ObjectDatabase.java

/*
 * Copyright (C) 2009, Google Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

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;
    }
}