ObjectDatabase.java
/*
* 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
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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;
}
}