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, not with this proxy. * *
Make sure that TransactionAwareDataSourceProxy is the outermost DataSource * of a chain of DataSource proxies/adapters. TransactionAwareDataSourceProxy * can delegate either directly to the target connection pool or to some * intermediary proxy/adapter like {@link LazyConnectionDataSourceProxy} or * {@link UserCredentialsDataSourceAdapter}. * *
Delegates to {@link DataSourceUtils} for automatically participating in
* thread-bound transactions, for example managed by {@link DataSourceTransactionManager}.
* getConnection calls and close 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.
*
*
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. * *
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. * *
NOTE: 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. *
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. *
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. *
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
*/
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 close() 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.
*
The default implementation returns true 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;
}
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] ? Boolean.TRUE : Boolean.FALSE);
}
else if (method.getName().equals("hashCode")) {
// Use hashCode of Connection proxy.
return new Integer(System.identityHashCode(proxy));
}
else if (method.getName().equals("toString")) {
// Allow for differentiating between the proxy and the raw Connection.
StringBuffer buf = new StringBuffer("Transaction-aware proxy for target Connection ");
if (this.target != null) {
buf.append("[").append(this.target.toString()).append("]");
}
else {
buf.append(" from DataSource [").append(this.targetDataSource).append("]");
}
}
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;
}
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);
}
}
}
}
}