Spring Framework example source code file (SessionReadCallback.java)

This example Spring Framework source code file (SessionReadCallback.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 - Spring Framework tags/keywords

object, object, session, session, sessionreadcallback, sessionreadcallback, toplinkcallback, toplinkexception, toplinkexception, unitofwork

The Spring Framework SessionReadCallback.java source code

/*
 * Copyright 2002-2005 the original author or authors.
 *
 * 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.springframework.orm.toplink;

import oracle.toplink.exceptions.TopLinkException;
import oracle.toplink.sessions.Session;
import oracle.toplink.sessions.UnitOfWork;

/**
 * Convenient abstract implementation of the TopLinkCallback interface,
 * exposing either the plain TopLink Session or the TopLink UnitOfWork
 * (which extends the Session interface) to code that reads persistent objects.
 *
 * <p>Exposes the UnitOfWork if there is an active one (that is, if we're running
 * within a non-read-only transaction); else exposes the Session itself.
 * This allows to modify returned objects within a transaction, which is
 * often desired, while the same code will return shared cache objects
 * if running outside a transaction.
 *
 * <p>If "enforceReadOnly" is demanded, the callback will always expose the
 * Session itself, avoiding the UnitOfWork overhead in any case.
 *
 * @author Juergen Hoeller
 * @since 1.2
 * @see oracle.toplink.sessions.Session#getActiveUnitOfWork()
 * @see #readFromSession(oracle.toplink.sessions.Session)
 */
public abstract class SessionReadCallback implements TopLinkCallback {

	private final boolean enforceReadOnly;

	/**
	 * Create a new SessionReadCallback, not enforcing read-only objects.
	 */
	public SessionReadCallback() {
		this.enforceReadOnly = false;
	}

	/**
	 * Create a new SessionReadCallback, enforcing read-only objects if demanded.
	 * @param enforceReadOnly whether to enforce returning read-only objects,
	 * even if running within a non-read-only transaction
	 */
	public SessionReadCallback(boolean enforceReadOnly) {
		this.enforceReadOnly = enforceReadOnly;
	}

	/**
	 * Determines the Session to work on (either the active UnitOfWork
	 * or the plain Session) and delegates to <code>readFromSession.
	 * @see #readFromSession(oracle.toplink.sessions.Session)
	 */
	public final Object doInTopLink(Session session) throws TopLinkException {
		Session sessionToUse = session;
		if (!this.enforceReadOnly) {
			UnitOfWork unitOfWork = session.getActiveUnitOfWork();
			if (unitOfWork != null) {
				sessionToUse = unitOfWork;
			}
		}
		return readFromSession(sessionToUse);
	}

	/**
	 * Called with a Session to work on, either the active UnitOfWork
	 * or the plain Session (as determined by the transaction status).
	 * @param session the TopLink Session to perform read operations on
	 * @return a result object, or <code>null if none
	 * @throws TopLinkException in case of TopLink errors
	 */
	protected abstract Object readFromSession(Session session) throws TopLinkException;

}