Commons DBCP example source code file (ManagedConnection.java)

This example Commons DBCP source code file (ManagedConnection.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons DBCP tags/keywords

auto-commit, commit, completionlistener, completionlistener, connection, connection, exception, exception, jdbc, managedconnection, read-only, sql, sqlexception, sqlexception, transactionregistry, unable

The Commons DBCP ManagedConnection.java source code

/**
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.commons.dbcp.managed;

import org.apache.commons.dbcp.DelegatingConnection;
import org.apache.commons.pool.ObjectPool;

import java.sql.Connection;
import java.sql.SQLException;

/**
 * ManagedConnection is responsible for managing a database connection in a transactional environment
 * (typically called "Container Managed").  A managed connection operates like any other connection
 * when no global transaction (a.k.a. XA transaction or JTA Transaction) is in progress.  When a
 * global transaction is active a single physical connection to the database is used by all
 * ManagedConnections accessed in the scope of the transaction.  Connection sharing means that all
 * data access during a transaction has a consistent view of the database.  When the global transaction
 * is committed or rolled back the enlisted connections are committed or rolled back.  Typically upon
 * transaction completion, a connection returns to the auto commit setting in effect before being
 * enlisted in the transaction, but some vendors do not properly implement this.
 *
 * When enlisted in a transaction the setAutoCommit(), commit(), rollback(), and setReadOnly() methods
 * throw a SQLException.  This is necessary to assure that the transaction completes as a single unit.
 *
 * @author Dain Sundstrom
 * @version $Revision$
 */
public class ManagedConnection extends DelegatingConnection {
    private final ObjectPool pool;
    private final TransactionRegistry transactionRegistry;
    private final boolean accessToUnderlyingConnectionAllowed;
    private TransactionContext transactionContext;
    private boolean isSharedConnection;

    public ManagedConnection(ObjectPool pool, TransactionRegistry transactionRegistry, boolean accessToUnderlyingConnectionAllowed) throws SQLException {
        super(null);
        this.pool = pool;
        this.transactionRegistry = transactionRegistry;
        this.accessToUnderlyingConnectionAllowed = accessToUnderlyingConnectionAllowed;
        updateTransactionStatus();
    }

    protected void checkOpen() throws SQLException {
        super.checkOpen();
        updateTransactionStatus();
    }

    private void updateTransactionStatus() throws SQLException {
        // if there is a is an active transaction context, assure the transaction context hasn't changed
        if (transactionContext != null) {
            if (transactionContext.isActive()) {
                if (transactionContext != transactionRegistry.getActiveTransactionContext()) {
                    throw new SQLException("Connection can not be used while enlisted in another transaction");
                }
                return;
            } else {
                // transaction should have been cleared up by TransactionContextListener, but in
                // rare cases another lister could have registered which uses the connection before
                // our listener is called.  In that rare case, trigger the transaction complete call now
                transactionComplete();
            }
        }

        // the existing transaction context ended (or we didn't have one), get the active transaction context
        transactionContext = transactionRegistry.getActiveTransactionContext();

        // if there is an active transaction context and it already has a shared connection, use it
        if (transactionContext != null && transactionContext.getSharedConnection() != null) {
            // A connection for the connection factory has already been enrolled
            // in the transaction, replace our delegate with the enrolled connection

            // return current connection to the pool
            Connection connection = getDelegateInternal();
            setDelegate(null);
            if (connection != null) {
                try {
                    pool.returnObject(connection);
                } catch (Exception ignored) {
                    // whatever... try to invalidate the connection
                    try {
                        pool.invalidateObject(connection);
                    } catch (Exception ignore) {
                        // no big deal
                    }
                }
            }

            // add a listener to the transaction context
            transactionContext.addTransactionContextListener(new CompletionListener());

            // set our delegate to the shared connection
            setDelegate(transactionContext.getSharedConnection());

