Java tutorial
/* * Copyright (C) 2009, Google Inc. * and other copyright owners as documented in the project's IP log. * * This program and the accompanying materials are made available * under the terms of the Eclipse Distribution License v1.0 which * accompanies this distribution, is reproduced below, and is * available at http://www.eclipse.org/org/documents/edl-v10.php * * All rights reserved. * * Redistribution and use in source and binary forms, with or * without modification, are permitted provided that the following * conditions are met: * * - Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * - Redistributions in binary form must reproduce the above * copyright notice, this list of conditions and the following * disclaimer in the documentation and/or other materials provided * with the distribution. * * - Neither the name of the Eclipse Foundation, Inc. nor the * names of its contributors may be used to endorse or promote * products derived from this software without specific prior * written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ package org.eclipse.jgit.lib; import java.io.IOException; import org.eclipse.jgit.errors.IncorrectObjectTypeException; import org.eclipse.jgit.errors.MissingObjectException; /** * Abstraction of arbitrary object storage. * <p> * An object database stores one or more Git objects, indexed by their unique * {@link org.eclipse.jgit.lib.ObjectId}. */ public abstract class ObjectDatabase { /** * Initialize a new database instance for access. */ protected ObjectDatabase() { // Protected to force extension. } /** * Does this database exist yet? * * @return true if this database is already created; false if the caller * should invoke {@link #create()} to create this database location. */ public boolean exists() { return true; } /** * Initialize a new object database at this location. * * @throws java.io.IOException * the database could not be created. */ public void create() throws IOException { // Assume no action is required. } /** * Create a new {@code ObjectInserter} to insert new objects. * <p> * The returned inserter is not itself thread-safe, but multiple concurrent * inserter instances created from the same {@code ObjectDatabase} must be * thread-safe. * * @return writer the caller can use to create objects in this database. */ public abstract ObjectInserter newInserter(); /** * Create a new {@code ObjectReader} to read existing objects. * <p> * The returned reader is not itself thread-safe, but multiple concurrent * reader instances created from the same {@code ObjectDatabase} must be * thread-safe. * * @return reader the caller can use to load objects from this database. */ public abstract ObjectReader newReader(); /** * Close any resources held by this database. */ public abstract void close(); /** * Does the requested object exist in this database? * <p> * This is a one-shot call interface which may be faster than allocating a * {@link #newReader()} to perform the lookup. * * @param objectId * identity of the object to test for existence of. * @return true if the specified object is stored in this database. * @throws java.io.IOException * the object store cannot be accessed. */ public boolean has(AnyObjectId objectId) throws IOException { try (ObjectReader or = newReader()) { return or.has(objectId); } } /** * Open an object from this database. * <p> * This is a one-shot call interface which may be faster than allocating a * {@link #newReader()} to perform the lookup. * * @param objectId * identity of the object to open. * @return a {@link org.eclipse.jgit.lib.ObjectLoader} for accessing the object. * @throws MissingObjectException * the object does not exist. * @throws java.io.IOException * the object store cannot be accessed. */ public ObjectLoader open(AnyObjectId objectId) throws IOException { return open(objectId, ObjectReader.OBJ_ANY); } /** * Open an object from this database. * <p> * This is a one-shot call interface which may be faster than allocating a * {@link #newReader()} to perform the lookup. * * @param objectId * identity of the object to open. * @param typeHint * hint about the type of object being requested, e.g. * {@link org.eclipse.jgit.lib.Constants#OBJ_BLOB}; * {@link org.eclipse.jgit.lib.ObjectReader#OBJ_ANY} if the * object type is not known, or does not matter to the caller. * @return a {@link org.eclipse.jgit.lib.ObjectLoader} for accessing the * object. * @throws org.eclipse.jgit.errors.MissingObjectException * the object does not exist. * @throws org.eclipse.jgit.errors.IncorrectObjectTypeException * typeHint was not OBJ_ANY, and the object's actual type does * not match typeHint. * @throws java.io.IOException * the object store cannot be accessed. */ public ObjectLoader open(AnyObjectId objectId, int typeHint) throws MissingObjectException, IncorrectObjectTypeException, IOException { try (ObjectReader or = newReader()) { return or.open(objectId, typeHint); } } /** * Create a new cached database instance over this database. This instance might * optimize queries by caching some information about database. So some modifications * done after instance creation might fail to be noticed. * * @return new cached database instance */ public ObjectDatabase newCachedDatabase() { return this; } }