * @param targetDataSource DataSource that the Connection came from * @return the wrapped Connection * @see java.sql.Connection#close() * @see DataSourceUtils#doReleaseConnection */ protected Connection getTransactionAwareConnectionProxy(DataSource targetDataSource) { return (Connection) Proxy.newProxyInstance(ConnectionProxy.class.getClassLoader(), new Class[] { ConnectionProxy.class }, new TransactionAwareInvocationHandler(targetDataSource)); } /** * Determine whether to obtain a fixed target Connection for the proxy * or to reobtain the target Connection for each operation. * <p>The default implementation returns <code>true</code> for all * standard cases. This can be overridden through the * {@link #setReobtainTransactionalConnections "reobtainTransactionalConnections"} * flag, which enforces a non-fixed target Connection within an active transaction. * Note that non-transactional access will always use a fixed Connection. * @param targetDataSource the target DataSource */ protected boolean shouldObtainFixedConnection(DataSource targetDataSource) { return !TransactionSynchronizationManager.isSynchronizationActive() || !this.reobtainTransactionalConnections; } /** * Invocation handler that delegates close calls on JDBC Connections * to DataSourceUtils for being aware of thread-bound transactions. */ private class TransactionAwareInvocationHandler implements InvocationHandler { private final DataSource targetDataSource; private Connection target; private boolean closed = false; public TransactionAwareInvocationHandler(DataSource targetDataSource) { this.targetDataSource = targetDataSource; } @SuppressWarnings("rawtypes") @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { // Invocation on ConnectionProxy interface coming in... if (method.getName().equals("equals")) { // Only considered as equal when proxies are identical. return proxy == args[0]; } else if (method.getName().equals("hashCode")) { // Use hashCode of Connection proxy. return System.identityHashCode(proxy); } else if (method.getName().equals("toString")) { // Allow for differentiating between the proxy and the raw Connection. StringBuilder sb = new StringBuilder("Transaction-aware proxy for target Connection "); if (this.target != null) { sb.append("[").append(this.target.toString()).append("]"); } else { sb.append(" from DataSource [").append(this.targetDataSource).append("]"); } return sb.toString(); } else if (method.getName().equals("unwrap")) { if (((Class) args[0]).isInstance(proxy)) { return proxy; } } else if (method.getName().equals("isWrapperFor")) { if (((Class) args[0]).isInstance(proxy)) { return true; } } else if (method.getName().equals("close")) { // Handle close method: only close if not within a transaction. DataSourceUtils.doReleaseConnection(this.target, this.targetDataSource); this.closed = true; return null; } else if (method.getName().equals("isClosed")) { return this.closed; } if (this.target == null) { if (this.closed) { throw new SQLException("Connection handle already closed"); } if (shouldObtainFixedConnection(this.targetDataSource)) { this.target = DataSourceUtils.doGetConnection(this.targetDataSource); } } Connection actualTarget = this.target; if (actualTarget == null) { actualTarget = DataSourceUtils.doGetConnection(this.targetDataSource); } if (method.getName().equals("getTargetConnection")) { // Handle getTargetConnection method: return underlying Connection. return actualTarget; } // Invoke method on target Connection. try { Object retVal = method.invoke(actualTarget, args); // If return value is a Statement, apply transaction timeout. // Applies to createStatement, prepareStatement, prepareCall. if (retVal instanceof Statement) { DataSourceUtils.applyTransactionTimeout((Statement) retVal, this.targetDataSource); } return retVal; } catch (InvocationTargetException ex) { throw ex.getTargetException(); } finally { if (actualTarget != this.target) { DataSourceUtils.doReleaseConnection(actualTarget, this.targetDataSource); } } } } }