            // remember that we are using a shared connection so it can be cleared after the
            // transaction completes
            isSharedConnection = true;
        } else {
            // if our delegate is null, create one
            if (getDelegateInternal() == null) {
                try {
                    // borrow a new connection from the pool
                    Connection connection = (Connection) pool.borrowObject();
                    setDelegate(connection);
                } catch (Exception e) {
                    throw (SQLException) new SQLException("Unable to acquire a new connection from the pool").initCause(e);
                }
            }

            // if we have a transaction, out delegate becomes the shared delegate
            if (transactionContext != null) {
                // add a listener to the transaction context
                transactionContext.addTransactionContextListener(new CompletionListener());

                // register our connection as the shared connection
                try {
                    transactionContext.setSharedConnection(getDelegateInternal());
                } catch (SQLException e) {
                    // transaction is hosed
                    transactionContext = null;
                    throw e;
                }
            }
        }
    }

    public void close() throws SQLException {
        if (!_closed) {
            try {
                // don't actually close the connection if in a transaction
                // the connection will be closed by the transactionComplete method
                if (transactionContext == null) {
                    getDelegateInternal().close();
                }
            } finally {
                _closed = true;
            }
        }
    }

    /**
     * Delegates to {@link ManagedConnection#transactionComplete()} 
     * for transaction completion events. 
     */
    protected class CompletionListener implements TransactionContextListener {
        public void afterCompletion(TransactionContext completedContext, boolean commited) {
            if (completedContext == transactionContext) {
                transactionComplete();
            }
        }
    }

    protected void transactionComplete() {
        transactionContext = null;

        // if we were using a shared connection, clear the reference now that the transaction has completed
        if (isSharedConnection) {
            // for now, just set the delegate to null, it will be created later if needed
            setDelegate(null);
            isSharedConnection = false;
        }

        // if this connection was closed during the transaction and there is still a delegate present close it
        Connection delegate = getDelegateInternal();
        if (_closed && delegate != null) {
            try {
                setDelegate(null);

                // don't actually close the connection if in a transaction
                if (!delegate.isClosed()) {
                    // don't use super.close() because it calls passivate() which marks the
                    // the connection as closed without returning it to the pool
                    delegate.close();
                }
            } catch (SQLException ignored) {
                // not a whole lot we can do here as connection is closed
                // and this is a transaction callback so there is no
                // way to report the error
            } finally {
                _closed = true;
            }
        }

    }

    //
    // The following methods can't be used while enlisted in a transaction
    //

    public void setAutoCommit(boolean autoCommit) throws SQLException {
        if (transactionContext != null) {
            throw new SQLException("Auto-commit can not be set while enrolled in a transaction");
        }
        super.setAutoCommit(autoCommit);
    }


    public void commit() throws SQLException {
        if (transactionContext != null) {
            throw new SQLException("Commit can not be set while enrolled in a transaction");
        }
        super.commit();
    }

    public void rollback() throws SQLException {
        if (transactionContext != null) {
            throw new SQLException("Commit can not be set while enrolled in a transaction");
        }
        super.rollback();
    }


    public void setReadOnly(boolean readOnly) throws SQLException {
        if (transactionContext != null) {
            throw new SQLException("Read-only can not be set while enrolled in a transaction");
        }
        super.setReadOnly(readOnly);
    }

    //
    // Methods for accessing the delegate connection
    //

    /**
     * If false, getDelegate() and getInnermostDelegate() will return null.
     * @return if false, getDelegate() and getInnermostDelegate() will return null
     */
    public boolean isAccessToUnderlyingConnectionAllowed() {
        return accessToUnderlyingConnectionAllowed;
    }

    public Connection getDelegate() {
        if (isAccessToUnderlyingConnectionAllowed()) {
            return getDelegateInternal();
        } else {
            return null;
        }
    }

    public Connection getInnermostDelegate() {
        if (isAccessToUnderlyingConnectionAllowed()) {
            return super.getInnermostDelegateInternal();
        } else {
            return null;
        }
    }
}